LED driver with transformerless hysteretic boost
View Patent ↗A system and apparatus including a light emitting diode (LED) driver provides an operating DC voltage to a plurality of LEDs connected in series (LED array) for providing illumination. A rectifier circuit and a filter are coupled to an AC power supply and provide a rectified and filtered DC source voltage to a transformerless voltage boost circuit, which provides the operating DC voltage to the LED array. A hysteretic self-oscillating circuit drives the transformerless voltage boost circuit at an oscillation frequency. A tap is connected between two LEDs in the LED array, which provides an auxiliary DC voltage, which is used to power the oscillating circuit and which eliminates the need for the LED driver to have a conventional transformer or auxiliary DC-DC power converter. The transformerless voltage boost circuit includes an inductor, a capacitor, a diode, and a switch wherein the switch is controlled by the oscillating circuit.
1. A light emitting diode (LED) driver for providing an operating direct current (DC) voltage to an LED array, the LED array including a plurality of LEDs connected in series for providing illumination, comprising:
a transformerless voltage boost circuit configured to receive a filtered DC source voltage and to provide the operating DC voltage to the LED array;
a hysteretic self-oscillating circuit for driving the transformerless voltage boost circuit at an oscillation frequency; and
a tap connected between two of the plurality of LEDs in the LED array for providing an auxiliary DC voltage to the hysteretic self-oscillating circuit, wherein the auxiliary DC voltage is at least a part of the operating DC voltage provided to the LED array from the transformerless voltage boost circuit and the auxiliary DC voltage provided by the tap connected between the two of the plurality of LEDs in the LED array powers the hysteretic self-oscillating circuit for driving the transformerless voltage boost circuit at the oscillation frequency.
2. The LED driver of claim 1 , wherein the transformerless voltage boost circuit is comprised of an inductor, a capacitor, a diode, and a switch.
3. The LED driver of claim 2 , wherein the switch is controlled by the hysteretic self-oscillating circuit for switching current from the inductor between ground and the LED array.
4. The LED driver of claim 2 , wherein the switch is a transistor.
5. The LED driver of claim 2 , wherein the switch is a MOSFET.
6. The LED driver of claim 1 , further comprising (i) a rectifier circuit coupled to an alternating current (AC) power supply and configured to rectify an AC voltage from the AC power supply into a DC power source for providing a DC source voltage and (ii) a filter for filtering the DC source voltage and for outputting the filtered DC source voltage.
7. The LED driver of claim 1 , wherein the auxiliary DC voltage is less than the operating DC voltage.
8. The LED driver of claim 1 , wherein the hysteretic self-oscillating circuit comprises an oscillator and a push-pull amplifier.
9. The LED driver of claim 8 , wherein the oscillator drives the transformerless voltage boost circuit through the push-pull amplifier.
10. The LED driver of claim 1 , wherein the transformerless voltage boost circuit is self-oscillating.
11. A method of providing an operating direct current (DC) voltage to a light emitting diode (LED) array using an LED driver, the LED array including a plurality of LEDs connected in series for providing illumination, the method comprising:
receiving a filtered DC source voltage by a transformerless voltage boost circuit in the LED driver for providing the operating DC voltage to the LED array;
driving the transformerless voltage boost circuit at an oscillation frequency by a hysteretic self-oscillating circuit in the LED driver; and
providing an auxiliary DC voltage to the hysteretic self-oscillating circuit by connecting a tap between two of the plurality of LEDs in the LED array, wherein the auxiliary DC voltage is at least a part of the operating DC voltage provided to the LED array from the transformerless voltage boost circuit and the auxiliary DC voltage provided by the tap connected between the two of the plurality of LEDs in the LED array powers the hysteretic self-oscillating circuit for driving the transformerless voltage boost circuit at the oscillation frequency.
12. The method of claim 11 , wherein the transformerless voltage boost circuit is comprised of an inductor, a capacitor, a diode, and a switch.
13. The method of claim 12 , further comprising controlling the switch by the hysteretic self- oscillating circuit for switching current from the inductor between ground and the LED array.
14. The method of claim 12 , wherein the switch is a transistor.
15. The method of claim 12 , wherein the switch is a MOSFET.
16. The method of claim 11 , further comprising (i) rectifying, by a rectifier circuit coupled to an alternating current (AC) power supply, an AC voltage from the AC power supply into a DC power source for providing a DC source voltage and (ii) filtering, by a filter, the DC source voltage and outputting the filtered DC source voltage.
17. The method of claim 11 , wherein the auxiliary DC voltage is less than the operating DC voltage.
18. The method of claim 11 , wherein the hysteretic self-oscillating circuit comprises an oscillator and a push-pull amplifier.
19. The method of claim 18 , further comprising driving, by the oscillator, the transformerless voltage boost circuit through the push-pull amplifier.
20. The method of claim 11 , wherein the transformerless voltage boost circuit is self-oscillating.