Boosting technique for a bi-directional switch in a power converter
A bi-directional switch for a power converter comprises first and second transistors (SW 1 , SW 2 ) and a floating supply capacitor (C 2 ) associated with the second transistor (SW 2 ). The drive circuit and/or gate of the first transistor (SW 1 ) is charged by the floating supply capacitor (C 2 ) of the second transistor (SW 2 ). The charging takes place at a predetermined moment in the switching cycle, and in particular at a moment in the switching cycle when the voltage across the bi-directional switch is substantially a minimum.
1. A bi-directional switch for a power converter comprising first and second transistors and a floating supply capacitor, wherein the first and second transistors are connected together in anti-series between a first node and a second node, the first transistor connected to the first node and the second transistor to the second node, and the floating capacitor is connected between a floating supply node and the second node connected to the second transistor, wherein the floating capacitor is connected to charge a drive circuit dedicated to the first transistor at a predetermined moment in the switching cycle of the bi-directional switch.
2. A bi-directional switch as claimed in claim 1 , wherein the predetermined moment in the switching cycle is when the voltage across the bi-directional switch is substantially a minimum.
3. A bi-directional switch as claimed in claim 1 , wherein the drive circuit of the first transistor comprises a transistor and a diode coupled in series between the floating supply node and the gate of the first transistor.
4. A bi-directional switch as claimed in claim 3 , wherein the drive circuit directly drives the gate of the first transistor in response to receiving charge from the floating supply capacitor.
5. A bi-directional switch for a power converter comprising first and second transistors and a first floating supply capacitor and a second floating supply capacitor, wherein the first and second transistors are connected together in anti-series between a first node and a second node, the first transistor connected to the first node and the second transistor to the second node, the first floating supply capacitor is connected between a first floating supply node and the first node connected to the first transistor, the second floating supply capacitor is connected between a second floating supply node and the second node connected to the second transistor, wherein a switch is provided for coupling together the first and second floating supply nodes.
6. The bi-directional switch as claimed in claim 5 , wherein the switch connected between respective first plates of the first floating supply capacitor and the second floating supply capacitor is operable to electrically connect the respective first plates of the first and second floating supply capacitors so that the first floating supply capacitor takes charge from the second floating supply capacitor.
7. A bi-directional switch as claimed in claim 6 , wherein the switch is operated when the respective second plates of the first and second floating supply capacitors are connected together.
8. A bi-directional switch as claimed in claim 5 , wherein a drive circuit is connected in parallel with the first floating supply capacitor to drive the gate of the first transistor.
9. A bi-directional switch as claimed in claim 8 , wherein the drive circuit of the first transistor includes a latch and a buffer.
10. A bi-directional switch as claimed in claim 5 , wherein the switch comprises a pair of high voltage components comprising at least one transistor.
11. A switched mode power converter comprising a bi-directional switch as claimed in claim 5 connected to one end of a winding of a secondary side of a transformer thereof.
12. A switched mode power converter as claimed in claim 11 , wherein the bi-directional switch is connected to the high side of the secondary side of the transformer.