Pioneer XW-NAV1-K Service Manual page 30

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(4) Protection Circuit of Power Supply Part
Overview
POWER CONTROL 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 Voltage 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.
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Detection and Movement of Protection
1. OVP (Over Voltage Protection) Detection: IC501/3 pin (Vcc)
When second side over voltage outputs, OVP circuit activates by detects Vcc terminal Voltage (Vcc terminal Voltage is
supplied from auxiliary winding of the transformer (T501/14-15 pin) which is in proportion to output voltage of the trans-
former.)
When OVP motion power source voltage which is more than 28.5 V (typ) is applied to pin between 3 to 2 of IC50, OVP
circuit in control IC operates and becomes latch mode, and control IC stops oscillatory.
2. OLP (Over Load Protector) Detection: IC501/4 pin (FB)
When partial short which exceeds restriction on use of parts of semiconductor, OLP circuit operates by detecting rise in
photocoupler (IC502/4 pin) voltage.
When voltage between 4 pin to 2 pin of IC501reaches threshold of OLP latch off voltage 9.6 V (typ), OLP circuit in control
C
IC operates and becomes latch mode, and control IC stops oscillatory.
3. OCP (Over Current Protection) Detection: IC501/6 pin (OCP)
When each part of power source goes through short, OCP circuit operates by detecting rise in overcurrent detection
resistance R502's both ends of voltage. TE
L 13942296513
When 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.
Processing and Return
1, 2. Latch Movements
When each OVP and OLP circuit operates, output oscillatory which is inside of control IC is kept "L", and the output makes
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movements of power source circuit stopped.
After latch movements, 3 pin Vcc 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 Vcc voltageVcc to 7.5 V (typ) which releases
Latch power source voltage.
Afterwards, turning AC ON makes it work normally. Then, return is done.
3. Auto Restart Movements
When OCP circuit operates, auto restart by intermittent movements starts.
During auto restart is done, because motive electricity turns reduction mode, periods which oscillatory stops is expanded,
and generation of heat by switching chip is restrained.
When overcurrent is released, it becomes possible to return automatically.
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