transformer leakage inductance

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Dear PI
I am designed a LED supply using DI-136 for 28V 1A, the out put voltage is goes high up to 40V as I increase load current 100mA voltage drop down to 25V. if i place a capacitor 3.3nF 1Kv across D7(FR305)I got 28V and good load regulation but top250 become hot.can I go for this practice? is it due to transformer primary leakage inductance? How can I measure leakage inductance? which factors are affected for leakage inductance? what functions of core cancellation winding and shielded winding in transformer? which performances effect without it? I attach schematic.

thanks & regards

Amit patel

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schematic_3.pdf562.5 KB

Amit -

Regarding the capacitor across D7, please see my response to your other forum post.

Reply:
http://www.powerint.com/en/forum/led-driver-design/over-voltage-output-no-load-regulation#comment-8791

Original Post:
http://www.powerint.com/en/forum/led-driver-design/over-voltage-output-no-load-regulation

If you're unfamiliar with making measurements of transformer parameters, this is a very good article:
http://www.ridleyengineering.com/index.php/transformer-measurements.html

-The Traveler