MS1003SH datasheet(37/41 Pages) SHINDENGEN

37 / 41 page

MS1003SH･MS1004SH

Application Note Ver.2.2

SHINDENGEN ELECTRIC MFG. CO. , LTD

37/41

(6) Calculating the number of turns in the control coil

Formula 15:







=10.03[Turn]

Round the result to the nearest integer, i.e., Nc = 10 turns.

(Round up the result when adjusting the voltage upwards. When adjusting it downwards, round it

down.)

(7) Recalculating the transformer design

The actual design values of a transformer differ from initial design values because results are rounded

to integers during the design process and because actual resistances and inductances differ from

calculations.

The differences are corrected and the OCL resistance R(OCL) and transformer core gap are determined as

follows:

1) Correcting the main SW peak current and determining OCL resistance R(OCL)

Calculate R(OCL) based on the relationship between the main SW peak current obtained in Section

(3) and the VTH (OCL) clamp.

484

)

(



OCL

=0.3638[Ω]

To adjust resistance, change R(OCL) to 0.37 Ω (e.g., 0.22 Ω + 0.15 Ω).

The main SW peak current changes to



=1.46[A].

2) Determining the core gap and correcting the inductance

To specify the core gap when ordering a transformer, you can use the result of Formula 12 in

Section 5.3. Note that using the inductance coefficient “AL-value” is more common.

The AL-value is among the key parameters that determine transformer core performance, together

with the NI-limit expressed in [

] and magnetic saturation condition.

The inductance is corrected based on the assumption that the AL-value is 140.

(Standard AL-values vary from manufacturer to manufacturer. Contact the transformer manufacturer

to obtain more information.)

Since the

value



, the result is

140



= 647360 nH.

The inductance Lp is corrected to 0.647 mH.

3) Correcting initial design values

From the IDP and Lp obtained in Sections 1) and 2), the initial design values are corrected as

follows:

Formula 10:

102

647

(min)

(max)











=9.26 [μs]

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