| 摘要 |
PURPOSE: An overvoltage protection circuit for a piezo transformer(PZT) inverter is provided to enable a stable operation of a PZT inverter by controlling an input voltage of the PZT inverter to be kept constant and protecting a high voltage from being output from the PZT inverter. CONSTITUTION: A constant voltage unit regulates an input voltage. A switching unit(Q1) switches a voltage received from the constant voltage unit. The switched voltage is input to a piezo transformer(PZT) unit(30). A cold cathode ray tube(40a) is turned on by an output voltage from the PZT unit. An output unit(40b) regulates and smoothes the output voltage from the cold cathode ray tube. A comparing unit compares the output voltage from the output unit with a reference voltage. A control unit receives the output from the control unit. A driving unit(20a) receives the output from the control unit and drives the switching unit. A protecting unit(70) is provided to receive the output from the control unit(10) or the input voltage, thereby controlling the constant voltage unit(60) to be protected. The protecting unit is comprised of a transistor(Q2) wherein a capacitor is connected between the power supply(Vcc) and the base, the emitter is connected to the shut-down terminal of the constant voltage unit(60), and the base is connected to the output voltage of the output unit(40b).
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