Frequency jittering control circuit and method for a PFM power supply

Patent metadata

Field	Value
Publication number	US-9479063-B2
Application number	US-201213567272-A
Country	US
Kind code	B2
Filing date	Aug 6, 2012
Priority date	Aug 26, 2011
Publication date	Oct 25, 2016
Grant date	Oct 25, 2016

Abstract

A frequency jittering control circuit for a PFM power supply includes a pulse frequency modulator to generate a frequency jittering control signal to switch a power switch to generate an output voltage. The frequency jittering control circuit jitters an input signal or an on-time or off-time of the pulse frequency modulator to jitter the switching frequency of the power switch to thereby improve EMI issue.

First claim

What is claimed is:

1. A frequency jittering control circuit for generating a frequency jittering control signal to switch a power switch of a pulse frequency modulation power supply to generate an output voltage, the frequency jittering control circuit comprising:
a pulse frequency modulator connected to the power switch, for triggering the control signal responsive to a first signal to turn on the power switch, and terminating the control signal responsive to a second signal to turn off the power switch;
a current limit signal generator for providing a jittering current limit signal;
a current detector for detecting a current of the power switch to generate a current sense signal; and
a comparator connected to the pulse frequency modulator, the current limit signal generator and the current detector, for comparing the current sense signal with the current limit signal to generate the second signal;
wherein the current limit signal generator comprises:
a first voltage-to-current converter for converting a reference voltage into a first current;
a first current mirror connected to the first voltage-to-current converter, for mirroring the first current to generate a second current;
a ramp generator for generating a ramp signal;
a counter or a random number generator connected to the ramp generator, for adjusting the ramp signal;
a second voltage-to-current converter connected to the ramp generator, for converting the ramp signal into a third current;
a second current mirror connected to the second voltage-to-current converter, for mirroring the third current to generate a fourth current; and
a resistor connected to the first and second current mirrors, for generating the uttering current limit signal according to a sum of the second and fourth currents.

2. A frequency jittering control circuit for generating a frequency jittering control signal to switch a power switch of a pulse frequency modulation power supply to generate an output voltage, the frequency jittering control circuit comprising:
a pulse frequency modulator connected to the power switch, for triggering the control signal responsive to a first signal to turn on the power switch, and terminating the control signal responsive to a second signal to turn off the power switch;
a current limit signal generator for providing a jittering current limit signal;
a current detector for detecting a current of the power switch to generate a current sense signal; and
a comparator connected to the pulse frequency modulator, the current limit signal generator and the current detector, for comparing the current sense signal with the current limit signal to generate the second signal;
wherein the current limit signal generator comprises:
a voltage-to-current converter for converting a reference voltage into a first current;
a current mirror connected to the voltage-to-current converter, for mirroring the first current to generate a second current;
a variable resistor connected to the current mirror, for generating the current limit signal according to the second current; and
a resistance controller connected to the variable resistor, for adjusting a resistance of the variable resistor to jitter the current limit signal, wherein the resistance controller comprises a counter or a random number generator.

3. A frequency jittering control circuit for generating a frequency jittering control signal to switch a power switch of a pulse frequency modulation power supply to generate an output voltage of the pulse frequency modulation power supply, the frequency jittering control circuit comprising:
a pulse frequency modulator connected to the power switch, for triggering the control signal responsive to a first signal to turn on the power switch, and terminating the control signal responsive to a second signal to turn off the power switch;
an output voltage feedback circuit for detecting the output voltage of the pulse frequency modulation power supply to generate a feedback signal indicating the output voltage of the pulse frequency modulation power supply;
a comparator connected to the output voltage feedback circuit, for comparing the feedback signal indicating the output voltage of the pulse frequency modulation power supply with a reference voltage to generate the first signal;
a programmable delay circuit connected between the comparator and the pulse frequency modulator, for delaying the first signal generated by comparing the feedback signal indicating the output voltage of the pulse frequency modulation power supply with the reference voltage for a delay time and then sending the first signal to the pulse frequency modulator; and
a delay time controller connected to the programmable delay circuit, for adjusting the delay time of the programmable delay circuit.

4. The frequency jittering control circuit of claim 3 , wherein the delay time controller comprises a counter or a random number generator.

5. A frequency jittering control circuit for generating a frequency jittering control signal to switch a power switch of a pulse frequency modulation power supply to generate an output voltage, the frequency jittering control circuit comprising:
a pulse frequency modulator connected to the power switch, for triggering the control signal responsive to a first signal to turn on the power switch, and terminating the control signal responsive to a second signal to turn off the power switch;
a current detector for detecting a current of the power switch to generate a current sense signal indicating the current of the power switch;
a comparator connected to the current detector, for comparing the current sense signal indicating the current of the power switch with a current limit signal to generate the second signal;
a programmable delay circuit connected between the comparator and the pulse frequency modulator, for delaying the second signal generated by comparing the current sense signal indicating the current of the power switch with the current limit signal for a delay time and then sending the second signal to the pulse frequency modulator; and
a delay time controller connected to the programmable delay circuit, for adjusting the delay time of the programmable delay circuit.

6. The frequency jittering control circuit of claim 5 , wherein the delay time controller comprises a counter or a random number generator.

7. A frequency jittering control circuit for generating a frequency jittering control signal to switch a power switch of a pulse frequency modulation power supply to generate an output voltage, the frequency jittering control circuit comprising:
a pulse frequency modulator connected to the power switch, for triggering the control signal responsive to a first signal to turn on the power switch, and terminating the control signal responsive to a second signal to turn off the power switch;
a current detector for detecting a current of the power switch to generate a current sense signal;
a gain circuit connected to the current detector, for amplifying the current sense signal;
a comparator connected between the gain circuit and the pulse frequency modulator, for comparing the amplified current sense signal with a current limit signal to generate the second signal; and
a gain controller connected to the gain circuit, for adjusting a gain of the gain circuit.

8. The frequency jittering control circuit of claim 7 , wherein the gain controller comprises a counter or a random number generator.

9. A frequency jittering control circuit for generating a frequency jittering control signal to switch a power switch of a pulse frequency modulation power supply to generate an output voltage, the frequency jittering control circuit comprising:
a pulse frequency modulato

Assignees

• Pan Jiun-Hung
• Tang Chien-Fu
• Chen Isaac Y
• Richtek Technology Corp

Inventors

• Pan Jiun-Hung
• Tang Chien-Fu
• Chen Isaac Y

Classifications

• H02M3/33523

  with galvanic isolation between input and output of both the power stage and the feedback loop · CPC title

• H02M3/33507 Primary

  with automatic control of the output voltage or current, e.g. flyback converters (H02M3/33561, H02M3/33569 take precedence) · CPC title

• H02M1/44

  Circuits or arrangements for compensating for electromagnetic interference in converters or inverters · CPC title

• H02M3/156

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

• H02M2003/1566

  Electricity · mapped topic