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3-1. Outline
The YS-W270 has four camera connection terminals and
sends a power supply and sync signal to the camera by
connecting one coaxial cable from the BNC connector on
the rear panel of each channel to a camera. Moreover, the
YS-W270 can output the video signal (from the camera)
from the BNC connector on the rear panel to a monitor.
The sound around the camera can also be heard by
connecting a microphone built-in camera.
3-2. AC-214 Board
This power supply is a switching regulator based on a
PWM (pulse width modulation) flayback system. +31
VDC is produced from the commercial power supply, and
+9 V and +5 V are produced from +12.0 V using a three-
terminal regulator.
1. Line filter block
The line filter consists of a two-stage common mode choke
coil so as to take measures for power disturbance. The DC
resistance of this choke coil also serves as a rush current
limiting resistor.
2. Rectifier circuit on primary winding
After AC is full-wave rectified by D1, it is smoothed by
C7 and C8. Moreover, a rush current is limited by the DC
resistance of L3. The improvement in a power factor and
the suppression of a harmonic current are also performed
by inductance.
YS-W270/W270P (E)
Section 3
Circuit Description
3. High-voltage switching block
A high-voltage pulse amplitude is obtained when the
voltage applied to the No. 1 to No. 3 windings (main
winding on the primary winding) of T1 is turned on and off
between the drain and source of a semiconductor switch
(IC1). IC1 controls the pulse width modulation when the
voltage induced to the No. 5 and No. 6 windings (auxiliary
winding on the primary winding) of T1 controlled by PH1
is applied to the control terminal of IC1. Since IC1 has an
internal overcurrent protection circuit, the internal
protection circuit of IC1 is activated during overload and
the output is drooped to a constant voltage. D4, R4, and
C9 are a snubber circuit. This snubber circuit is a
destructive prevention circuit using the high-voltage surge
noise of IC1. A high-voltage surge noise is generated due
to the leakage inductance of a transformer as soon as IC1 is
turned off. The noise is added to a high-voltage pulse and
then output. Since IC1 is destroyed when the voltage
exceeds the withstand voltage of IC1, the high-voltage
surge noise is buffered using a snubber circuit consisting of
D4, R4, and C9.
4. + + + + + 31 V output
After the voltage induced to the No. 11 and No. 12
windings (secondary winding) of T1 is rectified by D8, it is
smoothed by C15, C16, and C17 to produce a voltage of
+31 V.
R9 and C14 are a snubber circuit. This snubber circuit is a
buffer circuit that suppresses the surge noise generated in
D8. Since the surge noise generated when D8 is turned on
and off is output, it is buffered using a snubber circuit
consisting of R9 and C14.
5. + + + + + 9 V and + + + + + 5 V outputs
After the voltage induced to the No. 7 and No. 8 windings
(secondary winding) of T1 is rectified by D10, it is
smoothed by C23 to produce a voltage of +12 V. A
voltage of +9 V is produced from the +12 voltage by IC2
(three-terminal regulator). Moreover, a voltage of +5 V is
produced from the +9 V voltage by IC3 (three-terminal
regulator).
6. Voltage fluctuation detection block on
secondary winding
This block monitors an output voltage of +31 V on the
secondary winding to improve the precision of an output
voltage and feeds the cathode current of IC4 (shunt
regulator) back to the primary winding via PH1.
3-1
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