Table of Contents
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MZ3500
9. POWER CIRCUIT DESCRIPTION
1. BLOCK DIAGRAM
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RectIfy/smoother
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lIne
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Transformer
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Rectlfv/smoo ther
4
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CirCUIt
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Control P'OII"C\
CirCUIt
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OSCIllator
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Alarm c,fcull
-12V d,oppef
CirCUIt
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Alarm
-12V
outPut
(Ala.m)
(Block diagram)
A. +5V and +12V supplies
1. Functions
a. Supply voltage is first rectified in the rectifier circuit
and sent out to the switching regulator via the over·
current detector provided in the overcurrent protect
circuit.
b. Next, the voltage is converted to the +5/+12V output
in the switching regulator and sent out to the noise
\filter.
l..
Change in the switching regulator output voltage is
sensed by the control circuit and is fed back to the
switching regulator after being amplified in the amplifier
located in the control circuit, for maintaining the output
voltage to a constant level.
d. The signal from the oscillator is supplied to the switch·
ing regulator through the control circuit for driving the
switching regulator.
e. For prevention of overcurrent, the protect circuit is used
for stopping the oscillator when an overcurrent is met,
and it makes the switching regulator to halt in order to
shut off +12V/+5V supply.
2. Description of each block
a. Overcurrent protect (control/protect) circuit
When an overcurrent is met in the +5V/+12V circuit, it
causes to increase the voltage at both ends of the over·
current detector resistor R1, which in turn causes to
increase the 03 collector current, for, there arises larger
voltage difference between the emitter and base of the
- 07-
transistor 03. This makes the gate voltage of the thyns·
tor increased owing to activation of SR. WitL Jctlvation
of SR it makes the oscillator voltage dropped to the
GND level at the point "a" to stop oscillation, which
also makes the switching regulator stopped by the de·
activation of the transistor 05 oscillation. This causes
the transistor 05 inactive, and it shug off the +5V /
+12V supply.
b. Oscillation circuit
As the 01 emitter voltage is at almost GND level
wile'
the transistor 01 is active, the 02 base voltage tem-
porarily drops close to the GND level by means of C6,
which in turn makes 02 inactive and the 02 emitte.
voltage increases.
Then, the 02 base voltage comes to rise as C6 begins to
be charged through R6, and the transistor 02 starts to
activate again. With activation of the transistur 02, the
Q2 emitter voltage starts to drop and the 01 base
voltage is temporarily dropped by means of C5, to shut
off the transistor 01, which causes to increase the
transistor 01 emitter Voltage.
Next, as C5 is charged by R5, it makes the 01 base
voltage increased which puts the transistor 01 Iflto
activation. In this manner, transistors
Q1 'Olfld
Q2 3re
alternately turned on and off to keep oscillating.
C5 and C6 are charged through R5 and R6 by on/off
action of the 01 and 02, and discharged through 01 and
02.
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