Switch circuit with active snubber circuit and DC-DC converter
A switch circuit includes a first switch element defined by an FET, and an active snubber circuit connected between a drain and a source of the first switch element and including a second switch element defined by an FET, a capacitor connected in series to the second switch element, a third switch element connected to a gate of the second switch element and turned on to extract an electric charge of capacitance between the gate and a source of the second switch element, and a delay circuit that turns on the third switch element at a timing delayed from a timing at which the second switch element is turned on.
1. A switch circuit comprising:
a first switch element defined by an FET; and
an active snubber circuit connected between a drain and a source of the first switch element; wherein
the active snubber circuit includes:
a second switch element defined by an FET;
a third switch element defined by an FET;
a capacitor connected in series to the second switch element; and
a delay circuit connected to the third switch element;
the third switch element is connected to a gate of the second switch element and is turned on to extract an electric charge of capacitance between the gate and a source of the second switch element; and
the delay circuit includes a connecting capacitor configured to generate a control terminal voltage for the third switch element, a constant current circuit configured to charge the connecting capacitor, and a diode configured to discharge the connecting capacitor; and
the delay circuit is configured to turn on the third switch element at a timing delayed from a timing at which the second switch element is turned on.
2. The switch circuit including the active snubber circuit according to claim 1 , wherein
the constant current circuit includes a transistor and a first resistor which is connected between a base and a collector of the transistor; and
the diode is connected in parallel between the collector and an emitter of the transistor.
3. The switch circuit including the active snubber circuit according to claim 1 , wherein the second switch element and the capacitor define a series circuit that is connected between the drain and the source of the first switch element.
4. The switch circuit including the active snubber circuit according to claim 1 , wherein a second resistor is connected between a gate and the source of the first switch element.
5. The switch circuit including the active snubber circuit according to claim 1 , further comprising a snubber driving circuit connected to the gate of the second switch element.
6. The switch circuit including the active snubber circuit according to claim 1 , wherein the third switch element is connected between the gate and a source of the second switch element.
7. The switch circuit including the active snubber circuit according to claim 1 , further comprising a delay circuit connected to a gate of the third switch element.
8. The switch circuit including the active snubber circuit according to claim 1 , wherein the second switch element is defined by a P-channel MOS-FET.
9. The switch circuit including the active snubber circuit according to claim 1 , wherein the third switch element is defined by a P-channel MOS-FET.
10. A DC-DC converter comprising:
the switch circuit including the active snubber circuit according to claim 1 ;
a voltage input section that receives a DC voltage;
a voltage output section to which a load is connected;
a transformer including a primary winding and a secondary winding;
a main switch element provided between the voltage input section and the primary winding of the transformer; and
a synchronous rectifier circuit including the active snubber circuit and provided between the voltage output section and the secondary winding of the transformer.
11. The DC-DC converter according to claim 10 , wherein
the transformer further includes an auxiliary winding; and
a voltage of the auxiliary winding of the transformer is input to the delay circuit and the third switch element is turned off.
12. The DC-DC converter according to claim 10 , further comprising a clamp circuit including a clamp switch element and a clamp capacitor provided between the voltage output section and the secondary winding of the transformer.
13. The DC-DC converter according to claim 10 , wherein
the constant current circuit includes a transistor and a first resistor which is connected between a base and a collector of the transistor; and
the diode is connected in parallel between the collector and an emitter of the transistor.
14. The DC-DC converter according to claim 10 , wherein the second switch element and the capacitor define a series circuit that is connected between the drain and the source of the first switch element.
15. The DC-DC converter according to claim 10 , wherein a second resistor is connected between a gate and the source of the first switch element.
16. The DC-DC converter according to claim 10 , further comprising a snubber driving circuit connected to the gate of the second switch element.
17. The DC-DC converter according to claim 10 , wherein the third switch element is connected between the gate and a source of the second switch element.
18. The DC-DC converter according to claim 10 , further comprising a delay circuit connected to a gate of the third switch element.
19. The DC-DC converter according to claim 10 , wherein the second switch element is defined by a P-channel MOS-FET.
20. The DC-DC converter according to claim 10 , wherein the third switch element is defined by a P-channel MOS-FET.