Power Supply - Tait TM8100 mobiles Service Manual

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Data Communication

Power Supply

TMAA01-01 Line-Interface Board

The comparators (in U1) operate off a single sided regulated 5V supply.

U1 pins 2,4 and 5 provide receiver gate delay. Once the busy signal is not

active, C4 charges through R12 and causes U4 to go low. Once charging

exceeds the voltage at U1 pin5. This also locks out the keying state until this

delay has occurred (U6 pin 5).

The Line Interface circuitry is designed to provide RS-232 and RS-422 data

communication. RS-232 is provided by U9, but if RS-422 is required, U9

is removed and replaced by U2 and U10. Also resistors R15,16,43 and 47

need to be fitted.

The power supply for the line-interface board comes from the radio via

the internal options connector and is a 13.8 V switched supply. Digital

logic components are used in the line-interface board so there is a 5 V

regulator provided.

Initially the 13.8V from the radio is filtered and used for the audio line

driver (U5) with reference to analogue ground. This 13.8V is also used to

supply the 5V regulator, which is filtered separately for either 5V digital or

analogue devices. A simple voltage divider is used to provide a 2.5V half-rail

for the digital and a 2.2V rail for the analogue sections.

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