Multiple output power supply having soft start protection for load over-current or short circuit conditions

• US 6,813,170 B2
• Filed: 08/19/2002
• Issued: 11/02/2004
• Est. Priority Date: 08/19/2002
• Status: Expired due to Fees

• Current Assignee: Semtech Corporation
• Original Assignee: Semtech Corporation
• Inventors: Yang, Jian
• Primary Examiner(s): HAN, YOUNGHUIE JESSICA
• Application Number:
  US10/224,269
• Publication Number:
  US 20040032754A1
• Time in Patent Office: 806 Days
• Field of Search: 363/49, 363/50, 363/56.09, 363/56.1, 323/901, 323/908, 361/93.1, 361/93.2, 361/93.9, 361/87
• US Class Current: 363/56.09
• CPC Class Codes: H02M 1/32 Means for protecting converters other than automatic disconnection
• CPC Class Codes: H02M 1/36 Means for starting or stopping converters
• CPC Class Codes: H02M 3/33561 having more than one ouput with independent control
• CPC Class Codes: Y10S 323/901 Starting circuits

Abstract

A protection circuit for a multiple output switching mode power converter protects against an over-current or short circuit failure condition. The protection circuit activates the soft-start circuit of the PWM control circuit upon detection of the over-current or short circuit condition. The soft-start circuit then shuts off operation of the power converter and restarts the power converter after a period of time defined by the soft-start circuit. The protection circuit is effective with any type of power converter topology (e.g., buck, boost, flyback, and forward converter), isolated or non-isolated, having dual or multiple outputs.

Claims

1. A switching mode power converter, comprising:

a transformer having a primary winding and a plurality of secondary windings, said plurality of secondary windings providing respective plural outputs through respective rectifiers;

a switch connected in series with said primary winding;

an input voltage source coupled to said primary winding;

a controller adapted to control operation of said switch to control a flow of current through said primary winding, said controller including a feedback circuit to determine a duty cycle of said switch in response to a detected output voltage of at least one of said plural outputs and a detected current through said primary winding, said controller further including a soft-start circuit used to inhibit activation of said switch for a predetermined period of time; and

an over-current protection circuit coupled to said plural outputs so as to detect a change in a voltage of any one of said plural outputs due to a load over-current or short circuit condition, wherein upon detection of said voltage change, said over-current protection circuit activates said soft-start circuit to shut off delivery of said flow of current through said primary winding for said predetermined period of time.

2. The switching mode power converter of claim 1, wherein said plural outputs further comprise at least a positive output and a negative output.

3. The switching mode power converter of claim 1, wherein said soft-start circuit further comprises a capacitor coupled to an internal current source of said controller, said period of time being defined by a charge time of said capacitor.

4. The switching mode power converter of claim 3, wherein said over-current protection circuit discharges said capacitor upon detection of said voltage change.

5. The switching mode power converter of claim 3, wherein said over-current protection circuit further comprises a switch coupled to said capacitor, said switch connecting said capacitor to ground upon detection of said voltage change.

6. The switching mode power converter of claim 1, wherein said change in voltage further comprises a drop in voltage relative to ground.

7. The switching mode power converter of claim 1, wherein said over-current protection circuit further comprises an opto-isolator providing electrical isolation between said plural outputs and said controller.

8. The switching mode power converter of claim 1, wherein said over-current protection circuit maintains said soft-start circuit in an activated state for a second predetermined period of time, said power converter restarting by operation of said soft-start circuit after completion of said second predetermined period of time.

9. In a switching mode power converter comprising plural outputs and a controller adapted to control a flow of current to said plural outputs, said controller including a soft-start circuit used to inhibit said flow of current during start-up of said power converter, a method for protecting said power converter from an over-current or short circuit condition comprises the steps of:

detecting a change in voltage of any one of said plural outputs;

activating said soft-start circuit upon detection of said voltage change; and

after a predetermined period of time, resuming normal operation of said power converter.

10. The method of claim 9, wherein said soft-start circuit further comprises a capacitor coupled to an internal current source of said controller, said activating step further comprising discharging said capacitor.

11. The method of claim 10, further comprising isolating said plural outputs from said controller.

12. The method of claim 9, further comprising maintaining said soft-start circuit in an activated state for a second predetermined period of time, wherein said resuming step occurring after completion of said second predetermined period of time.

13. A switching mode power converter, comprising:

an inductor coupled to a rectification stage having a plurality of outputs;

a switch connected in series with said inductor;

an input voltage source coupled to said inductor;

a controller adapted to control operation of said switch to control a flow of current through said inductor, said controller including a feedback circuit to determine a duty cycle of said switch in response to a detected voltage of at least one of said plurality of outputs and a detected current through said inductor, said controller further including a soft-start circuit used to inhibit activation of said switch for a predetermined period of time; and

an over-current protection circuit coupled to said plurality of outputs so as to detect a change in a voltage of any one of said outputs due to a load over-current or short circuit condition, wherein upon detection of said voltage change, said over-current protection circuit activates said soft-start circuit to shut off delivery of said flow of current through said inductor for said predetermined period of time.

14. The switching mode power converter of claim 13, wherein said plurality of outputs further comprise at least a positive output and a negative output.

15. The switching mode power converter of claim 13, wherein said soft-start circuit further comprises a capacitor coupled to an internal current source of said controller, said period of time being defined by a charge time of said capacitor.

16. The switching mode power converter of claim 13, wherein said voltage change further comprises a drop in voltage relative to ground.

17. The switching mode power converter of claim 15, wherein said over-current protection circuit discharges said capacitor upon detection of said voltage change.

18. The switching mode power converter of claim 15, wherein said over-current protection circuit further comprises a switch coupled to said capacitor, said switch connecting said capacitor to ground upon detection of said voltage change.

19. The switching mode power converter of claim 13, wherein said over-current protection circuit further comprises an opto-isolator providing electrical isolation between said plurality of outputs and said controller.

20. The switching mode power converter of claim 13, wherein said converter further comprises at least one of a buck converter, a boost converter, a flyback converter, and a forward converter.