Method and apparatus for a control circuit responsive to an impedance coupled to a control circuit terminal

• US 8,004,864 B2
• Filed: 07/02/2009
• Issued: 08/23/2011
• Est. Priority Date: 10/04/2006
• Status: Expired due to Fees

• Current Assignee: Power Integrations Incorporated
• Original Assignee: Power Integrations Incorporated
• Inventors: Matthews, David Michael Hugh, Wang, Zhao-Jun, Bäurle, Stefan
• Primary Examiner(s): Riley; Shawn
• Application Number:
  US12/497,366
• Publication Number:
  US 20090268362A1
• Time in Patent Office: 782 Days
• Field of Search: 363/21.12, 363/56.11, 363/21.13
• US Class Current: 363/21.12
• CPC Class Codes: H02M 1/32 Means for protecting converters other than automatic disconnection
• CPC Class Codes: H02M 3/33507 with automatic control of the output voltage or current, e.g. flyback converters H02M3/33561, H02M3/33569 take precedence
• CPC Class Codes: H02M 3/33523 with galvanic isolation between input and output of both the power stage and the feedback loop

Abstract

An example power supply includes a controller and a detection circuit. The controller includes a sense terminal coupled to provide a sense terminal current representative of an input voltage of the power supply during normal operation. The detection circuit is external to the controller and is coupled to the sense terminal. The detection circuit includes a Zener diode coupled to conduct a current to adjust the sense terminal current during a fault condition, where during the fault condition the controller is responsive to a measured impedance of the detection circuit which is determined in response to the sense terminal current.

Claims

1. A power supply, comprising:

a controller including a sense terminal coupled to provide a sense terminal current representative of an input voltage of the power supply during normal operation; and

a detection circuit external to the controller and coupled to the sense terminal, the detection circuit including a Zener diode coupled to conduct a current to adjust the sense terminal current during a fault condition,

wherein during the fault condition the controller is responsive to a measured impedance of the detection circuit which is determined in response to the sense terminal current.

2. The power supply of claim 1, further comprising a bias capacitor coupled to the detection circuit such that the bias capacitor provides the current to adjust the sense terminal current in response to a voltage across the bias capacitor.

3. The power supply of claim 2, wherein the Zener diode is coupled to isolate the sense terminal from the voltage across the bias capacitor under normal operating conditions.

4. The power supply of claim 1, wherein the controller is further coupled to regulate an output of the power supply in response to the sense terminal current during normal operation.

5. The power supply of claim 1, wherein the detection circuit is an over voltage protection circuit.

6. The power supply of claim 1, wherein the Zener diode only conducts the current when the voltage across the bias capacitor reaches the Zener threshold voltage.

7. The power supply of claim 1, wherein the power supply is a flyback configuration.

8. The power supply of claim 1, wherein the detection circuit further includes a resistor coupled to the Zener diode, wherein during the fault condition the current through Zener diode and the resistor is substantially equal.

9. The power supply of claim 8, wherein the measured impedance of the detection circuit during the fault condition substantially consists of an impedance of the resistor.

10. The power supply of claim 8, wherein a value of the resistor is chosen to determine a type of response by the controller.

11. The power supply of claim 1, wherein sense terminal is regulated at a first threshold voltage when sense terminal current is below a first current threshold.

12. The power supply of claim 11, wherein sense terminal is regulated at a second threshold voltage when sense terminal current reaches the first current threshold.

13. The power supply of claim 12, wherein the controller is coupled to respond depending on the value of the sense terminal current when the sense terminal is regulated at the second voltage level.

14. The power supply of claim 11, wherein the fault condition is determined when the sense terminal current reaches the first current threshold.