Zero voltage switching buck converter
The present invention is directed generally to a buck converter that achieves zero voltage switching (ZVS). According to various embodiments, the buck converter comprises a ZVS circuit for storing reverse recovery current from the diode of the buck converter and using the energy from the reverse recovery current to discharge parasitic capacitance of the primary switch of the buck converter prior to turn-on of the primary switch such that the primary switch turns on with substantially zero voltage across the switch. The ZVS circuit may comprise a capacitor, an auxiliary switch connected in series with the capacitor, and an auxiliary inductor connected in parallel with the series-connected capacitor and auxiliary switch. The control circuit controls the primary switch and the auxiliary switch of the ZVS circuit such that (i) the auxiliary switch and the primary switch are not both on at the same time, and (ii) there is a time interval between the end of the on-time of the auxiliary switch and the beginning of the on-time of the primary switch. The time interval (which may be a fixed duration) is of sufficient duration such that the energy from the reverse recovery current substantially discharges the parasitic capacitance of the primary switch during the time interval. Interleaved embodiments of the buck converter are also disclosed.
1 . A DC/DC converter for converting an input voltage to an output voltage, comprising:
a buck converter including a primary switch, a diode and an inductor, such that when the primary switch is on the inductor is connected to the input voltage and when the primary switch is off the inductor is disconnected from the input voltage;
a control circuit for periodically turning on and off the primary switch; and
a ZVS circuit for storing reverse recovery current from the diode of the buck converter and using energy from the reverse recovery current to discharge parasitic capacitance of the primary switch of the buck converter prior to turn-on of the primary switch such that the primary switch turns on with substantially zero voltage across the primary switch.
2 . The DC/DC converter of claim 1 , wherein the ZVS circuit comprises:
a capacitor;
an auxiliary switch connected in series with the capacitor; and
an auxiliary inductor connected in parallel with the series-connected capacitor and auxiliary switch.
3 . The DC/DC converter of claim 1 , wherein the control circuit is for controlling the auxiliary switch such that:
the auxiliary switch and the primary switch are not both on at the same time; and
there is a time interval between the end of the on-time of the auxiliary switch and the beginning of the on-time of the primary switch, wherein the time interval is of sufficient duration such that the energy from the reverse recovery current substantially discharges the parasitic capacitance of the primary switch during the time interval.
4 . The DC/DC converter of claim 3 , wherein the ZVS circuit is connected in series with the diode of the buck converter.
5 . The DC/DC converter of claim 3 , wherein the ZVS circuit is converter is connected in series with the primary switch.
6 . The DC/DC converter of claim 3 , wherein the time interval is of a fixed duration.
7 . The DC/DC converter of claim 6 , wherein the ZVS circuit is connected in series with the diode of the buck converter.
8 . The DC/DC converter of claim 6 , wherein the ZVS circuit is converter is connected in series with the primary switch.
9 . The DC/DC converter of claim 1 , further comprising:
a second buck converter connected in parallel with the buck converter, the second buck converter including a second primary switch, a second diode and a second inductor, such that when the second primary switch is on the second inductor is connected to the input voltage and when the second primary switch is off the second inductor is disconnected from the input voltage; and
a second ZVS circuit for storing reverse recovery current from the second diode of the second buck converter and using energy from the reverse recovery current to discharge parasitic capacitance of the second primary switch of the second buck converter prior to turn-on of the second primary switch such that the second primary switch turns on with substantially zero voltage across the second primary switch.
10 . The DC/DC converter of claim 9 , wherein the control circuit operates the second primary switch of the second buck converter 180 degrees out of phase with the primary switch of the buck converter.
11 . The DC/DC converter of claim 1 , wherein the diode of the buck converter has a non-zero reverse recovery time.
12 . The DC/DC converter of claim 3 , wherein the ZVS circuit further comprises an auxiliary diode connected across the auxiliary switch.
13 . A DC/DC converter for converting an input voltage to an output voltage, comprising:
a buck converter including a primary switch, a diode and an inductor, such that when the primary switch is on the inductor is connected to the input voltage and when the primary switch is off the inductor is disconnected from the input voltage;
a ZVS circuit for storing reverse recovery current from the diode of the buck converter and using energy from the reverse recovery current to discharge parasitic capacitance of the primary switch of the buck converter prior to turn-on of the primary switch such that the primary switch turns on with substantially zero voltage across the primary switch, wherein the ZVS circuit comprises:
a capacitor;
an auxiliary switch connected in series with the capacitor; and
an auxiliary inductor connected in parallel with the series-connected capacitor and auxiliary switch; and
a control circuit for periodically turning on and off the primary switch such that:
the auxiliary switch and the primary switch are not both on at the same time; and
there is a time interval between the end of the on-time of the auxiliary switch and the beginning of the on-time of the primary switch, wherein the time interval is of sufficient duration such that the energy from the reverse recovery current substantially discharges the parasitic capacitance of the primary switch during the time interval.
14 . The DC/DC converter of claim 13 , wherein the ZVS circuit is connected in series with the diode of the buck converter.
15 . The DC/DC converter of claim 13 , wherein the ZVS circuit is converter is connected in series with the primary switch.
16 . The DC/DC converter of claim 13 , wherein the time interval is of a fixed duration.
17 . An AC/DC converter for converting an AC input voltage to a DC output voltage for powering a load, the AC/DC comprising:
a bridge rectifier for rectifying the AC input voltage;
a boost converter coupled to the bridge rectifier; and
a DC/DC converter coupled to the output of the boost converter, wherein the DC/DC converter comprises at least one buck converter stage, wherein the at least one buck converter stage comprises:
a buck converter including a primary switch, a diode and an inductor, such that when the primary switch is on the inductor is connected to the input voltage and when the primary switch is off the inductor is disconnected from the input voltage;
a control circuit for periodically turning on and off the primary switch; and
a ZVS circuit for storing reverse recovery current from the diode of the buck converter and using energy from the reverse recovery current to discharge parasitic capacitance of the primary switch of the buck converter prior to turn-on of the primary switch such that the primary switch turns on with substantially zero voltage across the primary switch.
18 . The AC/DC converter of claim 17 , wherein the ZVS circuit of the buck converter stage comprises:
a capacitor;
an auxiliary switch connected in series with the capacitor; and
an auxiliary inductor connected in parallel with the series-connected capacitor and auxiliary switch.
19 . The AC/DC converter of claim 18 , wherein the control circuit of the buck converter stage is for controlling the auxiliary switch such that:
the auxiliary switch and the primary switch are not both on at the same time; and
there is a time interval between the end of the on-time of the auxiliary switch and the beginning of the on-time of the primary switch, wherein the time interval is of sufficient duration such that the energy from the reverse recovery current substantially discharges the parasitic capacitance of the primary switch during the time interval.
20 . The AC/DC converter of claim 19 , wherein the ZVS circuit is connected in series with the diode of the buck converter.
21 . The AC/DC converter of claim 19 , wherein the ZVS circuit is converter is connected in series with the primary switch.
22 . The AC/DC converter of claim 19 , wherein the time interval is of a fixed duration.