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D. +5v Supply
The components that supply the +5v are as follows: D1 - D4 i.e. 4x 1N 5402, TR2 TIP 3055, (TR3 when
fitted, TIP 3655) ICI, MC 1723, VR2, 1K 0.5W, R2 100R, R4 100R, R5 100R, R11 1K81%, R12 2K2,
R13 2K2, R15 6K8, R24 1R, R26 5K6 C13 100n. (C9 remote 2,200mF 16v).
The +5v supply consists of basically a push pull type rectifier, a remote smoothing capacitor C13
22000mf 16v, a series pass transistor, TR1 and a current source resistor.
The overall closed loop voltage and current control is achieved using a MC 1723 IC2. which is a variable
voltage regulator .
The supplies output characteristic is a constant voltage curve up to 115% set load current, folding back to
50% under short circuit conditions.
E.
+5v Under Voltage Circuit
There is an under voltage circuit built into the 5v supply whose components are IC3 LM311P ZD2 5V6
ZD3 5V6 VR3 1K C6 - C7 47MF 25V, R6 220R, R7 - R9 1K, R18 - R19 47K, R25 1M 5%.
The under voltage circuit uses an LM 311 (IC3) which is a fast comparitor which monitors the 5 volt
unregulated supply. If the 5v unregulated supply falls below a certain limit the LM 311 (C3) will inhibit
the MC 1723 (IC1), which is a voltage regulator before the +5 volt falls below bottom limit. The +5v
under voltage circuitry is self resetting.
F. +5v Over Voltage
As the 5v supplies the voltage for the logic circuitry on the main MPS 2 board, it is imperative that the 5v
stays within very accurate tolerances, which is why there is need tor a 5v under and over voltage circuitry.
The +5v overvoltage circuitry consists of TH1 C106Y1 , ZD1 6V2 R147R C5100 mf 10v and the crowbar
fuse cartridge F7 2A.
The over voltage circuit functions as a single shot crowbar circuit i.e. if the output ot the 5v line exceeds
6.2v, the 6v2 zener diode ZD1 will conduct so causing the thyrister C106Y1 TH1 to be activated, which
will then either put the regulator into current limit or blow a fuse in the 5v Iline F7 2A.
G. + 12v Supply
The components used to create the + 12v supply in the power supply are as follows:
D9 INS 5402 D10 - D12 IN 5402, IC2 MC1723, TR1 TIP 3055, R3 100R 5%, R16 6K8, R17 4K7 R23
25R, VR1 1K 20%, C12 100m 35v and C10 remote 1000mf 25v.
The + 12v supply is made up a push pull type rectifier, a remote smoothing capacitor C14, a series pass
transister TR2 TIP 3055 and a current series resistor. The overall closed loop voltage and current control
is achieved using a MC 1723 (IC2), which is a variable voltage regulator.
The only difference between the generation ot the 5v supply and the 12v supply is that the 12v supply has
a constant current and constant voltage characteristic.
H. -12v Supply
The components which make up the -12v supply are as follows D13 - D14 1N4002 IC4 LM 7912 C8 47uf
C11 470 mf 25v R10 1K.
The -12v supply comprises of a push pull type rectifier, smoothing capacitor C11 470mf 25v and a MC
7912 CT which is a monolithic voltage regulator, which is placed under resistive capacitive load.
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