System and method for driving a cascode switch

• US 8,310,281 B2
• Filed: 11/30/2010
• Issued: 11/13/2012
• Est. Priority Date: 11/30/2010
• Status: Active Grant

• Current Assignee: Infineon Technologies AG
• Original Assignee: Infineon Technologies AG
• Inventors: Draxelmayr, Dieter
• Primary Examiner(s): LUU, AN T
• Application Number:
  US12/956,696
• Publication Number:
  US 20120133398A1
• Time in Patent Office: 714 Days
• Field of Search: 327108-112, 327387-391, 327588-589, 326 26- 27, 326 82- 83, 326/86, 326/89, 326/90, 326/92
• US Class Current: 327/108
• CPC Class Codes: H02M 3/33571 Half-bridge at primary side of an isolation transformer
• CPC Class Codes: H02M 3/33573 Full-bridge at primary side of an isolation transformer
• CPC Class Codes: H03K 17/165 by feedback from the output circuit to the control circuit
• CPC Class Codes: H03K 2017/6875 using self-conductive, depletion FETs
• CPC Class Codes: H03K 2217/0081 Power supply means, e.g. to the switch driver

Abstract

In accordance with an embodiment, a method of driving switches includes sensing a control node of a first switch, sensing a control node of a second switch, and driving the control node of the first switch to a first active state after the control node of the second switch transitions to a second active state. The method also includes driving the control node of the second switch to a second inactive state after the control node of the first switch transitions to a first inactive state. Driving the control node of the first switch is based on sensing the control node of the second switch, and driving the control node of the second switch is based on based on sensing the control node of the first switch.

Claims

1. A method of driving switches, the method comprising:

sensing a control node of a first switch;

sensing a control node of a second switch;

driving the control node of the first switch to a first active state after the control node of the second switch transitions to a second active state, based on sensing the control node of the second switch; and

driving the control node of the second switch to a second inactive state after the control node of the first switch transitions to a first inactive state based on sensing the control node of the first switch.

2. The method of claim 1, further comprising

driving the control node of the second switch to the second active state based on a logic input;

and

driving the control node of the first switch to the first inactive state based on the logic input.

3. The method of claim 1, wherein

driving the control node of the first switch comprises driving a gate of a JFET;

and

driving the control node of the second switch comprises driving a gate of a MOSFET coupled in series with the JFET.

4. The method of claim 3, further comprising operating the JFET and the MOSFET in a switched-mode power supply.

5. The method of claim 1, wherein sensing the control node of the first switch comprises:

sampling a voltage of the control node of the first switch though a series transistor; and

changing a state of a latch when the control node of the first switch transitions from the first active state to the first inactive state.

6. The method of claim 5, further comprising

resetting the latch and shutting off the series transistor when the first output driver transitions from the first inactive state to the first active state.

7. The method of claim 5, wherein

the latch comprises a forward inverter and a feedback inverter;

and

the feedback inverter comprises weak transistors.

8. A circuit for driving a switch comprising a JFET in series with a MOSFET, wherein

the circuit comprises a controller that operates the MOSFET and the JFET together by turning on the JFET after turning on the MOSFET by sensing a gate voltage of the MOSFET, and turning off the MOSFET after turning off the JFET by sensing the a gate voltage of the JFET.

9. The circuit of claim 8, wherein the controller comprises

a first logic gate comprising a first input coupled to a circuit input signal;

a first gate controller circuit comprising

a gate controller input coupled to an output of the first logic gate,

a gate control node, and

a logic output node;

a second logic gate coupled to the circuit input signal at a first input and the logic output node of the first gate controller at a second input; and

a second gate controller comprising

a gate controller input coupled to an output of the second logic gate,

a gate control node, and

a logic output node coupled to a second input of the first logic gate.

10. The circuit of claim 9, wherein:

the first logic gate comprises an AND gate;

the second logic gate comprises an AND gate; and

the circuit further comprises an inverter coupled between the first input of the first logic gate and the first input of the second logic gate.

11. The circuit of claim 9, wherein the first gate controller and the second gate controller each comprise:

a transistor network coupled between the gate controller input and the gate control node; and

a latch coupled between the transistor network and the logic output node.

12. The circuit of claim 11, wherein the transistor network comprises a first transistor comprising a control node coupled to a power supply node, a first output coupled to the gate control node, and a second output coupled to the input of the latch.

13. The circuit of claim 12, further comprising a second transistor comprising a control node coupled to the gate controller input, a first output coupled to a power supply node, and a second output coupled an input of the latch.

14. The circuit of claim 12, wherein the first transistor comprises a high-voltage device.

15. The circuit of claim 11, wherein the latch comprises a forward inverter and a feedback inverter, the feedback inverter comprising weak transistors.

16. The circuit of claim 8, wherein the circuit is disposed on an integrated circuit.

17. A circuit comprising:

a first driver having a first output configured to be coupled to a control node of a first switch, wherein

the first driver asserts a first active state at the first output, where the first active state configured to turn on the first switch, and

the first driver asserts a first inactive state at the first output, where the first inactive state configured to turn off the first switch;

a first sensor configured to sense the control node of the first switch;

a second driver having a second output configured to be coupled to a control node of a second switch, wherein

the second driver asserts a second active state at the second output, the second active state configured to turn on the second switch, and

the second driver asserts a second inactive state at the second output, the second inactive state configured to turn off the second switch; and

a second sensor configured to sense the control node of the second switch, wherein

the first driver is configured to enter the first active state after the second sensor senses that the control node of the second switch is in an on state, and

the second driver is configured to enter the second inactive state after the first sensor senses that the control node of the first switch is in an off state.

18. The circuit of claim 17, wherein the first driver is configured to drive a JFET and the second driver is configured to drive a MOSFET.

19. The circuit of claim 18, wherein the MOSFET comprises a PMOS device.

20. The circuit of claim 18, wherein the first driver, second driver, first sensor and second sensor is disposed on an integrated circuit.