Switching regulator with improved Dynamic response

• US 5,422,562 A
• Filed: 01/19/1994
• Issued: 06/06/1995
• Est. Priority Date: 01/19/1994
• Status: Expired due to Term

• Current Assignee: Unitrode Corp. (Texas Instruments, Inc.)
• Original Assignee: Unitrode Corp. (Texas Instruments, Inc.)
• Inventors: Mammano, Robert A., O'Connor, John A.
• Primary Examiner(s): Dougherty, Thomas M.
• Assistant Examiner(s): BERHANE, ADOLF D
• Application Number:
  US08/183,720
• Time in Patent Office: 503 Days
• Field of Search: 323/222, 323/224, 323/268, 323/266, 323/282, 323/284, 323/285, 307/491
• US Class Current: 323/282
• CPC Class Codes: G05F 1/44 semiconductor devices only
• CPC Class Codes: H02J 1/10 Parallel operation of dc sources
• CPC Class Codes: H02M 1/0045 Converters combining the concepts of switch-mode regulation and linear regulation, e.g. linear pre-regulator to switching converter, linear and switching converter in parallel, same converter or same transistor operating either in linear or switching mode
• CPC Class Codes: H02M 3/156 with automatic control of output voltage or current, e.g. switching regulators

Abstract

A switching regulator having improved dynamic response to load variations includes a load compensation circuit coupled to the output terminal. The load compensation circuit supplies current to a load coupled to the output terminal when the output voltage is less than a first predetermined level and/or diverts current away from the load when the output voltage is greater than a second predetermined level. The load compensation circuit operates in this manner until the output voltage is between the first and second predetermined levels. The load compensation circuit responds faster to load variations than the switching regulator to accommodate sudden changes in the load demand.

Claims

1. A power supply having an input terminal adapted for coupling to an input voltage source and an output terminal adapted for coupling to a load, said power supply providing a DC output voltage and a first, load current at said output terminal and comprising:

a power switch for alternately coupling and decoupling said input voltage source to said output terminal at a predetermined frequency and with a predetermined duty cycle;

a feedback circuit for controlling said duty cycle of said power switch to maintain said DC output voltage within a specified tolerance range;

a filter coupled between said power switch and said output terminal and including an inductor and a capacitor for providing said DC output voltage at said output terminal; and

a load compensation circuit coupled to said output terminal and activated to source a second current from said load compensation circuit to said load when said output voltage is less than a first predetermined voltage level or to divert a portion of said first, load current from said load when said output voltage is greater than a second predetermined voltage level, wherein said load compensation circuit is de-activated when said output voltage is between said first and second predetermined levels.

2. The power supply recited in claim 1 wherein said load compensation circuit is activated both to source said second current to said load when said output voltage is less than said first predetermined voltage level and to divert said portion of said first, load current from said load when said output voltage is greater than said second predetermined voltage level.

3. The power supply recited in claim 2 wherein said load compensation circuit includes a first current amplifier coupled between said input voltage source and said output terminal for sourcing said second current from said load compensation circuit to said load when said output voltage is less than said first predetermined voltage level and a second current amplifier coupled between said output terminal and ground for diverting said portion of said first, load current from said load when said output voltage is greater than a second predetermined voltage level.

4. The power supply recited in claim 3 wherein said first current amplifier has a control terminal responsive to a first threshold voltage and said second current amplifier has a control terminal responsive to a second threshold voltage, wherein said first and second threshold voltages are related to said first and second predetermined voltage levels, respectively.

5. The power supply recited in claim 4 wherein said feedback circuit includes a pulse width modulator and an error amplifier receiving a signal indicative of said DC output voltage and a reference voltage and providing an error signal to said pulse width modulator.

6. The power supply recited in claim 5 wherein said reference voltage, said first threshold voltage coupled to said control terminal of said first current amplifier, and said second threshold voltage coupled to said control terminal of said second current amplifier are derived from a common reference voltage source with a resistor divider network.

7. The power supply recited in claim 6 further comprising a first buffer amplifier coupled between said resistor divider network and said control terminal of said first current amplifier and a second buffer amplifier coupled between said resistor divider network and said control terminal of said second current amplifier.

8. The power supply recited in claim 1 further comprising an inhibit circuit for preventing said load compensation circuit from sourcing said second current to said load when said output voltage is below a third predetermined voltage level indicative of said output terminal being shorted to ground.

9. The power supply recited in claim 8 wherein said inhibit circuit comprises a comparator receiving a voltage proportional to said output voltage and a voltage equal to said third predetermined voltage level, said comparator providing a disable signal to decouple said first buffer amplifier from said control terminal of said first current amplifier in response to said proportional voltage being less than or equal to said third predetermined voltage level.

10. The power supply recited in claim 3 further comprising an inhibit circuit for limiting the duration of activation of said first current amplifier.

11. The power supply recited in claim 10 wherein said inhibit circuit comprises a resistor and a capacitor coupled between said first buffer amplifier and said control terminal of said first current amplifier.

12. The power supply recited in claim 3 wherein the amount of said second current sourced by said first current amplifier or diverted by said second current amplifier varies linearly with the output voltage.

13. A load compensation circuit adapted for coupling to an output terminal of a switching power supply at which an output voltage and a first, load current is provided, said load compensation circuit comprising:

a current source circuit portion for supplying a second current to said output terminal when said output voltage is less than a first predetermined level; and

a current sink circuit portion for diverting a portion of said first, load current from said output terminal when said output voltage is greater than a second predetermined level, wherein said second predetermined level is greater than said first predetermined level.

14. The load compensation circuit recited in claim 13 wherein said current source circuit portion comprises a first current amplifier having a first terminal coupled to a voltage source, a second terminal coupled to said output terminal, and a third, control terminal responsive to a first threshold voltage related to said first predetermined level of said output voltage and said current sink circuit portion comprises a second current amplifier having a first terminal coupled to ground, a second terminal coupled to said output terminal, and a third, control terminal responsive to a second threshold voltage related to said second predetermined level of said output voltage.

15. The load compensation circuit recited in claim 14 further comprising a reference voltage source providing said first threshold voltage and said second threshold voltage.

16. The load compensation circuit recited in claim 15 further comprising a first buffer amplifier coupled between said reference voltage source and said control terminal of said first current amplifier for providing a drive signal to said control terminal of said first current amplifier and a second buffer amplifier coupled between said reference voltage source and said control terminal of said second current amplifier for providing a drive signal to said control terminal of said second current amplifier.

17. The load compensation circuit recited in claim 13 further comprising an inhibit circuit for disabling said current source circuit portion when said output voltage is less than a third predetermined voltage level indicative of said output terminal being shorted to ground.

18. The load compensation circuit recited in claim 17 wherein said inhibit circuit comprises a comparator responsive to a voltage proportional to the output voltage and a voltage equal to said third predetermined voltage level for providing a disable signal to prevent said current source from supplying said second current to said output terminal when said proportional voltage is less than said third predetermined voltage level.

19. The load compensation circuit recited in claim 13 wherein the amount of said second current supplied by said current source circuit portion and the amount of said portion of said first, load current diverted by said current sink circuit portion varies linearly with the output voltage.

20. The load compensation circuit recited in claim 16 further comprising inhibit circuit for limiting the duration of activation of said first current amplifier.

21. The load compensation circuit recited in claim 20 wherein said inhibit circuit comprises a resistor and a capacitor coupled between the output of said first buffer amplifier and said control terminal of said first current amplifier.

22. A power supply comprising:

a power switch adapted for coupling to an input voltage source;

an output terminal adapted for coupling to a load, said power supply providing a DC output voltage and a first, load current at said output terminal;

a feedback circuit coupled between said output terminal and said power switch for controlling said power switch; and

a load compensation circuit coupled to said output terminal and activated to source a second current to said load when said output voltage is less than a first predetermined voltage level or to divert a portion of said first, load current from said load when said output voltage is greater than a second predetermined voltage level, wherein said load compensation circuit is de-activated when said output voltage is between said first and second predetermined levels.

23. The power supply recited in claim 22 wherein said load compensation circuit is activated both to source said second current to said load when said output voltage is less than said first predetermined voltage level and to divert said portion of said first, load current from said load when said output voltage is greater than said second predetermined voltage level.

24. The power supply recited in claim 23 wherein said load compensation circuit includes a first current amplifier coupled between said input voltage source and said output terminal for sourcing said second current from said load compensation circuit to said load when said output voltage is less than said first predetermined voltage level and a second current amplifier coupled between said output terminal and ground for diverting said portion of said first, load current from said load when said output voltage is greater than said second predetermined voltage level.

25. The power supply recited in claim 24 wherein said first current amplifier has a control terminal responsive to a first threshold voltage and said second current amplifier has a control terminal responsive to a second threshold voltage, wherein said first and second threshold voltages are related to said first and second predetermined voltage levels, respectively.

26. The power supply recited in claim 25 wherein said first threshold voltage coupled to said control terminal of said first current amplifier and said second threshold voltage coupled to said control terminal of said second current amplifier are derived from a common reference voltage source with a resistor divider network.

27. The power supply recited in claim 26 further comprising a first buffer amplifier coupled between said resistor divider network and said control terminal of said first current amplifier and a second buffer amplifier coupled between said resistor divider network and said control terminal of said second current amplifier.

28. The power supply recited in claim 22 further comprising an inhibit circuit for preventing said load compensation circuit from sourcing said second current to said load when said output voltage is below a third predetermined voltage level indicative of said output terminal being shorted to ground.

29. The power supply recited in claim 23 further comprising an inhibit circuit for limiting the duration of activation of said first current amplifier.