MS1003SH･MS1004SH

Application Note Ver.2.2

SHINDENGEN ELECTRIC MFG. CO. , LTD

39/41

1) VDC voltage

This is the same as the input capacitor voltage. Formula 2 gives the maximum value. In this

example, the maximum value is 186.7 V.

2) Flyback voltage

This is the transformer’s flyback voltage:

1

1

1

)

(

S

F

O

N

V

V

Np





The following formula gives the voltage:

8

)

6

.

0

12

(

68





=107.1[V]

3) Surge voltage

This surge voltage attributable to leakage inductance varies from specification to specification and

from transformer to transformer. In this example, it is estimated to be 150 V at maximum. This

parameter must be confirmed using actual equipment.

4) Quasi-resonance trough voltage

The higher this voltage, the greater the switching loss. This is obtained by subtracting (2) from (1)

above. In this example, it is 186.7 V – 107.1 V = 79.6 V.

The maximum voltage of the main switching device is 186.7 V + 107.1 V + 150 V = 443.8 V. For

instance, a MOSFET capable of withstanding 500 V is suitable for use with a margin exceeding 10%

(450 V). If the withstand voltage is too low, reduce on duty ratio D. Increase the on duty ratio D to

make the most of quasi-resonance effects.