Chapter III – Subassemblies
3-67
C
996-0255 rev. b
3. Principle of Operation
The capacitor banks have a current source power supply for simmer
operation. The current source power supply consists of logic to monitor
simmer operation, a conventional switching power supply to produce
the current for simmer operation (see pages 3-74 & 75) and an under
voltage detector for the +24V and the unregulated -600V. Q5 will be
biased off if the +24V is low and Q6 will be biased on if the -600 V under
regulator is low. U2 monitors the simmer current when simmer current is
low. Output of U2 pin 1 goes low when the simmer current is correct. The
current source power supply consists of a PWM 3524 Pulse Width
Monitor (U3), switching transistors Q3 and Q4. The sense resistors R6-
R10 monitors the current for the U3 which controls the duty cycle as a
function of load requirement.
The schematics of the circuit are shown on following pages. Three inputs
are required by the capacitor banks:
1) The power unit provides the current to charge the capaci-
tors to a high voltage of <-2000 volts.
2) Single phase 205-255 volt power is used for the current
source supply to simmer the lamps.
3) The 24 volts is used both for controlling the security loop
and to carry the trigger order from the power unit to the
capacitor bank.
Security Loop
1) The 24 volts provides power to activate relay K1 (page 3-
78) as part of the security loop. Interruption of the security
loop is accomplished by breaking the common line that
goes through the power head. When the common line is
interrupted, 24 V is removed from the HV relay and the
high voltage capacitors are discharged through the resis-
tor bank and K1 (located on the HV input PCBA).
2) Relay K1 connects the high voltage from the power unit to
the capacitor bank. The relay ground circuit is completed
by connecting the head cable to its laser bench connector.
The capacitor cannot be charged if the head cable is not
connected. Turning off relay K1 causes the capacitor to be
discharged through a resistor bank R1-R4.
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