Patent Application
20140145645
1. Field of the Invention
The aspects of the present disclosure relate generally to driver circuits for light emitting diode devices and in particular to dimming driver circuits for light emitting diode devices and arrays.
2. Description of Related Art
Light Emitting Diodes (LED) are widely used in general lighting. An LED is generally understood as a semiconductor device that generates light when electrical energy is applied to the device. LED arrays, in which multiple LEDs are formed into an array and powered as a unit, are gaining popularity in lighting and signaling applications. LED arrays are typically connected to a direct current (DC) power source where the amount of applied current controls the brightness of emitted light.
LEDs are voltage sensitive devices. An LED must be supplied with a voltage that is above a threshold voltage and a current that is below the rating of the particular LED device. Generally, the current that is supplied to an LED is dependent exponentially on the voltage, referring to the Shockley diode equation. A small change in voltage can cause a large change in current. If the maximum voltage rating is exceeded by a small amount, the current rating can be exceeded by a large amount, potentially damaging the LED.
An LED driver or driving circuit is a type of power conversion circuit that delivers constant current instead of constant voltage. The typical LED driving circuit, or driver device, will convert a line voltage alternating current (“VAC”) to a direct current (“DC”). Some LED systems have two sub-systems. The first or upstream sub-system is generally a stand-alone constant voltage LED driver. The second or downstream sub-system is the LED module, which has one or more of an internal ballast resistor, linear regulator or switched power supply, to convert the DC voltage to DC current. The downstream LED module will typically include a low voltage protection circuit. The low voltage protection circuit will lower the power delivered to drive the LED when the input voltage is below a predetermined input voltage threshold level.
High powered LEDs (HPLED) can be driven at currents that range from hundreds of milliamperes to more than an ampere and emit over one thousand lumens. Low powered LEDs are driven at currents that are in the tens of milliamperes. The basic driver types for high power LEDs include constant current drivers and constant voltage/wattage type drivers.
A constant current LED driver will provide a constant current (amperage) to the LED(s). The output voltage from such an LED driver will vary depending upon the load. A constant current LED drive will maximize the energy efficiency with less loss. However, the fixed LED current load within the driver output current limits the flexibility of the design. The constant current LED driver is typically used in applications with a fixed number of LEDs.
A constant output voltage/wattage type of LED driver will provide a constant voltage to the LED(s). The wattage will remain constant with variations in the load. Because the voltage is constant, the constant voltage type of driver finds particular application where the types and numbers of LEDs vary.
LED dimming solutions generally include constant current reduction (“CCR”) or pulse-wave modulation dimming (“PWM”). Constant current dimming generally involves linear adjustment of the current through the LEDs. Pulse-wave modulation will drive the LEDs at one current level, but will turn the LEDs on or off at a frequency that is generally greater than 120 Hz. However, pulse wave modulation can have some drawbacks. For example, the costs associated with pulse-wave modulation solutions can be expensive. Also, pulse-wave modulation can generate in-rush currents, which can negatively affect the LED, such as by shorting the LED rated life, as well as generating electromagnetic interference (EMI).
Some pulse-wave modulation dimming solutions will also use a field effect transistor (FET) in series with the LED lamp to pulse-wave modulate the lamp current when dimming is desired. However, this type of approach can be subject to losses in the FET.
Accordingly, it would be desirable to provide a dimming LED driver circuit that resolves at least some of the problems identified above.
As described herein, the exemplary embodiments overcome one or more of the above or other disadvantages known in the art.
One aspect of the present disclosure relates to a dimming control circuit for an LED module. In one embodiment, the dimming control circuit includes an LED driver configured to provide an output voltage that is used to drive the LED module, a voltage divider coupled to the output voltage, and a dimming control module coupled to the voltage divider. The dimming control module is configured to change a resistance of the voltage divider to reduce the output voltage from the LED driver and dim the LED module.
Another aspect of the disclosed embodiments is directed to a step-dimming LED lighting system. In one embodiment, the step-dimming LED lighting system includes an LED driver configured to provide a constant voltage output, an LED module driven by the LED driver, and a voltage divider. The voltage divider is configured to control the constant voltage output of the LED driver between a high output state and a low output state, wherein in the high output state the LED module operates at a full power condition, and in a low output state the LED module operates at a low power condition.
These and other aspects and advantages of the exemplary embodiments will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. Additional aspects and advantages of the invention will be set forth in the description that follows, and in part will be obvious from the description, or may be learned by practice of the invention. Moreover, the aspects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
In the drawings:
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The AC voltage input 104 is any suitable AC mains input, such as for example 120-277 VAC, 50/60 Hz, as is generally understood. In the embodiment shown in
In one embodiment, the LED driver 102 includes a voltage divider, generally indicated by reference 120. The voltage divider 120, also referred to as a resistor divider, generally comprises a series resistance. In one embodiment the series resistance comprises one or more resistors. In the embodiment shown in
As is illustrated in the example of
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In one embodiment, the dimming control module 140 comprises a switching device, such as a switch or a relay. The switching device can be controlled manually, such as by a user, or automatically, such as a by a program, sensor or timer that is configured to determine periods when the load 130 should be dimmed. For example, in one embodiment, the dimming control module 140 comprises or is coupled to an occupancy sensor application or device. When the dimming control module 140 is coupled to an occupancy sensor, the dimming control signal 146 can be received from the occupancy sensor. An occupancy sensor application can include a relay or switch to provide a dimming control signal 146 that will cause the dimming control module 140 to short or open the dimming control leads 142, 144 based on a detected occupancy of an area, such as a room. For example, when a monitored area is determined to be occupied, the occupancy sensor can generate a dimming control signal 146 that will enable the dimming control module 140 to maintain the dimming control leads 142, 144 in an electrically open state, resulting in the full voltage output from the LED driver 102. When a non-occupied state is detected, the occupancy sensor can enable the dimming control module 140 to cause control leads 142, 144 to electrically short resistor R2 in the voltage divider 120 of the LED driver 102, thus reducing the constant voltage output of the LED driver 102. Although the aspects of the disclosed embodiments are generally described herein with respect to the dimming control signal 146 be provided by a device external to the dimming control module 140, in one embodiment, the dimming control module 140 can generate the dimming control signal 146. For example, in one embodiment, the dimming control module 140 comprises an occupancy sensor device or such other device that is used to control the LED driver 102 to dim the LED load 130. In this example, dimming control module 140 internally generates the dimming control signal 146 that enable the dimming control module 140 to electrically short the dimming control leads 142, 144 across resistor R2. Although the aspects of the present disclosure are generally described with respect to electrically shorting resistor R2, in alternate embodiments, any one or more of the resistors in the voltage divider 120 can be electrically shorted to switch between a high output state and a low output state.
The aspects of the disclosed embodiments are directed to a dimming LED driver circuit 100 that changes an output of the LED driver 102 between two voltage output levels to realize dimming of the LED 130, while not utilizing pulse wave modulation dimming and can be applied in any LED system where a LED lighting dimming solution is desired. For example, in one embodiment, one or more of the LED modules 302, 304 or 306 can comprise a display or signage lighting application. As another example, in store refrigerator display lighting applications, dimming is used when there is no activity near the display. For example, one type of commercial refrigerator includes an LED bar/module that is located inside the refrigerator. When a customer is in proximity to the refrigerator, the LED bar/module is configured to operate at full power, corresponding to the high state described herein. When no one is in proximity to the refrigerator, meaning the occupancy sensor does not detect a presence, the LED bar/module can be dimmed. In accordance with the aspects of the disclosed embodiments, the LED Driver 102 will be commanded by the dimming control signal 146 to reduce the voltage output of the LED driver 102, which will result in the LED bar/module reducing the current delivered to the LEDs, thus dimming the LED bar/module.
Thus, while there have been shown, described and pointed out, fundamental novel features of the invention as applied to the exemplary embodiments thereof, it will be understood that various omissions and substitutions and changes in the form and details of devices and methods illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit and scope of the invention. Moreover, it is expressly intended that all combinations of those elements and/or method steps, which perform substantially the same function in substantially the same way to achieve the same results, are within the scope of the invention. Moreover, it should be recognized that structures and/or elements and/or method steps shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.
