Dimmable LED driver based on self-oscillating soft-switching LLC series resonant inverter topology

A driver circuit configured to provide power to a load from a direct current (DC) power rail, the driver circuit comprising:

• a self-oscillating inductor-inductor-capacitor (LLC) series resonant inverter configured to connect to the DC power rail, receive DC power from the DC power rail, and provide an alternating current (AC) output signal;
• a current limiting circuit coupled to the self-oscillating LLC series resonant inverter, wherein the current limiting circuit is configured to receive the AC output signal from the self-oscillating LLC series resonant inverter and provide an AC current signal as a function of a DC current provided to the load by the driver circuit;
• a rectifier circuit coupled to the current limiting circuit, wherein the rectifier circuit is configured to receive the AC current signal from the current limiting circuit and provide a DC current to the load;
• wherein the self-oscillating LLC series resonant inverter comprises a transformer having an output secondary winding, the output secondary winding has a first terminal and a second terminal, and the current limiting circuit comprises
• a current limiting capacitor having a first terminal connected to the first terminal of the output secondary winding of the transformer and a second terminal connected to the rectifier circuit, and
• an output current regulator connected between the second terminal of the current limiting capacitor and the second terminal of the output secondary winding of the transformer, the output current regulator comprising
• a dimming capacitor,
• a bidirectional switch connected in series with the dimming capacitor between the second terminal of the current limiting capacitor and the second terminal of the output secondary winding of the transformer, and
• a controller configured to provide a pulse width modulated signal to the bidirectional switch as a function of the DC current provided to the load by the driver circuit.

A light fixture configured to receive power from a power source and provide light, the light fixture comprising:

• an input stage configured to receive power from the power source and provide a direct current (DC) power rail, wherein the DC power rail has a substantially constant DC voltage;
• a light source configured to provide light in response to receiving power;
• a driver circuit configured to provide power to the light source from the DC power rail, the driver circuit comprising
• a self-oscillating inductor-inductor-capacitor (LLC) series resonant inverter connected to the DC power rail, wherein the self-oscillating LLC series resonant inverter is configured to receive DC power from the DC power rail, and provide an alternating current (AC) output signal,
• a current limiting circuit connected to the self-oscillating LLC series resonant inverter, wherein the current limiting circuit is configured to receive the AC output signal from the self-oscillating LLC series resonant inverter and provide an AC current signal as a function of a DC current provided to the light source by the driver circuit, and
• a rectifier circuit connected to the current limiting circuit, wherein the rectifier circuit is configured to receive the AC current signal from the current limiting circuit and provide a DC current to the light source;
• and
• a housing configured to support the input stage, the light source and the driver circuit;
• wherein the driver circuit further comprises a current sensing resistor configured to connect in series with the light source and provide to the current limiting circuit a current sensing signal indicative of the DC current provided to the light source by the driver circuit;
• and
• wherein the DC power rail has an associated ground, and the self-oscillating LLC series resonant inverter comprises
• a first switch having a first terminal connected to the DC power rail, a second terminal, and a control terminal,
• a second switch having a first terminal connected to the second terminal of the first switch, a second terminal connected to the ground associated with the DC power rail, and a control terminal,
• a resonant capacitor having a first terminal and a second terminal, wherein the first terminal is connected to the ground associated with the DC power rail, and
• a transformer having a primary winding, a first secondary winding, a second secondary winding, and an output secondary winding, wherein
• the primary winding of the transformer is connected between the second terminal of the first switch and the second terminal of the resonant capacitor,
• the first secondary winding is connected between the control terminal of the first switch and the second terminal of the first switch,
• the second secondary winding is connected between the control terminal of the second switch and the second terminal of the second switch, and
• the output secondary winding is configured to provide the AC output signal.