Philips Electronics North America Corporation

Majid Naveed

Erwin G Seinen

Ton Mobers

Robert J Fronen

Edwin Kluter

In a switched-mode power supply, when the controller and the switching device are encapsulated together with a heat sink, in which the drain of the switching device is connected to the heat sink, the heat sink and the paths to the various pins of the controller forms various parasitic capacitances which, when the switching device switches, injects and withdraws inordinately large currents into and from the pins of the controller. In the case of the V.sub.CTRL pin to which is connected a discharge capacitor, the resulting under voltage across the capacitor may be used by circuitry connected to the V.sub.CTRL pin to control the switching of the switching device resulting in throwing the switched-mode power supply out of regulation. A track-and-hold circuit is now connected between the V.sub.CTRL pin and the circuitry to mirror the voltage across the discharge capacitor. During the times when current would be withdrawn from the discharge capacitor due to capacitance coupling, the track-and-hold circuit isolates the circuitry from the resulting under voltage.

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Mohegan Lake, NY, United States of America

Majid Naveed