GE Brivo OEC 715, Service Manual, Page: 110 / 551

Brivo OEC 715/785/865/865 Mobile C-Arm X-Ray Product Service Manual
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Pulses PWMA and PWMB are produced by SG3525, pulse width modulator control integrated circuits.
Installed on J5 or J6 by jumper, compatible old Monoblock (without blue mark) and new Monoblock (with
blue mark). If Monoblock is without blue mark please install the jumper on J5, If Monoblock is with blue mark
please install the jumper on J6.
The duty ratio is controlled by regulating circuit of MAC_FDB from MCB that is current setting by the
preheat table lookup and feedback filament current value that is provided by hall current sensor. The
FILDIS_FDB from MCB can shut down SG3525 outputs directly.
Filament select circuit
The filament selection is made by applying logic high or low to FCSSW_FDB, or the filament selection is by J7
position.If the FCSSW_FDB is logic high or switch of J7 on 'large' position, under these conditions, this turns
on Q7 and operates relay K1, the large filament is selected and LED HL3 will be lights. The filament drive
outputs FILLA1 and FILLA2 are connected to the large filament primary side. If the FCSSW_FDB is logic low
and switch of J7 on 'small' position, the FILSM1 and FILSM2 are connected to the small filament primary
side.The FCSSW_FDB line will be pulled low by a resistor R28 if the connection is broken.
Condition Filament
FCSSW_FDB logic J7 Position
Low small Small filament
Low large Large filament
High small Large filament
High large Large filament
Hall current detect
The FIL HALL are connected to source of Q3 and Q4. The return filament current passes through FILCOM to
24V_GND. If the filament current via the hall current sensor CSNE151 is 5A, the current through Pin.13 of
CSNE151 will be 25mA, which is a RMS value, the voltage on TP1 will be 2.5V. The analog signal goes through
RC filter composed of R10, C4 and R93, C41 to filament current regulator.
Filament current control
The FCSSW_FDB determines the scale factors of regulating circuit towards MAC_FDB when the filament is
selected. Proportional gain in large and small filament feedback loops can be adjusted by adjusting two
potentiometers, respectively.
Subtracting return filament current value LEMF from MAC_FDB through different scale operation circuit, the
result is sent to SG3525 to control duty ratio.
Normally, MAC_FDB is less than 5V, more than 3V. IF MAC_FDB is much more than 5V, filament current will
be maximized and SMAC will exceed 3.3V of input threshold of PWM comparator of SG3525, Duty cycle will
be maximized, FWMC_FDB will be send out to MCB until disposed.
Both of the delay circuit and the signal FILDIS_FDB from MCB are able to drive U3(2/4) on to pull SMAC to -
15V, and OC_ALM_S is able to drive U3(1/4) on to pull SMAC to -15V, SG3525 outputs will shut down.
L/S focus switch