MR4530 datasheet(38/43 Pages) SHINDENGEN

38 / 43 page

Shindengen Electric MFG.CO.,LTD

- 68 -

Problem

Possible cause

Solution

Place the secondary F/B pin in front of L.

Adjust the circuit around the shunt regulator.

Abnormal oscillation

during steady-state

operation

This results in hunting.

The phase has shifted.

Adjust the circuit around the photocoupler.

Adjust the OCL resistance.

The droop operation is

ineffective.

The droop circuit is inadequate.

Adjust the resistance between the F/B pin and GND

pin.

The ON duty ratio is large.

Redesign ON duty ratio.

The transformer coupling is poor.

Review the transformer coil structure.

The ratio of numbers of turns in coils is

inappropriate.

Review the transformer design.

Adjust the resonating capacitor.

Provide a snubber circuit.

Add a power clamper.

VDS or VCE exceeds the

withstand level.

The surge is large.

Connect a resistor in series with the resonating

capacitor.

The current to the photodiode is too low.

Adjust the current-limiting resistance of the

photodiode.

Increase the capacity of the capacitor between the

Z/C pin and GND pin.

The IC cannot enter

standby mode.

Noise is superimposed on the Z/C pin.

Improve the PCB pattern.

Adjust the number of turns in the NC coil.

Review the transformer coil structure.

Combine a zener diode and a resistor to clamp VCC.

The oscillation halts

when the output load is

increased.

The overvoltage latch is on.

Add a damper resistor for VCC.

Reinforce impregnation (e.g., double impregnation,

use of adhesive)

The transformer

generates an oscillating

tone in standby mode.

Transformer vibrations

Optimize the load.

Noise is superimposed on the Z/C pin.

Increase the capacity of the capacitor between the

Z/C pin and GND pin.

Increase the current rating of the diode.

The VF of the secondary diode is large.

Use a Schottky diode.

The input power is large

in the case of a load

short.

The transformer coupling is poor.

Review the transformer coil structure.

15 The droop point varies.

The resistor between the F/B pin and

GND pin is operating.

Make sure the voltage droops only with the OCL pin

resistance.

The tan

δ of the resonating capacitor is

large.

Use a capacitor with a smaller tan

δ.

The standby power is

large.

The capacity of the resonating capacitor

is large.

Adjust the resonating capacitor (carefully monitor

VDS or VCE to ensure that the withstand level is not

exceeded.)

6. Supplementary design information

MR4530 Datasheet(PDF) 38 Page - Shindengen Electric Mfg.Co.Ltd

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