MR4530 datasheet(12/43 Pages) SHINDENGEN

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Shindengen Electric MFG.CO.,LTD

- 12 -

3.12 Malfunction prevention circuit (patent pending)

The current-critical operation of the MR4000

Series ensures that the main transformer does not

become saturated as long as the droop setting is

optimized.

At startup and in the event of a load short, the

output voltage is significantly lower than the set

voltage. Since the control coil voltage is

proportional to the output voltage, it also drops

significantly, and the on-trigger timing may be

incorrectly detected due to the ringing voltage

generated while the main switching device is OFF.

The device may then be turned on before the

current-critical point.

To counter this problem, the MR4000 Series

incorporates a circuit to prevent on-trigger error at

startup or in the event of a load short. This

function disables the on-trigger for a period, tondead,

after the main switching device in the IC is turned

off (On-dead time). This prevents false detection

due to the ringing voltage while the device is OFF.

This design permits detection of the transformer

secondary current of 0 A to turn on the main

switching device even at startup or in the event of

a load short. This prevents the magnetic

saturation of the transformer.

3.13 Overcurrent protection circuit

A current detection resistor is connected between

the Source/OCL (Emitter/OCL) pin and GND to

detect currents between the source (emitter) of

the main switching device and the source

(emitter) current detection pin.

During stable operation, the main switching

device current is limited by pulse-by-pulse

operation with the Vth(OCL) threshold.

During standby, the threshold changes to Vth(burst

OCL), and the oscillation noise from the transformer

due to burst oscillation is reduced.

[Secondary rectification diode]

[VDS(VCE)]

[VOUT]

[VZ/C]

Enlarged

view

[IC(ID)]

[VZ/C]

On-trigger is disabled during this period.

tondead

[Secondary rectification diode]

Approx.

0.3 V

[ID(IC)]

Fig. 3.11 Malfunction prevention circuit

Fig. 3.12 Current detection resistor

3. Operating principles

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