MR4530 datasheet(21/43 Pages) SHINDENGEN

21 / 43 page

Shindengen Electric MFG.CO.,LTD

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6.1 Supplementary notes on design

6.1.1 VCC control

Since the IC control current is very low, VCC can be significantly affected by the ringing voltage caused by

transformer leakage inductance. This will increase the VCC voltage of the MR4000 Series beyond the design value.

Under certain load conditions, the IC may be latched and stopped or the VCC may become too low. The ringing

voltage caused by the transformer leakage inductance is reduced with a DCR snubber circuit. Several other

solutions are also available, as shown below.

(1) Increasing the damper resistance

Increasing this resistance reduces voltage variations. Increasing the

resistance will affect VCC. Make sure the design accounts for possible

stoppage of MR4000 Series products due to a fall in VCC. Set the

resistance on an actual board between several ohms and tens of ohms.

Note that a light load may decrease efficiency under certain

circumstances.

(2) NC coil winding method

Bring the NC coil into closer contact with a

secondary coil that has limited contact with

the primary coil. Doing so will reduce the

ringing generated in the NC coil. This is our

recommended winding method.

(3) Adding a dummy resistor

If using a dummy resistor increases power consumption and

decreases efficiency, this circuit will improve these performance

somewhat.

If the VCC voltage exceeds the level determined by the zener diode,

the dummy resistor will control the voltage increase. We recommend

a zener diode for 16 V or higher.

MR4000

Increase this

resistance.

Fig. 6.1 Damper resistance

Fig. 6.2 Transformer winding to improve contact

Fig. 6.3 Adding a dummy resistor

6. Supplementary design information

MR4530 Datasheet(PDF) 21 Page - Shindengen Electric Mfg.Co.Ltd