Isolated Switched-mode Power Supply With Output Regulation From Primary Side

• US 20090067201A1
• Filed: 09/06/2007
• Published: 03/12/2009
• Est. Priority Date: 09/06/2007
• Status: Active Grant

• Current Assignee: CAI Jun
• Original Assignee: CAI Jun
• Inventors: Cai, Jun
• Granted Patent: US 7,808,802 B2
• Time in Patent Office: Days
• US Class Current: 363/21.120
• CPC Class Codes: H02M 3/33523 with galvanic isolation between input and output of both the power stage and the feedback loop

Abstract

Embodiments disclosed herein describe an isolated switched-mode power supply with its output regulated from the primary side, by generating a sensing current using a sensing element coupled to the output of the power supply, and measuring a scaled version of the sensing current which depends on the output voltage, and calculating an estimate voltage representing the output voltage, and regulating the output of the isolated switched-mode power supply based on the estimate voltage.

Claims

1. An electronic circuit, comprising:

a switched-mode power supply with an input side and an output side isolated from each other,

a sensing element coupled to said output side of said switched-mode power supply, generating a sensing current based on an output voltage on said output side of said switched-mode power supply, and

a measuring means coupled to said input side of said switched-mode power supply, to measure a scaled version of said sensing current and then to calculate an estimate voltage representing said output voltage on said output side of said switched-mode power supply,

said switched mode power supply regulating said output voltage based on said estimate voltage,

whereby said output voltage on said output side of said switched-mode power supply can be regulated from said input side of said switched-mode power supply.

2. The electronic circuit of claim 1 wherein:

said switched-mode power supply is of flyback type, with single-ended or double-ended power switch.

3. The electronic circuit of claim 1 wherein:

said switched-mode power supply is of flyback type and working in discontinuous conduction mode.

4. The electronic circuit of claim 1 wherein:

said switched-mode power supply is using voltage mode control or current mode control.

5. The electronic circuit of claim 1 wherein:

said sensing element is a or a group of passive components.

6. The electronic circuit of claim 1 wherein:

said sensing element includes at least a resistor.

7. The electronic circuit of claim 1 wherein:

said measuring means includes a sample and hold means to sample said scaled version of said sensing current at a plurality of times.

8. A switched-mode power supply, comprising:

an energy transfer element with a primary side and a secondary side isolated from each other,

at least a power switch coupled to said primary side of said energy transfer element,

at least a rectifying element coupled to said secondary side of said energy transfer element, and

an energy storage element coupled to said rectifying element,

a control means to control said power switch on and off to let energy transferred from said primary side to said secondary side of said energy transfer element, then to said energy storage element through said rectifying element, and

a sensing element coupled to said energy storage element, generating a sensing current based on an output voltage on said energy storage element, and

a measuring means coupled to said primary side of said energy transfer element, to measure a scaled version of said sensing current and therefore to calculate an estimate voltage representing said output voltage on said energy storage element, said estimate voltage used by said control means to control said power switch,

whereby said output voltage on said energy storage element at said secondary side of said energy transfer element can be regulated from said primary side of said energy transfer element.

9. The switched-mode power supply of claim 8 wherein:

said energy transfer element is transformer.

10. The switched-mode power supply of claim 8 wherein:

said power switch is MOS transistor.

11. The switched-mode power supply of claim 8 wherein:

said energy storage element is a capacitor or a group of capacitors.

12. The switched-mode power supply of claim 8 wherein:

said rectifying element is diode.

13. The switched-mode power supply of claim 8 wherein:

said sensing element is a or a group of passive components.

14. The switched-mode power supply of claim 8 wherein:

said sensing element includes at least a resistor.

15. The switched-mode power supply of claim 8 wherein:

said energy transfer element, said power switch, said rectifying element, and said energy storage element form a flyback type circuit.

16. The switched-mode power supply of claim 15 wherein:

said flyback type circuit works in discontinuous conduction mode.

17. The switched-mode power supply of claim 8 wherein:

said rectifying element is connected in a high-sided rectifying topology or a low-sided rectifying topology.

18. The switched-mode power supply of claim 8 wherein:

said measuring means includes a sample and hold means to sample said scaled version of said sensing current at a plurality of times, to avoid the transient current glitch caused by the turning on of said power switch.

19. The switched-mode power supply of claim 8 wherein:

said rectifying element is synchronous rectifier.

20. A method to regulate an output voltage of an output side of an isolated switched-mode power supply from an input side of said isolated switched-mode power supply, comprising steps of:

(a) measuring a scaled version of a sensing current at said input side of said isolated switched-mode power supply,

said sensing current generated by a sensing element coupled to said output side of said isolated switched-mode power supply, and

said sensing current depending on said output voltage of said output side of said isolated switched-mode power supply, an input power supply voltage at

said input side of said isolated switched-mode power supply, the resistance value of said sensing element, and a transfer ratio of said isolated switched-mode power supply, and

(b) calculating an estimate voltage which representing said output voltage of said output side of said isolated switched-mode power supply, based on said scaled version of said sensing current measured, said input power supply, the resistance value of said sensing element, and said transfer ratio, and

(c) regulating said output voltage of said output side from said input side of said isolated switched-mode power supply based on said estimate voltage.