Kenwood TH-28A Service Manual page 9

TH-28A/E
CIRCUIT DESCRIPTION
» Reset and backup circuits
5V AVRUF)
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GND
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TIMING CHART
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LITHIUM
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B POWER
B POWER
BATTERY
VDD
ON
OFF
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RESET
5V
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5V LINE
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Fig. 11 Reset and backup circuits
° Battery voltage detector circuit
The supply voltage is divided and input to the analog
port of the microprosessor. The voltage input to the
microprocessor is digitized to drive the LCD battery
display.
+ Lamp circuit
» Lithium battery charging circuit
™7HS constant current circuit consisting of O1 and D3 ~
is switched using the output signal at the shift register
1C4 LAMP. The LED is then turned on or off.
LCD
B
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B b-COM DY LAMP}
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une | LAMP ON:
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Fig. 12 Battery voltage detector and lamp circuits
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B
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BV AVR (IF) D5
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