Power supply circuit and method thereof to detect...

Details Power supply circuit and method thereof to detect... Power supply circuit and method thereof to detect...

2001-02-20

2002-10-22

Berhane, Adolf Deneke (Department: 2838)

Electricity: power supply or regulation systems

Output level responsive

Using a three or more terminal semiconductive device as the...

C363S097000

Reexamination Certificate

active

06469484

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates in general to electronic devices and, more particularly, to switching regulators used in power supplies.
Most switching power supplies have a transformer with a power switching transistor coupled to one side of the transformers primary winding. The power transistor turns on and off as determined by a regulator circuit to alternately store energy in the magnetic field of the transformer and transfer the stored energy to the secondary winding. The secondary winding of the transformer develops a DC output voltage across a shunt capacitor coupled across the secondary winding as a function of the energy transfer.
One type of switching power supply, a flyback power supply, can be operated in a continuous conduction mode (CCM) or discontinuous conduction mode (DCM). DCM involves switching the power switching transistor to reenergize the primary winding only after it is completely demagnetized, whereas CCM involves switching the power switching transistor even though the primary winding is still magnetized. It is preferable to operate a flyback power supply in DCM because CCM is more difficult to stabilize and turn-on losses can be significantly higher.
To operate a flyback power supply in DCM it is necessary to detect when the transformer core of the primary winding is demagnetized. At a point in time t
O
, the transformer core is demagnetized, which corresponds to the point when the primary current I
P
reaches zero. By indirectly measuring a voltage across an auxiliary winding of the flyback power supply the point when the primary current I
P
reaches zero can be determined. However, the auxiliary winding represents an additional element that increases manufacturing cost. Elimination of the auxiliary winding used to detect demagnetization is beneficial to reduce manufacturing cost of switching power supplies.
Accordingly, a flyback power supply that detects when the transformer core of the primary winding is demagnetized without using an auxiliary winding is needed in the art. The invention disclosed herein will address the above problems.


REFERENCES:
patent: 5638260 (1997-06-01), Bees
patent: 5729443 (1998-03-01), Pavlin
patent: 6049471 (2000-04-01), Korcharz et al.
patent: 6088243 (2000-07-01), Shin
patent: 6104622 (2000-08-01), Shin
patent: 19643136 (1997-04-01), None

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