HK1148160A - Led lamp replacement of low power incandescent lamp - Google Patents

Description

LED lamp replacement for low power incandescent lamps

Technical Field

The present application relates to LED (light emitting diode) lamps, and more particularly to LED lamps that replace standard incandescent lamps.

Background

Incandescent lamps have existed for over a hundred years. Incandescent lamps are pleasing and aesthetically pleasing due to their high Color Rendering Index (CRI) and warm color temperature. However, inefficiency, short life, and waste of energy have been major drawbacks that have forced consumers to turn to more efficient light sources such as fluorescent lamps.

Incandescent lamps have been no longer used for decades if not fluorescent lamps have a low CRI, are physically large, have a flickering effect and comprise harmful substances such as mercury.

Until the late eighties of the twentieth century, LEDs were mainly used as indicator lights in electronic devices. The high efficiency compared to incandescent lamps makes LEDs very popular. By the late nineties of the twentieth century, high intensity LEDs, including white LEDs, began to rise. Today, advances in LED chip design and manufacture have made it more practical to replace incandescent lamps than ever before.

However, there are several challenges that make LED lamps slow in popularity:

1. lower maximum LED junction temperature and heat dissipation

LED to equal the voltage drop V_DAnd a drive current I_DThe rate of the product of (a) generates heat,

where P is power and Q is the thermal energy generated by the LED. The LED junction temperature rise is related to the difference between the heat generated and the heat dissipated. Heat dissipation is related to the heat sink surface area, the thermal conductivity of different media and interfaces, and the temperature difference between the heat sink and the ambient temperature. Most LEDs have a maximum junction temperature of 125 ℃ and a few manufacturers claim to reach 180 ℃. The light output from an LED is limited by how quickly heat can dissipate from the die. As the junction temperature increases, the luminous output of the LED decreases. FIG. 1 is a plot of luminous output versus junction temperature for a typical LED.

2. Luminous output and efficacy.

Luminous efficacy is the ratio of luminous flux (Lm) to applied power (watts). Typical values for energy efficiency of low power incandescent lamps are:

luminous efficiency LM/W

Burning candle 0.3

5W incandescent lamp 5

40W incandescent lamp 12

Over the last few years, the energy efficiency of LEDs has improved and exceeded 100 Lm/W. Typically, the available power LEDs can measure up to 85 Lm/W. It should be noted, however, that these measurements were made at a junction temperature of 25 ℃ and reduced drive current.

As noted previously, as die temperature increases, luminous output decreases. Increasing the drive current has an even greater impact on reducing energy efficiency. As shown in fig. 2, as the current increases, the light output increases in a non-linear manner, but as shown in fig. 3, the voltage also increases.

In other words, if the current I is increased by a factor (1+ K, where 0 < K < 1), not only will the luminous output be increased by a factor (K +1, where 0 < K), but also the LED voltage V will be increased by a factor (1+ V). The new LED power consumption will become:

P＝(I+K)×(V+v)＝(I+K)×V+(I+K)×v

where the first term represents the power increase due to the increase in current only and the second term represents the power increase due to the increase in current and voltage.

Thus, increasing the LED current will increase the LED output at the expense of reducing its energy efficiency. The percentage increase in lumens is lower than the increase in current, which will lower the energy efficiency at a higher rate.

LEDs being unidirectional light sources

The LED emits light in a cone shape smaller than half the space, which makes it difficult to use in a conventional "a" type lamp, as shown in fig. 4. When mounted on a heat sink and placed in a bulb-like housing, some of the light will be absorbed by the encapsulation and lens material, which will reduce the energy efficiency of the system. For the LEDs to work successfully in an "a" type lamp, the LEDs need to be raised to the center of the bulb, but this reduces the heat dissipation capability.

4. Requiring power conversion

LEDs are current driven devices that require a constant current source power (fig. 5). As shown in fig. 3, the voltage reflected by the LED is an exponential function of the drive current. Since the voltage source must be matched to the LED voltage, the LED cannot be driven by the voltage source. Otherwise, the difference between the voltage divided by the total circuit resistance would cause the current to easily exceed the maximum LED rating and cause the device to fail.

Constant current source power increases the cost and reduces the reliability and efficiency of the LED lamp system. Flyback (flyback-back) power supplies below 5 watts have a typical efficiency of less than 80%, which reduces the luminous energy efficiency of the entire lamp system.

The power supply takes up valuable space (real estate) in the lamp system and special measures need to be taken in order to isolate the power supply from the heat generated by the LEDs.

5. Light adjustable property

The dimmer controls the light output by phase controlling the AC input voltage. However, the constant current power supply will compensate for any variations in the input voltage to keep the output current constant. There is a special power supply that allows for dimmability. These power supplies are designed to produce an output current that is proportional to the RMS input voltage. Such power supplies are generally more complex and have lower efficiency.

Fig. 5 is a block diagram of an offline switched-mode power supply. A switch mode power supply is required to convert a 120Vac line voltage to a low DC current (10mA-350 mA). Power supplies with 5 watts or less of output power are almost flyback and have a typical efficiency of less than 80%. They are also prone to failure if subjected to a surge (surge), where a spike in high voltage can damage the MOSFET switch, especially when no surge suppressor such as an MOV (metal oxide varistor) is incorporated.

Another common method of driving low voltage LEDs is to limit the current by using an impedance in series with the AC line and drop the excess voltage across the impedance. The impedance may be a resistor, a capacitor or an inductor. The resistor is the cheapest and most readily available, but loses the energy E ═ I it dissipates²R.DELTA.t and cannot be recovered. As the voltage difference between the source voltage and the LED voltage increases, the loss increases, as shown in fig. 6.

Suppose V_s166V, 36V and 20mA, then

The power dissipation across the resistor is P_R＝I²×R＝2.6W

The efficiency of the system becomes

Obviously, this system is not feasible.

Another solution is to replace R by an impedance that does not dissipate energy, such as an inductor or a capacitor. Capacitors are more usable than inductors in terms of size and value. The only limiting factor is the maximum allowable voltage drop across the capacitor. However, this solution makes the LEDs non-dimmable and results in an increased size of the circuit board due to the large size of the AC capacitor that needs to be rated to the line voltage plus the margin.

A resistor impedance scheme would be feasible if the power dissipation is reduced, if the voltage difference (V) is reduced_s-V), this can be achieved. This is done by increasing the number of LEDs in series until the total LED voltage drop approaches the source voltage V_sTo proceed with source voltage V_sWill reduce the voltage difference (V)_sV) and the value of R required to limit the current.

For example, assume that several LEDs are connected in series to produce a total load voltage V of 136V. The new value of R is

The new power dissipation is

P_R＝I² _Load(s)R＝0.6W

New system efficiency becomes

Obviously, this result is good for an acceptable range of power supply efficiency, which is achieved by converting more wasted power into useful power.

Disclosure of Invention

The present invention relates to an LED lamp comprising a base and a raised light source. The light source is comprised of a first plurality of LEDs connected in series and mounted on one side of a substantially planar substrate and a second plurality of LEDs connected in series and mounted on an opposite side of the substrate, the substrate being spaced apart from the submount and the second plurality of LEDs being positioned substantially in registration with the first plurality of LEDs. A heat sink is in the substrate, each of the first and second plurality of LEDs mounted adjacent the heat sink. Providing a drive circuit for the LED, the drive circuit being located near the base and electrically connected to the base.

According to a preferred form of the invention, the base is a screw-type base. The drive circuit is mounted on a circuit board extending from the planar substrate, the circuit board extending into the base.

In one form of the invention, the heat sink comprises at least one thermally conductive heat island on each side of the substrate, each LED of the first plurality of LEDs being adjacent a heat island on the one side of the substrate and each LED of the second plurality of LEDs being adjacent a heat island on the opposite side of the substrate. The heat sink further comprises at least one thermally conductive thermal diffuser, each thermal island being connected to the thermal diffuser. The thermal diffuser is positioned in the substrate and extends to the pedestal. Preferably there are first and second thermal diffusers, each thermal island on one side of the substrate being connected to the first thermal diffuser and each thermal island on the opposite side being connected to the second thermal diffuser. Each heat spreader is preferably a unitary structure, although the heat spreader may be a series of thermally conductive elements connected to one another.

Preferably, the present invention is in the shape of a conventional light bulb. It therefore comprises a globe attached to the base. The first and second plurality of LEDs are oriented substantially in an arc within the globe.

The driving circuit includes a surge suppressor, a rectifier, a smoothing capacitor, and a resistor, the first and second pluralities of LEDs being connected in parallel and they being connected in parallel to the resistor.

In one form of the invention, the substrate is oriented parallel to a line extending from the base. In a second form of the invention, the substrate is oriented perpendicular to a line extending from the base. In the form of the invention, the heat sink includes a plurality of thermally conductive heat spreader bars extending from adjacent the base to the substrate.

Drawings

The invention will be described in more detail in the following description of an example of the best mode for carrying out the invention, taken in conjunction with the accompanying drawings, in which:

figure 1 is a graph of luminous intensity versus junction temperature for a typical LED,

figure 2 is a graph of light output versus current drive for an LED,

figure 3 is a graph of LED voltage versus LED current,

figure 4 is a cone plot of the light emission of an LED,

figure 5 is an off-line switch mode power supply for LEDs,

figure 6 illustrates how the losses increase with increasing voltage difference between the source voltage and the LED voltage,

figure 7 is a front view of a circuit board according to the present invention,

figure 8 illustrates a simple circuit for connecting LEDs in series,

figure 9 is an exemplary circuit for use with the present invention,

figure 10 shows the waveforms of the input ac voltage, the rectified voltage and the LED current for the circuit of figure 9,

figure 11A is a front view similar to figure 7 of one form of the invention,

figure 11B is a side view of figure 11A,

fig. 11C is the substrate of fig. 11A and 11B, showing the thermal diffuser,

figure 12A is a front view of another form of the invention,

figure 12B is a front view of another form of the invention,

figure 12C is a front view of yet another form of the invention,

fig. 13A is a schematic perspective view of another form of the invention, wherein the LEDs are oriented perpendicular to the earlier embodiments of the invention,

figure 13B is a perspective view of the form of the invention shown in figure 13A as a complete lamp,

FIG. 14 is an exploded view of the lamp shown in FIG. 13B, an

Fig. 15 shows a slightly modified version of the invention shown in fig. 11, where fig. 15A shows the base, fig. 15B shows the circuitry and light source, and fig. 15C shows the globe.

Detailed Description

The present invention produces an LED-based lamp that overcomes the above-mentioned limitations of the prior art:

simple robust power converter

High system luminous energy efficiency

Dimmable

Effective 360 ° light output

Efficient thermal management system

Direct replacement of any low-power incandescent lamp

Designed for manufacturability

The present invention utilizes a plurality of low cost surface mount LEDs connected in series on a surface board to increase the load voltage drop as well as the useful light output and system efficiency (fig. 7 and 8). This is also achieved by mounting the LED dice directly onto the printed circuit board (chip on board) in the same series combination.

The LED emitters can be packaged by combining LED dice in series to produce a high combined LED voltage at a rated current. Such a series of LEDs will sink the same current as a single LED, but will reflect a voltage very close to the rectified source voltage. This is in contrast to the seoul semiconductor "Acriche" LED where the die is connected in anti-parallel, thereby eliminating the need for a rectifier and converting the LED to a high voltage AC LED. The series combination LED results in a high voltage DC LED, which would require the rectifier to be off the AC source when operating. The advantage is that a smoothing capacitor can be added to reduce current ripple and achieve a steady state light source without flicker. Since the rectification process is located inside the package, Acrich LEDs do not consider mounting a smoothing capacitor.

The assembly of Surface Mount Devices (SMDs) is an automated and low cost process. It is therefore critical that all components are SMD type. This is another reason that high voltage AC capacitors are not feasible due to the difficulty of implementation in SMDs.

Fig. 9 is a schematic diagram of an exemplary circuit, generally designated 10, according to the present invention. The invention is described in connection with an ac source 12, although it will be apparent that if dc is available, a rectifier is not required. The ac source 12 is supplied to the rectifier 16 via a fuse. Rectifier 16 rectifies the alternating current to produce a voltage source, shown at 18. Behind the series resistor 20 described above are two parallel combinations of series connected LEDs 22 and series connected LEDs 24. To increase the reliability of the circuit 10, a surface mount MOV (metal oxide varistor) surge suppressor 26 is also included. The smoothing capacitor 28 reduces current ripple and eliminates flicker.

Efficiency can be further improved by adding more LEDs in series, thus increasing the total voltage drop.

Usually,. DELTA.V.V_sV, av is the voltage across the resistor 20. For a given load current I,

and P is_R＝I×ΔV

The negative effect of low av is poor regulation. Since the LED voltage drop is insensitive to current (fig. 3), the change in input voltage will only adapt to av, which will cause the current to change in a proportional manner.

If δ V is the source voltage V_sThen R, which is now constant, will change the same. New current will become

Where δ V may be positive or negative. Let δ I represent the change in load current. Then

The adjustment may be defined as a percentage change in output:

in order to minimize the variation in the output as an input variation, the adjustment is made as small as possible. But a lower value for the adjustment means that for larger values of av, as mentioned earlier, this increases losses and reduces efficiency. Recall to

And efficiency

It is an object of the invention to specify a voltage V for the source_sA maximum acceptable adjustment for a given change in δ V. This will define a minimum av, which will be used to determine R and the efficiency of the system.

Fig. 10 shows waveforms of an input AC voltage, a rectified voltage, and an LED current.

LEDs are most efficient when driven at relatively low currents, where losses are minimal. However, this also means that the overall flow is lower. For example, if an LED has an efficiency of 100Lm/W at 0.03W, its output will be 3 lumens. An efficient LED does not necessarily mean a bright LED. Conversely, the most efficient LED may be so dark that it cannot be used as an illumination source.

Some existing LEDs are constructed of multiple smaller LEDs mounted on an insulated aluminum substrate, but arranged in series and combined in parallel, which keeps the total LED voltage low and keeps its current high. Since the LEDs are packaged close to each other, the extraction of the total light will be inefficient, wherein part of the light will be absorbed by neighboring LEDs. Driving the LEDs at high currents will further reduce energy efficiency.

In the present invention, low cost-effective LEDs 22 and 24 are placed in series on two layers of a printed circuit board or substrate to maximize the total lumen output and reduce absorption. The LEDs are driven at low current to keep energy efficiency high. The low lumen output is compensated by increasing the number of LEDs. The only disadvantage is the LED cost due to the small size of the LED and the low cost of the PCB layout of the surface mount components.

Consider two equivalent incandescent LED lamps emitting at 15 watts/75 Lm and 25 watts/200 Lm.

For a 75Lm system, 36 LEDs are arranged in series, 18 LEDs each in the same location on each side of the circuit board. Fig. 7 shows the system and is driven according to the diagram in fig. 9 with a LED current of 10 mA. The lumen output of each LED at this current was 2 lumens, yielding a total of 75 lumens and a total system luminous energy efficiency of 60Lm/W with a total input power of 1.2W.

The high output version has two parallel circuits of 36 LEDs, one on each side of the PCB, as shown in fig. 11A-11C. The LED current for each series circuit was increased to 30 mA.

Due to this method of arranging and mounting the LEDs inside the lamp, more lumens leave the lamp due to less absorption and blocking.

Although a large number of LEDs in each circuit will ensure the same current sharing, a series resistor 30 is added for each circuit 10 to help dissipate the increased losses due to higher output and improve current sharing. Surface mount MOV surge suppressors 26 and fuses 14 may also be added to increase reliability.

Although the previous discussion was limited to two power levels, the same principles can be applied to achieve higher powers of equivalent 40 watts or higher. By utilizing more LEDs and reducing the drive current, the overall system energy efficiency may be increased.

The brightness of the LED is limited by the maximum junction temperature. In most cases, the junction temperature is 125 ℃. Assuming a temperature difference of 10 ℃ between the junction and the case (case), the case temperature of not higher than 95 ℃ is empirically maintained with a margin of 15 ℃. The more heat dissipated from the LED junction, the higher the light output achievable.

For prior art 6 watt or higher power LED lamps, an external heat sink is typically applied, on which the LEDs are placed directly, which reduces their susceptibility (afterease) and increases costs.

The present invention provides an alternative method of heat dissipation for LEDs. Rather than dissipating heat from one power LED through an external heat sink, the plurality of low power LEDs 24 and 26 dissipate their heat through thermal spreader copper islands 32 and 34 located on the top and bottom layers of a multilayer PCB board or substrate 36. The islands 32 and 34 transfer heat to the two inner layers of copper heat spreaders 38 and 40. Each copper heat spreader is in close proximity to a heat island 32 and 34 on the outer layer. The internal diffusers 38 and 40 conduct heat internally to the threaded base 42 of the lamp, which in turn will dissipate the heat through fixtures and electrical leads (not shown). Since the threaded base 42 is connected to the AC line, it needs to be completely insulated from the rest of the circuit 10. The core thickness of the substrate 36 between the outer islands 32 and 34 and the inner thermal diffusers 38 and 40 should have a minimum thickness that allows for safety standards to minimize thermal resistance and maximize heat transfer.

Since heat is dissipated in the present invention by conduction to the threaded base, the lamp can be placed inside a sealed globe 44 (fig. 12A, etc.) without air circulation. Since the LED is elevated and more visible, more light radiation will be allowed as well.

At the bottom of the LED substrate 36, thermal diffusers 38 and 40 are thermally bonded together by printed circuit board vias, which are a way to provide electrical connections between traces on different layers of the circuit board by maximizing power dissipation to the threaded base by thermally conducting heat from one layer to the other.

The LEDs 22 and 24 are disposed on the substrate 36 in an arc-shaped configuration, similar to the filament of an incandescent light bulb, maintaining its classical appearance. The power conversion portion of the system is mounted on the circuit board portion of the substrate 36 to minimize cost and simplify assembly. All components are surface mount devices allowing automation.

The LEDs 22 and 24 are placed in register on each side of the substrate 36, preferably in exactly the same position, which gives the impression of transparency. Since no external heat sink is used, globe 24 can be made entirely of transparent material, raising LEDs 22 and 24 to maximum lumen efficiency. To better resemble an incandescent lamp, the Correlated Color Temperature (CCT) of an LED should be 2800 ° K, which is close to that of an incandescent lamp, and the Color Rendering Index (CRI) should typically be 95. The effect would be to create the same application, effect and appearance of an incandescent light bulb.

The LEDs are placed precisely on either side of the substrate 36 so that the substrate is not visible. The effect is that only the traces of visible light are seen by the viewer. The shape and structure of the LED may vary depending on the desired effect.

Fig. 12A shows an a19 type lamp, and fig. 12B and 12C illustrate a B10 type lamp. The present invention allows the use of LEDs of this construction in any incandescent lamp application, including decorative lamps. The mode of setting the LEDs is not limited to the case shown in fig. 12, and may be extended to any structure to produce any desired effect.

Fig. 13A, 13B and 14 are other embodiments of the invention in which the heat collector is a solid bar 46 bonded to the heat island. In this case the lamp will remain more similar to a classical incandescent lamp. The elements are the same as in the first form of the invention, but since the substrate is horizontal, all elements have an identifier "a". The power circuit 10 is located in the threaded base 42 of the lamp.

The LEDs 22 and 24 may be incorporated into a plastic polymer that is shaped into a filament. The LEDs 22 and 24 may be arranged to illuminate the polymer, which will effectively conduct light and give the impression of a continuous filament of light.

Another embodiment is to mount the LED dice directly on the substrate 36 in the same pattern (chip on board) and apply phosphor to all of the dice. This will cause the LED die set to emit light as a single body. Because the LED is not packaged separately, the cost of the LED can be reduced.

The resistance impedance R is selected so as to be usable with conventional triac dimmers in a manner similar to incandescent lamps. The only limitation is the LED current which must be higher than the triac holding current, which is usually due to the fact that low intensity B10 type lamps are usually arranged in groups of 5 or more in chandeliers.

The present invention is comprised of three main parts (fig. 15), a threaded base 42, an LED circuit 10, and a globe 44. The substrate 36 carrying the LEDs is mounted in the threaded base 42 by first soldering the intermediate terminals and then bonding the board side to the barrel of the threaded base 42. This will ensure electrical contact and provide a thermal path to conduct heat generated by LEDs 22 and 24 to threaded base 42 and electrical leads (not shown) that act as extended heat sinks.

Various modifications may be made to the present invention without departing from the spirit thereof and the scope of the following claims.

Claims (15)

1. An LED lamp comprising:

a. a base;

b. an elevated light source comprising:

i. a first plurality of LEDs connected in series and mounted on one side of a substantially planar substrate, the substrate being spaced apart from the submount, an

A second plurality of LEDs connected in series and mounted on opposite sides of the substantially planar substrate and equal in number to the first plurality of LEDs, the second plurality of LEDs positioned in substantial alignment with the first plurality of LEDs,

b. a heat sink in the substrate, each of the first and second plurality of LEDs mounted near the heat sink, an

c. A drive circuit for the LED, the drive circuit positioned proximate to the base and electrically connected to the base.

2. The LED lamp of claim 1, wherein the base is a screw-type base.

3. The LED lamp of claim 1, wherein the driver circuit is mounted on a circuit board extending from the planar substrate, the circuit board extending into the base.

4. The LED lamp of claim 1, wherein the heat sink comprises at least one thermally conductive heat island on each side of the substrate, each LED of the first plurality of LEDs being adjacent to a heat island on the one side and each LED of the second plurality of LEDs being adjacent to a heat island on the opposite side.

5. The LED lamp of claim 4, wherein the heat sink comprises at least one thermally conductive thermal diffuser, each thermal island being connected to the thermal diffuser.

6. The LED lamp of claim 5, wherein the thermal diffuser is positioned in the substrate, the thermal diffuser extending to the base.

7. The LED lamp of claim 5, comprising first and second thermal diffusers, each thermal island on the one side of the substrate being connected to the first thermal diffuser and each thermal island on the opposite side being connected to the second thermal diffuser.

8. The LED lamp of claim 7, wherein the thermal diffuser is integral.

9. The LED lamp of claim 1, comprising a globe attached to the base.

10. The LED lamp of claim 1, wherein the first and second plurality of LEDs are oriented substantially in an arc.

11. The LED lamp of claim 1, wherein the drive circuit comprises a surge suppressor, a rectifier, a smoothing capacitor, and a resistor, the first and second pluralities of LEDs being connected in parallel to the resistor.

12. The LED lamp of claim 1, wherein the substrate is oriented parallel to a line extending from the base.

13. The LED of claim 1, wherein the substrate is oriented perpendicular to a line extending from the submount.

14. The LED lamp of claim 13, wherein the heat sink comprises a plurality of thermally conductive heat spreading bars extending from near the base to the substrate.

15. The LED lamp of claim 14, wherein the heat sink comprises at least one thermally conductive heat island on each side of the substrate, each LED of the first plurality of LEDs being adjacent the heat island on the one side and each LED of the second plurality of LEDs being adjacent the heat island on the opposite side.