Funai Electric Company Ltd.

Kazuo Nishinosono

Hitoshi Miyamoto

The present invention discloses a separately excited inverter circuit whose switching circuit having a plurality of switching elements and which is capable of minimizing the damage of other switching elements even if any of the plurality of switching elements is short circuited and damaged. The separately excited inverter circuit includes: a switching circuit of which a full bridge circuit applies an AC voltage to the primary winding of the step-up transformer; a control circuit Cfor performing the switching control of a switching circuitwhen receiving a command signal for commanding the control circuit to oscillate from a transmission line for transmitting the command signal for commanding it to start and stop oscillation; terminal voltage monitoring circuitsandfor monitoring a terminal voltage across a gate of MOS-FET forming the switching circuitand outputting a reference voltage when the gate voltage exceeds a predetermined threshold; and a thyristor circuitwhich is connected to the transmission line and to the gate of which the reference voltage is inputted to cause the thyristor circuit to flow a gate current to be turned on, bringing the command signal on the transmission line into cutting off oscillation to stop the oscillation of the control circuit.

Separately excited inverter circuit and liquid crystal display television

The separately-excited inverter circuit for performing the protecting operation upon the rise in the output voltage caused by the contact failure includes a switching circuitwhich applies the AC to a primary coil of a pressure-rising transformer, a control circuit Cwhich starts a switch control of the switching circuitupon an input of a command signal to set an oscillation state ON from a transmission line for the command signal to command to set the oscillation state ON and OFF, an output voltage monitor circuitwhich allows a comparatorto compare an output voltage of the separately-excited inverter circuit with a predetermined voltage, and to output a predetermined reference voltage when the output voltage is higher than the predetermined voltage, and a thyristor circuitwhich is turned ON to set the transmission line of the command signal into an oscillation OFF state upon the input of the reference voltage to the gate to stop a switch control of the control circuit C. The output voltage monitor circuitoutputs the reference voltage to make a time width sufficient to turn the thyristor circuitON using a hysteresis of the comparator

Separately-excited inverter circuit and liquid crystal television

The present invention discloses enabling readily determining which circuit, among a plurality of circuits including an optical source lighting circuit and a power supply circuit, has a failure and repairing the circuits easily in a short period. A liquid crystal televisioncomprising a power supply circuitthat produces and outputs various power supply voltages from an inputted commercial AC power supply, a microcomputerthat outputs a control signal to a plurality of circuits, respectively, including at least the power supply circuitand an inverter circuitthat is driven by a power supply voltage output by the power supply circuitto controls turning on and off of each circuit, is provided with an input terminalfor providing a power supply voltage from the outside of the liquid crystal television, and an inspection auxiliary circuitconnected to the power supply circuitand inverter circuit, generating a constant voltage that starts the power supply circuitand inverter circuitwhen a power supply voltage is provided from the input terminaland outputs the constant voltage as a control signal.

Display device and liquid crystal television

A cold-cathode tube driving circuit for driving a plurality of substantially-C-shaped cold-cathode tubes, includes: a first transformerhaving primary windings which induce voltages, and secondary windings which apply voltages of opposite polarities (&#x2212;V, +V) to respective ends of the respective substantially-C-shaped cold-cathode tubes; and a second transformerhaving third and fourth primary windings which respectively induce voltages, and third and fourth secondary windings which apply voltages of opposite polarities (&#x2212;V, +V) to respective ends of the respective substantially-C-shaped cold-cathode tubes. In the cold-cathode tube driving circuit, the first and second transformersapply an in-phase voltage to adjacent ends of the substantially-C-shaped cold-cathode tubes.

Driving circuit for cold-cathode tube

This backlight light source drive device includes a plurality of backlight light source drive circuits which drive a plurality of respective backlight light sources, and a control circuit which turns those drive circuits ON and OFF. Each of the drive circuits includes a protection signal output circuit which, when its corresponding tube electrical current decreases, outputs to the control unit a protection signal for stopping the operation of all of the drive circuits. This protection signal output circuit includes an LED illumination circuit which, when the tube electrical current thus decreases, illuminates an LED to indicate the anomalous state, and an LED power supply circuit which always supplies power to the LED illumination circuit. And the control circuit stops the operation of all of the plurality of backlight light source drive circuits, when it receives a protection signal from any one or more of the protection signal output circuits.

Backlight light source drive device

A secondary winding Wof a step-up transformer of a self-excited inverteris grounded at the midpoint thereof. High-frequency voltages differing in polarity from each other are outputted from both terminals OTand OTof the secondary winding W. Two U-shaped cold-cathode tubes Land Lseries-connected to each other are provided directly below a liquid crystal panel. One of terminals of the secondary winding Wis connected to the terminal OTthrough the ballast capacitor C. The other terminal thereof is connected to the terminal OTof the ballast capacitor C. The connecting point P between the two U-shaped cold-cathode tubes Land Lis ungrounded. Thus, electric currents flowing through the cold-cathode tubes are equal in value to each other.

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Osaka, Japan

Kazuo Nishinosono