Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
1999-05-28
2001-03-27
Riley, Shawn (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
Reexamination Certificate
active
06208532
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The invention lies in the electrical and electronics fields. Specifically, the invention pertains to a switched-mode power supply with a switching element through which a rectified AC voltage can be applied to a primary winding of a transformer, at the secondary winding of which a rectified output voltage to be controlled can be tapped. The power supply further has a control device through which the switching element can be clock-pulse controlled in dependence on a control signal. The transformer contains an E-shaped core with a middle limb surrounded by the primary and the secondary winding.
Switched-mode power supplies are known devices used to generate one or more different load-independent DC output voltages from a single rectified AC mains voltage. For this purpose the primary side rectified AC voltage is applied in a clocked manner over a switching element to the primary winding of a transformer. The output voltage can be tapped at the secondary winding after rectification and smoothing.
The output voltage is regulated through the clock-pulse control or duty cycle of the switching element. In German published patent application DE 44 07 709 this is done by tapping a control signal from an additional primary winding, whereby regulation of the clock frequency and thus of the secondary side output voltage are dependent on the control signal. The inadequate coupling between the primary side control winding and the secondary side load winding is problematical. The result is that the output voltage cannot be held sufficiently constant at load changes.
A so-called current pump for sinusoidal current input is provided in the circuit disclosed in the afore-mentioned document. Influences of the mains frequency are amplified through the current pump. A mains system hum is therefore superimposed on the output voltage and the mains system hum cannot be completely compensated because the control voltage is tapped on the primary side.
As a remedy, the control voltage can be tapped on the secondary side, as shown for example in the German utility model (Gebrauchsmuster) G 94 10 995. An optical coupler is necessary for the transmission of the control signal to the control device on the primary side. An optical coupler module is relatively costly, however, and that solution is therefore uneconomical.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a switched-mode power supply unit, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which can be manufactured at low cost and which provides as well-regulated an output voltage as possible.
With the foregoing and other objects in view there is provided a switched-mode power supply. The power supply includes a transformer having a primary winding receiving a rectified AC voltage and a secondary winding outputting a rectified output voltage. The transformer has an E-shaped core with a middle limb surrounded by the primary winding and the secondary winding. The E-shaped core also has a first outer limb and a second outer limb. A first winding is provided around the first outer limb for conducting a current controlled in dependence on the output voltage, and a second winding is provided around the second outer limb for generating a control signal. The power supply also includes a switching element connected to the primary winding of the transformer for supplying a rectified AC voltage to the primary winding, and a control device connected to the switching element for clock-pulse controlling the switching element in dependence on the control signal.
The switched-mode power supply described by the invention does not require an optical coupler. Transmission of the control information from the secondary to the primary side is performed through asymmetric displacement of the magnetic field of the transformer between the outer limbs of the transformer core. The leads for the control signal start directly at the output voltage to be regulated, so that both load changes and mains system hum are well compensated. The windings to be attached to the outer limbs are generally simple enough to be produced by automatic equipment and are therefore economical.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in switched-mode power supply with feedback control of the output voltage, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.
REFERENCES:
patent: 4646319 (1987-02-01), Engel et al.
patent: 3501052A1 (1986-07-01), None
patent: 4407709A1 (1995-09-01), None
patent: 9410995 (1995-09-01), None
patent: 0018186A1 (1980-10-01), None
patent: 0332095A2 (1989-09-01), None
patent: 0653831A1 (1995-05-01), None
patent: 0778659A2 (1997-06-01), None
Japanese Patent Abstract No. 59-178969 (Kouno), dated Oct. 11, 1984.
Greenberg Laurence A.
Lerner Herbert L.
Riley Shawn
Siemens Aktiengesellschaft
Stemer Werner H.
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