Design Notes - ON Semiconductor Fairchild FAN302HL Design Manualline

AN-6094
6. Final Schematic of Design Example
Figure 25 shows the final schematic of the 6 W charger
design example. EI12.5 core is used for the transformer.
Figure 26 shows the transformer winding structure. Figure
27 and Figure 28 show the PCB pattern.

Design Notes


The leakage inductance is measured as 52 µH with an
LCR meter. Calculation with the measured resonance
period yields 18 µH of effective leakage inductance
Figure 25. Final Schematic of the FAN302UL 6W Design Example

Core: EI12.5, Bobbin: EI12.5.

W1 is space winding in one layer.

W2 consists of three layers with a different number of turns. The number of turns for each layer is
specified below.

W3 consists of two layers with triple-insulated wire. The leads of positive and negative; fly lines are 3.5 cm
and 2.5 cm, respectively.
© 2012 Fairchild Semiconductor Corporation
Rev. 1.0.0 • 9/27/12


Figure 26. Transformer Winding Structure
17
Clamping circuit resistor R10 is adjusted to 390 kΩ
based on test results from the actual power supply.
Note that the sensing resistor is fine tuned to 1.2 Ω
based on test result of actual prototype power supply.
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