System and method for bootstrapping a switch driver

• US 8,994,411 B2
• Filed: 10/14/2013
• Issued: 03/31/2015
• 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): CHENG, DIANA
• Application Number:
  US14/053,369
• Publication Number:
  US 20140035626A1
• Time in Patent Office: 533 Days
• Field of Search: 327108-112, 327387-391, 327588-589, 326 26- 27, 326/82, 326/83, 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: H02M 7/538 in a push-pull configuration H02M7/5375 takes precedence ; with oscillating arrangements H02M7/53832, H02M7/53846
• CPC Class Codes: H03K 17/94 characterised by the way in which the control signals are generated
• 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
• CPC Class Codes: H03K 5/1515 non-overlapping

Abstract

In accordance with an embodiment, a driver circuit includes a low-side driver having a first output configured to be coupled to a control node of a first semiconductor switch, and a reference input configured to be coupled to a reference node of the first semiconductor switch. The low-side driver also includes a first capacitor coupled between an output node of the first semiconductor switch and a first node, a first diode coupled between the first node and a first power input of the driver, and a second capacitor coupled between the first power input of the low-side driver and the reference node of the first semiconductor switch.

Claims

1. A method of operating a switch driver, the method comprising:

charging a supply node of the switch driver with a network coupled between an output of a switch and a supply node of the driver, wherein the switch comprises a normally-on device in series with a switch transistor, and the normally-on device conducts electricity when a voltage between a control node of the normally-on device and a reference node of the normally-on device is about zero volts.

2. The method of claim 1, wherein the network comprises a capacitor in series with a first diode.

3. The method of claim 1, wherein the normally-on device comprises a JFET and the switch transistor comprises a MOSFET.

4. The method of claim 1, further comprising:

operating the normally-on device and the switch transistor together when supply nodes of the switch driver are charging up after the switch driver has started up; and

keeping the switch transistor on while turning the normally-on device on and off after the supply nodes of the switch driver are charged to a full operating state.

5. A circuit comprising:

a first driver circuit configured to be coupled to a first switch having a first normally-on device coupled in series with a first switch transistor, wherein the normally-on device conducts electricity when a voltage between a control node of the normally-on device and a reference node of the normally-on device is about zero volts; and

a first network coupled between an output of the first switch and a supply node of the first driver circuit, wherein the first network is configured to charge a supply node of the first driver circuit.

6. The circuit of claim 5, wherein the normally-on device comprises a JFET and the first switch transistor comprises a MOSFET.

7. The circuit of claim 5, wherein the first network comprises a capacitor in series with a first diode.

8. The circuit of claim 5, wherein the first driver circuit comprises a low-side driver circuit.

9. The circuit of claim 5, further comprising:

a second driver circuit configured to be coupled to a second switch having a second normally-on device coupled in series with a second switch transistor; and

a second network coupled between an output of the second switch and a supply node of the second driver circuit, wherein the second network is configured to charge a supply node of the second driver circuit.

10. The circuit of claim 9, wherein the second driver circuit comprises a high-side driver circuit.

11. A circuit comprising:

a first switch comprising a normally-on device coupled in series with a switch transistor, wherein the normally-on device conducts electricity when a voltage between a control node of the normally-on device and a reference node of the normally-on device is about zero volts;

a low-side driver; and

a first network coupled between an output of the first switch and a supply node of the low-side driver, wherein the first network comprises a capacitor in series with a first diode, and the first network is configured to charge a supply node of the low-side driver.

12. The circuit of claim 11, wherein the first network is configured to charge the supply node of the low-side driver below ground potential.

13. The circuit of claim 11, further comprising:

a high-side driver coupled to a second switch, wherein the second switch is coupled in series with the first switch; and

a second network coupled between an output of the second switch and supply node of the high side driver, wherein the second network comprises the capacitor in series with a second diode, and the second network is configured to charge a supply node of the high-side driver.

14. The circuit of claim 11, wherein:

the first switch comprises a JFET device in series with a MOSFET device; and

the low-side driver and the first network are configured to

operate the JFET device and the MOSFET device together when supply nodes of the circuit are charging up after the circuit has started up, and

keep the MOSFET device on while turning the JFET device on and off after the supply nodes of the circuit are charged to a full operating state.

15. The circuit of claim 14, wherein the low-side driver and the first network are further configured to keep MOSFET device off during startup of the circuit.

16. The circuit of claim 11, wherein:

the first switch comprises a JFET device in series with a MOSFET device; and

the low-side driver and the first network are configured to

operate the JFET device and the MOSFET device together when a reference supply voltage is between a first threshold voltage and a second threshold voltage, and

keep the MOSFET device on while turning the JFET device on and off when the reference supply voltage is greater than the second threshold voltage.

17. The circuit of claim 16, wherein the low-side driver and the first network are further configured to keep the MOSFET device off when the reference supply voltage is below the first threshold voltage.

18. The circuit of claim 16, wherein the low-side driver and the first network are configured to operate the JFET device and the MOSFET device together by turning on the MOSFET device before turning on the JFET device, and turning off the JFET device before turning off the MOSFET device.

19. The circuit of claim 11, wherein the low-side driver and the first network are configured to:

operate the normally-on device and the switch transistor together when supply nodes of the circuit are charging up after the circuit has started up; and

keep the switch transistor on while turning the normally-on device on and off after the supply nodes of the circuit are charged to a full operating state.

20. The circuit of claim 11, wherein the normally-on device comprises a JFET and the switch transistor comprises a MOSFET.