U.S. Philips Corporation

Thomas Durbaum

Manfred Albach

A switched mode power supply includes a transformer having a primary winding and a secondary winding. A primary current flows through the primary winding during a first time period and a secondary current flows through the secondary winding during a second time period. A first switching device is connected in series to the primary winding, and a second switching device is connected in series to the secondary winding. In addition, the power supply includes primary and secondary control units. The secondary-side control unit switches the second switching device to control the power supply output by changing the energy returning back to the transformer during the second period of time. The primary-side control unit switches the first switching device to limit the supplied energy supplied by the transformer during the first period of time toward the input of the switched mode power to a predetermined value. This eliminates the need for transmission of a control signal from the secondary side to the primary side where DC decoupling is necessary.

Switched mode power supply with reduced reflected power

Switched-mode power supply

A circuit arrangement for generating at least a DC output voltage (at 18, 19) from an at least substantially sine-shaped AC input voltage (at 2, 3) of a first frequency by a first rectifier arrangement (1) to which the AC input voltage can be applied (at 2, 3) and which has a DC output (4, 5) from which a rectified voltage is obtainable, a first inductance (6), a second rectifier arrangement (7) and a first filter capacitance (8) which, in this order, constitute a series arrangement connected parallel to the DC output (4, 5), a switched-mode power supply (9) having two input terminals (10, 11) with which it is arranged parallel to the first filter capacitance (8) and between which it includes a series arrangement of a second inductance (12) and a switching device (13) which is alternately switchable in the conducting state and in the blocked state at a second frequency and from which the DC output voltage(s) is (are) obtainable (at 18, 19), as well as a first control capacitance (23) by which the junction point (22) between the first inductance (6) and the second rectifier arrangement (7) is combined with the junction point (24) between the second inductance (12) and the switching device (13), as well as the series arrangement of a second control capacitance (28) and a second switching device (29) which is arranged parallel to the first control capacitance (23) between the junction points (22) and (24), the first inductance (6) and the first control capacitance (23) being dimensioned in such a way that a resonance frequency determined thereby is larger than the second frequency and the last-mentioned frequency is chosen to be large with respect to the first frequency, while the second control capacitance (28) is chosen to be large with respect to the first control capacitance (23). While using a small number of components, both the voltage rise at the switching device and thus the high-frequency interference originating therefrom can be reduced under all occurring circumstances, and the harmonics of the line current can also be reduced. Moreover, the maximum voltage occurring at the switching elements may be limited to a predetermined value without any additional losses.

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Aachen, Germany

Thomas Durbaum