PWM generation for DC/DC converters with frequency switching

Patent metadata

Field	Value
Publication number	US-9825527-B2
Application number	US-201414457636-A
Country	US
Kind code	B2
Filing date	Aug 12, 2014
Priority date	Aug 12, 2014
Publication date	Nov 21, 2017
Grant date	Nov 21, 2017

Abstract

A method and apparatus for generating a pulse width modulation (PWM) control signal generates a sawtooth ramp signal at a first frequency under standard operating conditions using a ramp generator, and generates a sawtooth ramp at a second frequency under alternative operating conditions. The sawtooth ramp is combined with an error threshold by a PWM controller to generate a square wave PWM control signal. The error threshold is adjusted simultaneous with adjusting the frequency of the sawtooth ramp, thereby preventing either a voltage overshoot and a voltage undershoot.

First claim

The invention claimed is:

1. A method for generating a pulse width modulation (PWM) control signal comprising:
generating a sawtooth ramp signal at a first frequency under standard operating conditions using a ramp generator;
generating a PWM square wave having a rising edge at a falling edge of the sawtooth ramp signal and a falling edge when the sawtooth ramp signal exceeds an error threshold;
adjusting the frequency of the sawtooth ramp signal in response to a changed operating parameter of the ramp generator; and
adjusting the error threshold applied to the sawtooth ramp signal simultaneous with adjusting the frequency of the sawtooth ramp signal, thereby preventing one of a voltage overshoot and a voltage undershoot,
wherein adjusting the frequency of the sawtooth ramp signal comprises adjusting the frequency by a first factor, and adjusting the error threshold applied to the sawtooth ramp signal comprises adjusting the error threshold by a second factor, and
wherein the second factor is the square root of the first factor.

2. The method of claim 1 , wherein the changed operating parameter of the ramp generator is at least one of an increase in a load, a decrease in a load, and a decrease in an available input power.

3. The method of claim 1 , wherein generating a sawtooth ramp signal at a first frequency under standard operating conditions using a ramp generator comprises utilizing a single-ended primary-inductance converter (SEPIC) to generate the sawtooth ramp signal.

4. The method of claim 3 , further comprising maintaining the SEPIC in a discontinuous mode and thereby maintaining a stability of the SEPIC.

5. The method of claim 4 , wherein the step of maintaining the SEPIC in a discontinuous mode is performed utilizing a compensation loop.

6. The method of claim 1 , wherein
the first factor and the second factor are related to each other such that one of the first factor is based upon the second factor and the second factor is based upon the first factor.

7. The method of claim 1 , wherein a positive peak and a negative peak of the sawtooth ramp signal are constant.

8. The method of claim 2 , wherein adjusting the frequency of the sawtooth ramp signal and adjusting the error threshold applied to the sawtooth ramp signal result in a duty cycle of the generated PWM square wave signal being adjusted by the first factor.

9. A pulse width modulation (PWM) controlled power stage comprising:
a voltage source;
a pulse width modulation controller including a ramp generator operable to generate a sawtooth ramp and a threshold input operable to receive a voltage threshold from an error amplifier, wherein the pulse width modulation controller is operable to output a pulse width modulation control signal;
a power stage operable to receive said pulse width modulated control signal and output a voltage;
a comparator having a first input connected to the voltage source and a second input connected to a reference voltage such that said comparator compares the output of the voltage source against the reference voltage;
said comparator further comprising an output operable to control at least a first switch and a second switch, wherein said first switch is operable to set a frequency of said sawtooth ramp, and wherein said second switch is operable to activate a voltage divider connecting the output of the error amplifier to the threshold input of the pulse width modulation controller;
wherein the voltage divider is inactive when said sawtooth ramp is a first frequency and wherein said voltage divider is active when said sawtooth ramp is a second frequency.

10. The pulse width modulation (PWM) controlled power stage of claim 9 , wherein said error amplifier comprises an error amplifier reference voltage input and a feedback input and is operable to output an error voltage dependent upon a difference between said reference voltage and said feedback input.

11. The pulse width modulation (PWM) controlled power stage of claim 9 , wherein said voltage divider is operable to adjust the voltage threshold of the pulse width modulation controller by a first factor, and wherein the comparator is operable to adjust the frequency of the ramp generator by a second factor.

12. The pulse width modulation (PWM) controlled power stage of claim 11 , wherein the first factor is a square root of the second factor.

13. The pulse width modulation (PWM) controlled power stage of claim 11 , wherein a duty cycle of a generated PWM signal is adjusted by the first factor simultaneous with the frequency adjustment.

14. The pulse width modulation (PWM) controlled power stage of claim 9 , wherein the first switch comprises a switch network operable to select a sawtooth ramp frequency from at least three possible sawtooth ramp frequencies.

15. The pulse width modulation (PWM) controlled power stage of claim 9 , wherein the second switch comprises a switch network including multiple switches, and wherein each switch in said switch network is operable to activate one of a plurality of voltage dividers.

16. The pulse width modulation (PWM) controller power stage of claim 15 , wherein each of said plurality of voltage dividers is active when at least one corresponding sawtooth ramp frequency is selected.

17. A method for generating a pulse width modulation (PWM) control signal comprising:
generating a sawtooth ramp signal at a first frequency under standard operating conditions using a ramp generator;
generating a PWM square wave having a rising edge at a falling edge of the sawtooth ramp signal and a falling edge when the sawtooth ramp signal exceeds an error threshold;
adjusting the frequency of the sawtooth ramp signal in response to a changed operating parameter of the ramp generator; and
adjusting the error threshold applied to the sawtooth ramp signal simultaneous with adjusting the frequency of the sawtooth ramp signal, thereby preventing one of a voltage overshoot and a voltage undershoot,
wherein generating a sawtooth ramp signal at a first frequency under standard operating conditions using a ramp generator comprises utilizing a single-ended primary-inductance converter (SEPIC) to generate the sawtooth ramp signal.

18. The method of claim 17 , further comprising maintaining the SEPIC in a discontinuous mode and thereby maintaining a stability of the SEPIC.

19. The method of claim 18 , wherein the step of maintaining the SEPIC in a discontinuous mode is performed utilizing a compensation loop.

Assignees

• Continental automotive systems inc

Inventors

• Zarkhin Mikhail
• Fisch Alfons

Classifications

• H02M3/158

  including plural semiconductor devices as final control devices for a single load · CPC title

• H02M3/156 Primary

  with automatic control of output voltage or current, e.g. switching regulators · CPC title

• H02M2003/1557

  Electricity · mapped topic

• H02M3/1557

  Single ended primary inductor converters [SEPIC] · CPC title