Method and apparatus for trimming current limit and frequency to maintain a constant maximum power

• US 7,345,462 B2
• Filed: 08/11/2006
• Issued: 03/18/2008
• Est. Priority Date: 08/31/2001
• Status: Expired due to Fees

• Current Assignee: Power Integrations Incorporated
• Original Assignee: Power Integrations Incorporated
• Inventors: Matthews, David Michael Hugh, Balakrishnan, Balu, Djenguerian, Alex B.
• Primary Examiner(s): STERRETT, JEFFREY L
• Application Number:
  US11/503,448
• Publication Number:
  US 20060273773A1
• Time in Patent Office: 585 Days
• Field of Search: 323/284, 323/282, 323/285, 323/901, 361/18
• US Class Current: 323/284
• CPC Class Codes: G05F 3/262 using field-effect transistors only
• CPC Class Codes: H02M 1/0093 wherein the output is created by adding a regulated voltage to or subtracting it from an unregulated input
• CPC Class Codes: H02M 1/32 Means for protecting converters other than automatic disconnection
• CPC Class Codes: H02M 3/156 with automatic control of output voltage or current, e.g. switching regulators
• 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 7/003 Constructional details, e.g. physical layout, assembly, wiring or busbar connections
• CPC Class Codes: H03K 17/0822 in field-effect transistor switches

Abstract

A method which regulates a power supply is disclosed. In one aspect of the invention, the method includes sensing an excess control current through a control terminal with a control current sensor circuit. A transistor is switched with a control circuit in response to the control current sensor circuit and an oscillator that is coupled to a trim circuit, which is trimmed during manufacture of a circuit, to regulate the output of a power supply. A current through the transistor is limited with a current limit circuit that is coupled to the trim circuit, which is trimmed during manufacture of the circuit. A maximum deliverable power value of the power supply is determined by said trimming of the trim circuit during manufacture of the circuit.

Claims

1. A method, comprising:

sensing an excess control current through a control terminal with a control current sensor circuit;

switching a transistor with a control circuit in response to the control current sensor circuit and an oscillator coupled to a trim circuit trimmed during manufacture of a circuit to regulate an output of a power supply; and

limiting a current through the transistor with a current limit circuit coupled to the trim circuit trimmed during manufacture of the circuit, wherein a maximum deliverable power value of the power supply is determined by said trimming of the trim circuit during manufacture of the circuit.

2. The method of claim 1 wherein the maximum deliverable power of the power supply is substantially constant with a maximum deliverable power of another power supply.

3. The method of claim 1 wherein the excess control current through the control terminal is substantially equal to a total control terminal current less a supply current of the circuit.

4. The method of claim 3 wherein the control current through the control terminal is to be responsive to a reflected voltage from an energy transfer element of the power supply.

5. The method of claim 1 wherein said trimming of the trim circuit during manufacture of the circuit comprises trimming a frequency trim circuit coupled to the oscillator and trimming a peak current limit threshold trim circuit coupled to the current limit circuit.

6. The method of claim 5 wherein the an operating frequency f of the oscillator is determined in response to the frequency trim circuit and a peak current limit threshold (I_p) is determined in response to the peak current limit threshold trim circuit.

7. The method of claim 6 wherein the frequency trim circuit and the peak current limit threshold trim circuit are trimmed during manufacture of the power supply such that a product of a square of the peak current limit threshold I_p and the operating frequency f is substantially constant with a product of a square of a peak current limit threshold I_p and an operating frequency f of another power supply.

8. The method of claim 6 wherein the frequency trim circuit and the peak current limit threshold trim circuit are trimmed during manufacture of the power supply such that a product of a square of the peak current limit threshold I_p and the operating frequency f is substantially constant with a product of a square of a peak current limit threshold I_p and an operating frequency f of another power supply.

9. The method of claim 1 wherein the power supply is a flyback converter power supply.

10. The method of claim 1 wherein the power supply is a buck converter power supply.