HK1139274A - Dimming circuit for controlling electrical power - Google Patents

Description

Dimming circuit for controlling electric power

Technical Field

The present invention relates to controlling electrical power to a load. More particularly, the present invention relates to a dimming circuit for controlling electric power to a load.

Background

Devices for controlling electrical power to a load, such as a lamp, are well known. Most basic are switches that allow an individual to turn a light (or other device) on or off. Some switches include a dimming function that allows an individual to customize the amount of power supplied to the lamp to achieve a desired level of illumination. For example, some switches contain manual regulators that allow an individual to select the brightness of the light.

Various dimmer switch (dim switch) configurations have been disclosed. Some dimmers are used to control the power available through a conventional wall socket. One example of the use of such dimmer switches is to provide light control in a room without the need to provide a dedicated light source and switch on separate circuits. However, builders sometimes provide dimmable wall sockets into which lamps can be plugged as a way of providing dimmable light in a room. This is cheaper than providing separate lighting circuits and switches.

While various configurations of such devices are known, those skilled in the art are constantly striving to make improvements. One area where improvements are desired is where it is desirable to reduce the cost and complexity of such devices. Many such devices include an inverting control circuit that includes two MOSFET switches configured in a known manner. It is difficult to control the MOSFET over the entire AC current cycle. It has been proposed to include an RC circuit for controlling the voltage applied to the gate and source of the MOSFET switch. The introduction of a full wave rectifier reduces the efficiency of the overall circuit. A more economical alternative is thus desired.

Disclosure of Invention

One example dimming circuit includes an isolated DC voltage source selectively coupled to a gate and a source of a MOSFET switch, where the MOSFET switch controls power to a load.

In one example, the control module controls a switch that selectively couples the isolated DC voltage source to the gate and source of the MOSFET switch, thereby controlling the amount of power supplied to the load through the MOSFET switch.

The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description. The drawings that accompany the detailed description can be briefly described as follows.

Drawings

Fig. 1 is a block diagram of the entire electric power control system.

Figure 2 is a schematic diagram of a dimmer circuit designed according to one embodiment of this invention.

Detailed Description

Fig. 1 shows a lighting control circuit 20 for a building. The plurality of dimmer switches 22A, 22B communicate with the multi-channel receiver 24 via a wireless connection. One example of receiver 24 includes a commercially available component. One example is the product RCM130C available from Enocean. The use of a wireless receiver and a wireless switch is not limiting to the invention, but is mentioned only as one possible type of system. The wireless connection between switch 22 and receiver 24 allows the switch to be located remotely from receiver 24. For example, the receiver 24 may be located at or near an electrical outlet (outlet) in a selected room, while the switch may be located at any convenient other location in or near the room.

The receiver 24 communicates with a microcontroller 26, which microcontroller 26 in turn communicates with a dimmer circuit 28. The dimmer circuit 28 controls the brightness of several lamps 30A, 30B. The illustrated dimmer circuit 28 includes a timing circuit 40, a dimmer portion 42, and a power train portion 44. The illustrated example also includes an overload protection portion and a heat treatment portion.

One embodiment of the dimmer circuit 28 is shown in fig. 2. The microcontroller 28 provides a timing control signal input to the timing section 40. The timing control signal in one example comprises a pulse width modulation control signal. The timing control signal controls when the dimming portion 42 activates the MOSFET switch 46 of the power train portion 44 to control the amount of power supplied to the load 50. The microcontroller 26 determines how to set the timing control signal based on a user selected setting, such as a desired dimming level. In one embodiment, the microcontroller 26 provides a pulse width modulation input using existing techniques to achieve the corresponding desired amount of dimming.

In the example shown, power train portion 44 includes MOSFET46 because MOSFET46 is effective for certain power values (e.g., up to about 600W). Another example is effective for higher power values and includes IGBTs in place of the MOSFETs 46.

An example of the load 50 is a light bulb. Controlling the light intensity of the light bulb is one example of the use of the illustrated device. In this example, the load 50 is inserted into a wall socket having terminals (terminal) shown as 52 and 54.

In one example, the MOSFETs 46 operate according to a known inverted control strategy to supply the load 50 with power (e.g., line AC) from the source 56 when the gate and source of each MOSFET46 is coupled to a voltage sufficient to set that MOSFET46 to an operating state (e.g., conductive). In this example of inverted control, the MOSFET46 is turned on at 0 volts and turned off at high voltage. In another example, a positive phase control strategy is used in which the MOSFET46 is turned on at a high voltage and turned off at 0 volts. Another example includes the MOSFET46 turning on at a non-zero voltage and turning off at another non-zero voltage.

The dimming portion 42 controls when the power train portion 44 is on and thus controls the amount of power provided to the load 50. For example, the amount of power supplied to a light bulb is controlled to control the luminous intensity of the bulb.

In this example, the isolated DC voltage source 60 is selectively coupled directly to the gate and source of the MOSFETs 46 to set them to direct the power delivered to the load. The isolated DC voltage source 60 has a floating ground 62. The switch 64 is responsive to a timing control signal input from the microcontroller 26 and enters an operative state (e.g., conductive) to couple the isolated DC voltage source 60 to the MOSFET 46. In the example shown, the switch 64 includes an optocoupler component. Other examples include a delay switch or transformer component to selectively couple the isolated DC voltage source 60 to the MOSFETs 46.

In one example, the isolated DC voltage source 60 provides 12 volts. In another example, a lower voltage is used. The voltage of the isolated DC voltage source 60 is selected to be sufficient to turn on the MOSFET46 to the saturation region.

One example includes using a stand-alone DC-DC converter to implement the stand-alone DC voltage source 60. Another example includes a second order transformer. Those skilled in the art who have the benefit of this description will realize what components will be best suited to include an independent DC voltage source in a particular embodiment.

The illustrated example includes voltage control components for controlling the voltage to the gate and source of the MOSFET 46. The illustrated example includes resistors 66 and 68 and a zener diode 70. The resistor 66 sets the turn-on speed and the time required to turn on the MOSFET 46. The resistors 66 and 68 set the turn-off speed and the time required to turn off the MOSFET 46. In one example, the resistance of the resistor 68 is much greater than the resistance of the resistor 66 so that the resistor 68 is effective to set the turn-off time of the MOSFET 46. The turn-off speed and the turn-on speed are selected to avoid oscillation of the MOSFETs 46 and to avoid heat generation due to the MOSFETs 46 being in the linear operating region for too long.

For example, the zener diode 70 provides over-voltage protection to protect the MOSFETs from voltage spikes and noise. The zener diode 70 is configured in a known manner to maintain the voltage supplied to the MOSFET gate and source inputs at or below the diode's reverse breakdown voltage. One example does not include a zener diode.

One advantage of the disclosed example is that the MOSFETs can be fully controlled during a complete AC cycle without requiring a rectifier. The disclosed example is a more efficient circuit configuration than other circuits that rely on an RC circuit and rectifier control MOSFETs.

The preceding description is exemplary rather than limiting in nature. Those skilled in the art will recognize certain modifications to the disclosed examples that do not depart from the essence of this invention. The following claims should be studied to determine the true scope and content of this invention.

Claims (14)

1. A dimmer circuit comprising:

at least one switch configured to be placed between a power source and a load; and

an independent DC voltage source selectively coupled to the at least one switch to set the switch to provide power from a source to a load.

2. The dimmer circuit of claim 1, wherein the at least one switch comprises two MOSFETs, and the isolated DC voltage source is selectively coupled to the gate and source of the MOSFETs.

3. The dimmer circuit of claim 1, comprising:

a second switch positioned between the isolated DC voltage source and the at least one switch, the second switch having a first operating state in which the isolated DC voltage source is coupled to the at least one switch and a second operating state in which the isolated DC voltage source is not connected to the at least one switch.

4. The dimmer circuit of claim 3, wherein the second switch comprises an optocoupler.

5. The dimmer circuit of claim 3, comprising:

a controller providing a timing control signal that controls an operating state of the second switch to selectively couple the isolated DC voltage source to the at least one switch.

6. The dimmer circuit of claim 5, wherein the timing control signal comprises a pulse width modulated signal configured to achieve a desired amount of power delivered to the load through the at least one switch.

7. The dimmer circuit of claim 1, comprising at least one voltage control component between the isolated DC voltage source and at least one switch for limiting the voltage applied to the at least one switch.

8. The dimmer circuit of claim 7, wherein the at least one voltage-controlled component comprises a zener diode.

9. The dimmer circuit of claim 7, wherein the at least one voltage-controlled component comprises a first resistor operable to control an on-time of the at least one switch and a second resistor operable to control an off-time of the at least one switch.

10. A method of controlling a dimmer circuit, comprising the steps of:

an isolated DC voltage source is selectively coupled to at least one switch through which power is provided from the source to the load.

11. The method of claim 10, comprising:

selectively controlling a second switch between the isolated DC voltage source and the at least one switch such that the second switch controls when the isolated DC voltage source is coupled to the at least one switch.

12. The method of claim 10, comprising:

limiting the voltage provided by the isolated DC voltage source to the at least one switch to maintain the provided voltage at and below a selected value.

13. The method of claim 10, wherein the at least one switch comprises two MOSFETs.

14. The method of claim 13, comprising using two MOSFETs for inverting control.