Power Supply & Regulator Circuits - Tait T880 II Series Adjustment Manual

C2.10 T881 Circuit Operation
2.6 Power Supply & Regulator Circuits
(Refer to the regulators circuit diagram (sheet 6) in Section 6.2.)
Tx Enable
13.8V Nom.
From Rear
D-Range
Crowbar
Diode
13.8V
Nom.
The T881 is designed to operate from a 10.8-16V DC supply (13.8V nominal). A 5.3V
regulator (IC630) runs directly from the 13.8V rail, driving much of the synthesiser cir-
cuitry. It is also used as the reference for a DC amplifier (IC640, Q630, Q620) which pro-
vides a medium current capability 9V supply. The T881 has a regulator (IC370) which
produces 9V for use in the exciter and audio circuits.
A switching power supply (Q660, Q670) runs from the 9V supply and provides a low
current capability +20V supply. This is used to drive the synthesiser loop filter (IC750),
giving a VCO control voltage range of up to 20V.
Ultimate control of the transmitter is via the Tx-Reg. supply, switched from 9V by Q610.
This is enabled via the Tx-Enable signal from the audio processor, and microprocessor.
A crowbar diode is fitted for protection against connection to a power supply of incor-
rect polarity. It also provides transient overvoltage protection.
Note: A fuse must be fitted in the power supply line for the diode to provide effec-
tive protection.
10/07/00
Buffer
Micro-
controller
DC
Amp
5V
Reg
5V 9V
Figure 2.6 T881 Power Supply & Regulators Block Diagram
+9V
Power
Tx Reg.
Switch
5V Dig
Switching
Reg
PS
20V 5V Dig
M880-00
Watchdog
µP
Timer
µP
LVI
Reset
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