Advertisement
7
Control amplifier
The control amplifier sets a suitable welding current in relation to the current setting
and arc voltage. The circuit can be divided up into three main parts:
Average current control
S
Starting current control
S
Short- - circuit current limit
S
8
Pulse Width Modulator
The pulse width modulator determines the frequency and pulse time of the control
pulses to the MOSFET transistors.
Pulse frequency is adjusted to 36.5 kHz 0.5 kHz.
Maximum pulse time is 41%
maximum current and arc voltage. When no pulses are supplied by the pulse width
modulator, no welding current will flow.
IC3 controls the pulse frequency, pulse time and blocking of pulses. The reference
voltage from IC3 is +5.1 V on circuit board 0486 886 880.
On circuit boards 0481 870 880 and 0481 870 885 the voltage is +2.5 V.
Transistor Q5 controls the primary winding of the pulse transformer.
The frequency and pulse time are very important parameters. If incorrectly ad-
justed, they can result in transistor failure in the main circuit.
cmha2de1
±
1.5% of the cycle time. Maximum pulse time results in
NOTE:
- - 17 - -
Advertisement
