Casio CTK-731 - Page 9

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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.
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.
LC Filter
Switching
Transistors
Regulator IC
From
Batteries or
AC Adaptor
(To back light)
(To LCD)
(To FDD)
(To digital)
(To analog)
+9V ~ +12 V
LC Filter
CPU
HD6433042SB51F
LSI9
PA 7
NMI
PW/SW
APO
NMI
PW/ON
APO