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Old 21st September 2012, 02:28 PM   #1
estudent is offline estudent  India
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I am trying to build this half bridge SMPS, modified/improved PC design, operating from 230V AC providing about 13.8V DC with MOSFET rectifiers. Operates at 50kHz.
250 W S.M.P.S. with Power-FETs James Arthur
1. There is a snubber of 2.2nF / 100 Ohms across the primary winding. The resistor wattage is given as 2W. I tried calculating the wattage, as
50000 X 4 X (CV^2) / 2, as there are 4 transitions per cycle, with V taken as 190V, half of peak voltage, at input high 230*1.15*1.414. With that I am getting a Pd of around 6W.
2. There is a snubber of 10nF / 10 Ohms across the secondary. Here also the resistor is specified as 2W, but my calculation like the above, with a secondary peak voltage of 33.25 X 2, gives a Pd of 4.4W! Am I making a missing something or my snubber calculation is wrong?
3. Can I use a still lower RdsOn MOSFET like 2.2 mOhm NXP PSMN2R0-60PS,127 instead of the IRFZ44 used in the original schematic, for output rectification to improve efficiency further? Will those parameters like, higher gate charge, capacitance matter?

Thanks in advance.
Old 21st September 2012, 08:20 PM   #2
Mooly is offline Mooly  United Kingdom
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Help with SMPS

Non isolated supplies of this kind are potentially lethal and are against the forum rules.

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