Thomson Multimedia S.a.

Thomson Licensing S.a.

Thomson Licensing

Seng Huat Ng

Kum Yoong Zee

Kian Meng Koh

Chun-Hsing Wu

Hsu Flame

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

Circuitry to control a power supply of a degaussing coil of a cathode ray tube, said degaussing coil is coupled to a main voltage supply through a switching device the circuitry has inputs coupled to a direct source of current of a switched mode power supply, the switched mode power supply comprises a switched mode transformer with primary windings coupled to the main source of voltage, and secondary windings and the switched mode power supply is switched in a first range of frequencies when the power supply is in a 'standby' mode and in a second range of frequencies when the power supply is in an 'on' mode wherein said circuitry comprising a detecting circuit which detectes a change in the range of switching frequencies when the power supply is switched from standby to on, the detecting circuit having an input coupled to a direct current source being downstream of a primary winding of the switched mode transformer and an output coupled to an input of a control circuit of the switching device the control circuit, having an output to carry an output signal having an 'on' state and an 'off' state, the 'on' state lasting for a predetermined duration after a change in a value present at the output of said detection circuit, the change occurring when the power supply is switched to the 'on' mode, in the 'on' state of said signal at the output of said control circuit, the switching device is on and current coming from the main is flows through the degaussing coil and in the 'off' state of said signal the switching device is off and no current is circulates in the degaussing coil.

Auto deguassing from stand-by to on

The most popular method for reducing stray emission effects in a cathode ray tube is to install a bleeder resistor at the flyback transformer of the tube. Such a bleeder resistor is, however, quite expensive. Therefore, the stray emission reduction circuit according to the invention differentiates the H pulse when the TV set is switched from 'on' to 'standby' which results in a higher duty cycle of the control transistor, implying a lower duty cycle of the horizontal output transistor HOT. This results in a lower voltage at the tuning capacitor and hence lowers the flyback peak voltage at the anode. This results in a drop of the EHT voltage.

Growing community of inventors

Singapore, Singapore

Seng Huat Ng