HK1234585B - System and device for driving a plurality of high powered led units - Google Patents

Description

System and apparatus for driving multiple high-power LED units

This application is a divisional application of patent application 201280017590.8, filed on November 2, 2012, with the invention name “System and device for driving multiple high-power LED units”.

Technical Field

The present invention relates to a system and apparatus for driving a plurality of high-power light emitting diode (LED) units. The apparatus is particularly suitable for, but not limited to, use in high-power LED lamp units such as downlights, T5, T8, troffers, Hi-Bay lamps, and MR16 bulbs.

Background Art

The following discussion of the background to the invention is intended to facilitate an understanding of the invention. However, it should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was published, known or part of the common general knowledge in any jurisdiction as at the priority date of the application.

Traditional lighting systems typically have a configuration that individually drives the lamp products used in the system. For example, lamp products such as downlights have their own built-in power supply or ballast, which converts the incoming AC power to a higher AC voltage and the required current. This voltage and current are needed to provide the power, such as to ignite and excite the gas (referred to as a CFL lamp) to illuminate the downlight. Examples of such other lamp products include T5, T8, troffers, Hi-Bay lamps, streetlights, and floodlights.

Similarly, when light-emitting diodes (LEDs) were introduced into lighting systems, the configuration they adopted was based on the "one ballast (controller) to one lamp" arrangement of traditional lighting systems. Consequently, each LED lamp unit had its own built-in LED driver or controller, which converted the incoming AC power to DC voltage and current to illuminate the LED downlight. This meant that each LED lamp unit in the lighting system had its own controller dedicated to that specific LED lamp unit, which converted the incoming AC power to DC voltage and current to illuminate it. In other words, a series of 10 LED downlights in the lighting system would require 10 corresponding LED controller circuits. These LED controllers increased the cost and overall form factor of each lamp unit.

A prior art LED lamp unit and system are shown in Figures 1 and 2, respectively. The LED lamp unit comprises an AC power supply via an AC input 4, an AC-DC LED driver 3, an LED light/lamp module 1 and a heat sink 2.

When connected, the AC mains current flows to the input of the AC-DC LED driver 3. The AC mains current is rectified by the switch-mode power supply circuit in the AC-DC LED driver 3 to provide the required DC voltage and current to the LED light module 1. For continuous lighting operation, since both the AC-DC LED driver 3 and the LEDs on the LED light module 1 will generate heat, the introduction of the heat sink 2 is important to ensure that the heat generated during lighting operation is appropriately drawn away from the heat source and dissipated. The heat sink 2 must handle the heat dissipation from both the LED light module and the AC-DC LED driver. As a result, if at any time during lighting operation, the heat sink 2 reaches its maximum heat dissipation capacity due to design limitations on the size of the standard form factor for a particular LED lighting unit, this can lead to a decrease in light performance and product life.

The above configuration has the following disadvantages:

Since each LED light unit requires its own built-in controller circuit 3 for lighting, the LEDs and controller circuitry generate considerable heat when the LED light unit is in continuous operation. To reduce this heat, a heat sink must be provided in each LED light unit to absorb heat from the heat source and dissipate it to the surrounding environment, thereby providing a cool environment for the LEDs and controller circuitry to operate in. It is important that the LEDs and controller circuitry operate in a cool environment because this reduces power consumption and therefore improves efficiency. However, due to the standard form factor, there are limitations on the size of the heat sink in each LED light unit. Since each LED light unit contains two heat-generating sources (i.e., the LED light unit and the LED controller), the heat sink 2 typically reaches its maximum heat dissipation capacity during continuous operation, when considerable heat is generated. This results in a decrease in the light performance and product life of the LED light unit.

LED light units with built-in controller circuitry and a heat sink 2 are generally more expensive to manufacture because they increase the number of components required for manufacturing. Furthermore, the heat sink must be designed to handle heat dissipation from two heat sources while being constrained by its size due to standard form factors. This further increases the overall cost of producing the LED light unit.

Safety-related issues must be addressed due to the conversion of AC power to DC voltage and current in the LED light unit by the controller circuit 3. Therefore, LED light units must be designed so that they meet standard safety requirements and size restrictions imposed by the standard form factor.

It is therefore an object of the present invention to overcome or at least alleviate the aforementioned problems.

Summary of the Invention

The present invention provides a system and apparatus to alleviate the aforementioned issues and provide a "one driver for multiple high-power LED lamp units" solution. To achieve this, the system and apparatus are adapted to provide a relatively "ripple-free" current that is at least less than 5% of a specified rated current. The specified rated current is typically (but not limited to) approximately 350 mA to 700 mA per lamp unit.

Additionally, references to "flow" and "connection" refer to electrical current and electrical connections unless otherwise specified.

According to a first aspect of the present invention, a system for driving a plurality of high-power LED units includes a single driver for providing a ripple-free constant DC to the plurality of high-power LED lamp units, wherein the single driver has an inductive element as a transformer, the inductive element being connected to the plurality of high-power LED units at a secondary side of the transformer, the single driver being configured to operate in at least one of the following configurations: an isolated AC flyback configuration and a non-isolated configuration, wherein the single driver includes a digital controller programmable to adjust the ripple-free constant DC at each predetermined time interval based on detecting and calculating a duration taken to release energy to the LED lamp units, thereby adjusting the ripple-free constant DC, wherein the detection and calculation are based on a discharge time value of the transformer core measured by a voltage divider and compared with a reference voltage.

Preferably, the digital controller is an application-specific integrated circuit (ASIC); the ASIC is further operable to detect and calculate the duration of energy released from the transformer core to the plurality of high-power LEDs to regulate and provide a ripple-free output DC current. The ASIC is preferably programmed to receive feedback as input every clock cycle based on the duration of energy released from the transformer core to determine the amount of ripple-free constant DC current for the next clock cycle. More preferably, the ASIC is programmed to provide a voltage waveform every clock cycle to turn the electronic switch on or off.

Preferably, each high-power LED lamp unit in the plurality of high-power LED lamp units is connected in series with other high-power LED lamp units.

Preferably, the single driver is electrically connected to a dimmer circuit for adjusting the brightness of the plurality of high-power LED lamp units. The dimmer circuit preferably comprises a potentiometer, an infrared interface, a motion sensor or an environmental sensor.

Preferably, the system includes a filter capacitor operable to vary its capacitance to maintain a power factor of at least 0.9 when the dimmer is adjusted.

Where the dimmer is a potentiometer, the potentiometer may be operable to operate within a voltage range of 0 to 10V.

Preferably, in the isolated flyback mode, the secondary side of the transformer is electrically connected to the short-circuit protection circuit.

Preferably, the ASIC is coupled to an active power factor controller. More preferably, the active power factor controller includes at least one voltage follower. In this case, the ASIC is preferably a 14-pin configuration to control the active power factor controller and adjust the ripple-free constant DC current.

Preferably, each high power LED lamp is provided with a heat sink shaped and arranged to dissipate heat only from the high power LEDs.

Preferably, the system further comprises an electronic switch, wherein a ripple-free constant DC current is achieved by means of voltage control according to the following equation:

Where _VOUT is the voltage across the output terminals; _VIN is the input voltage; _TOFF is the discharge time of the isolation transformer core; _TON is the on-time of the electronic switch; _L1 is the inductance value of the primary winding of the transformer, and _L2 is the inductance value of the secondary winding of the transformer.

As an alternative to the isolated configuration mode, a single driver can be operated in a non-isolated configuration with the inductive element operating in continuous mode according to the following equation:

Where _TOFF is a fixed constant; _TON is the on-time of the electronic switch; T is the sum of _TON , _TOFF , and _TCALC , where _TCALC is the time after the discharge time of the inductive element used to calculate the formula; _I1 is the desired reference current, and _IMAX is the peak current. In the hysteretic controller configuration, the values of _IMAX and _I1 are fixed and determine the _TON and _TOFF timing.

According to a second aspect of the present invention, a single driver for the above-mentioned system for driving a plurality of high-power LED units comprises:

At least one integrated circuit (IC) programmable using a hardware description language; a first electronic switch operable to provide a first switching period to control a power factor voltage, the first switching period programmable by the at least one IC; and a second electronic switch operable to provide a second switching period to regulate a ripple-free constant DC current flowing into at least one LED, the second switching period programmable by the at least one IC. Such an LED driver provides additional current control in the form of a power controller to achieve a ripple-free DC current.

Preferably, the first and second electronic switches are power MOSFETs.

Preferably, said at least one IC is an ASIC.

According to a third aspect of the present invention, a device has an input port and multiple output ports, wherein the input port is operable to connect to a single driver of the above-mentioned system for driving multiple high-power LED units, and the device includes: a reverse polarity protector arranged to be electrically connected to the input port and each of the multiple output ports; and multiple open circuit protection circuits, each of the multiple open circuit protectors being operable to be connected to an output port; wherein the reverse polarity protector is operable to reject the polarity requirement when a load is connected to any output port with an incorrect polarity; and the open circuit protection circuit is operable to form a closed-loop series connection when no load is connected to the output port or the load is broken down.

Preferably, the reverse polarity protector is a diode bridge rectifier.

Preferably, each output port includes a corresponding open circuit protector.

Preferably, the input port is adapted to be connected to an LED driver, and each output port is adapted to be connected to a load comprising a high-power LED lamp unit.

According to a fourth aspect of the present invention, a system according to the first aspect, wherein the loads are connected in series, further comprises devices according to the second and third aspects of the present invention; wherein the input port of the device is operable to be connected to a single driver.

According to a fifth aspect of the present invention, a dimmer circuit is used with the above-mentioned single driver of the system for driving multiple high-power LED units, the dimmer circuit comprising at least one dimming interface operable to be connected to at least one dimming controller; and a capacitive element adjustable to maintain a power factor of at least 0.9 within the dimmer circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

The following invention will be described with reference to the accompanying drawings, in which:

FIG1 is a perspective side view of a prior art LED lamp unit with a driver and a heat sink;

FIG2 is a system configuration of a “one driver one lamp unit” configuration of a conventional LED lamp system;

FIG3 is a system diagram of a “one driver multiple lamp units” or “string driver” according to an embodiment of the present invention;

4 is a circuit diagram of an LED driver circuit for isolated alternating current (AC) applications according to an embodiment of the present invention;

5a and 5b are circuit diagrams of an LED driver circuit having a power factor converter driven by a 14-pin ASIC for isolated alternating current (AC) applications according to another embodiment of the present invention;

FIG6 is a table summarizing the advantages of the present invention over prior art systems for multiple MR 16 LED lamps;

FIG7 shows the simulation results of ripple-free constant DC current based on MR 16 load;

FIG8 shows another embodiment having a circuit arrangement in which the decoupling transformer operates in continuous mode;

FIG9 shows the current flowing through the rectifier circuit in continuous mode;

FIG10 shows the structure of a hysteresis controller for continuous operation of the circuit;

FIG11 is a PCB layout of an intermediate connector between an LED driver and a load according to another embodiment of the present invention;

FIG12 is a diagram showing a possible arrangement of a lighting system using an intermediate connector between the driver and the load;

FIG13 is another possible arrangement showing a lighting system using two intermediate connectors;

FIG14 shows a circuit diagram of an intermediate connector; and

FIG15 shows an overall block diagram of a dimmer circuit.

Other arrangements of the invention are possible, and consequently, the accompanying drawings are not to be understood as superseding the generality of the preceding description of the invention.

DETAILED DESCRIPTION

In the context of the present invention, references to "ripple-free" current and near-ripple-free current refer to an allowable ripple of less than (<) 5% of the specified rated current.

In the context of the present invention, a high power LED lamp unit refers to any LED lamp unit requiring a power of at least 5 Watts.

According to an embodiment of the present invention, there is an LED driver 10 for driving a plurality of high-power LED lamps 100, as shown in FIG4 . The LED driver 10 is particularly suitable for isolated alternating current (AC) applications and includes a primary side and a secondary side. The primary side of the LED driver 10 is decoupled from the secondary side by a decoupling transformer 11. The primary side includes an electronic switch 14, a bridge rectifier circuit 16, and an integrated circuit (IC) controller 18. Although FIG4 shows an isolated configuration, skilled artisans will appreciate that the circuit can be modified for a non-isolated configuration, wherein the decoupling transformer 11 can be replaced by other inductive elements.

To fulfill the decoupling function, transformer 11 is an isolation transformer, preferably a planar transformer. Transformer 11 is operable to operate in either continuous or discontinuous mode, although for illustrative purposes, Figures 4, 5a, and 5b illustrate circuitry suitable for transformer 11 operating in discontinuous mode. In continuous mode, as shown in Figures 8 or 10, certain output capacitors may be omitted. In the case of a planar transformer based on printed circuit board technology, the printed circuit board may be FR4 PCB, polyimide, or other thick copper foil (lead frame).

Resistor _RP and capacitor _CP are connected in a parallel configuration to the primary side of transformer 11. Diode _DP is connected to resistor _RP , capacitor _CP , and transformer 11. A conducting end of diode _DP is connected in a series configuration to the primary side of transformer 11. A non-conducting end of diode _DP is connected in a series configuration to resistor _RP and capacitor _CP .

Capacitor _CS is connected in parallel to the secondary side of transformer 11 for filtering the output voltage. A diode _DS is connected to the secondary side of transformer 11 and capacitor _CS . The conducting end of diode _DS is connected in series to the secondary side of transformer 11. The non-conducting end of diode _DS is connected in series to the positive terminal of capacitor _CS (where applicable). LED loads 100 are connected in parallel to capacitor _CS . Each LED load 100 can be connected in series with another LED load 100. The secondary side may optionally include a short-circuit protection circuit 44, which will be described in detail later.

Electronic switch 14 is typically a power transistor. In this embodiment, electronic switch 14 is more preferably a power MOSFET. In a MOSFET configuration, the drain of electronic switch 14 is connected to the conductive end of diode _DP and the primary terminal of transformer 11. The gate of electronic switch 14 is connected to an output pin of IC 18, and the source of electronic switch 14 is connected to ground potential.

It should be understood that the electronic switch 14 may be replaced by other functionally equivalent components.

IC controller 18 includes an internal oscillator configured to turn on the gate of electronic switch 14 for a specific on-time period T _ON (switching frequency) per clock cycle determined by the internal oscillator. IC controller 18 is preferably an application specific integrated circuit (ASIC) that is programmable to sense and calculate the discharge time of inductive elements _L1 and _L2 as primary inputs. ASIC 18 is programmable and configured to turn on the gate of electronic switch 14 with an on-time period T _ON per clock cycle based on the following inputs:

(a.) Reference constant K based on the discharge time of inductive elements _L1 and _L2 ;

(b.) Required output DC ripple-free current for LED I _OUT ;

(c.) The digitized voltage value V _DD (V _in ) tapped and digitized from the voltage divider 22 , the voltage divider 22

connected in parallel with the bridge rectifier 16;

(d.) The voltage of the core of the transformer 11 is measured by the voltage divider 30 and compared with the reference voltage.

a discharge time value T _OFF ; and

(e.) Switching period T (ie, the switching period of the electronic switch 14 determined by the oscillator).

Using the five inputs received, IC 18 calculates an output, T _ON , which is the on-time of electronic switch 14 expressed mathematically in equation (1).

The reference constant K is calculated as described in Formula 2 based on the inductance values of the primary winding and the secondary winding of the transformer 11 .

Where _L1 is the inductance of the primary winding of the transformer 11, and _L2 is the inductance of the secondary winding of the transformer 11. The value of reference K can be stored in a memory within IC 16. For a non-isolated DC flyback configuration, the reference constant K is calculated according to the following mathematical expression:

Where _L3 is the inductance value of the inductive element in the flyback configuration.

Using equations (1) and (2), I _OUT is derived as follows:

IC controller 18 may further include a dimming pin coupled to variable resistor 40 for dimming LED load 100. The dimming pin facilitates flexibility in dimming via various dimming devices such as a potentiometer, motion sensor, or infrared sensor.

The IC controller 18 is typically 8-pin. A high-resolution IC controller can be used to fine-tune the control level of the IC controller 18. In addition to fine-tuning the desired ripple-free current I _OUT , an active power factor controller (PFC) improves circuit performance.

In another embodiment below, a high resolution IC controller is described that has the capability to fine tune the control of the desired ripple-free current and provide active power factor control.

Another embodiment of the present invention (emphasis on the primary side) is shown in Figures 5a and 5b in the form of an LED driver 500 for driving multiple high-power LED lamp units 100. LED driver 500 includes a first electronic switch 513, a second electronic switch 514, a bridge rectifier circuit 516, and an integrated circuit controller 518. LED driver 500 further includes an active power factor controller (PFC) circuit 520. Compared to the previous embodiment, the active power factor controller (PFC) is operable to form an additional current controller stage to achieve an improved ripple-free constant DC current. Integrated circuit controller 518 is operable to control the switching frequency of first and second electronic switches 513, 514 to achieve a desired power factor and output a ripple-free current, _IOUT .

Integrated IC controller 518 is similar to IC controller 18 and includes an internal oscillator, a built-in analog-to-digital converter, and more. It also includes more pins for further control of the PFC controller. In this embodiment, IC controller 518 includes 14 pins. The overall resolution is higher (10 bits), allowing for better adjustment and fine-tuning of the switching frequency of electronic switches 513 and 514 and I _OUT .

The bridge rectifier 516 is operable to receive an AC input and generate a rectified voltage output. The rectified voltage output is passed through a capacitor _C4 . _C4 is operable to act as an input voltage filter to further filter the rectified voltage from the rectifier circuit 516. Capacitor _C4 is connected in parallel to resistors _R8 and _R9 and in series with an inductor _L4 .

Resistors _R8 and _R9 form an input voltage divider. In operation, the voltage between _R8 and _R9 is tapped as the input voltage (denoted as _VinP ) to the ASIC.

Inductor _L4 is connected in series with resistors _R10 and _R11 . Resistors _R10 and _R11 form a PFC voltage divider for providing a PFC feedback voltage to controller 518 via the _T2P pin input for PFC output voltage measurement.

The first electronic switch 513 is connected in series with the inductive element _L4 and in parallel with the PFC voltage divider. The first electronic switch 513 provides a variable frequency to control the PFC output voltage. Both the first and second electronic switches 513 and 514 are N-channel power MOSFETs. The gate of the first electronic switch 513 is triggered by the ASIC (MOSOUT pin), its drain is connected in series with _L4 , and its source is grounded.

In operation, the controller 518 drives the first electronic switch 513 to provide a necessary power factor voltage at the drain of the first electronic switch 513 .

It should be understood that the first electronic switch 513 may be replaced by other functionally equivalent components.

The power diode _D3 is connected in series with the inductive element _L4 . It allows the forward passage of the rectified PFC current; this is regulated by the first electronic switch 513.

_C5 is a capacitive filter used to filter the PFC output voltage.

Inductive element L ₄ can be a standard inductor, as shown in Figure 5a, or a transformer, as shown in Figure 5b. If L ₄ is a transformer, the transformer includes a primary inductor, L _4p , and a secondary inductor, L _4s . As shown in Figure 5b, L _4p is connected from pin 1 to pin 6; L _4s is connected from pin 1 to pin 7 of IC controller 518.

The following equation (4) is applied to the transformer variant to control the output voltage of the PFC:

V _PFC,OUT is the PFC output voltage, L _4p is the PFC transformer primary inductor value, L _4s is the PFC transformer secondary inductor value, V _in is the input voltage, T _Q2on is the on-time of first electronic switch 513, and T _Q2off is the discharge time of the PFC transformer. T _Q2on is controlled via the MOSOUT pin of controller 518. V _in and T _Q2off are feedback values used to ensure and verify that V _PFC,OUT correctly tracks the desired output voltage V _OUT .

Equation (4) is called a voltage follower, where V _PFC,OUT follows V _OUT ; in the sense that after solving the equation, if V _PFC,OUT is less than expected (within the allowable deviation), T _Q2on is increased, otherwise T _Q2on is decreased.

V _OUT is determined based on the total number of LED units and the desired current I _OUT to be supplied to the LED units.

For the second electronic switch 514, the operations and equations for adjusting and calculating _IOUT are the same as those described in equations (1) to (3).

As described above, the secondary side of the LED driver 10, 500 may further include a voltage protection circuit 44. Referring to FIG4, although not explicitly shown in FIG5a and 5b, the voltage protection circuit that may be included in the secondary side of the LED driver 500 includes a Zener diode 46, a silicon controlled rectifier (SCR) 48, and a resistor 50. When a short circuit is detected, the Zener diode 46 will conduct, thereby enabling the SCR 48 and reducing the output voltage of the LED 100.

The LED driver 10, 500 is described in the following example in the context of operation of driving a string of LED light units:

To operate the circuit, the variable resistor is adjusted to generate a voltage value N for _VR (LED driver 10) or _VinP (for LED driver 500), where the value N is an adjustment of the on-time period T _ON of the electronic switches 14, 514 corresponding to the generation of a maximum approximately ripple-free constant current to drive the plurality of LED lamp units 100. Adjusting the value of N by decreasing or increasing it will be based on feedback and directly result in a change in T _ON , T, and thus a corresponding change in I _OUT based on the variable resistor _VR to dim or brighten the LED lamp units 100.

For the optimization of equations (1) to (3), the circuit equations can be expressed in an alternative form:

A＝V _IN *T _ON *T _OFF (5)

B＝1/K*I _OUT *(T _ON +T _OFF +T _CALC ) (6)

Where T _CALC is the time after the inductive element discharges and is used to calculate the formula. The switching time period of the electronic switch is the sum of T _ON , T _OFF , and T _CALC .

During each adjustment cycle of I _OUT , the values of A and B are compared.

If A is greater than B, ie, A>B, then T _ON is adjusted to T _ON −N for the next time period T.

If A is less than B, that is, A<B, then T _ON is adjusted to T _ON +N.

When A is equal to B, T _ON is not updated _and remains unchanged.

Depending on the number of lamp units 100 and the required current I _OUT , the user performs design optimization by changing several key components as follows:

Inductors _L1 and _L2 of transformer 11;

the switching frequency, drain-source voltage V _DS and drain current _ID of the electronic switch 14, 514;

The values of capacitor _CS and diode _DS must be taken to ensure that the voltage across capacitor _CS should be higher than the voltage of the LED load 100.

The forward current I _F and repetitive peak reverse voltage V _RRM of the diode are the parameters to be considered when selecting a suitable diode _DS .

Once the above components are adjusted to the load specifications, the IC controller 18, 518 detects and calculates the duration of energy released to the LED load 100 via the core of the transformer 11 (or the inductive element for a non-isolated flyback configuration) to regulate a constant output current. Therefore, the controller 18, 518 can operate over a wide range of load voltages and constant currents for high-power LED lamps 100.

The described embodiment provides a nearly ripple-free constant DC current to a plurality of high-power LED lamp units 100. This configuration of one driver to multiple lamps is referred to by the applicant as a "string configuration."

As an optional feature, the IC controller 18, 518 may further include a multi-point control unit (MCU) to enable communication with intelligent control modules such as power line, digital addressable lighting interface (DALI), wireless protocols for overall lighting control systems.

The described embodiments are based on the concept of a single LED driver 10, 500 for driving multiple high-power LED lamp units 100. Compared to the prior art MR 16 system, which requires a separate LED driver 3 for each LED lamp unit 4, each high-power LED lamp unit is provided with a heat sink and a single driver. The heat sink is shaped and configured to dissipate heat only from the high-power LEDs, and the single driver is configured to provide a nearly ripple-free constant DC current to the multiple high-power LED lamp units. This standard ASIC driver design solution operates at a constant current and offers a wide range of flexibility to drive any number of LEDs within the overall lighting system. The advantages of this solution are summarized in FIG6.

FIG. 7 shows I _OUT measured from a high power LED load 100 , illustrating a range of ripple-free constant DC current.

The above embodiments shown in Figures 4, 5a and 5b illustrate an IC controller implementation as a current controller (i.e., utilizing _IOUT ); and a transformer 11, 511 operating in discontinuous mode. Due to the flexibility of programming the ASIC-based controller 18, 518, four different combinations and/or modes can be implemented as follows:

A. Voltage control instead of current control;

B. Discontinuous current measurement using primary inductor current feedback instead of T _OFF based feedback (or monitoring)

model;

C. Continuous mode using primary inductor current feedback instead of T _OFF based feedback (or monitoring)

formula; and

D. Continuous mode for hysteresis controller.

A. Voltage control instead of current control

For using voltage control instead of current control, equation (3) can be rewritten as:

Where _VOUT is the output voltage. Where _L1 is equal to _L2 , the equation is modified to:

B. Discontinuous current measurement using primary inductor current feedback instead of T _OFF based feedback (or monitoring)

model

For the discontinuous mode with primary inductor current feedback instead of T _OFF -based feedback (or monitoring), the relationship between the peak current I _MAX , the input voltage V _IN and the inductive element L can be mathematically expressed as:

In the case where the inductive element L is a single inductor such as used in a non-isolated configuration,

Substituting equation (6) into equation (3), we obtain:

And, in the case where the inductive element L is a transformer, _L1 and _L2 represent the primary and secondary inductances respectively,

In order to apply equation (7) or (8), the circuits shown in Figures 4, 5a and 5b can be modified so that the primary current can be read by the ASIC controller through a resistor from the source of the electronic switch 14, 514 to ground, or using a current transformer in series with the electronic switch 14, 514, or a filter inductor in the case of a forward configuration.

C. Continuous mode using primary inductor current feedback instead of T _OFF based feedback (or monitoring)

For continuous mode with primary inductor current feedback instead of _TOFF based feedback (or monitoring), it is understood that the current flowing through the rectifier diode string to the LED is the same as the current on the LED.

The waveform of the current in continuous mode is shown in Figure 9. For a given on-time T _ON , if T _OFF is fixed, the current across the diode can be calculated as:

Here, T=T _ON +T _OFF +T _CALC ; T _CALC is the discharge timing of the transformer or inductor element.

All the above information can be obtained from the primary inductive element L. Specifically, the circuit arrangement shown in FIG8 includes:

i. A resistor in series with the electronic switch;

ii. A current transformer in series with an electronic switch; and

iii. Filter inductor.

The circuit arrangement shown in Figure 8 includes a first transformer 811 to isolate the load. A filter inductor 820 is used in the same way as the inductor in a hysteretic controller.

The output current I _OUT is controlled by means of feedback from a resistor 822 connected to the source of the electronic switch.

Resistor 822 is used for protection purposes rather than for control purposes. A reset circuit 812 comprising inductor 823 and diode 824 is used in the forward configuration to completely discharge the residual energy in the transformer core. This is used to prevent the core from saturating after a certain operating time.

D. Continuous Mode for Hysteretic Controllers

The structure of the hysteresis controller is shown in Figure 10. For implementation, the values of I _MAX and I ₁ can be fixed according to equation (9) and the determined T _ON and T _OFF timings. However, the current I _OUT will be the area below the graph.

It should be understood that the continuous mode described above is only particularly suitable for non-isolated flyback and feedforward configurations. However, it reduces the minimum number of required components and can provide ripple-free current without the need for load capacitors, thereby achieving cost savings.

In the embodiment described, the dimmer 40 can be used as a module for SSL lighting dimming control to save energy, replacing a traditional triac dimmer. The dimmer 40 is arranged and operable to use energy only when light is needed; otherwise, the light is automatically dimmed to a reduced intensity or turned off completely (both of which save energy compared to turning the light fully on).

As shown in Figures 4, 5a, and 5b, the IC controller is connected to a dimmer 40 for better dimming performance and energy saving, for example, at a low dimming level, less than 10% of the total light output, the power factor is maintained at or above 0.9 to meet the purpose of energy saving. Although the dimmer 40 is shown in Figures 4, 5a, and 5b, it is readily understood by those skilled in the art that the dimmer 40 can be easily included in the circuit shown in the isolated/non-isolated configuration and continuous or discontinuous mode.

Referring to FIG. 15 , further explanations regarding the operation of the dimmer 40 are elaborated in detail to meet the above purposes of energy saving and maintaining a high power factor. FIG. 15 constitutes another embodiment, including a dimmer circuit for use with an LED driver, the dimmer circuit including at least a dimming interface operable to be connected to at least one dimming controller; and a capacitive element adjustable to maintain a power factor of at least 0.9 within the dimmer circuit.

As shown in FIG. 15 , the dimmer 40 may include various devices that can be connected to a dimming interface 1670 , including pins of an IC controller 18 , 518 for lighting dimming control.

When the power is turned on, current flows to rectifier 1516, which then turns on switching power supply 1600, including ASIC controllers 18, 518. This provides an isolated or non-isolated supply of ripple-free, constant DC output current 1610. Switching power supply 1600 can be isolated or non-isolated, and depending on the configuration, inductive element 1511 can be an isolation transformer. The output of inductive element 1511 provides an isolated or non-isolated, ripple-free, constant DC output current 1610 to LED load 1700 to turn on the light. By default, LED load 1700 consumes 100% of the energy to turn on the light unless the power is turned off.

The dimmer 40 may be a 0-10V dimmer 1708. When the dimmer is set to 10V, the DC output current 1610 sets the light output to 100%. When the dimmer is set to 5V, the DC output current 1610 sets the light output to 50% of the total light. At 0V, no light is provided.

An infrared (IR) remote control 1711 can also be used for remote lighting control. This configuration requires the dimming interface to have a suitable IR receiver so that when the IR transmitter sends a signal, the IR receiver will decode the signal and accordingly generate a PWM duty cycle from a range of 0-100% for dimming control. When the duty cycle is set to 100%, the DC output current 1610 will then set the light output to 100%. When the IR transmitter sends a 50% duty cycle, the DC output current 1610 will deliver 50% of the total light output. If the IR transmitter sends a 0% duty cycle PWM signal, no light is provided.

Another type of dimmer can be embodied as a motion sensor 1712. When the motion sensor 1712 does not detect motion, the DC output current 1610 changes the output current from 100% to 20% for dimming purposes, or even turns off the output current. This means that energy is only used when the motion sensor 1712 detects motion.

Another option is to use an environmental sensor 1714 to detect environmental conditions, for example, when dawn comes, the DC output circuit 1610 will turn off the output current and turn off the light 1700. When the environmental sensor 1714 detects that the environment becomes dusk, the DC output circuit 1610 turns on the output current to 100%.

It should be understood that any other device designed with a 0-100% PWM output duty cycle can be connected to the dimmer interface for LED lighting dimming control. The dimmer interface is a circuit comprising one or more microcontroller devices that detects dimming signals from various dimmers (IR remote, motion, ambient, etc.) and converts the input dimming signal into an analog voltage for the ASIC controller for dimming control. It can also be included in the ASIC controller mentioned in other embodiments. In terms of implementation, the "dimmer interface" can be a small module board mounted on the power supply PCB or integrated into the power supply circuit PCB.

Capacitor 1630 is a component that affects the power factor. When the dimming circuit is activated, the switching power supply 1600 will automatically charge the capacitor 1630 to maintain the power factor ≥ 0.9, so that no matter how low the dimming level becomes, the power factor is always maintained at ≥ 0.9.

The dimmer design according to various embodiments enables users to dim their LED lighting units to as low as 1-2% of the original driving current without any flickering.

According to another embodiment of the present invention, a device 1100 is provided for use with any of the LED drivers 10 and 500 described in the previous embodiments. As shown in FIG11 , the device 1100 is an intermediate connector between the LED driver 10 and 500 and the LED load 100. The intermediate connector is hereinafter referred to as a "junction box."

Figure 11 shows the PCBA design of a junction box 1100. The junction box 1100 includes an input connector 1120 and a plurality of output connectors 1140 arranged to achieve the following:

a. Easy to install high power LED lamp load 100;

b. It is beneficial for multiple LED lamps 100 connected in series and reduces the problem of a complete open circuit of the system in the event of damage to the high-power LED lamp 100;

c. Reduce or completely eliminate common errors during installation, especially those related to electrical polarity reversal.

Regarding point (b.) above, the series connection of LED lighting units 100 ensures that each lamp unit 100 will be driven with exactly the same current, so each LED lighting unit 100 will produce the same brightness. For lighting systems where uniform brightness is important, series connection is advantageous over parallel connection.

To achieve the above, the junction box includes a reverse polarity protector 1160 and an open circuit protector 1180. The reverse polarity protector is preferably a rectifier 1160.

As shown in Figure 11, there are nine output connectors 1140. The input connectors 1120 are arranged to connect to the driver output connectors, and the junction box output connectors 1140 are arranged to connect to the LED load 100, which includes an SSL driverless lighting unit strip end cable.

The input connector 1120 is typically a header type connector for coupling with the output connector of the LED driver 10, 500, which is typically a cable entry plug-in type. The output connector 1140 is typically a cable entry type so that an electrical connector of the LED lamp 100, such as a strip end SSL driverless cable type, can be plugged into it to create a closed electrical circuit.

FIG. 12 shows a lamp system comprising a single LED driver 10 , 500 , a single junction box 1100 and an SSL driverless light unit/load 100 .

The LED driver 10, 500 with the cable plug-in connector 1100 is connected to the input connector 1120 and the SSL driverless lighting unit with the ribbon end cable is plugged into the output connector 1140 to create a fully networked lighting system for lighting purposes once powered up.

FIG. 13 shows another possible arrangement with two junction boxes 1100 , where the entire system includes a single string driver 10 , 500 , a dual junction box 110 , and an SSL driverless lighting unit 100 .

The required driver output voltage predetermined by qualified personnel will determine the total number of SSL driverless lighting units 100 or the number of junction boxes that should be used for the entire lighting network in order to drive all SSL driverless lighting units with the required designed ripple-free constant current.

As a simplified example, if the driver 10, 500 is designed with a maximum output voltage rating of 170V DC and only a single junction box is present in the lighting system, the forward voltage per SSL driverless lighting unit is limited to 18.8V DC per unit (170V DC divided by 9 units). If two junction boxes 1100 are used, the forward voltage per SSL driverless lighting unit is limited to 10V DC per unit (170V DC divided by 17 units).

FIG14 shows a circuit diagram between the input and output connectors, and the arrangement of the rectifier 1160 and the open circuit protection circuit 1180. The bridge rectifier 1160 acts as reverse polarity protection to prevent polarity issues between the driver 10, 500 and the junction box 1100 during installation. If the installer mistakenly connects the lamp unit 100 with reverse polarity, the reverse polarity protector in the form of the bridge rectifier 1160 protects the driver 10, 500 and the junction box 1100 from damage. The open circuit protection circuit 1180 preferably includes a Zener diode 1220, a silicon controlled rectifier (SCR) 1240, and a resistor 1260 at each output port 1140.

An additional rectifier can be added to the lighting unit 100. This solves the following problems:

Although the rectifier 1160 provides reverse polarity protection between the driver 10, 500 and the junction box 1100, a particular lighting load 100 must be connected with the correct polarity in order for that particular lighting unit to operate correctly. If the lighting unit 100 is connected with reverse polarity, the system will not operate. To overcome this problem, the lighting unit must also have a rectifier to provide reverse polarity protection.

When any open circuit occurs at any output connector 1140, and/or when the voltage exceeds the specified reverse breakdown voltage of the Zener diode 1220, causing the Zener diode 1220 to operate in reverse bias mode, the silicon controlled rectifier (SCR) 1240 will be triggered at the gate terminal to allow current to flow through the silicon controlled rectifier (SCR) 1240, thereby maintaining a closed loop for the entire lighting system so that other connected lighting units 100 in the network continue to operate normally. Resistor 1260 acts as a current limiter for the Zener diode 1220 to prevent excessive current from flowing through the Zener diode 1220. Another resistor 1280 can be connected in parallel with the open circuit protection circuit and in parallel with the output connector 1140.

As an alternative or in addition to the open circuit protector 1180, it should be understood that the resistor 1280 can be configured to act as a jumper/bypass resistor for placement on specific output connectors 1140 that are not connected to their loads 100, so as to maintain a closed loop for the entire lighting system. In the event that specific output connectors 1140 are permanently assumed to be without any load connected, the open circuit protectors connected to these output connectors can be removed.

Therefore, the junction box 1100 is designed and implemented together with the string driver to overcome the above-mentioned disadvantages caused by the series connection.

Examples of Operational Technical Specifications

The following are the recommended operating specifications for the LED driver 10, 8-pin (low resolution) configuration:

Operating voltage: US 100 to 120VAC; Europe 220 to 240VAC

Operating frequency: 50/60 Hz

AC current: US 0.2 amperes (A); Europe 0.1A

Inrush current: The maximum allowable current in the United States is 4A; the maximum allowable current in Europe is 12A

Leakage current: less than (<) 0.7 mA

Efficiency (full load): greater than (>) 83%

Power factor (full load): greater than (>) 0.98

The following lists the output specifications based on 120VAC (US) / 230VAC (Europe) input, rated load and 25 degrees Celsius ambient temperature (8-pin configuration):

Output channels: 1

Output voltage range: 12 to 36 VDC

Output current: 600 or 700mA

Current tolerance: ±5%

Current adjustment range: not adjustable

Rated power: 21.6W _MAX (at 600mA) and 25.2W _MAX (at 700mA)

The following lists the recommended operating input specifications for the LED driver 10, 500, and 14 pin configurations:

Operating voltage: US 100 to 120VAC; Europe 220 to 240VAC

Operating frequency: 50/60 Hz

AC current: US 1.3 amperes (A); Europe 0.6A

Inrush current: The maximum allowable current in the United States is 7A; the maximum allowable current in Europe is 30A

Leakage current: less than (<) 0.7 mA

Efficiency (full load): greater than (>) 86%

Power factor (full load): greater than (>) 0.96

The following are the output specifications for a 10, 500, 14-pin LED driver with two output channels based on 120VAC (US) / 230VAC (Europe) input, rated load, and 25°C ambient temperature:

Output channels: 2

Output voltage range: 35 to 85 VDC (single channel), total 70 to 170 VDC

Output current: 600 or 700mA

Current tolerance: ±5%

Current adjustment range: not adjustable

Rated power: 102W _MAX (at 600mA) and 119W _MAX (at 700mA)

The LED driver 10 , 500 is particularly suitable for LED downlights, troffer LED lighting, and MR 16 , particularly in the temperature range of 0 degrees Celsius to 40 degrees Celsius.

In addition, the following advantages are also obvious:

a. Safer method for LED lighting units

Because LED drivers 10 and 500 are isolated DC devices and operate only with DC-driven LED lighting units, there are no safety concerns associated with AC current used in LED lighting units 100, which are on the secondary side and isolated from the power mains. Because LED drivers 10 and 500 are isolated from LED lighting units 100, there are no size limitations in the design. Since they are built into a built-in configuration, LED drivers 10 and 500 can be designed based on safety requirements.

b. High electrical efficiency

The LED driver 10, 500, known as a "string driver," operates in a cooler environment because it is isolated from the LED load unit 100 and is not affected by the heat dissipated by the LED unit 100 during continuous operation. This reduces heat losses in the LED driver 10, 500, thereby consuming less power during operation and improving efficiency. Compared to the prior art, where each LED lamp includes its own driver connected directly to the AC mains, power efficiency is significantly improved compared to AC-driven lighting units in a complete lighting system because the total power loss applies only to that specific individual driver, while AC-driven lighting units can have higher total power losses due to losses in each lighting unit.

c. High efficiency (lumens/watt)

As an associated advantage, the string configuration provides a cooler operating environment, which results in lower optical losses in the LED devices and therefore higher luminous flux presented by the LED devices, ultimately improving the efficiency (lumens/watt) of the overall lighting system.

d. Longer service life

The ASIC-controlled LED driver 10, 500 eliminates the need for short-life components such as aluminum electrolytic capacitors, which extends the life of the LED driver 10, 500. Regarding the LED lamp unit 100, operating cooler and at a near-ripple-free constant current significantly improves the performance and reliability of the LED device and slows down the overall performance degradation process on the LED device 100, ultimately extending the life of the entire LED lighting unit.

e. Wide range of application options

The flexible design for a single LED driver 10, 500 is applicable to any type of DC driven LED lighting unit and, with minor fine tuning of specific components as described earlier, can theoretically drive an unlimited number of LEDs in the overall lighting system.

f. Cost-saving solutions

The string driver configuration is a cost-effective solution because a single LED driver 10, 500 can drive a series of DC-driven LED lighting units, while the prior art configuration requires a driver for each LED lighting unit. In addition, this solution also provides more competitive manufacturing costs and design component costs, especially for heat sinks.

g.Easy to maintain

Since the individual LED drivers 10, 500 are isolated from the LED lighting unit 100, if any fault occurs in the lighting system due to a faulty LED driver 10, 500, the user only needs to replace the faulty LED driver without having to disassemble the entire LED lighting (built-in concept). This maintenance process is simple and can be completed in a relatively short period of time.

h. Miniaturization in form factor

The heat sink used in the luminaire can be smaller in size. Here, the heat sink is designed only to dissipate heat generated by the LED lighting unit 100; no heat is generated from the AC-DC LED driver due to the isolation between them. Furthermore, since the entire system requires fewer components and thus uses less material than integrated concepts, a single driver can be designed at this optimal size. Furthermore, the introduction of planar transformers, replacing the bulky form factors of conventional transformers, further enhances the slimmer appearance of the driver solution.

More significantly, compared to prior art systems where each LED lamp unit requires its own AC-to-DC driver, the LED drivers 10 and 500 require fewer components and fewer component copies, thereby reducing the driver solution form factor. Furthermore, the manufacturing process is simplified, resulting in improved production throughput and yield.

More significantly, in a string configuration, the heat sink form factor of each LED lighting unit 100 is reduced, as each heat sink only needs to handle the heat dissipated by the LED lighting unit 100. This is because the LED driver 10, 500 is isolated from the LED lighting unit 100. This benefits component costs due to reduced material usage. Furthermore, the overall design cycle is further shortened, as LED lighting unit 100 and LED driver 10, 500 design activities can be performed simultaneously, resulting in improved time-to-market.

The junction box 1100 further provides the following additional advantages to the string drive concept:

a. Correct installation

The junction box 1100 is designed with a "trouble-proof" design in mind, providing a seamless installation experience for the end user. Polarity is a concern during installation to ensure the entire lighting system functions as intended. By providing an interface with the driver 10, 500 and the SSL driverless lighting unit 100 through a bridge rectifier within each junction box, accidental reverse polarity connections are eliminated during installation. Regardless of polarity, as long as continuity exists between the driver 10, 500 and the SSL driverless lighting unit 100, the lighting units 100 within the lighting system will function properly. Furthermore, the interface between the driver output and the junction box input features a header and plug-in connector design, completely eliminating the possibility of connecting the driver output to any junction box output connector.

b.Easy to install

The junction box 1100 includes a connector design for connection purposes with the drivers 10, 500 and the driverless SSL lighting unit 100. Users will therefore find it easy to connect or plug the strip-end cables into the correct or dedicated connectors. Additionally, due to the simplified installation, less time is spent on installation and system setup, resulting in lower costs.

c. Safer installation

Since only DC power is present at the junction box 1100, a safe environment is created for installation.

d. Installation flexibility

Because the string driver concept has no wire length constraints during installation, users can flexibly arrange the SSL driverless lighting units according to their preferred design and/or needs. Users can easily extend the wires of the SSL driverless lighting unit 100 to their desired length to meet applications with specific wire specifications, such as American Wire Gauge (AWG) 16-24, to obtain a perfect match for the junction box input/output connectors 1120, 1140. Moreover, the junction box is also designed to support dual (or potentially a larger number of junction box connections), which provides additional flexibility in installation.

e.Easy to maintain

The specific design features of the junction box as described in the embodiments enable the user/installer to easily identify a faulty unit and perform the necessary maintenance as they would normally do, even if the string drives are operated in a series connection.

f. Reliable connection

Since the input/output connectors 1120, 1140 connected within the lighting system are either of a wire lead-in type or a latching type, a good connection is provided compared to the conventional screw fastening method widely used in the market.

It should be understood that the above embodiments are provided only as examples of the present invention, and further modifications and improvements thereof, which will be apparent to those skilled in the relevant art, are deemed to be within the broad scope and limits of the present invention. Moreover, although a single embodiment of the present invention has been described, it is intended that the present invention also covers various combinations of the described embodiments.

Claims (26)

1. A system for driving multiple high-power LED units, the system comprising a single driver for providing ripple-free constant DC to the multiple high-power LED units. The single driver has a sensing element that functions as a transformer, the sensing element being connected to the plurality of high-power LED units at the secondary end of the transformer. The single driver is configured to operate in at least one of the following configurations: isolated AC flyback configuration and non-isolated configuration. The single driver includes a digital controller that is programmed to adjust the ripple-free constant DC at predetermined time intervals based on the detection and calculation of the duration taken to release energy to the LED lamp unit, thereby adjusting the ripple-free constant DC, wherein the detection and calculation are based on the discharge time value of the transformer core measured by a voltage divider and compared with a reference voltage. 2. The system of claim 1, wherein the digital controller is an application-specific integrated circuit (ASIC); the ASIC is further operable to detect and calculate the duration for which the energy is released from the core of the transformer to the plurality of high-power LEDs, in order to regulate and provide the ripple-free constant DC. 3. The system of claim 2, wherein the application-specific integrated circuit is programmed to receive feedback as input for each clock cycle based on the duration of energy release from the core of the transformer to determine the amount of ripple-free constant DC for the next clock cycle. 4. The system of claim 3, wherein the application-specific integrated circuit is programmed to provide a voltage waveform at each clock cycle to turn the electronic switch on or off. 5. The system according to claim 1, wherein each of the plurality of high-power LED lamp units is connected in series with the other high-power LED lamp units. 6. The system of claim 1, wherein the single driver is electrically connected to a dimmer circuit for adjusting the brightness of the plurality of high-power LED lamp units. 7. The system according to claim 6, wherein the dimmer circuit includes a potentiometer, an infrared interface, and a motion sensor or an environmental sensor. 8. The system of claim 6, wherein the system includes a capacitor operable to change its capacitance to maintain a power factor of at least 0.9 when the dimmer circuit is adjusted. 9. The system of claim 7, wherein the potentiometer is operable within a voltage range of 0 to 10V. 10. The system according to claim 1, wherein the secondary terminal of the transformer is electrically connected to a short-circuit protection circuit. 11. The system of claim 2, wherein the application-specific integrated circuit is coupled to an active power factor controller. 12. The system of claim 11, wherein the active power factor controller comprises at least one voltage follower. 13. The system of claim 2, wherein the application-specific integrated circuit is configured with 14 pins. 14. The system of claim 1, wherein each high-power LED is provided with a heat sink, the heat sink being shaped and configured to dissipate heat only from the high-power LED. 15. The system of claim 2, wherein the system further comprises an electronic switch, wherein the ripple-free constant DC is achieved by means of voltage control according to the following equation: Wherein, _VOUT is the voltage across the output terminal; _VIN is the input voltage; _TOFF is the discharge time of the core of the isolation transformer; _TON is the turn-on time of the electronic switch; _L1 is the inductance value of the primary winding of the transformer, and _L2 is the inductance value of the secondary winding of the transformer. 16. The system of claim 1, wherein when the single driver operates in the non-isolated configuration, the sensing element operates in continuous mode according to the following equation: Wherein, _TOFF is the discharge time of the sensing element, which is fixed as a constant; _TON is the turn-on time of the electronic switch; T is the switching period of the electronic switch, which is the sum of _TON , _TOFF and _TCALC , where _TCALC is the time used to calculate the formula after the discharge time of the sensing element; _I1 is the required reference current, and _IMAX is the peak current. 17. The system of claim 16, wherein, for the hysteresis controller configuration, the values of _IMAX and _I1 are fixed, and the timings _TON and _TOFF can be determined. 18. A single driver for a system for driving a plurality of high-power LED units as claimed in claim 1, comprising: At least one integrated circuit (IC), said integrated circuit being programmable using a hardware description language; A first electronic switch operable to provide a first switching time period for controlling a power factor voltage, the first switching time period being programmable by the at least one integrated circuit; and A second electronic switch is operable to provide a second switching time period to regulate the ripple-free constant DC current flowing into the at least one LED, the second switching time period being programmable by the at least one integrated circuit. 19. The driver of claim 18, wherein the first and second electronic switches are power MOSFETs. 20. The driver of claim 18, wherein the at least one integrated circuit is an application-specific integrated circuit (ASIC). 21. A device having an input port and a plurality of output ports, the input port being operable as a single driver for connecting to a system according to claim 1 for driving a plurality of high-power LED units, the device comprising: A reverse polarity protector is arranged to be electrically connected to the input port and each of the plurality of output ports; and Multiple open-circuit protection circuits, each of the multiple open-circuit protectors being operable to be connected to an output port; The reverse polarity protector is operable to reject polarity requests when a load is connected to any of the output ports with incorrect polarity; and the open-circuit protection circuit is operable to form a closed-loop series connection when no load is connected to the output port or the load breaks down. 22. The device according to claim 21, wherein the reverse polarity protector is a diode bridge rectifier. 23. The device of claim 21, wherein each output port includes a corresponding open-circuit protector. 24. The device of claim 21, wherein the input port is adapted to be connected to an LED driver, and each of the output ports is adapted to be connected to a load comprising a high-power LED lamp unit. 25. A system according to claim 1, further comprising a device according to any one of claims 21 to 24; wherein the input port of the device according to any one of claims 21 to 24 is operable to be connected to the single driver. 26. A dimmer circuit for use with a single driver of a system for driving a plurality of high-power LED units according to claim 1, the dimmer circuit comprising at least one dimming interface operable to connect to at least one dimming controller; and a capacitive element adjustable to maintain a power factor of at least 0.9 within the dimmer circuit.