DC to DC converter method and circuitry

• US 6,621,256 B2
• Filed: 03/07/2002
• Issued: 09/16/2003
• Est. Priority Date: 05/03/2000
• Status: Expired due to Fees

• Current Assignee: Intersil Corporation (Renesas Electronics Corporation)
• Original Assignee: Intersil Corporation (Renesas Electronics Corporation)
• Inventors: Jochum, Thomas A., Hodgins, Robert G., Muratov, Volodymyr A.
• Primary Examiner(s): Berhane, Adolf D.
• Application Number:
  US10/093,197
• Publication Number:
  US 20020158613A1
• Time in Patent Office: 558 Days
• Field of Search: 323/282, 323/283, 323/284, 323/285, 323/288, 323/290, 323/351, 327/403, 327/404, 327/541, 327/543
• US Class Current: 323/282
• CPC Class Codes: H02M 1/0032 Control circuits allowing low power mode operation, e.g. in standby mode
• CPC Class Codes: H02M 3/1563 without using an external clock H02M3/158 takes precedence
• CPC Class Codes: H02M 3/158 including plural semiconductor devices as final control devices for a single load
• 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 DC-to-DC converter has a pulse width modulator PWM) and a hysteretic (ripple) modulator. For low current loads, the hysteretic modulator is selected; for high current loads, the PWM is selected. A mode selection switch senses the polarity of the switched output voltage at the end of each switching cycle. If the polarity changes from one cycle to the next, the mode may be instantly changed to the other mode. Counters are used to record the polarity at the end of each cycle and switching from one mode to another can be delayed by the counters to prevent changing modes based on spurious output voltage fluctuations.

Claims

1. A DC-to-DC converter circuit comprising:

a pulse width modulator controller and a hysteretic controller, each controller for converting a first voltage into a second voltage during a series of repeated switching cycles;

a mode selection circuit for selecting one of two controllers in accordance with current demand of a load coupled to the second voltage;

a comparator for comparing the second voltage to a reference voltage and generating a polarity signal representative of the second voltage at the end of each switching cycle; and

one or more counters coupled to the comparator and to the mode selection switch for maintaining the mode selection switch in its current mode so long as the polarity of the second voltage at the end of each cycle is the same as the last n number of cycles and for operating the mode selection switch to select the other controller when the polarity of the second voltage at the end of the cycle changes from the prior cycle and the change in polarity persists for n number of cycles.

2. The DC-to-DC converter circuit of claim 1 wherein the counters operate to switch the mode selection switch to the hysteric mode controller when the polarity of the second voltage for n number of cycles is positive.

3. The DC-to-DC converter circuit of claim 1 wherein the counters operate to switch the mode selection switch to the pulse width modulator controller when the polarity of the second voltage for n number of cycles is negative.

4. A method of switching between a first operation mode for relatively high current levels and a second operation mode for relatively low current levels in a DC to DC converter, the method comprising:

monitoring inductor current during switching cycles; and

changing an operation mode with one or more controllers after a select number of switching cycles have passed in which the inductor current has consecutively crossed zero.

5. The method of claim 4, wherein the select number of switch cycles is eight.

6. The method of claim 4, wherein the inductor current crosses zero when the polarity sign of the inductor current changes.

7. A method of switching between a first operation mode for relatively high current levels and a second operation mode for relatively low current levels in a DC to DC converter, the method comprising:

monitoring inductor current during switching cycles; and

switching from the first operational mode to the second operation mode when the inductor current has crossed zero for eight consecutive switching cycles, wherein switching between first and second operational modes is controlled by one or more controllers.

8. The method of claim 7, wherein monitoring the inductor current further comprises:

monitoring the polarity of an output voltage.

9. The method of claim 7, further comprising:

switching from the second operation mode to the first operational mode without counting eight consecutive switching cycles in which the inductor current crosses zero.

10. The method of claim 9, wherein switching from the second operation mode to the first operational mode further comprises:

detecting a load voltage feedback above a selected reference voltage.

11. A DC to DC converter comprising:

a comparator to compare a node voltage with a reference ground voltage, wherein the node voltage is used to monitor an inductor current;

one or more counters coupled to the comparator to count a number of switching cycles that have passed in which the inductor current has consecutively crossed zero; and

a mode selection controller coupled to the counter circuit to switch between controller modes based on a number of switching cycles that have passed in which the inductor current has consecutively crossed zero.

12. The DC to DC converter of claim 11, wherein the inductor current crosses zero when the node voltage changes polarity.

13. The DC to DC converter of claim 11, wherein the mode selection controller switches modes when 8 switching cycles have passed in which the inductor current has consecutively crossed zero.

14. The DC to DC converter of claim 11, wherein the one or more counters further comprise:

a first counter to count positive polarity; and

a second counter to count negative polarity.

15. The DC to DC converter of claim 11, wherein the mode selection controller switches between a first controller mode used for relatively high inductor current levels and a second controller mode is used for relatively low inductor current levels.

16. The DC to Dc converter of claim 15, further comprising:

a load current transient comparator adapted to compare the node voltage to a reference voltage when the DC to DC converter is in the second controller mode, wherein if the node voltage is greater than the reference voltage the mode selection controller switches to the first controller mode without counting the number of switching cycles that have past in which the inductor current has consecutively crossed zero.

17. A controller circuit for a DC-to-DC converter, the controller circuit comprising

at least one controller adapted to control the operation of the DC-to-DC converter between a first operational mode for relatively high load current levels and a second operational mode for relatively low load current levels;

and

a mode select logic, the mode select logic including,

a comparator adapted to monitor a signal indicative of an inductor current crossing zero during a switching cycle,

one or more counters adapted to increment based on the signal indicative of the inductor current crossing zero during a switching cycle, and

wherein the mode select logic is coupled to the at least one controller to switch operation from the first operational mode to the second operational mode when the inductor current crosses zero for a select number of consecutive switching cycles.

18. The controller circuit of claim 17, wherein the select number of consecutive switching cycles is eight.

19. The controller circuit of claim 17 wherein the at least one controller includes:

a first output adapted to drive an upper MOSFET; and

a second output adapted to drive a lower MOSFET, wherein the upper MOSFET and the lower MOSFET are coupled to an inductor to control the inductor current.

20. A method of operating a DC-to-DC converter, the method comprising:

monitoring a signal indicative of an inductor current crossing zero during a switching cycle;

incrementing a counter based on the signal indicative of the inductor current crossing zero during a switching cycle; and

when a select number of switching cycles have occurred in which the inductor current has consecutively crossed zero, switching operational modes with the use of one or more controllers.

21. The method of claim 20, wherein switching operational modes further comprises:

counting eight consecutive switching cycles in which the inductor current crosses zero.

22. The method of claim 21, wherein switching operational modes further comprises;

disabling a first operational mode adapted to accommodate relatively high load currents; and

enabling a second operational mode adapted to accommodate relatively low load currents.

23. A DC-to-DC converter comprising:

a first switching transistor having a first transistor output;

a second switching transistor having a second transistor output;

an inductor having a first end coupled to the first and second transistor outputs and a second end adapted to be coupled to a load; and

a control circuit adapted to switch between a first operational mode for relatively high load currents and a second operational mode for relatively low load currents, the control circuit having a first output coupled to drive the first switching transistor and a second output coupled to drive the second switching transistor, the control circuit further including,

a comparator coupled to monitor a signal indicative of the inductor current passing through zero during a switching cycle, and

one or more counters coupled to increment based on to signal indicative of the inductor current crossing zero during a switching cycle, wherein the control circuit switches operation from the first operational mode to the second operational mode when the inductor current crosses zero for a select number of consecutive switching cycles.

24. The DC-to-DC converter of claim 23, wherein the select number of consecutive switching cycles is eight.

25. A DC-to-DC converter comprising:

a switching means to create switching cycles;

an inductor means coupled to the switching means;

a controlling means having a first operational mode and a second operational mode, the controlling means coupled to control the switching means;

a comparator means coupled to monitor a signal indicative of current in the inductor crossing zero during a switching cycle;

a counter means to increment based on the signal indicative of current in the inductor crossing zero during a switching cycle; and

wherein the controller means is adapted to switch between the first and second operational modes when a select number of consecutive switching cycles have occurred in which the current through the inductor has crossed zero.

26. The DC-to-DC converter of claim 25, wherein the select number of consecutive switching cycles is eight.

27. The DC-to-DC converter of claim 25, wherein the first operational mode of the controller means is used for relatively high load power consumption and the second operational mode of the controller means is used for low load power consumption.

28. The DC-to-DC converter of claim 27, wherein the controller means switches from the first operational mode to the second operational mode when eight consecutive switching cycles have occurred in which the current through the inductor has crossed zero.