Power factor correction circuit
The present application relates to AC power supplies and in particular to power factor correction circuits in AC-DC converters. The application provides an active power factor correction circuit in which zero voltage switching is inherently achieved using a passive snubbing approach employing a saturable transformer.
1. A power factor correction circuit for a power supply, the power factor correction circuit accepting an AC input and providing a DC output, the power factor correction circuit comprising:
a first inductor coupled to receive the AC input,
a first capacitor,
a first switch connected between a first AC node and a second AC node,
a transformer having a first winding and a second winding and a saturable core which saturates under normal current operating conditions,
a rectifying bridge, wherein the second winding of the transformer and the first inductor are connected in series between the AC input and the rectifying bridge and wherein the first inductor, first capacitor, first switch and rectifying bridge are arranged in a boost switching topology where the first switch is employed in transferring energy from the input to the output using the first inductor and first capacitor, and
a passive snubber connected on a first end to the first node of the first switch and connected on a second end to the second node of the first switch, the snubber including the first winding of the transformer, wherein the first node of the first switch is connected to the rectifying bridge.
2. The power factor correction circuit according to claim 1 , wherein the passive snubber comprises a second capacitor in series with the first winding.
3. The power factor correction circuit according to claim 1 , wherein the passive snubber is connected at the second end to another node of the rectifying bridge.
4. The power factor correction circuit according to claim 1 , wherein the rectifying bridge comprises four diodes.
5. The power factor correction circuit according to claim 1 , wherein the rectifying bridge comprises two switches and two diodes.
6. The power factor correction circuit according to claim 5 , wherein one of the switches of the rectifying bridge is the first switch.
7. The power factor correction circuit according to claim 1 , further comprising a controller for controlling the first switch, wherein the controller is configured to control the first switch to ensure the operation of the power factor correction circuit in continuous mode.
8. The power factor correction circuit according to claim 7 , wherein the controller is configured to detect when the power factor correction circuit is not able to operate in continuous mode and upon detecting such a condition limits switching of the first switch for one or more intervals.
9. The power factor correction circuit according to claim 8 , wherein each of the one or more intervals comprises a full mains cycle.
10. The power factor correction circuit according to claim 9 , wherein each of the one or more intervals are during a half mains cycle such that the controller operates in a burst mode.
11. The power factor correction circuit according to claim 8 , wherein each of the one or more intervals comprises a period at a start and an end of each half mains cycle.
12. The power factor correction circuit according to claim 1 , further comprising a controller for controlling the first switch, wherein the controller is configured to control the first switch to operate the power factor correction circuit using zero-voltage switching conditions.
13. A power factor correction circuit for converting an AC input voltage to a DC output voltage, the power factor correction circuit comprising:
first and second AC input nodes for receiving the AC input voltage;
first and second DC output nodes providing the DC output voltage;
a switching circuit arranged in a boost switching topology, wherein the switching circuit includes:
a first inductor coupled to receive the AC input voltage,
a rectifying bridge having a first input node, a second input node, and two output nodes, wherein the second input node is electrically connected to the second AC input node,
a transformer having a first winding, a second winding and a saturable core that saturates under normal current operating conditions, wherein the first inductor and the second winding of the transformer are connected in series between the first AC input node and the first input node of the rectifying bridge,
a first semiconductor switch for switchably connecting the first input node of the rectifying bridge to the second AC input node,
a first capacitor connected between the two output nodes of the rectifying bridge, and
a passive snubber connected across the first and second input nodes of the rectifying bridge, wherein the passive snubber includes the first winding of the transformer.
14. The power factor correction circuit according to claim 13 , further comprising a controller for controlling the first semiconductor switch, wherein the controller is configured to control the first semiconductor switch to ensure the operation of the power factor correction circuit in continuous mode.
15. The power factor correction circuit according to claim 14 , wherein the controller is configured to detect when the power factor correction circuit is not able to operate in continuous mode and, upon detecting such a condition, limits switching of the first semiconductor switch for one or more intervals.
16. The power factor correction circuit according to claim 13 , further comprising a controller for controlling the first semiconductor switch, wherein the controller is configured to control the first semiconductor switch to operate the power factor correction circuit using zero voltage switching conditions.
17. A power factor correction circuit for accepting an AC input voltage across first and second AC input nodes and providing a DC output across first and second DC output nodes, the power factor correction circuit comprising:
a switching circuit arranged in a boost switching topology, wherein the switching circuit includes:
a first inductor coupled to receive the AC input voltage,
a transformer having a primary and secondary winding, where the secondary winding is electrically connected in series with the first inductor between the first AC input node and a switched node, the transformer having a saturable core that saturates under normal operating conditions,
a first semiconductor switch for switchably connecting the switched node to the first DC output node,
a second semiconductor switch for switchably connecting the switched node to the second DC output node,
first and second rectifiers connected in series between the first and second DC output nodes and sharing a common intermediate node, wherein the common intermediate node is connected to the second AC input node;
a first capacitor connected between the first and second DC output nodes; and
a second capacitor connected in series with the primary winding between the common intermediate node and the switched node.
18. The power factor correction circuit according to claim 17 , further comprising a controller for controlling the operation of the first and second semiconductor switches, wherein the controller is configured to control the first and second semiconductor switches to ensure the operation of the power factor correction circuit in continuous mode.
19. The power factor correction circuit according to claim 18 , wherein the controller is configured to detect when the power factor correction circuit is not able to operate in continuous mode and upon detecting such a condition limits switching of the first and second semiconductor switches for one or more intervals.
20. The power factor correction circuit according to claim 17 , further comprising a controller for controlling the operation of the first and second semiconductor switches, wherein the controller is configured to control the first and second semiconductor switches to maintain operation of the power factor correction circuit using zero voltage switching conditions.