Casio CTK-731 Service Manual page 9

POWER SUPPLY CIRCUIT
The power supply circuit provides various voltages as shown below.
The voltage VDD (+5 V) is provided as long as batteries or AC adaptor is set.
Other voltages are controlled by APO (Auto Power Off) signal from CPU.
From
+9V ~ +12 V
Batteries or
AC Adaptor
The regulator IC BA9700A generates square waveform from pin 5 as PWM (Pulse Wide Modulation).
The LC filter makes stable output voltage (+5 V) for each circuit as shown above.
PW/ON
NMI
APO
(To back light)
Switching
Transistors LC Filter
Regulator IC
— 8 —
CPU
HD6433042SB51F
APO
PA7
LSI9
NMI
PW/SW
(To LCD)
(To FDD)
(To digital)
(To analog)
LC Filter