Method and apparatus providing a multi-function terminal for a power supply controller

• US 6,351,398 B1
• Filed: 10/26/2000
• Issued: 02/26/2002
• Est. Priority Date: 09/24/1999
• Status: Expired due to Term

• Current Assignee: Power Integrations Incorporated
• Original Assignee: Power Integrations Incorporated
• Inventors: Balakrishnan, Balu, Lund, Leif O., Djenguerian, Alex B.
• Primary Examiner(s): HAN, YOUNGHUIE JESSICA
• Application Number:
  US09/697,870
• Time in Patent Office: 488 Days
• Field of Search: 323/282, 323/284, 323/901, 323/908, 363/16, 363/20-21, 363/49, 363/50, 363/97, 363/131, 363/56.03, 363/56.01, 361/22
• US Class Current: 363/56.03
• 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

Abstract

A power supply controller having a multi-function terminal. In one embodiment, a power supply controller for switched mode power supply includes a drain terminal, a source terminal, a control terminal and a multi-function terminal. The multi-function terminal may be configured in a plurality of ways providing any one or some of a plurality of functions including on/off control, external current limit adjustments, under-voltage detection, over-voltage detection and maximum duty cycle adjustment. The operation of the multi-function terminal varies depending on whether a positive or negative current flows through the multi-function terminal. A short-circuit to ground from the multi-function terminal enables the power supply controller. A short-circuit to a supply voltage from the multi-function terminal disables the power supply controller. The current limit of an internal power switch of the power supply controller may be adjusted by externally setting a negative current from the multi-function terminal. The multi-function terminal may also be coupled to the input DC line voltage of the power supply through a resistance to detect an under-voltage condition, an over-voltage condition and/or adjust the maximum duty cycle of power supply controller. Synchronization of the oscillator of the power supply controller may also be realized by switching the multi-function terminal to power or ground at the desired times.

Claims

1. A power supply controller circuit, comprising:

a current input circuit coupled to receive a current for adjusting a current limit of a power switch, the current input circuit to generate a current limit adjustment signal in response to the current; and

a control circuit coupled to receive the current limit adjustment signal, the control circuit coupled to adjust the current limit of a current through the power switch in response to the current limit adjustment signal.

2. The power supply controller circuit of claim 1 wherein the power switch is coupled to a primary winding of the power supply.

3. The power supply controller circuit of claim 1 wherein the control circuit is a pulse width modulation circuit that generates a switching waveform coupled to be received by the power switch to regulate a power supply output.

4. The power supply controller of claim 3 wherein the current is representative of a feedback signal from the power supply output, wherein a power supply voltage is regulated through current limit adjustment of the power switch in response to the feedback signal.

5. The power supply controller of claim 3 wherein the control circuit includes a first comparator coupled to compare a voltage representative of the current through the power switch with the current limit adjustment signal such that the power switch is disabled in response to an output of the first comparator when the current limit set by the current limit adjustment signal is exceeded.

6. The power supply controller of claim 5 wherein the control circuit is to generate said switching waveform controlled in response to the output of the first comparator such that the switching waveform is coupled to limit the current through the power switch.

7. The power supply controller circuit of claim 1 wherein the current limit of the current through the power switch is adjusted by the current when the current limit of the current through the power switch is below a predetermined maximum level.

8. The power supply controller circuit of claim 7 wherein the current limit of the current through the power switch is fixed at the predetermined maximum level for magnitudes of the currents that are higher than the current value corresponding to the predetermined maximum level.

9. The power supply controller of claim 1, wherein the current circuit also generates an enable/disable signal that deactivates the power supply when the magnitude of the current is below an on/off threshold, the on/off threshold having a hysteresis of zero or greater.

10. The power supply controller circuit of claim 9 further comprising an oscillator circuit coupled to an enable/disable signal, the oscillator circuit to start and stop generating a switching waveform in response to the current crossing the on/off threshold.

11. The power supply controller circuit of claim 10 wherein the oscillator circuit is to complete an existing cycle of the switching waveform before the oscillator is to stop generating the switching waveform in response to the enable/disable signal.

12. The power supply controller circuit of claim 10 wherein the oscillator circuit is to start a new complete cycle of the switching waveform if the oscillator circuit is to start generating the switching waveform in response to the enable/disable signal.

13. The power supply controller circuit of claim 1, wherein the current is received by the current input circuit on a low impedance terminal that has a reference voltage with respect to ground.

14. The power supply controller in claim 13, wherein the current limit of the power switch is set by the value of resistance connected between the reference voltage on the low impedance terminal and ground.

15. A method for controlling a power supply, comprising:

supplying a first current from a first terminal of a power supply controller;

deactivating the power supply if the first current supplied from the first terminal falls below a first threshold value; and

activating the power supply if the first current supplied from the first terminal rises above a second threshold value.

16. The method of claim 15 wherein deactivating the power supply comprises stopping a switching waveform to control a power switch coupled to a primary winding of the power supply.

17. The method of claim 15 wherein activating the power supply comprises starting a switching waveform to control a power switch coupled to a primary winding of the power supply.

18. The method of claim 17 wherein starting the switching waveform includes starting a new complete cycle of the switching waveform.

19. The method of claim 15 wherein the second threshold value is greater than the first threshold value.

20. The method of claim 15 further comprising limiting the first current supplied from the first terminal to a maximum value.

21. The method of claim 16 wherein stopping the switching waveform includes allowing to complete an existing cycle of the switching waveform.

22. The method of claim 15 further comprising coupling a switch between the first terminal and ground.

23. The method of claim 15 further comprising coupling a variable resistance between the first terminal and ground.

24. A method for controlling a power supply, comprising:

supplying a first current from a first terminal of a power supply controller;

controlling a second current flowing through a primary winding of the power supply with a power switch coupled to the primary winding; and

adjusting a current limit of the second current in response to the first current.

25. The method of claim 24 wherein adjusting the current limit of the second current comprises increasing the current limit of the second current in response to an increase in the first current.

26. The method of claim 24, wherein adjusting the current limit of the second current comprises decreasing the current limit of the second current in response to a decrease in the first current.

27. The method of claim 24 further comprising coupling a resistance between the first terminal and ground.

28. The method of claim 24 wherein controlling a second current flowing through the primary winding comprises:

switching the power switch in response to a switching waveform; and

adjusting the switching waveform in response to the first current.

29. The method of claim 28 wherein adjusting the switching waveform comprises:

generating a first voltage in response to the first current;

generating a second voltage in response to the second current; and

adjusting the switching waveform in response to a comparison of the first voltage and the second voltage.