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(4) Protection Circuit of Power Supply Part
Overview
PO
W
ER CO
N
TROL IC (IC501: STR-Y6476), which is used at power source of this model, is hybrid IC for use of false
resonance style switching power source.
This has MOSFET and IC which can contral many function built-in.
This has many functions of protection, such as 1. Over
V
oltage Protection, 2. Over Load Protector, and 3. Over current
Protection
built-in.
Above-mentioned functions are activated when abnormalities, such as short of second side output power source and over
load, are detected.
Detection and Movement of Protection
1. O
V
P (Over
V
oltage Protection) Detection: IC501/3 pin (
V
cc)
W
hen second side over voltage outputs, O
V
P circuit activates by detects
V
cc terminal
V
oltage (
V
cc terminal
V
oltage is
supplied from auxiliary winding of the transformer (T501/14-15 pin) which is in proportion to output voltage of the trans-
former.)
W
hen O
V
P motion power source voltage which is more than 28.5
V
(typ) is applied to pin between 3 to 2 of IC50, O
V
P
circuit in control IC operates and becomes latch mode, and control IC stops oscillatory.
2. OLP (Over Load Protector) Detection: IC501/4 pin (FB)
W
hen partial short which exceeds restriction on use of parts of semiconductor, OLP circuit operates by detecting rise in
photocoupler (IC502/4 pin) voltage.
W
hen voltage between 4 pin to 2 pin of IC501reaches threshold of OLP latch off voltage 9.6
V
(typ), OLP circuit in control
IC operates and becomes latch mode, and control IC stops oscillatory.
3. OCP (Over Current Protection) Detection: IC501/6 pin (OCP)
W
hen each part of power source goes through short, OCP circuit operates by detecting rise in overcurrent detection
resistance R502's both ends of voltage.
W
hen voltage between 6 pin to 2 pin of IC501exceeds over current detection voltage threshold 0.95
V
(typ),control IC
becomes bad quality of booting and changes into auto restart mode.
Processin
g
and Return
1, 2. Latch Movements
W
hen each O
V
P and OLP circuit operates, output oscillatory which is inside of control IC is kept "L", and the output makes
movements of power source circuit stopped.
After latch movements, 3 pin
V
cc voltage falls because of stopping oscillatory. C511 repeats charge and discharge
between
10.0
V
(typ) to 16.2
V
(typ).
Latch movements are released by blocking AC input voltage and lowering
V
cc voltage
V
cc to 7.5
V
(typ) which releases
makes it work normally. Then, return is done.
hen OCP circuit operates, auto restart by intermittent movements starts.
and generation of heat by switching chip is restrained.
hen overcurrent is released, it becomes possible to return automatically.
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