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7
2. POWER SUPPLY CIRCUIT
2-1. Discriminating Power Supplies
This unit can be operated on the following two types of the power supply.
• AC adapter (Output 3.0 [V] type)
• Size AAA, alkaline dry cell battery x 2
The system controller IC722 identifies which of either AC adapter or battery is used as the main power, by monitoring the input voltages of pin-150 [XDCIN] and pin-173 [BATT].
The system controller IC722 identifies that this unit is operated on the battery when pin-150 [XDCIN] is “H” and that this unit is operated on the AC adapter when pin-150
[XDCIN] is “L”. When this unit is operated on the AC adapter, the battery's remaining amount indication is not displayed on the LCD. When the input voltage at pin-173 [BATT]
has decreased to about 1.5 [V] or less (i.e., voltage from the battery has decreased to about 2.0 [V]), the system controller IC722 displays the message “LOW BATT” on the
LCD and stops the operation of this unit. This unit does not have the over-voltage protection circuit.
2
3
1
173
150
D2
C2
T1
D1
C3
R6
IN
GND
OUT
IC1
VOLTAGE
DETECTOR
VOLTAGE
DETECTOR
When operating on battery: H
When operating on AC adapter: L
When operating on AC adapter: L
Q1
C9
R2
R1
BATT
XDCIN
UN REG 2.5[V]
IC722 SYSTEM
CONTROLLER
Fig. 2-1 Discrimination of power supply
Table 2-1 shows the discrimination of the power supplies. Table 2-2 shows the relationship between the battery output voltage and the LCD display of the remaining amount of
battery.
Table 2-1 Discrimination of Power Supplies Table 2-2 Battery voltage and LCD display
Pin-150 [XDCIN]
LCD display of the
remaining amount of battery
When operating on AC adapter
L No
When operating on alkaline dry cell battery
H Yes
If the power supply from the AC adapter to the unit is stopped due to some reasons while the unit
is operating on an AC adapter, and if a battery having the sufficient capacity of charge is inserted
in the unit, operation of the unit is continued because the negative polarity of the battery is
connected to ground through the diode D2. When the AC adapter resumes to supply the power
voltage from this status, operation of the unit is continued.
is operating on an AC adapter, and if a battery having the sufficient capacity of charge is inserted
in the unit, operation of the unit is continued because the negative polarity of the battery is
connected to ground through the diode D2. When the AC adapter resumes to supply the power
voltage from this status, operation of the unit is continued.
Display
Battery voltage
Pin-173 [IC722]
About 2.6 [V] or more
About 1.95 [V] or more
About 2.3 to 2.6 [V]
About 1.73 to 1.94 [V]
About 2.2 to 2.3 [V]
About 1.65 to 1.72 [V]
About 2.1 to 2.2 [V]
About 1.58 to 1.64 [V]
Contents
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