Constant current source with output voltage range and self-clamping output voltage

A driver circuit operable to provide current to a light source from a direct current (DC) power source having a power rail and a ground, the driver circuit comprising:

• a half-bridge inverter comprising
• a first switch having a high terminal and a low terminal, and a control terminal, wherein the high terminal of the first switch is connected to the power rail of the DC power source,
• a second switch having a high terminal, a low terminal, and a control terminal, wherein the low terminal of the second switch is connected to the ground of the DC power source,
• the high terminal of the second switch is connected to the low terminal of the first switch at an inverter output node;
• a resonant tank circuit comprising
• one resonant capacitor having a first end and a second end, the second end of the resonant capacitor connected directly to the ground of the DC power source, and
• one resonant inductor having a first end connected directly to the inverter output node and a second end connected directly to the first end of the resonant capacitor;
• a first clamping diode having an anode connected to a junction between the resonant inductor and the resonant capacitor and a cathode connected to the power rail of the DC power source;
• a second clamping diode having an anode connected to the ground of the DC power source and a cathode connected to the junction between the resonant capacitor and the resonant inductor;
• an isolating transformer connected to the output of the resonant tank circuit, the isolating transformer comprising a primary winding connected on a first end to a node between the resonant inductor and the resonant capacitor and on a second end to the ground of the DC power source;
• an output rectifier having an input connected to a secondary winding of the isolating transformer and an output configured to connect to the light source;
• and
• a controller connected to a dimming circuit and configured to receive a dimming signal from the dimming circuit, and configured to
• sense a current provided to the light source from the output rectifier, and
• control the current provided to the light source as a function of the sensed current and the received dimming signal by adjusting a switching frequency of the half-bridge inverter.

A driver circuit operable to provide current to a light source from a direct current (DC) power source having a power rail and a ground, the driver circuit comprising:

• a half-bridge inverter comprising a first switch coupled in series with a second switch between the power rail and the ground, and configured to provide an alternating current (AC) signal corresponding to a switching frequency of the first and second switches at an inverter output node between the first and second switches;
• one resonant capacitor having a first end and a second end, the second end of the resonant capacitor connected directly to the ground of the DC power source;
• one resonant inductor having a first end connected directly to the inverter output node and a second end connected directly to the first end of the resonant capacitor;
• an isolating transformer comprising a primary winding connected on a first end to a node between the resonant inductor and the resonant capacitor and on a second end to the ground of the DC power source;
• and
• a clamping circuit connected to the node between the resonant inductor and the resonant capacitor, and configured to limit the voltage at the node between the resonant inductor and the resonant capacitor to a maximum of a voltage of the power rail of the DC power source and a minimum of a voltage of the ground of the DC power source;
• an output rectifier having an input connected to a secondary winding of the isolating transformer and an output operable to connect to the light source;
• and
• a controller connected to a dimming circuit and configured to
• receive a dimming signal from the dimming circuit,
• sense a current provided to the light source from the output rectifier, and
• adjust a switching frequency of the half-bridge inverter as a function of the sensed current and the received dimming signal to maintain the sensed current at a target current associated with the received dimming signal,
• wherein soft-switching operation of the half-bridge inverter is guaranteed by the limited voltage across the resonant capacitor.