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(2) During ON
@ The drain current at IC1 increases linearly. During this period, the gate voltage and current become constant
because of the saturation characteristics of the transformer.
(3) Shifting from ON to OFF
® This circuit applies a negative feedback signal from the 12V output. When the voltage across C208 reaches the
specified value, REG2 turns on and current flows to PQ8 @-@. This turns the secondary circuits on, sets IC1 pin
©® to "Hi', and turns IC1 off.
(4) During OFF
@ While IC1 is on, the following energy charges the primary windings of the transformer:
Energy = LI?/2. Here, L: Primary inductance
1: Current when IC1 is off
This energy discharges to the secondary windings during power off. That is, C208-C218
is charged according
to the turn ratio of each winding.
@ Atthe start, an overcurrent flows to IC1 because of the charged current at C208-C218.
@ The drain current at IC1 generates a voltage across R216. If it exceeds the IC1 base voltage, it sets the IC gate
voltage to "Hi".
@ R216 limits the gate voltage to prevent excessive collector current from flowing to IC1.
<Reference>
@ If the power circuit for P.W.B. seems to be faulty:
(1) Make sure that 5V and 12V on the control P.W.B., upper arm U, V and W, and the lower arm power voltage
are the specified values.
(2) When. only the 5V output is low:
REG 1 (regulator) faulty, 5V-OV shorted, output is too high, or REG 1 is abnormal.
(3) When 12V and 5V are abnormal:
The following defects can be considered:
@® Fan, operation, power, rush prevention relay (shorting in relay, etc.)
@ Microcomputer is abnormal.
@® REG 1 (regulator is abnormal), etc.
Shorting on primary circuits.
When shorting occurs in the secondary circuits, there is no abnormality in the primary circuits because of
overcurrent protection.
The voltage rises when an opening occurs in the primary circuits, or the feedback system is abnormal.
(4) When upper arm U, V or W phase, or lower arm power supply is abnormal:
D204, D208, D209, D210 or drive circuit is abnormal.
(5) When all voltages are abnormal:
IC1, R216, etc. are possibly abnormal.
* If1C1 is abnormal, be aware that other components, such as the power module, REG (regulator), etc. are
possibly defective.
[When the switching power supply seems to be abnormal, the voltage between IC1 pin @ (to be measured at the .
leads of R202 and R201) and IC1 pin © (to be measured at R216 lead) may be between 11 and 16 V. This is
because the protection circuit of IC1 is operating.]
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