Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Patent
1992-07-22
1994-03-01
Beha, Jr., William H.
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
323289, 363 49, H02M 75375
Patent
active
052913864
ABSTRACT:
A television receiver has a switched mode power supply for regulating an output voltage, including a power transformer having a primary winding coupled to an unregulated voltage via a power transistor. The power transistor is controlled by pulses from the output of a controller. In order to sweep the base-emitter charge from the power transistor in order to end collector-emitter conduction, the base of the power transistor is coupled to the output of the pulse generating controller via a capacitor in parallel with at least one diode. During a pulse from the controller, the capacitor is charged to a voltage equal to the forward biased drop across the diode(s). At the end of a pulse at the output of the controller, the voltage across the capacitor provides a negative voltage at the base of the transistor, thus sweeping out the base-emitter charge and sharply turning the transistor off. In order to assure this function of the capacitor even upon plug-in startup, the capacitor is precharged via a resistor coupled between the output of the controller and the unregulated voltage input.
REFERENCES:
patent: 4312029 (1982-01-01), Zellmer
patent: 4609980 (1986-09-01), Hoffman
patent: 4975823 (1990-12-01), Rilly et al.
Blaesner, "Erhohte Betriebssicherheit und Niedrigere Kosten" Elektronik (Germany), vol. 9, No. 39, pp. 134-140, Apr. 27, 1990.
Beha Jr. William H.
Laks J. J.
Sragow D. E.
Thomson Consumer Electronics S.A.
Tripoli J. S.
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