Barco GRAPHICS 1209S, Руководство по обслуживанию

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Date : 10/02/98 7621065
SM POWER StBy 7621065
15
SUB MODULE 762106S
ground level. This means now for this transistor an OFF state.
The zener Z100 on the motherboard can now i11 volts at the gate of the
thyristor allowing the charge of the capacitor C102.
The speed of the fans is regulated by means of a sensor (NTC resistor) mounted
close to the heatsink of the SMPS board.
IC2 is an integrated circuit regulating the speed of the fans by adapting the duty
cycle of the output drive for the power transistor Q4. L1 and C7 filters the output
voltage.
The feedback is applied to pin 5 which is protected against arcing with D4/D5.
MC34063 is a switching regulator. An oscillator trimmed with C6 is applied together
with a dc voltage to an RS-flipflop via an AND gate. That DC voltage now is the result
of a comparator output receiving an internal reference voltage of 1.25 volts and the
feedback voltage at pin 5 (comp). Consequently, the duty cycle depends on the DC
voltage that is built up as follows :
- it is determined by the output voltage via R13 / R14 / R11 in order to stabilize the
latter for a well-determined value of the NTC resistor.
- it is equally influenced by any change of the NTC resistor itself, sensing the
heatsink of the SMPS board.
The minimum voltage is set by Z5 at approximately 7.5 volts and the maximum
speed by Z4 + Z4. at 15 volts.
The maximum current output is limited by R10, and an RC feedback straight from
the output to pin 5 provides a more regular speed at any time.
Technical description
The EHT generator is supplied directly from the rectified mains voltage. The
+300M volts is leaving the board at the contacts 31/32 of the J8A connector for
the EHT board (see description of that board)
By above measure, we eliminate the influence of the EHT load on the perform-
ance of the power supply, and the maximum peak current of the EHT generator
is increased.
Power supply for the EHT
generator.
DC Fan control of the fans.