Ultra-low power switching regulator method and apparatus

• US 6,215,288 B1
• Filed: 02/25/2000
• Issued: 04/10/2001
• Est. Priority Date: 02/25/2000
• Status: Expired due to Term

• Current Assignee: Cadence Design Systems Incorporated (Cadence Group)
• Original Assignee: Cadence Design Systems Incorporated (Cadence Group)
• Inventors: Ramsey, Carl A., Naviasky, Eric H.
• Primary Examiner(s): Riley, Shawn
• Application Number:
  US09/513,338
• Time in Patent Office: 410 Days
• Field of Search: 323/282, 323/284, 323/283, 323/224, 323/285, 323/288
• US Class Current: 323/224
• CPC Class Codes: H02M 3/1588 comprising at least one synchronous rectifier element H02M3/1582, H02M3/1584 take precedence
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

A low-power controller for a discontinuous switched mode power converter. The controller has an inductor current sensing circuit to measure the inductor current flowing through an inductive charge storage element as well as an output voltage sensing circuit to monitor output voltage. The controller monitors both the converter output voltage and the inductor current and uses this information to modulate a peak inductor current trip point and controller switching frequency according to a control law curve in order to regulate converter output voltage. The controller prevents the switching frequency from falling below a predetermined minimum frequency. The control law curve is selectable to specify controller operation according to a desired combination of minimum switching frequency and maximum peak inductor current.

Claims

1. A power converter operating in a discontinuous mode and having a charge storage capacitor connected across a pair of output terminals, said power converter comprising:

a power source;

a first switch for controllably connecting said power source to an inductor, said inductor connected to a first one of said pair of output terminals;

a second switch for controllably connecting said inductor to a second one of said pair of output terminals; and

a controller connected to said first switch and to said second switch and providing control signals thereto, said controller adjusting a switching frequency of said control signals and adjusting a peak inductor current trip point according to a control law curve.

2. The power converter of claim 1, wherein said control law curve is characterized by a minimum switching frequency.

3. The power converter of claim 2, wherein said minimum switching frequency is above 20 kilohertz.

4. The power converter of claim 2, wherein said control law curve is characterized by a maximum current limit.

5. The power converter of claim 4, wherein said switching frequency increases as said peak inductor current trip point increases, and decreases as said peak inductor current trip point decreases, according to said control law curve, said switching frequency selected such that said peak current trip point approaches but does not exceed said maximum current limit as load impedance decreases.

6. The power converter of claim 4, wherein said peak inductor current trip point increases as said switching frequency increases, and decreases as said switching frequency decreases, according to said control law curve, said peak inductor current trip point selected such that said switching frequency approaches but does not fall below said minimum switching frequency as load impedance increases.

7. The power converter of claim 1, wherein said control law curve compensates for variations in component values within said power converter by adaptively adjusting an operating point of said controller on said control law curve.

8. The power converter of claim 1, wherein said control law curve maintains the efficiency of said power converter at a relatively constant level over a majority of its operating region.

9. The power converter of claim 1, further comprising:

a current sense circuit for measuring a current through said inductive element, said current sense circuit providing a current sense signal to said controller; and

a voltage sense circuit for measuring an output voltage of said power converter, said voltage sense circuit providing a voltage sense signal to said controller.

10. An apparatus for facilitating power conversion, comprising:

an inductor current sensing circuit for measuring a level of current through an inductive energy storage element used in the power converter;

a voltage sensing circuit for measuring an output voltage of the power converter; and

a control circuit for regulating a converter output signal in a switched mode control loop and for operating the power converter in a discontinuous switched operating mode, said control circuit comprising

a plurality of control signals for controlling electrical switches used in transferring power from an energy source to the converter output signal; and

a controller for simultaneously and adaptively modulating a peak current trip point of said inductor current sensing signal and a switching frequency of said control signals according to a predefined relationship so as to maintain said converter output signal at a desired DC voltage, while preventing said switching frequency from falling below a predetermined minimum frequency.

11. The apparatus of claim 10, wherein said control circuit is incorporated in a step-down power converter.

12. The apparatus of claim 10, wherein said predetermined minimum frequency is above 20 kilohertz.

13. The apparatus of claim 10, wherein said controller modulates said peak current trip point and said switching frequency according to a control law curve, said control law curve selected so as to keep the efficiency of said power converter relatively constant.

14. The apparatus of claim 13, wherein said control law curve is selected so as to prevent said switching frequency from falling below said predetermined minimum frequency and to prevent said level of current through said inductive energy storage element from exceeding a predetermined peak value.

15. The apparatus of claim 10, further comprising:

a first electronic switch having an input connected to a first control signal of said plurality of control signals of said controller, said first electronic switch having a first pair of switch terminals, a first one of said first pair of switch terminals connected to said power source;

a second electronic switch having an input connected to a second control signal of said plurality of control signals of said controller, said second electronic switch having a second pair of switch terminals, a first one of said second pair of switch terminals connected to a second one of said first pair of switch terminals of said first switch, said second pair of terminals being connected across said inductive energy storage element and a charge storage capacitor; and

a resistive feedback network connected across said pair of converter output terminals, said resistive feedback network generating a voltage feedback signal to said control circuit in response to said converter output signal.

16. A method of regulating an output of a power converter, said method comprising the steps of:

(a) connecting, through a first controllable switch, an energy source to an inductive element so as to allow an increase in a current level and stored energy in said inductive element;

(b) disconnecting said energy source from said inductive element by turning off said first controllable switch when said current level through said inductive element reaches an adjustable trip level;

(c) connecting, through a second controllable switch and after said first controllable switch is disconnected, said inductive element to a charge storage capacitor, said charge storage capacitor being connected between a pair of output terminals of said power converter, so as to allow the decrease of said current flowing through said inductive element, with the energy stored in said inductive element being transferred to said charge storage capacitor;

(d) disconnecting said inductive element from said charge storage capacitor by turning off said second controllable switch when said current flowing through said inductive element reaches a predetermined minimum floor; and

(e) repeating steps (a) through (d) at an adjustable frequency so as to regulate operation of the power converter at an output voltage level by adaptively and simultaneously selecting said adjustable frequency and said adjustable trip level according to a control law curve, whereby said adjustable frequency is maintained above a predetermined minimum frequency.

17. The method of claim 16, wherein said adjustable frequency and said adjustable trip level are selected at least in part in response to a measured output voltage level.

18. The method of claim 17, wherein said adjustable trip level is generated by applying a measured voltage across said charge storage capacitor to a buffer amplifier having an output coupled to ground through a resistive network, and producing a current thereby.

19. The method of claim 16, wherein said steps (a) through (e) effectuate discontinuous switching mode operation of the power converter in order to regulate said output voltage level.

20. The method according to claim 16 wherein said predetermined minimum frequency is above 20 kilohertz.

21. A power converter, comprising:

an input terminal for receiving an input voltage signal;

a pair of output terminals for providing a converter output voltage signal;

a first electronic switch;

a second electronic switch, said first electronic switch connected between said input terminal and said second electronic switch;

an inductive energy storage element connected between the output of said first electronic switch and said first output terminal;

a charge storage capacitor connected between the output of said inductive element and said second output terminal;

a resistive feedback network connected between said output terminals, said resistive feedback network generating a voltage feedback signal in response to said output voltage signal; and

a control circuit, said control circuit including;

a controller having a first drive signal controllably connected to said first electronic switch and a second drive signal controllably connected to said second electronic switch;

an output voltage sensing circuit that produces a first current control signal in response to said voltage feedback signal;

a current sensing circuit that produces a second current control signal in response to a level of current through said inductive energy storage element; and

a signal adder that produces an inductor current charging signal in response to said first current control signal or said second current control signal;

wherein said controller modulates said first drive signal and said second drive signal to prevent a switching frequency of said first drive signal and said second drive signal from falling below a predetermined minimum frequency; and

wherein said controller automatically and dynamically establishes a combination of a peak inductor current level and said switching frequency according to a control law curve so as to regulate said converter output voltage signal at a consistent level.

22. The power converter of claim 21 wherein said controller modulates said first drive signal and said second drive signal to control the current through said inductive energy storage element according to said control law curve in response to said inductor current charging signal;

and

said control law curve automatically selecting a particular combination of said peak inductor current level and said switching frequency in order to regulate said converter output voltage signal in response to different values of said level of current caused by variations in the values of said charge storage capacitor and said inductive energy storage element.

23. The power converter of claim 21 wherein said predetermined minimum frequency is about 20 KHz.

24. The power converter of claim 21, wherein said output voltage sensing circuit monitors the voltage ripple present in said output voltage signal and sets said first current control signal to a state that will cause said controller to terminate said level of current through said inductive element in response to a voltage ripple value present at said first output terminal exceeding a predetermined value.

25. The power converter of claim 21, wherein said output voltage sensing circuit controls a switching threshold of said voltage sensing circuit using a controlled offset to increase the range of said voltage sensing circuit.

26. The power converter of claim 21, wherein said control circuit further comprises a control voltage generator that produces a voltage control signal in response to said inductor current charging signal, said control voltage signal being converted to a peak inductor current control signal and provided to said current sensing circuit.

27. A control circuit for a power converter of the type having a pair of output terminals, a first electronic switch connected between an input terminal and a second electronic switch, an inductive energy storage element connected between an output of said first electronic switch and said first output terminal, and a charge storage capacitor connected between an output of said inductive energy storage element and said second output terminal, comprising:

a resistive feedback network that generates a voltage feedback signal in response to an output voltage signal;

a controller having a first drive signal connected to said first electronic switch and a second drive signal connected to said second electronic switch;

an output voltage sensing circuit that produces a first current control signal in response to said voltage feedback signal;

a current sensing circuit that produces a second current control signal in response to a level of current through said inductive energy storage element;

a signal adder that produces an inductor current charging signal in response to said first current control signal or said second current control signal; and

said controller modulating said first drive signal and said second drive signal to prevent a switching frequency of said first drive signal and said second drive signal from falling below a predetermined minimum frequency, and said controller automatically adjusting a peak current trip point and said switching frequency according to a control law curve so as to maintain the output voltage at a consistent level.

28. The power converter of claim 27 wherein said predetermined minimum frequency is above 20 kilohertz.

29. In a power converter having a capacitor connected across a pair of converter output terminals, a method for converting power supplied by a DC power source, comprising the steps of:

receiving a power source signal from the DC power source;

controllably connecting, through a first electronic switch operating at a controllable frequency, said power source signal to an inductive energy storage element, said first electronic switch and said inductive energy storage element forming a loop with the DC power source through which current can flow;

controllably connecting, through a second electronic switch operating at said controllable frequency, said inductive energy storage element to said capacitor across said converter output terminals, said second electronic switch and said inductive energy storage element forming a loop with said capacitor through which current can flow;

generating a first current control signal in response to an output voltage measured across the pair of converter output terminals;

generating a second current control signal in response to a level of current measured through said inductive energy storage element;

utilizing said first current control signal and said second current control signal in alternation to produce an inductor current charging signal;

modulating the inputs of said first electronic switch and said second electronic switch to cause operation at said controllable frequency in response to said inductor current charging signal;

preventing the switching frequency of said controllable frequency from falling below a predetermined minimum frequency; and

adaptively selecting a predefined combination of a peak inductor current level and controllable frequency according to a control law curve in order to regulate said output voltage at a consistent level.

30. The method of claim 29 wherein said predetermined minimum frequency is about 20 kilohertz.

31. The method of claim 29 wherein said step of generating a first current control signal further includes setting said first current control signal to a state that will cause said first electronic switch and said second electronic switch to terminate current flow through said inductive element in response to a voltage ripple value present at said first output terminal exceeding a predetermined value.