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NOISE FILTER CIRCUIT
Alternating
input
current
(AC)
is
led
to
the
transformer (P.T) through a Fuse (F1) and the noise
filter composed of C1 and L1 on the M1 board. The
filter components work not only to prevent internally
generated noise from being fed back to AC line, but
also to attenuate the spike voltage for prevent of
effects to power supply circuit.
The Ring core wound by the Ground wire of AC cord
also works as a noise filter.
POWER TRANSFORMER
The power transformer transforms the local AC input
to the internal AC (around 20V) voltage.
IMPORTANT
The transformer can be used for both of the rated
input voltage AC 120V and AC 230V by switching the
input terminal of 2-pin and 3-pin.
When replacing the power transformer, it must be
replaced complete assembly unit.
RECTIFIER AND SMOOTHING CIRCUIT
The internal AC (around 20V) voltage from the power
transformer is bridge-rectified by the Diodes (D1~
D4) and smoothed by the Capacitor (C3).
The voltage after rectification is about 21.5 ~22.5
VDC for the rated input (VPP).
DC-DC CONVERTER CIRCUIT
Transistor Q1 is turned on by making the base voltage
at least 0.7 volts higher than the emitter voltage which
is coming from VPP through out a register R1.
Transistor Q1 is supplying a current to terminal 1 and
2 of inverter transformer (T1). This allows a greater
current to flow between
terminal
7 and
8, thus
transistor Q1 will be turned on.
At the same
time, the voltage occurred
between
terminal 9 and 6 of inverter transformer (T1). When
this voltage exceeded the regulation value of zener
diode ZD1, the current will be flow into the zener
diode.
(Zener diode prevent reflection of incoming voltage
waves from external connections)
As a result, transistor Q1 will be turned off.
Above ON-OFF cycle happens repeatedly.
VCC, VCM PRODUCING CIRCUIT
At the AC plugged in, a voltage is generated between
the 6 pin and 7 pin of the inverter transformer (T1).
Half-wave rectifying is done at the diode D7 and then
this positive voltage (9V) will be supplied to the 1 pin
of 1C7. The
regulated output voltage (6V DC)
is
generated from the 3 pin of the voltage regulator IC7.
This output voltage is supplied to VCM line through
the diode D10. Also it supplied to VCC line through
though the diode D11.
Mainly the Ni-Cd
battery is used to back up the
memory.
It takes
approximately
48 hours to full
charge it through the charge circuit D9, R7 and R6
supplied by the VCM.
At the time of AC power off, the battery begins to
supply the dis-charge voltage to the VCM line through
R6, R7 and D9.
The dis-charge current is under 10 uA, and the full
charged battery will be able to back up the memory
minimum 1,000 hours.
Producing
Circuit
vcc
vCM
305
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