68805-M
ARC LAMP POWER SUPPLY
13
The reference voltage from the power module enters the meter board at J1 pin 1. It is then
connected to the front panel mounted adjustment potentiometer, R201, whose wiper is
connected to J3 pin 2. This variable voltage exits the meter board via J1 pin 2, and is then
reconnected to the power module. As the wiper voltage changes from 0–5 volts, the output
of the module changes.
J4 serves as the interface to the meter, the meter select switch, and the preadjust switch. See
schematic number 68805–3–1001.
J2 serves as the interface to the rear panel mounted remote socket to provide the signal
levels, or accept the external signal level for remote monitoring and control of the power
supply. The nomenclature for the pins is given on page 10.
The four, top mounted trimmer potentiometers are used only to calibrate the meter. They
have no interaction with the power module. Their function is as follows:
R6
Current display trimmer
R12
Power display trimmer
R13
Voltage display trimmer
R16
Preadjust display trimmer
See schematic number 68805-3-1211 for their location.
Ignitor Drive (68810-3-1601)
Please refer to schematic number 68810-3-1601 for this circuitry.
Ignitor Drive and Output Monitor Circuit
The ignitor drive PCB contains circuitry to generate the 25kHz square wave required by the
ignitor. It is a self oscillating inverter which starts when relay K401 energizes at an open circuit
voltage of 95 volts or more. Relay contact K401-1 is closed and the start switch is pressed
to apply 24 VAC to rectifier CR401. The filtered output is used by R402 to slightly bias Q401
into conduction.
Q401 goes into conduction more and more until T401 saturates.
At saturation, Q401's
collector current increases at the limit set by the beta of the transistor and input voltage. This
limits collector current to one ampere. Since di/dt is removed from T401, Q401 shuts off due
to lack of base drive.
The flyback voltage is of the correct polarity to bias Q402 into
conduction, and the action repeats but of opposite polarity. The result will be a two to one
unregulated step up on T401's secondary. This is nominally a 100V P-P square wave @
30kHz. This square wave is connected to the ignitor via J305 on the rear panel.
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