Instruction manual

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5.9. MOTHER BOARD
The mother board, A6, has no active circuits. This board connects signals between the oscillator
assembly, current limit assembly, the three power amplifiers, current transformer assembly, GPIB
and system interface connectors, and the isolated three phase AC power.
5.10. POWER AMPLIFIERS
The AC power system has three power amplifiers, A3, A4, and A5. In the three phase mode, one
amplifier is used for each of the three outputs. In the single phase mode, the three outputs are paral-
leled by the user at the output terminal block, TB3.
Each amplifier obtains its input signal from the current limit board. A signal of 5 vrms drives the
output to full scale. The amplifier generates 0-135 VAC at 44 amps at any frequency from 45 Hz to
120z. To achieve high efficiency operation, the power amplifiers operate in class D mode (pulse
width modulation at 75 kHz).
A power amplifier consists of 5 printed circuit assemblies, plugged together, mounted to a heat sink
in a steel case. LED's on each board indicate operational status of each board. See exploded layout,
Figure 5-3.
5.11. INPUT/OUTPUT BOARD
The +300 volt supply is connected to J9-3 and J9-4 of the input/output board. The DC supply is
filtered by large electrolytic capacitors that also provide storage and approximately 10 ms holdup
time. There are outputs of the conditioned 300 VDC to both the front and rear amplifiers and a
third output via a 2 amp fuse to the auxiliary switching power supply.
A green LED on this board is lit if DC above 50 volts (approximate) is present.
This assembly also includes part of the AC output filtering. The AC output is available on J9-1 and
J9-2.