Switching regulator with reduced conducted emissions

• US 20050218873A1
• Filed: 04/05/2004
• Published: 10/06/2005
• Est. Priority Date: 04/05/2004
• Status: Active Grant

• Current Assignee: Elster Electricity LLC (Honeywell International Inc.)
• Original Assignee: Elster Electricity LLC (Honeywell International Inc.)
• Inventors: Shuey, Kenneth C., Hemminger, Rodney C., Mason, Robert T.
• Granted Patent: US 7,218,531 B2
• Time in Patent Office: Days
• US Class Current: 323/282
• CPC Class Codes: H02M 1/0025 Arrangements for modifying reference values, feedback values or error values in the control loop of a converter
• CPC Class Codes: H02M 1/12 Arrangements for reducing harmonics from ac input or output
• CPC Class Codes: H02M 1/44 Circuits or arrangements for compensating for electromagnetic interference in converters or inverters
• CPC Class Codes: H02M 3/33507 with automatic control of the output voltage or current, e.g. flyback converters H02M3/33561, H02M3/33569 take precedence

Abstract

A fixed-frequency switching regulator having a noise injection circuit. Noise is injected into the feedback loop of the switching regulator to modify the switching waveform to reduce individual frequency harmonics of the resultant Fourier Series. The reduced frequency harmonics allow the switching regulator to achieve reduced conducted emissions.

Claims

1. A switching regulator comprising:

a transformer having a primary winding and a secondary;

a fixed-frequency switching element connected in series with said primary winding;

a controller provided to control said switching element;

a rectifying circuit connected to said secondary winding; and

a noise source injecting a signal into said rectifying circuit.

2. The switching regulator of claim 1, wherein said noise source injects a random noise signal into said rectifying circuit to create a ripple voltage in an output voltage of said switching regulator.

3. The switching regulator of claim 2, wherein a duty cycle of said fixed-frequency switching element is modified by said random noise signal.

4. The switching regulator of claim 3, wherein said random noise signal is between 50 and 75 mV.

5. The switching regulator of claim 2, further comprising an optical isolator circuit to provide closed-loop control of the switching regulator.

6. A switching regulator comprising:

a transformer having a primary winding and a secondary winding;

a controller having a fixed-frequency switching element, a duty cycle of said fixed-frequency switching element being determined in accordance with a closed-loop feedback circuit;

a rectifying circuit connected to said secondary winding; and

a random noise signal injected into said rectifying circuit, said random noise signal creating a ripple voltage in an output voltage of said switching regulator.

7. The switching regulator of claim 6, wherein the duty cycle of said fixed-frequency switching element is modified by said random noise signal.

8. The switching regulator of claim 7, further comprising an optical isolator circuit to provide closed-loop control of the switching regulator.

9. The switching regulator of claim 8, wherein said random noise signal is between 50 and 75 mV.

10. A method of controlling a fixed-frequency switching regulator, the regulator including a transformer having a primary winding and a secondary winding;

a fixed-frequency switching element connected in series with said primary winding;

a controller; and

a rectifying circuit connected to said secondary winding, the method comprising;

injecting a noise source into said rectifying circuit;

detecting an output voltage of said switching regulator; and

controlling a duty cycle of said fixed-frequency switching element in accordance with said output voltage.

11. The method of claim 10, further comprising:

generating a random noise signal as said noise source; and

creating a ripple voltage in said output voltage of said switching regulator.

12. The method of claim 11, further comprising altering a duty cycle of said fixed-frequency switching element in response to said random noise signal.

13. The method of claim 11, wherein said random noise signal is between 50 and 75 mV.

14. The method of claim 10, wherein said fixed-frequency switching regulator generates broadband conducted frequency components.

15. A method of controlling a fixed-frequency switching regulator, the regulator including a transformer having a primary winding and a secondary winding;

a fixed-frequency switching element connected in series with said primary winding;

a controller; and

a rectifying circuit connected to said secondary winding, the method comprising;

detecting an output voltage of said switching regulator;

randomly modifying an applied load receiving said output voltage; and

controlling a duty cycle of said fixed-frequency switching element in accordance with said output voltage.

16. The method of claim 15, wherein randomly modifying said applied load receiving said output voltage comprises:

generating a random noise signal in a microcontroller; and

creating a ripple voltage in said output voltage of said switching regulator by randomly pulling a pin on said microcontroller high and low.

17. The method of claim 16, wherein said applied load varies approximately 30 mA.