AC-DC converter having soft-switched totem-pole output
An AC-DC converter has a totem-pole output circuit having first and second semiconductor switches, each having a channel coupled to a switching node and having a parasitic capacitance associated with the channel. An inductor has one terminal thereof connected to a switching node. First and second bypass devices are coupled to a second terminal of the inductor and operable during at least a portion of an input voltage to allow reverse current from an output of the converter to generate soft-switching of the first semiconductor switch. An asymmetrical shunt for measuring current in a first direction and bypassing current in a second direction opposite the first direction allows accurate measurement of reverse current.
1. An AC-DC boost converter for power factor correction comprising:
a totem-pole output circuit having first and second semiconductor switches connected between an output rail and a reference rail, each switch having a channel coupled to a central switching node and having a parasitic capacitance associated with the channel;
an AC voltage source having a first terminal and a second terminal;
an inductor having a first terminal connected to the switching node and having a second terminal connected to the first terminal of the AC voltage source;
a first bypass device connected between the output rail and the second terminal of the AC voltage source;
a second bypass device connected between the reference rail and the second terminal of the AC voltage source;
an output capacitor and a load resistance having first terminals connected to the output rail and second terminals connected together;
a shunt resistor having a first terminal connected to the reference rail and a second terminal connected to the second terminals of the output capacitor and the load resistance; and
a shunt diode having a cathode terminal connected to the reference rail and an anode terminal connected to the second terminals of the output capacitor and the load resistances.
2. The AC-DC converter of claim 1 in which the bypass devices are semiconductor switches.
3. The AC-DC converter of claim 1 in which the bypass devices are capacitors.
4. The AC-DC converter of claim 1 including a first rectifier diode in parallel with the first bypass device; and a second rectifier diode in parallel with the second bypass device.
5. The AC-DC converter of claim 1 in which the shunt diode is a Schottky diode.