CASIO TK800
Manual de Servicio

5-11. VPP sensor circuit
Protection circuit

To prevent the circuit breakage, the protection circuit watches the voltage level of VCC, VDD and VPP. When the each voltage level is more than following condition, this circuit cuts the voltage. VCC,VDD: In case these voltages are become over voltage, this circuit outputs �SCR� signal(High signal) and burn out the fuse. In case the VPP voltage is more than 15 V or less than 13.9 V, the �VPP.S� level is inverted and CPU cut the �VPP.ON� signal.

VPP:

Detection voltage level (Unit: V) VCC >= +6.5 V VDD >= +6.5 V +13.9 V =< VPP <=15.0 V

5-12.Power supply circuit for display

VC VP GND

This circuit is making the power for display tube. Voltage level: -VN VF1 - VF2 Est. -31.2 V Est. AC4.85 V

� 15 �