68805-M
ARC LAMP POWER SUPPLY
12
SPECIFIC DESCRIPTIONS
Power Module (27–20–007)
This module is not meant to be field serviceable, therefore only a general theory of operation is
provided.
The module is easily replaced in the field, and should be treated as a replaceable
component. Please contact your representative if any problems arise.
This module is an off–line two transistor forward converter operating at a frequency of 40kHz.
The switching stage operates in current mode for increased reliability and for improved line
voltage regulation. The input stage is connected directly to the AC mains, and line voltage
selection is done by S301. This is then rectified and filtered to provide the bulk, unregulated
DC voltage for the switching stage. An on board, low current transformer steps down, and line
isolates the control circuit’s power source. An advanced secondary side filter network, and
feedback loop serve to maintain a constant DC output current with excellent regulation and
control.
Meter Board (68805–1210)
Please refer to schematic number 68805–3–1211 for this circuitry.
J1 pins 7 and 9 provide the AC for this circuit. This is rectified and filtered by CR1, C1 and
C3. The raw DC is applied to VR1 and VR2 which then supply the reg/- 15 volts for
the supervisory circuits.
The output current signal enters the board via J1 pin 6 where it is then amplified by a two
stage operational amplifier (U1). The nominal voltage gain is 85. The output of the second
stage is present at one of the inputs to U2, and is also scaled by R5 and R6 to provide the
current for the meter.
The output voltage signal enters the board via J1 pin 10. A resistive voltage divider consisting
of R8 and R11 scale this to a 0–10 volt level which is then present at the other input to U2.
Scaling for the meter is done by the R9, R13 combination.
The power reading is derived by analog multiplier U2. This integrated circuit multiplies the
proportional input representation of output current and voltage at pins 1 and 3. The output
from U2 at pin 7 is then scaled for the meter to display power.
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