Controlling a switched mode power supply with maximised power efficiency

Patent metadata

Field	Value
Publication number	US-9929658-B2
Application number	US-201214406243-A
Country	US
Kind code	B2
Filing date	Jun 8, 2012
Priority date	Jun 8, 2012
Publication date	Mar 27, 2018
Grant date	Mar 27, 2018

Abstract

A control circuit operable to generate a control signal to control the duty cycle of a switched mode power supply is provided. The control circuit comprises an input terminal for receiving a signal indicative of an input voltage (V in ) of the switched mode power supply, and a reference signal generator to generate, in dependence upon the received signal, a reference signal (V R ) that is a function of the input voltage (V in ). The control circuit further comprises an error signal generator to receive a signal indicative of an output voltage (V out ) of the switched mode power supply and to generate an error signal (V E ) based on the reference signal (V R ) and based on the output voltage, a low pass filter, and a duty cycle control signal generator to generate the control signal to control the duty cycle of the switched mode power supply in dependence upon the error signal (V E ).

First claim

The invention claimed is:

1. A control circuit operable to generate a control signal to control a duty cycle of a switched mode power supply, the control circuit comprising:
an input terminal for receiving a signal indicative of an input voltage (V in ) of the switched mode power supply;
a reference signal generator operable to generate, in dependence upon the received signal, a reference signal (V R ) that is a function of the input voltage (V in );
an error signal generator arranged to receive a signal indicative of an output voltage (V out ) of the switched mode power supply and operable to generate an error signal (V E ) based on the reference signal (V R ) and based on the output voltage (V out );
a low pass filter connected between the input terminal and the error signal generator, in series with the reference signal generator; and
a duty cycle control signal generator operable to generate the control signal to control the duty cycle of the switched mode power supply in dependence upon the error signal (V E );
wherein the reference signal generator is operable in a first mode to generate the reference signal (V R ) as a function of the input voltage (V in ) and operable in a second mode to generate a predetermined reference signal (V Rdes ) independent of the input voltage (V in ), the reference signal generator being configured to operate in the second mode when the input voltage (V in ) exceeds a threshold value, and to operate in the first mode when the input voltage (V in ) is equal to or smaller than said threshold value.

2. The control circuit according to claim 1 , wherein the low pass filter has a user adjustable time constant.

3. The control circuit according to claim 1 , wherein the low pass filter is arranged to respond to an increase in the input voltage (V in ) of the switched mode power supply with a first time constant, and to a decrease in the input voltage (V in ) of the switched mode power supply with a second time constant that is different from the first time constant.

4. The control circuit according to claim 1 , wherein the reference signal generator comprises:
an offset reference signal generator operable in the first mode to generate an offset reference signal (V R _ offset ) by combining the reference signal (V R ) generated as a function of the input voltage (V in ) with an offset signal (V offset ), the offset signal (V offset ) being independent of the input voltage (V in );
wherein the error signal generator is operable to generate the error signal (V E ) based on the offset reference signal (V R _ offset ) and based on the output voltage (V out ).

5. The control circuit according to claim 1 , wherein the error signal generator is arranged to generate the error signal (V E ) by subtracting one of the output voltage (V out ) of the switched mode power supply and the reference signal (V R ) from the other of the output voltage (V out ) of the switched mode power supply and the reference signal (V R ).

6. The control circuit according to claim 1 , wherein the error signal generator is arranged to receive a signal indicative of an output current (I out ) of the switched mode power supply and operable to generate the error signal (V E ) based on the reference signal (V R ), the output voltage (V out ) and the output current (I out ).

7. The control circuit according to claim 1 , wherein the reference signal generator comprises a reference signal selector operable to select the smaller of the generated reference signal (V R ) and the predetermined reference signal (V Rdes ) for output by the reference signal generator.

8. A switch mode power supply having a control circuit according to claim 1 .

9. The control circuit according to claim 3 , wherein the first time constant is between 0.3 ms and 3 ms, and the second time constant is between 0.06 ms and 0.6 ms.

10. The control circuit according to claim 4 , wherein the offset reference signal generator comprises an offset signal generator operable to generate a variable offset signal (V offset ).

11. A method of generating a control signal by a control circuit to control a duty cycle of a switched mode power supply, the method comprising:
a reference signal generation process comprising:
receiving a signal indicative of an input voltage (V in ) of the switched mode power supply;
generating, when the input voltage (V in ) is equal to or smaller than a threshold value, a reference signal (V R ) that is a function of the input voltage (V in ); and,
generating, when the input voltage (V in ) exceeds said threshold value, a predetermined reference signal (V Rdes ) independent of the input voltage (V in );
wherein at least one low-pass filtering operation is performed as part of the reference signal generation process so that the reference signal is a filtered signal;

an error signal generation process comprising:
receiving a signal indicative of an output voltage (V out ) of the switched mode power supply; and,
generating an error signal (V E ) based on the reference signal (V R ) and based on the output voltage (V out ); and,

a duty cycle control signal generation process, comprising generating a control signal to control the duty cycle of the switched mode power supply in dependence upon the error signal (V E ).

12. The method according to claim 11 , further comprising adjusting a time constant of a low pass filter used in said low-pass filtering operation in accordance with a capacitance of a load capacitor connected to an output of the switched mode power supply so as to maintain a size of the charge or discharge current of the load capacitor within a predetermined range of values.

13. The method according to claim 11 , wherein the error signal (V E ) is generated by subtracting one of the output voltage (V out ) of the switched mode power supply and the reference signal (V R ) from the other of the output voltage (V out ) of the switched mode power supply and the reference signal (V R ).

14. The method according to claim 11 , wherein:
the error signal generation process further comprises receiving a signal indicative of an output current (I out ) of the switched mode power supply; and,
the error signal (V E ) is generated based on the reference signal (V R ), the output voltage (V out ) and the output current (I out ).

15. The method according to claim 11 , wherein:
the reference signal generation process further comprises generating an offset reference signal (V R _ offset ) by combining the reference signal (V R ) with an offset signal (V offset ), the offset signal (V offset ) being independent of the input voltage (V in ); and,
the error signal (V E ) is generated based on the offset reference signal (V R _ offset ) and based on the output voltage (V out ).

16. The method according to claim 15 , wherein a variable offset signal (V offset ) is generated.

17. The method according to claim 12 , wherein the low pass filter is arranged to respond to an increase in the input voltage (V in ) of the switched mode power supply with a first time constant, and to a decrease in the input voltage (V in ) of the switched mode power supply with a second time constant, the method comprising adjusting the first and second time constants in accordance with the capacitance of the load capacitor so as to maintain the size of the charge and discharge currents of the capacitor within respective predetermined ranges of values.

Assignees

• Karlsson Magnus
• Persson Oscar
• Ericsson Telefon Ab L M

Inventors

• Karlsson Magnus
• Persson Oscar

Classifications

• G05F1/10

  Regulating voltage or current  (G05F1/02 takes precedence) · CPC title

• H02M3/3378

  in a push-pull configuration of the parallel type (H02M3/3374 takes precedence) · CPC title

• H02M2001/0025

  Electricity · mapped topic

• H02M2001/0022

  Electricity · mapped topic

• H02M3/33546 Primary

  with automatic control of the output voltage or current (H02M3/33561 takes precedence) · CPC title