ESAB Caddy Tig 1500i TA34, Service Manual

Page: 21 / 50

DESCRIPTION OF OPERATION
0740 800 186 - 21 - © ESAB AB 2016
15AP1 Power board
WARNING!
Dangerous voltage - mains
voltage.
Never make any measurements
on this board when the machine
is connected to the mains supply.
CAUTION!
There are different versions of the
power board available. See the
spare parts list to find the correct
spare part for the machine.
The power module is a single forward
converter, operating at a switching frequency
of 65 kHz. The switch transistors are built into
a semiconductor module, PM1. See chapter
"Service Instructions" for measurement
instructions.
If the power board has failed, a replacement
board must be mounted in accordance with
the instructions in chapter "Service
Instructions".
The power board carries the mains rectifier,
the charging circuit, the PFC circuit, the gate
circuits and the switching circuits.
The mains rectifier, the switching transistors
and parts of the charge and PFC circuits are
integrated in a semiconductor module, PM1,
which is part of the power board.
Charging circuit
When the mains power supply is turned on, the rectified mains voltage charges smoothing
capacitor 15C1 via resistor R31. Thyristor TY1 short-circuits charge resistor R31 when the
machine is loaded. If TY1 did not conduct, resistor R31 would burn out when the unit is on
load.
Power factor corrector (PFC)
The aim with the power factor corrector is to keep the mains current sinusoidal and in phase
with the mains voltage. The PFC circuit holds the intermediate voltage at 365 V. At mains
currents above 26 A the PFC does not work, the intermediate voltage is then 325 V or less.
When the PFC is working properly the voltage across capacitor 15C1 is 365 V.