Partially clamped resonant half-bridge converter for highly efficient constant power LED driver with inherent hard-switching protection

A DC-to-DC converter that receives a rectified DC voltage on a voltage rail and that generates a DC output voltage, the DC-to-DC converter comprising:

• a gate driver circuit that drives at least a first switching device and a second switching device, the first switching device connected between the voltage rail and a switching node, the second switching device connected between the switching node and a voltage reference;
• a tank circuit having an input connected to the switching node and having an output connected to a resonant tank output node, the resonant tank circuit comprising:
• a resonant inductor having a first terminal connected to the switching node and having a second terminal connected to the resonant tank output node;
• a first capacitor having a first terminal connected to the voltage reference and having a second terminal connected to a capacitor branch node;
• a second capacitor having a first terminal connected to the capacitor branch node and having a second terminal connected to the resonant tank output node;
• a first diode connected across the first capacitor between the voltage reference and the capacitor branch node;
• and
• a second diode connected from the capacitor branch node to the voltage rail;
• an output transformer having a primary circuit and a secondary circuit, the primary circuit having a first terminal connected to the resonant tank output node and having a second terminal connected to the voltage reference;
• and
• a rectifier circuit connected to the secondary circuit of the output transformer, the rectifier circuit generating the DC output voltage.

A method for preventing hard-switching of at least first and second switching devices in a half-bridge circuit in a DC-to-DC converter that receives an input voltage from a voltage rail, the input voltage referenced to a reference voltage from a voltage reference, the method comprising:

• providing an output of the half-bridge circuit to a resonant tank circuit, the resonant tank circuit comprising a resonant inductor having an input connected to the output of the half-bridge circuit and having an output connected to a primary circuit of an output transformer;
• connecting a first capacitor and a second capacitor in series between the output of the resonant inductor and the voltage reference, the first and second capacitors connected at a capacitor branch node;
• connecting a first diode across the first capacitor between the voltage reference and the capacitor branch node;
• connecting a second diode from the capacitor branch node to the voltage rail;
• and
• clamping a voltage on the first capacitor at the capacitor branch node to prevent the voltage on the first capacitor from exceeding the input voltage by more than a voltage drop of the second diode and to prevent the input voltage from being less than the reference voltage by more than a voltage drop of the first diode, wherein clamping the voltage across the first capacitor prevents hard-switching of the switching devices in the half-bridge circuit.