| 摘要 |
PURPOSE: To prevent destruction of a switching element due to in-tube discharge by providing an overvoltage protection means in a high voltage generating circuit of the CRT display device. CONSTITUTION: A resistor 12 is connected to one terminal of a secondary side 23b of a flyback transformer and a short-circuit current (discharge current of a capacitor Ca) due to in-tube discharge is detected by a voltage drop across the resistor 12. When a voltage Vd of a detection terminal 28 is decreased and transistors(TRs) Q11, Q12 of a suppression circuit 26 are turned on, the voltage level of its output terminal 29 reaches 0V resulting that an input voltage Vc of a reference voltage input terminal 21a of a high voltage control circuit 21 is rapidly dropped (to nearly 0.7V) and an output VE of a high voltage power supply 22 having been increased is suppression control and is going to be decreased. Thus, the increase in a flyback pulse voltage is suppressed to prevent destruction of a switching TR Q10. An anode voltage Va is gradually restored by a circuit time constant of a holding circuit 27. |
