Power Supplies And Methods For Reducing Common Mode Noise

• US 20170163145A1
• Filed: 12/02/2015
• Published: 06/08/2017
• Est. Priority Date: 12/02/2015
• Status: Active Grant

• Current Assignee: Astec International Limited (Emerson Electric Company)
• Original Assignee: Astec International Limited (Emerson Electric Company)
• Inventors: CHENG, Wing Ling, SHING, Yuk Man
• Granted Patent: US 10,320,279 B2
• Time in Patent Office: Days
• CPC Class Codes: H02M 1/12 Arrangements for reducing harmonics from ac input or output
• CPC Class Codes: H02M 1/123 Suppression of common mode voltage or current

Abstract

An example switched-mode power supply includes an input for receiving an input voltage from a voltage source, an output for providing an output voltage to a load, and a transformer having a primary winding, a secondary winding, and a conductive shield disposed between the primary winding and the secondary winding. The power supply also includes a neutralization signal generator circuit coupled to the conductive shield to apply a neutralization signal to the conductive shield to reduce a common mode noise between the primary winding and the secondary winding of the transformer. The neutralization signal has an adjustable amplitude and/or phase. Other example power supplies and methods are also disclosed.

Claims

1. A switched-mode power supply comprising:

an input for receiving an input voltage from a voltage source;

an output for providing an output voltage to a load;

a transformer having a primary winding, a secondary winding, and a conductive shield disposed between the primary winding and the secondary winding; and

a neutralization signal generator circuit coupled to the conductive shield and adapted to apply a neutralization signal to the conductive shield to reduce a common mode noise between the primary winding and the secondary winding of the transformer, wherein the neutralization signal has an adjustable amplitude and/or phase.

2. The power supply of claim 1, wherein the neutralization signal generator circuit is adapted to adjust the neutralization signal in response to user input or automatically.

3. The power supply of claim 2, wherein the transformer includes an auxiliary winding disposed on a primary side of the transformer.

4. The power supply of claim 2, wherein the neutralization signal generator circuit is adapted to apply the neutralization signal to the conductive shield to substantially cancel the common mode noise between the primary winding and the secondary winding of the transformer.

5. The power supply of claim 1, wherein the neutralization signal generator circuit includes a potentiometer.

6. The power supply of claim 1, wherein the transformer is a first transformer and the neutralization signal generator circuit includes a second transformer adapted to adjust the amplitude and/or phase of the neutralization signal.

7. The power supply of claim 1, wherein the neutralization signal generator circuit includes at least one winding of the transformer.

8. The power supply of claim 1, wherein the neutralization signal generator circuit includes an adjustable gain amplifier.

9. The power supply of claim 1, further comprising an interference measurement component positioned to measure the common mode noise between the primary winding and the secondary winding of the transformer.

10. The power supply of claim 9, wherein the interference measurement component includes a sense resistor.

11. The power supply of claim 9, wherein the neutralization signal generator circuit includes a controller and a programmable gain amplifier to automatically adjust the neutralization signal during operation of the power supply based on the common mode noise measured by the interference measurement component.

12. A method of reducing common mode noise in a switched-mode power supply, the power supply including an input for receiving an input voltage from a voltage source, an output for providing an output voltage to a load, and a transformer having a primary winding, a secondary winding, and a conductive shield disposed between the primary winding and the secondary winding, the method comprising:

measuring a common mode noise between the primary winding and the secondary winding of the transformer;

applying a neutralization signal to the conductive shield to reduce the common mode noise between the primary winding and the secondary winding of the transformer, wherein the neutralization signal has an adjustable amplitude and/or phase.

13. The method of claim 12, wherein applying the neutralization signal includes adjusting the neutralization signal to substantially cancel the common mode noise between the primary winding and the secondary winding of the transformer.

14. The method of claim 12, wherein the neutralization signal has substantially the same amplitude and opposite phase of the measured common mode noise between the primary winding and the secondary winding of the transformer.

15. The method of claim 12, wherein applying the neutralization signal includes adjusting the amplitude and/or phase of the neutralization signal based on the measured common mode noise between the primary winding and the secondary winding of the transformer.

16. The method of claim 15, wherein applying the neutralization signal includes adjusting a potentiometer and/or selecting one or more resistor values.

17. The method of claim 15, wherein applying the neutralization signal includes adjusting an adjustable gain amplifier.

18. The method of claim 12, wherein applying the neutralization signal includes adjusting the neutralization signal during operation of the power supply in response to a change in the measured common mode noise.

19. The method of claim 18, wherein the power supply includes a controller and a programmable gain amplifier, and applying the neutralization signal includes adjusting the neutralization signal via the controller and the programmable gain amplifier.

20. The method of claim 12, wherein measuring a common mode noise includes measuring the common mode noise via a sense resistor.