US 2005/0030767 A1 · Circuit for reducing losses at light load in a soft switching full bridge converter

Abstract

A circuit for reducing the internal power losses of a soft switching full bridge converter at light loads and enables very high frequency operation without using a cold plate approach. In a preferred embodiment, the circuit includes a resonant inductor and blocking inductor on the primary side of the converter arranged so as to provide the reduced losses for zero voltage switching bridge converter. The circuit provides the above benefits even for converters having a power transformer with very low leakage inductance. The circuit is not dependent on the presence of a high leakage inductance for the power transformer. The circuit can be used in soft switched half bridge or full bridge converters. The inventive circuit can also be used in a hard switching full bridge or half bridge converter for achieving zero voltage switching at reduced cost with reduced losses at light load, if the operating duty cycle of the converter is set near fifty percent.

Claims19

Dependent claims

In a DC-DC converter for providing substantially zero voltage switching (ZVS) having first and second input terminals to which an input DC voltage is coupled and two output terminals where the output DC power is provided, a bridge having a first and second switching leg, each leg comprising two controlled switches connected in series, each switch having a switch capacitance and a control input, each switching leg connected between the input terminals and having a junction point between its series-connected switches, a transformer having a primary winding and a secondary winding each having a first and second end, and a rectifier and output filter circuit coupled between said secondary winding and said output terminals, a circuit for reducing power losses at light loads and enabling very high frequency operation comprising:

a first inductor connected between said junction points for charging and discharging each of said switch capacitances;
and
a second inductor for providing high impedance to a sudden reversal of current, having an end connected to said junction point of said first switching leg and another end connected to said first end of said primary winding, said second end of said primary winding is connected to said junction point of said second switching leg.

A DC-DC converter for providing substantially zero voltage switching (ZVS) having first and second input terminals to which an input DC voltage is coupled and two output terminals where the output DC power is provided comprising:

a bridge having a first and second switching leg, each leg comprising two controlled switches connected in series, each switch having a switch capacitance, each switching leg connected between the input terminals and having a junction point between its series-connected switches;
a transformer having a primary winding and a secondary winding each having a first and second end;
a rectifier and output filter circuit coupled between said secondary winding and said output terminals;
a first and a second diode;
a first inductor connected in series with said first diode between said junction points;
and
a second inductor connected in series with said second diode between said junction points;
wherein said first diode has a cathode connected to an end of said first inductor and an anode connected to said junction point of said second switching leg and said second diode has a cathode connected to the anode of said first diode and an anode connected to an end of said second inductor;
and
a third inductor for providing high impedance to a sudden reversal of current having an end connected to said junction point of said first switching leg and another end connected to said first end of said primary winding, said second end of said primary winding is connected to said junction point of said second switching leg.

7 more elements

A method of operating a bridge DC-DC converter for substantially zero voltage switching, said converter having first and second input terminals to which an input DC voltage is coupled and two output terminals where the output DC power is provided and which comprises a bridge having two switching legs, each leg comprising two controlled switches connected in series, each switch having a switch capacitance and a control input, each switching leg connected between the input terminals and having a junction point between its series-connected switches, a transformer having a primary winding and a secondary winding each having a first and second end, and a secondary circuit for deriving an output of the converter from said secondary winding, comprising the steps of:

supplying substantially complementary control signals to said control inputs of said switches in said first switching leg so that the corresponding switches conduct alternately with dead times therebetween;
supplying relatively phase shifted substantially complementary control signals to said control inputs of said switches in said second switching leg so that the corresponding switches conduct alternately with dead times therebetween;
and
during the dead time when one of said switches in said first switching leg has been turned off, charging the switch capacitance of said turned-off switch and discharging the switch capacitance of the other said switch in said first switching leg via a resonant inductor connected between said junction points;
and
during the dead time when one of said switches in said second switching leg has been turned off, charging the switch capacitance of said turned-off switch and discharging the switch capacitance of the other said switch in said second switching leg via said resonant inductor connected between said junction points.

3 more elements

Dependencies are inferred from the claim text.

Circuit for reducing losses at light load in a soft switching full bridge converter

Life of this patent

Circuit for reducing losses at light load in a soft switching full bridge converter

Life of this patent

Abstract

Claims19