Thomson Multimedia S.a.

Thomson Licensing S.a.

Thomson Licensing

Kian Meng Koh

Kum Yoong Zee

Seng Huat Ng

Chun-Hsing Wu

The protection circuit comprises a clamping circuit with a switching element for reducing a supply voltage in case of an over voltage condition, and a holding circuit for providing a holding current for the clamping circuit. The clamping circuit comprises a threshold circuit, which provides a switching voltage for a switching element when the supply voltage reaches an upper voltage limit. The switching element is connected to a charge capacitor, which provides the switching-on voltage for the switching transistor, and by reducing this supply voltage, the switching of the switching transistor is disabled. The holding circuit comprises in particular a capacitor, which is coupled via a resistor to the clamping circuit for providing an additional current in case of an over voltage condition.

Protection circuit for a switched mode power supply

The protection circuit comprises a storage capacitor which is coupled with a terminal of a secondary winding which charges said storage capacitor during the on-interval of the switching transistor. During the off-interval of the switching transistor the charge of the storage capacitor is fed to the driver stage or the control capacitor for closing or keeping closed the switching transistor when one of the secondary windings has a short circuit.

Protection circuit for a switched-mode power supply

The invention relates to a switch mode power supply (SMPS) comprising control means (IP1) including an oscillator (OS) for generating a pulse-width modulated signal (V2). The object is to provide a fast start-up time over a wide mains input-voltage range (AC). According to the invention, the switch mode power supply comprises a network (T2, R52, R51, R24) which provides in case of a high input voltage a soft start with a low oscillating frequency and in case of low input voltage a start-up with essentially the normal oscillating frequency. The invention provides a fast start-up time over a wide mains input voltage range of 90 Volt up to 265 Volt. The network includes a transistor (T2) used in inverse mode as a switching element which provides a threshold value of about 150 Volt. The power supply can be used advantageously as part of a TV receiver.

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Singapore, Singapore

Kian Meng Koh