System and method for driving a switch

• US 8,754,675 B2
• Filed: 07/03/2013
• Issued: 06/17/2014
• Est. Priority Date: 11/30/2010
• Status: Active Grant

• Current Assignee: Infineon Technologies AG
• Original Assignee: Infineon Technologies AG
• Inventors: Draxelmayr, Dieter, Norling, Karl
• Primary Examiner(s): LUU, AN T
• Application Number:
  US13/934,980
• Publication Number:
  US 20130293268A1
• Time in Patent Office: 349 Days
• Field of Search: 327108-112, 327387-391, 327/588, 327/589
• US Class Current: 327/108
• CPC Class Codes: H02M 1/08 Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
• CPC Class Codes: H02M 3/33553 with galvanic isolation between input and output of both the power stage and the feedback loop
• CPC Class Codes: H03K 17/063 in field-effect transistor switches
• CPC Class Codes: H03K 17/691 using transformer coupling

Abstract

In accordance with an embodiment, a circuit for driving a switch includes a driver circuit. The driver circuit includes a first output configured to be coupled to a gate of the JFET, a second output configured to be coupled to a gate of the MOSFET, a first power supply node, and a bias input configured to be coupled to the common node. The switch to be driven includes a JFET coupled to a MOSFET at a common node.

Claims

1. A circuit for driving a switch, the switch comprising a normally-on device coupled to a switch transistor at a common node, the circuit comprising:

a driver circuit comprising

a first output configured to be coupled to a control node of the normally-on device,

a second output configured to be coupled to a control node of the switch transistor,

a first power supply node, and

a bias input configured to be coupled to the common node, wherein the driver circuit is configured to receive power from the bias input during startup of the circuit.

2. The circuit of claim 1, wherein the driver circuit is configured to operate with:

a capacitor coupled between the first power supply node and a first output of the normally-on device; and

a first network coupled between the first power supply node and a second output of the normally-on device, wherein the first network comprises a diode and a second capacitor coupled in series.

3. The circuit of claim 1, wherein:

the driver circuit is configured to keep the switch transistor off when a reference supply voltage is below a first threshold voltage;

the driver circuit is configured to operate the switch transistor and the normally-on device together when the reference supply voltage is between the first threshold voltage and a second threshold voltage; and

the driver circuit is configured to keep the switch transistor on when the reference supply voltage is greater than the second threshold voltage.

4. The circuit of claim 3, wherein the reference supply voltage is proportional to a voltage of an internal power supply source.

5. The circuit of claim 3, wherein the reference supply voltage is proportional to a voltage of the bias input.

6. The circuit of claim 3, wherein the driver circuit is configured to operate the switch transistor and the normally-on together by turning on the switch transistor before turning on the normally-on device, and turning off the normally-on device before turning off the switch transistor.

7. The circuit of claim 1, further comprising the normally-on device and the switch transistor.

8. The circuit of claim 7, wherein the normally-on device comprises a JFET.

9. The circuit of claim 7, wherein the switch transistor comprises a MOSFET.

10. A method of operating a switch driver comprising a first switch driver output configured to be coupled to a control node of a normally-on device, a second switch driver output configured to be coupled to a control node of a switch transistor, a first power supply node, and a bias input configured to be coupled to a first output node of the normally-on device and a first output node of the switch transistor, the method comprising:

switching the first switch driver output during startup, switching the first switch driver output during startup comprising receiving power from the bias input.

11. The method of claim 10, further comprising:

switching the first switch driver output and the second switch driver output together when supply nodes of the switch driver are ramping up from an initial startup condition; and

keeping the second switch driver output in a state configured to keep the switch transistor on while switching the first switch driver output on and off after the supply nodes of the switch driver are charged to a full operating state.

12. The method of claim 11, further comprising keeping the second switch driver output in a state configured to keep the switch transistor off at an initial startup of the switch driver.

13. The method of claim 10, further comprising:

switching the first switch driver output and the second switch driver output together when a reference supply voltage is between a first threshold voltage and a second threshold voltage; and

keeping the second switch driver output in a state configured to keep the switch transistor on while switching the first switch driver output on and off when the reference supply voltage is greater than the second threshold voltage.

14. The method of claim 13, further comprising keeping the second switch driver output in a state configured to keep the switch transistor off when the reference supply voltage is below the first threshold voltage.

15. The method of claim 13, wherein switching the first switch driver output and the second switch driver output together comprises:

activating the second switch driver output to turn on the switch transistor before activating the first switch driver output to turn on the normally-on device; and

deactivating the first switch driver output to turn off the normally-on device before deactivating the second output to turn off the switch transistor.

16. A method of operating a switch driver comprising a first output configured to be coupled to a control node of a normally-on device, and a second output configured to be coupled to a control node of a switch transistor coupled in series with the normally-on device, wherein the method comprises:

switching the first output and the second output together when a supply node of the switch driver is ramping up from an initial startup condition;

keeping the second output in a state configured to keep the switch transistor on while switching the first output on and off after the supply node of the switch driver is charged to a full operating state; and

keeping the second output in a state configured to keep the switch transistor off at an initial startup of the switch driver.

17. The method of claim 16, further comprising:

determining if the supply node of the switch driver is ramping up from an initial startup condition;

determining if the supply node of the switch driver is charged to a full operating state; and

determining if the switch driver is at an initial startup state.

18. The method of claim 16, wherein:

determining if the supply node of the switch driver is ramping up from an initial startup condition comprises determining if a reference supply voltage is within a first voltage range;

determining if the supply node of the switch driver is charged to a full operating state comprises determining if the reference supply voltage is within a second voltage range; and

determining if the switch driver is at an initial startup state comprises determining if the reference supply voltage is within a third supply voltage range.

19. The method of claim 16, further comprising driving the normally-on device with the first output and driving the switch transistor with the second output.

20. The method of claim 16, further comprising switching the first output during startup, switching the first output during startup comprising operating the switch driver using a bias input as a power supply, wherein the bias input is configured to be coupled to a common node between the normally-on device and the switch transistor.