Circuit Function Description; Circuit Description - Ceronix 1493 Service Manual

The basic function of the ISO XFR-75W and ISO XFR-100W is to
isolate the line power for monitors requiring an isolation transformer.
The transformer is designed to have a low leakage flux value which
allows it to be mounted close to the CRT. To accomplish the low
leakage flux, the transformer has two sets of primary and secondary
coils mounted on a modified toroid type core. The ideal transformer
would be a toroid but this type transformer is expensive because it is
difficult to wind.
A relay is used to connect the two primary coils in series or parallel to
accommodate 240VAC or 120VAC line voltages. Before power is
applied, the relay connects the transformer primary windings in series to
avoid excessive primary current for the 240VAC case. The control
circuit energizes the relay when the line voltage is 120VAC.
240VAC
or
120VAC
50 or 60 Hz
Input
The fuse
T506
506
The power transformer has two internal 2 amp temperature sensitive fuses.
Each primary half has one, built in, series connected fuse.
A resettable fuse
This fuse protects the relay control circuit from square wave input which would
occur if an inverter is used as the power source. Capacitor
current from the line to capacitor
control, power supply. Diode
going part of the line wave. Transient Voltage Suppressor
24V power supply and protects the relay coil from over heating.
The Mos Fet
voltage is 240VAC.
The input line voltage, at which the Mos Fet turns on, is set by the Mos Fet turn
on voltage (about 4V), the voltage drops across resistors
the zener diode
relay switches. Capacitor
T518
518
on for the complete AC cycle to eliminate ripple current in the capacitor
Resistor
T504
504
due to line transients. The zener diode
Fet source to gate protects the Mos Fet gate against over voltage. Resistor
is needed to limit the mains current when the relay arcs across both sets of
T519
519
contacts. Capacitors
may be generated when switching.
116

Circuit Function Description.

240VAC
or
120VAC
Relay Control

Circuit Description.

protects the mains wires and the control PCB.
is connected to the relay driver power supply.
T507
507
T513
513
T511
511
shorts out the 24 volt power supply when the input line
T514
514
. 154VAC is the approximate line voltage at which the
T503
503
T508
508
limits the peak current to capacitor
and
T517 T520
517 520
through diode
T510
510
charges capacitor
T512
512
and diode keep the Mos Fet turned
T502
502
to avoid relay switching
T508
508
which is connected from the Mos
T515
515
reduce the relay
T518
T518
Output
supplies
T512
512
which forms the, relay
during the negative
regulates the
516
T516
, , , and
T509 T505 T504
509 505 504
.
T513
513
contact noise which