Power supply having reduced transformer commutation noise

Patent metadata

Field	Value
Publication number	US-9847724-B2
Application number	US-201514876538-A
Country	US
Kind code	B2
Filing date	Oct 6, 2015
Priority date	Oct 6, 2015
Publication date	Dec 19, 2017
Grant date	Dec 19, 2017

Abstract

Embodiments of the present invention provide improved techniques and devices for reducing transformer commutation distortion caused by large load currents. Traditional power supplies which have two or more phases typically commutate a transformer during the end of each phase. When the load current is large, energy stored in the transformer's leakage inductance can cause undesirable effects during commutation. Embodiments of the present invention reduce these effects by lowering the voltage across the primary side of the transformer prior to commutation. In one embodiment, a capacitor is added to the primary side of the transformer. A switch directs current through the capacitor prior to commutation, allowing the capacitor to absorb the transformer's leakage inductance energy and lower the primary side voltage. Other suitable components, such as resistors, diodes, transistors, or additional transformer windings, may also be used to reduce the primary-side voltage prior to commutation.

First claim

What is claimed is:

1. A power supply that has at least two phases, comprising:
first and second power terminals;
a transformer that has at least one primary winding coupled to the first power terminal;
a first switch, configured to couple a first side of the primary winding to the second power terminal during a first state of the first switch;
a second switch, configured to couple a second side of the primary winding to the second power terminal during a first state of the second switch; and
a third switch that has at least a first state and a second state, configured to provide a current path through the third switch during the first state of the third switch, and to reduce the magnitude of a voltage across the primary winding during the second state of the third switch.

2. The power supply of claim 1 , wherein
the third switch is coupled to the second power terminal;
the third switch is coupled to a capacitor; and
the third switch is configured to provide a current path through the capacitor when the third switch is in the second state.

3. The power supply of claim 2 , wherein the capacitance of the capacitor is larger than a capacitance across the primary winding.

4. The power supply of claim 1 , wherein
the third switch is coupled to a resistor;
the third switch is coupled to the second power terminal; and
the third switch is further configured to provide a current path through the resistor when the third switch is in the second state.

5. The power supply of claim 1 , wherein the third switch;
is configured to provide a current path through a first number of primary windings when the third switch is in the first state; and
is configured to provide a current path through a second number of primary windings when the third switch is in the second state.

6. The power supply of claim 1 , configured to change the third switch to its second state at a first time, and to change the first switch or second switch from a first state to a second state once a load current in the power supply has substantially reached zero.

7. A power supply, comprising:
first and second power terminals;
a transformer that has at least one primary winding coupled to the first power terminal;
a first switching circuit, configured to couple a first end of the primary winding to the second power terminal when the first switching circuit is in a first state;
a second switching circuit, configured to couple a second end of the primary winding to the second power terminal when the second switching circuit is in a first state; and
wherein the first and second switching circuits each comprise:
a series arrangement comprising a first switch connected in series to a capacitor; and
a second switch, connected in parallel to the series arrangement.

8. The power supply of claim 7 , wherein the capacitors in the first and second switching circuits have substantially the same capacitance.

9. The power supply of claim 7 , wherein the capacitance of at least one capacitor is larger than a capacitance across the primary winding.

10. The power supply of claim 7 , configured to turn off a second switch in the first or second switching circuit at a first time, and to turn off the first switch in the same first or second switching circuit once a load current in the power supply has substantially reached zero.

11. A power supply, comprising:
first and second power terminals;
a transformer that has at least one primary winding coupled to the first power terminal;
a first switching circuit coupled in parallel to the primary winding, wherein the first switching circuit comprises a first switch connected in series to a second switch; and
a second switching circuit, comprising a third switch connected in parallel to a capacitor;
wherein one end of the second switching circuit is coupled to the second power terminal and the other end of the second switching circuit is connected to the first switching circuit at a point between the first and second switches.

12. The switching circuit of claim 11 , configured to turn off the third switch at a first time, and to turn off one of the first or second switches at a second time, once a load current of the power supply has reached substantially zero.

13. The switching circuit of claim 11 , wherein the capacitance of the capacitor is larger than a capacitance across the primary winding.

14. A method of operating a power supply that has a transformer with at least one primary winding, the method comprising:
applying a voltage having a first magnitude and polarity to the primary winding for a first period of time;
prior to commutating the transformer, reducing the voltage magnitude to a second value that is substantially greater than zero, for a second period of time; and
disconnecting the applied voltage for a third period of time while the transformer commutates.

15. The method of claim 14 , wherein the method is repeated after the commutation is complete, with substantially the same the voltage magnitudes but an opposite voltage polarity.

16. The method of claim 14 , wherein the second voltage magnitude is at least eighty percent of the first voltage magnitude.

17. The method of claim 14 , wherein the step of reducing the voltage magnitude to a second value comprises directing a current path of the primary winding to flow through one or more components in order to reduce the magnitude of the voltage across the primary winding.

18. The method of claim 17 , wherein at least one of the components is a capacitor.

19. The method of claim 17 , wherein at least one of the components is a resistor.

20. The method of claim 14 , wherein the step of reducing the voltage magnitude to a second value comprises directing a current path that flows through a first number of primary windings to flow through a second, larger, number of primary windings.

Assignees

• Keithley Instruments
• Keithley Instruments

Inventors

• Goeke Wayne C

Classifications

• H02M2001/342

  Electricity · mapped topic

• H02M3/33507 Primary

  with automatic control of the output voltage or current, e.g. flyback converters (H02M3/33561, H02M3/33569 take precedence) · CPC title

• H02M3/337 Primary

  in push-pull configuration {(H02M3/33576 takes precedence; with self-oscillating arrangements H02M3/3382, H02M3/3385)} · CPC title

• H02M3/33569

  having several active switching elements (H02M3/3353 takes precedence) · CPC title

• Y02B70/1491

  Cross-Sectional Technologies · mapped topic