DER-57
Industrial – LNK501P
April 20, 2005
used for these capacitors such as Z5U and Y5U are not stable and can cause output
instability as their value changes with voltage and temperature. Stable dielectrics such
as COG/NPO are acceptable but are costly when compared to a Metalized plastic film
capacitor.
R3 was selected to program the peak power point to be 250mA when a transformer with
a nominal LP value was used. The expression used to size R3 is from Power Integrations
Application note, AN-35. C1 sets the auto-restart period and also the time the output has
to reach regulation before entering auto-restart from start-up.
4.5 Output Stage
Diode D4 should be rated for 80% of applied reverse voltage and thermally for average
current multiplied by forward voltage at maximum ambient. Here a 1 A, 100 V Schottky
diode was used to reduce the losses and improve efficiency. R2 and C4 from a snubber
network to reduce ringing on D4. Capacitor C7 should be rated for output voltage and
ripple current.
Power Integrations
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