TTI EX752M, Руководство по обслуживанию

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Again referring to channel A, the +15V is peak rectified by D40 and zener regulated by D42.
The +5V rail is rectified by D18, D19 and filtered by L4 and C23. The inductor L4 is held in
continuous conduction and thus the voltage at the input to the three terminal regulator IC2 is
maintained at low value.
The –5V rail is peak rectified by D13 and zener regulated by D20.
Mode Switching
The opto-isolators IC14 – IC16 and associated components which provide control signal isolation
between the two channel are described in the Control Board section.
Control Board
Component references are given for Channel A, the left-hand (slave) channel viewed from the
front; components of Channel B, the right-hand (master) channel, are all numbered from 100
upwards,e.g.RP3, C9 and R24 on Channel A are RP103, C109 and R124 on Channel B.
The linear regulator is in series with the positive output but, because of the way in which the
control and metering works, it is convenient to consider the regulator output (OP) as 0V and to
regard the negative output as the controlled output voltage (-V).
Supply rail and signal names on the schematics are followed by /A or /B for Channels A and B
respectively, e.g. OP/A.
Voltage Control
IC7C buffers the voltage control potentiometers VR1 and VR2; VR5 sets the maximum output
voltage. D6 provides the reference (V
REF
) which is nominally 2.45V.
IC7A is a differential amplifier with a voltage gain of 14.7; for an output voltage of 75V the voltage
at IC7C pin 8 will be 5.1V. VR9 trims differential gain to ensure good voltage regulation, see
Calibration section.
The output of IC7C drives the input of IC7A when the ON-OFF switch, SW1B, is in the ON
position. When SW1B is in the OFF position the input of IC7A is grounded via R50, setting the
output volts to zero.
The output of IC7A provides the gate drive (GATE) to the regulating MOSFET Q14 (Q15) on the
main pcb via D3.
Current Control
IC7D is the error amplifier which compares the voltage on the wiper of VR3, the current limit
control with the voltage generated across the current sense resistor R21. When the output current
reaches the set limit IC7D takes control via D4, changing the supply from constant voltage to
constant current mode. At the same time Q1 is turned on by IC7D, making ILIMIT go high; this is
read by the microcontroller IC3 which turns on the constant current lamp, LED2.
VR4 sets the maximum output current; VR8 adjusts the output current to be the same as the
preset current at low levels, see Calibration section.
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