Cebora POWER ROD 1535 Manual De Servicio página 12

− the rectifier bridge of the T3 power transformer
secondary current;
− the main microprocessor for the power source control
G
functions.
B
The input rectifier bridge PD1 is equipped with a DC-
capacitors pre-charge circuit, made up of the ptc, PT1 and
relay RL1, controlled by control circuit on power board
(13).
The boost converter, connected downstream the input
rectifier, contributes to optimize the "Power Factor" and
to reduce the harmonic distortion of the current absorbed
from the line.
Thanks to its use the power source can be powered with
a wide range of input voltage and the inverter always
operates with the same value of DC voltage, stabilized
by the boost converter, irrespective of the mains voltage
value.
Connected directly to the DC-capacitors, a flyback con-
verter, present on power board (13), generates the supply
voltages for all power source circuits.
These voltages are measurable on the connectors J2 and
J4, on power board (13), as indicated in Fig. 2.3.2.
THE CIRCUITS OF THE FLYBACK PRIMARY
SIDE (SEE J2) ARE DIRECTLY CONNECTED TO
THE MAINS POTENTIAL AND THEREFORE
The flyback converter starts running automatically when
the voltage on the DC-capacitors becomes higher than 100
Vdc approximately.
12
WARNING
DANGEROUS.
Fig. 2.3.1
In case of flyback circuit failure, for example due to
a fault, the DC-capacitors discharge time can become
much longer (several minutes).
In this case, before working on the power board (13)
wait until the DC-capacitors voltage, measured on
DC-capacitors terminal on soldering side of power
board (13), falls to a safe level (<40 Vdc).
The inverter is made up of 2 igbt connected in "Forward"
configuration, driven by the driver circuits located in
proximity of the igbt and directly controlled by the control
circuit of power board (13). In reality each igbt is made up
of 4 igbt parallel connected between them.
The task of the inverter is to generate the square-wave
alternating voltage for the T3 power transformer. The
welding current is adjusted by modulating this voltage
appropriately.
On the power board (13) is installed a TA, TA1, inserted
in the T3 power transformer primary circuit, that provides
the current feedback signal, used to regulate the welding
current.
This signal does not normally affect the welding current
adjustment.
The T3 power transformer secondary circuit is connected
to the secondary diodes group, present on power board
(13), which rectifies the alternating current generated by
the inverter, making it available at the power source out-
put.
The secondary diodes group is made up of 6 diodes
connected to a shared cathode on L3 inductor terminal,
used for welding current levelling, and provides, on this
terminal, a positive output voltage with respect to the T3
power transformer terminal connected to J16 on power
board (13). In reality these diodes are enclosed in modules
with two diodes each.
WARNING
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