Service manual

FO-4700U
FO-47UC
5 – 21
4. Inverter circuit
In the RCC system, FET, which is connected to a converter transformer
in series, performs an ON/OFF switching operation and the energy stored
in the transformer upon ON is supplied to the secondary side upon OFF.
That is, the DC voltage in the rectification smoothing circuit is converted
into the switching pulse by a switching operation of Q10 controlled through
a signal from a control circuit and the high frequency power is supplied
to the secondary side through T1.
Fig. 10
T1
Q10
5. Secondary rectification and smoothing circuit
Voltage of high frequency pulse generated by an inverted circuit is de-
creased by a converter transformer, the pulse is rectified by a high fre-
quency diode D3 and is smoothed into +5V by C17, +24V circuit also
performs the same operation.
Fig. 11
C17
D3
AB
5V
Across A-C
Across B-C
C
7. Over-current prevention circuit
Any over-current of FET is detected and a signal is sent to a control
circuit to drop the secondary output.
CONTROL
CIRCUIT
R18
VR1
R16
IC1
PC1
Fig. 13
8. Output detection circuit
R18, VR1 and R16 detect any 5V-system output voltage. The detected
voltage is compared with the reference voltage in IC1. Varying controls
the output voltage the cathode current of IC1, i.e., the current of light
emitter of PC1, based on such comparison and by sending a signal to
the primary control.
Fig. 14
6. Control circuit
This circuit performs the RCC method through the primary control sys-
tem, which uses the power MOS. FET as switching element. Therefore,
an output detection circuit detects the secondary output voltage and a
detection signal is sent to a control circuit to stabilize an output voltage
through a photo-coupler (PC1).
CONTROL
CIRCUIT
OUTPUT
DETECTION
CIRCUIT
Fig. 12
[6] Circuit description of RS232C I/F PWB
(Option : FO-47IF)
Since the PWB uses RS232C as the interface with PC, the voltage of
the signal from PC to the control PWB is converted to +5V level and the
voltage of the signal from the control PWB to PC is converted to +12V
level with IC1 (ADM207) on the PWB.