Reducing output ripple current and protecting inverter switches during non-zero voltage switching for isolated buck converters

摘要

An isolated buck converter protects inverter switches during non-zero voltage switching and reduces output ripple current by maintaining operation of an output inductor of the isolated buck converter in a continuous current mode. Continuous current mode operation is maintained by various combinations of: shifting the frequency of operation of the inverter switches of the isolated buck converter as a function of output current of the isolated buck converter; employing pulse density modulation to decrease the off time of the isolated buck converter which will decrease the magnitude of the current ripple; and use a step gap core (i.e., a swinging choke) for the output inductor that saturates to a lower value of inductance for high load current and a higher value of inductance at low load current.

主权项

1. An isolated buck converter operable to receive a direct current (DC) voltage from a power source and provide a substantially DC output voltage to a load, said isolated buck converter comprising:
a high switch connected to the power source; a low switch connected to the high switch and a ground of the power source, the connection between the high switch and the low switch forming a first junction; a high bulk capacitor connected to the power source; a low bulk capacitor connected to the high bulk capacitor and to the ground of the power source, the connection between the high bulk capacitor and the low bulk capacitor forming a second junction; an isolating transformer having a primary winding and a secondary winding, wherein the primary winding is connected between the first junction and the second junction; a rectifier connected to the secondary winding of the isolating transformer; an output inductor connected to an output of the rectifier, wherein the output inductor is configured to provide the DC output voltage to the load; and a switch controller connected to the high switch and to the low switch, wherein said switch controller is configured to
control the high switch and the low switch via pulse width modulation, andincrease a frequency of the pulse width modulation as a current from the output inductor to the load decreases to operate the output inductor in a continuous current mode.