Methods and apparatus for biasing a magnetic circuit to reduce audible noise from a switching power supply

Patent metadata

Field	Value
Publication number	US-11250984-B2
Application number	US-202016822342-A
Country	US
Kind code	B2
Filing date	Mar 18, 2020
Priority date	May 31, 2019
Publication date	Feb 15, 2022
Grant date	Feb 15, 2022

Abstract

Presented herein are methods and apparatus for biasing magnetic circuits to reduce audible noise from a switching power supply. A magnetic component (e.g., a magnet) is constructed and provided to a core (e.g., a ferromagnetic core) to offset (i.e., bias) an applied magnetomotive force. By selecting and/or manufacturing the magnetic component based on a circuit operating condition, the offset may be tailored to advantageously shift a frequency of mechanical deformation outside the audible noise range. In a switching power supply with fixed peak current, the offset to the applied magnetomotive force may be determined, at least in part, by the fixed peak.

First claim

What is claimed is:

1. A switching power supply comprising:
a magnetic circuit comprising:
a magnetic core configured to receive an applied magnetomotive force;
a coil configured to receive an electric current and to provide the applied magnetomotive force in proportion to the electric current whereby the applied magnetomotive force varies to a maximum magnetomotive force in response to the electric current transitioning to a fixed peak current; and
a magnet coupled with the magnetic core and configured to provide an offset to the applied magnetomotive force whereby the offset is adjusted to be substantially equal to one half an additive inverse of the maximum magnetomotive force.

2. The switching power supply of claim 1 , wherein the coil is wrapped around a segment of the magnetic core.

3. The switching power supply of claim 1 , wherein the coil is wrapped around the magnet.

4. The switching power supply of claim 1 , wherein the magnet is an electromagnet.

5. The switching power supply of claim 1 , wherein the magnet is a permanent magnet.

6. The switching power supply of claim 1 , wherein the magnetic core comprises a ferrite.

7. The switching power supply of claim 1 ,
wherein the magnetic core comprises a gap; and
wherein the magnet is positioned within the gap.

8. The switching power supply of claim 1 , wherein the applied magnetomotive force and the offset to the applied magnetomotive force induce a total magnetic flux density.

9. The switching power supply of claim 8 , further comprising a second coil, the second coil configured to provide a second electric current induced by the total magnetic flux density.

10. The switching power supply of claim 9 ,
wherein the electric current transitions to the fixed peak current during a switching cycle; and
wherein during the switching cycle the total magnetic flux density varies between a positive value and a negative value.

11. The switching power supply of claim 10 , wherein the positive value is substantially equal to the negative value.

12. The switching power supply of claim 10 , wherein the switching power supply is a flyback converter.

13. A method of reducing audible noise in a power supply including a magnetic circuit, the method comprising:
determining an operating condition of the magnetic circuit whereby the operating condition includes a current of a winding and a magnetomotive force induced by the winding in response to the current; and
providing an offset magnetomotive force, wherein the offset magnetomotive force is selected to be substantially equal to one half an additive inverse of a peak value of the magnetomotive force induced by the winding.

14. The method of claim 13 , wherein determining the operating condition of the magnetic circuit comprises:
determining a peak current in the winding during a switching cycle.

15. The method of claim 13 , wherein providing the offset magnetomotive force comprises:
coupling a magnet to a magnetic core;
adjusting a dimension of the magnet; and
placing the magnet in a gap of the magnetic core.

16. The method of claim 15 , further comprising:
wrapping the winding around the magnet.

17. A method of reducing audible noise in a switching power supply comprising a magnetic circuit, the method comprising:
determining a switching cycle energy;
selecting a magnetic core, the magnetic core comprising a standard gap and a permanent magnet;
determining a winding turns number in relation to a peak current and a peak flux density, the peak flux density substantially equal to twice a flux density offset of the magnetic core;
providing a power supply circuit configured to operate with the peak current; and
assembling the magnetic circuit comprising the magnetic core and a winding, the winding comprising the winding turns number.

18. The method of claim 17 , wherein the determining the switching cycle energy comprises:
determining a power delivered to a load during a switching cycle.

19. The method of claim 17 , wherein the magnetic core is an off-the-shelf (OTS) magnetic core.

20. The method of claim 17 , wherein the winding is a primary coil.

Assignees

• Power Integrations Inc

Inventors

• Polivka William M

Classifications

• H01F3/10

  Composite arrangements of magnetic circuits · CPC title

• H02M3/33523 Primary

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

• H01F27/28

  Coils; Windings; Conductive connections · CPC title

• H01F3/14

  Constrictions; Gaps, e.g. air-gaps (in magnetic shunt paths H01F3/12) · CPC title

• H02M3/003

  Constructional details, e.g. physical layout, assembly, wiring or busbar connections · CPC title