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5.
Principle of Operation
5.1.
General
An explanation of the circuits in the AC Source is given in this section. Refer to Figure 5-1
for a block diagram of the system.
AC
Power Factor
Input
Corrector (PFC)
5.2.
Overall Description
The AC input is fed to the power factor correction, boost type converter. The converter steps
the voltage to 385 VDC while drawing near sinusoidal current from the input power line.
The DC to DC converter provides isolation and changes the voltage to 250 VDC or 400 VDC
depending on whether the low output range or high output range is selected.
The DC to AC converter develops an AC sine wave voltage at the output frequency and
amplitude programmed by the oscillator.
The oscillator board provides the reference signal to the DC to AC converter and has the
front panel shuttles and switches to control and view the setting of voltage, frequency and
current limit.
5.3.
Power Factor Correction Module (PFC)
The PFC consists of the boost converter circuitry. The boost converter is PWM controlled by
a single chip that adjusts the pulse width during the cycle so that near sine wave current is
drawn from the supply. An auxiliary winding on the boost inductor provides "bootstrap" power
to the logic circuits and is self sustaining.
RP Series
DC - DC
Converter
Figure 5-1: AC Source block diagram
March 2011
DC - AC
AC
Converter
Output
Oscillator &
Controls
19
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