Boost regulator using synthetic ripple regulation

• US 8,085,011 B1
• Filed: 06/06/2008
• Issued: 12/27/2011
• Est. Priority Date: 08/24/2007
• Status: Active Grant

• Current Assignee: Intersil Americas LLC (Renesas Electronics Corporation)
• Original Assignee: Intersil Americas LLC (Renesas Electronics Corporation)
• Inventors: Petricek, Shea Lynn
• Primary Examiner(s): BERHANE, ADOLF D
• Application Number:
  US12/134,910
• Time in Patent Office: 1,299 Days
• Field of Search: 323/247, 323/259, 323/265, 323/273, 323/282, 323/328, 323/344
• US Class Current: 323/259
• CPC Class Codes: H02M 1/0003 Details of control, feedback or regulation circuits
• CPC Class Codes: H02M 3/1582 Buck-boost converters H02M3/1584 takes precedence

Abstract

A boost regulator for converting an input voltage to a higher output voltage including an inductor, an error circuit, a switching circuit, a ripple circuit, and a hysteretic comparator circuit. The inductor has a first end coupled to the input voltage and a second end. The error circuit determines an error of the output voltage and provides an error voltage indicative thereof. The switching circuit switches the second end of the inductor between the output voltage and ground as controlled by a pulse width modulation signal. The ripple circuit synthetically replicates ripple current through the inductor based on voltage applied across the inductor and provides a ripple voltage indicative thereof. The hysteretic comparator circuit develops the pulse width modulation signal based on comparing the ripple voltage within a hysteretic window voltage range based on the error voltage.

Claims

1. A boost regulator for converting an input voltage to a higher output voltage, comprising:

an inductor having a first end receiving the input voltage and a second end;

an error circuit which determines an error of the output voltage and which provides an error voltage indicative thereof;

a switching circuit which switches said second end of said inductor between the output voltage and ground as controlled by a pulse width modulation signal;

a ripple circuit which synthetically replicates ripple current through said inductor based on voltage applied across said inductor and which provides a ripple voltage indicative thereof; and

a hysteretic comparator circuit which develops said pulse width modulation signal based on comparing said ripple voltage within a hysteretic window voltage range based on said error voltage.

2. The boost regulator of claim 1, wherein said switching circuit comprises:

a first electronic switch having current terminals coupled between said second end of said inductor and ground and having a control terminal receiving said pulse width modulation signal;

a second electronic switch having current terminals coupled between said second end of said inductor and an output node developing the output voltage and having a control terminal receiving said pulse width modulation signal; and

wherein said first electronic switch is turned on while said second electronic switch is turned off and wherein said first electronic switch is turned off while said second electronic switch is turned on.

3. The boost regulator of claim 1, wherein said ripple circuit comprises:

a ripple capacitive circuit; and

an amplifier circuit having an input for determining voltage applied across said inductor and an output providing a ripple current proportional to said voltage applied across said inductor to charge said ripple capacitive circuit.

4. The boost regulator of claim 1, wherein said ripple circuit comprises:

a ripple capacitive circuit which develops said ripple voltage on a first node;

a switch having a control input receiving said pulse width modulation signal and having current terminals coupled between a second node and ground, wherein said switch switches said second node between the output voltage and ground based on said pulse width modulation signal; and

a transconductance amplifier having a first input receiving a voltage indicative of the input voltage, a second input coupled to said second node, and an output coupled to said first node for providing a ripple current to said ripple capacitive circuit.

5. The boost regulator of claim 4, wherein said ripple capacitive circuit comprises:

a ripple capacitor and a ripple resistor coupled in parallel between said first node and a third node; and

an offset voltage source coupled between ground and said third node.

6. The boost regulator of claim 1, wherein said hysteretic comparator circuit comprises:

a hysteretic circuit which switches a first node, based on said pulse width modulation signal, between said error voltage and a hysteresis voltage, wherein said hysteresis voltage comprises said error voltage added to a window voltage; and

a comparator which compares said ripple voltage with the voltage of said first node and which provides said pulse width modulation signal indicative thereof.

7. The boost regulator of claim 1, wherein said hysteretic comparator circuit comprises:

a combiner which combines a window voltage with said error voltage and which provides a hysteresis voltage;

a first comparator which compares said hysteresis voltage with said ripple voltage and which provides a reset signal indicative thereof;

a second comparator which compares said ripple voltage with said error voltage and which provides a set signal indicative thereof; and

a logic circuit which receives said set and reset signals and which toggles said pulse width modulation signal based on said set and reset signals.

8. The boost regulator of claim 1, further comprising:

said switching circuit comprising an electronic switch having a pair of current terminals coupled between said second end of said inductor and an output node which develops the output voltage; and

a diode emulation circuit which keeps said electronic switch turned off during a diode emulation mode to decouple said output node from said second end of said inductor when current through said inductor reaches a minimum level.

9. The boost regulator of claim 8, wherein said diode emulation circuit comprises:

a current sensor which senses current through said inductor and which asserts a current sense signal indicative thereof; and

a comparator circuit having an input coupled to said current sensor and an output coupled to control said electronic switch.

10. The boost regulator of claim 8, further comprising a clamp circuit which clamps said ripple voltage to a predetermined level when said electronic switch is kept off during said diode emulation mode.

11. An electronic device, comprising:

a power source providing an input voltage;

a load which receives a source voltage which is higher than said input voltage; and

a boost regulator for converting said input voltage to said source voltage, said boost regulator comprising;

an inductor having a first end receiving the input voltage and a second end;

an error circuit which determines an error of said source voltage and which provides an error voltage indicative thereof;

a switching circuit which switches said second end of said inductor between said source voltage and ground as controlled by a pulse width modulation signal;

a ripple circuit which synthetically replicates ripple current through said inductor based on voltage applied across said inductor and which provides a ripple voltage indicative thereof; and

a hysteretic comparator circuit which provides said pulse width modulation signal based on comparing said ripple voltage within a hysteretic window voltage range based on said error voltage.

12. The electronic device of claim 11, wherein said ripple circuit comprises:

a ripple capacitive circuit; and

an amplifier circuit having an input which senses voltage applied across said inductor and an output providing a ripple current proportional to said voltage applied across said inductor to charge said ripple capacitive circuit.

13. The electronic device of claim 11, wherein said ripple circuit comprises:

ripple capacitive circuit which develops said ripple voltage on a first node;

a switch having a control input receiving said pulse width modulation signal and having current terminals coupled between a second node and ground, wherein said switch switches said second node between the source voltage and ground based on said pulse width modulation signal; and

a transconductance amplifier having a first input receiving a voltage indicative of the input voltage, a second input coupled to said second node, and an output coupled to said first node for providing a ripple current to said ripple capacitive circuit.

14. The electronic device of claim 13, wherein said ripple capacitive circuit comprises:

a ripple capacitor and a ripple resistor coupled in parallel between said first node and a third node; and

an offset voltage source coupled between ground and said third node.

15. The electronic device of claim 11, wherein said hysteretic comparator circuit comprises:

a hysteretic circuit which switches, based on said pulse width modulation signal, a first node between said error voltage and a hysteresis voltage, wherein said hysteresis voltage comprises said error voltage added to a window voltage; and

a comparator which compares said ripple voltage with the voltage of the first node and which provides said pulse width modulation signal indicative thereof.

16. The electronic device of claim 11, wherein said hysteretic comparator circuit comprises:

a combiner which combines said window voltage with said error voltage and which provides a hysteresis voltage;

a first comparator which compares said hysteresis voltage with said ripple voltage and which provides a reset signal indicative thereof;

a second comparator which compares said ripple voltage with said error voltage and which provides a set signal indicative thereof; and

a logic circuit which receives said set and reset signals and which toggles said pulse width modulation signal based on said set and reset signals.

17. The electronic device of claim 11, further comprising:

said switching circuit comprising an electronic switch having a pair of current terminals coupled between said second end of said inductor and an output node developing said source voltage; and

a diode emulation circuit which keeps said electronic switch turned off to decouple said output node from said second end of said inductor while current through said inductor is at a minimum level.

18. The electronic device of claim 11, wherein said power source comprises a battery.

19. A method of controlling a boost regulator which converts an input voltage to an output voltage, comprising:

applying the input voltage to a first end of an inductor;

switching a second end of the inductor between the output voltage and ground as controlled by a pulse width modulation signal;

determining an error of the output voltage and providing an error voltage indicative thereof;

synthetically replicating ripple current through the inductor based on voltage applied across said inductor and providing a ripple voltage indicative thereof; and

comparing the ripple voltage within a window voltage range based on the error voltage and providing the pulse width modulation signal indicative thereof.

20. The method of claim 19, further comprising:

switching a first node between the output voltage and ground based on the pulse width modulation signal; and

wherein said synthetically replicating ripple current through the inductor based on voltage applied across said inductor and providing a ripple voltage indicative thereof comprises;

determining a difference voltage between the input voltage and the voltage of the first node and converting the difference voltage to a ripple current indicative thereof; and

charging a capacitor with the ripple current.

21. The method of claim 19, wherein said comparing the ripple voltage within a window voltage range based on the error voltage and providing the pulse width modulation signal indicative thereof comprises:

asserting the pulse width modulation signal to cause current through the inductor when the ripple voltage falls to a voltage level of the error voltage; and

de-asserting the pulse width modulation signal when the ripple voltage rises to a voltage level of the error voltage plus a window voltage.

22. The method of claim 19, further comprising:

said switching a second end of the inductor comprising turning on a first switch to couple the second end of the inductor to an output node which develops the output voltage and turning off the first switch to decouple the second end of the inductor from the output node; and

keeping the first switch turned off for diode emulation when the current through the inductor drops to a minimum current level.

23. The method of claim 22, further comprising clamping the ripple voltage to a predetermined level when the first switch is kept turned off for diode emulation.