I found this circuit from here and have been thinking about to build it:

enter image description here

The author present it as Ćuk converter but I understand it as SEPIC, after reading this and this.

Q: My main concern is, whether it is safe to use electrolytic capacitor for C6?

  • My thinking says, the polarity will get reversed for C6 when MOSFET is turned off. Then if there is no load, electrolytic capacitor is going get damaged/exploded?

  • Also, chance for MOSFET get damaged because of absence of flyback diode?


1 Answer 1


The Electrolytic cap does see a DC voltage in your converter. So it will not blow up due to reverse volts. Ripple current is an issue ,Film and ceramic caps are better in this respect. Check your ripple current ratings for your anticipated product life at your expected operating temp. If you want high power high reliability at high temperature then you will struggle to find a suitable electro. The coupled coil does have some leakage inductance so there will be voltage spikes on the MOSFET Drain which will get worse at high current. Consider a snubber if there are EMC concerns.

  • \$\begingroup\$ Yes, ceramic or film capacitor could be used. But I only have maximum of 4.7uF of film capacitor that too way too expensive. I assume I need at leave 1000uF here. I never seen ceramic or film capacitor having that much rating. It would be working in normal room temperature. May be I nee to use snubber, but it would reduce the efficiency? \$\endgroup\$
    – Junaid
    Jul 24, 2019 at 13:37

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