Vpp Sensor Circuit; Power Supply Circuit For Display - Casio CE-300 (EX-247) Service Manual

4-9. 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:
VPP:
Detection voltage level (Unit: V)
VCC >= +6.5 V
VDD >= +6.5 V
+13.9 V =< VPP <=15.0 V

4-10. Power supply circuit for display

VC
VP GND
This circuit is making the power for display tube.
Voltage level:
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.
-VN
VF1 - VF2
— 11 —
Est. -31.2 V
Est. AC4.85 V