Lh20/1:6 Power Supply; Lh20/1:7 Regulator And Current Shunt Amplifier - ESAB LHF 405 PIPEWELD Service Manual

LH20/1:6 Power supply
Power supply is placed on LH20/1 board and consists of positive and negative
voltage sources.
Positive power supply.
+24V supplies thyristor control circuitry;
+15V supplies pulse circuitry on LH20/1 board and supplies function board LH10/2;
+14,5V supplies regulator and current shunt amplifier.
Negative power supply.
--15V supplies operational amplifiers on LH10/2 board;
--14,5V supplies regulator and current shunt amplifier.
LH20/1:7 Regulator and current shunt amplifier
The feedback signal from the current shunt is amplified by the rate of 50 in the
differential amplifier made of the A1 operational amplifier and resistors R12, R13,
R10, R11. Then, through the resistor R14, signal is given to the PI regulator made
of the operational amplifier A2, R17, C7, C8 and voltage limiting diode V13.
The current setting signal is given to the regulator summing point (inverting input of
the A2 OA), via potentiometer R6 and resistor R5 . The power supply may be
disabled by the setting positive voltage through the resistor R15 and thus achieving
the regulator output voltage that blocks thyristors firing circuit.
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Edition 071024