During On; Shifting From On To Off; During Off - Hitachi RAF-50FX8 Service Manual

(2) During On

The drain current at IC901 increases linearly. During this period, the gate voltage and current become constant
because of the saturation characterstics of the transformer.

(3) Shifting from ON to OFF

This circuit applies a negative feedback signal from the 12V output. When the voltage across C919 reaches the
specified value, REG2 turns on and current flows to PQ2
IC901 pin to "Hi", and turns IC901 off.

(4) During OFF

While IC901 is on, the following energy charges the primary windings of the transformer;
2
Energy=LI /2. Here, L : Primary inductance
This energy discharges to the secondary windings during power off. That is, C910, C911, C912C, C914 is
charged according to the turn ratio of each winding.
At the start, an overcurrent flows to IC901 because of the charged current at C910, C911, C912, C914.
The drain current at IC901 generates a voltage across R906. If it exceeds the IC901 base voltage, it sets the
IC901 gate voltage to "HI"
R906 Limits the gate voltage to prevent excessive collector current from flowing to IC901.
<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:
REG1 (regulator) faulty, 5V-0V 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, ruch 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 12V and 5V are abnormal:
D907, D908 or drive circuit is abnormal.
(5) When all voltage are abnormal:
IC901, R906, etc. are possibly abnormal.
* If IC901 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 IC901 pin
R904 and R903) and IC901 pin
circuit of IC901 is operating.]
I : Current when IC901 is off
(to be measured at R906 lead) may be between 11 and 16V. This is because the protection
- . This turns the secondary circuits on, sets
– 128 –
(to be measured at the leads of