I am making a boost converter using the LM3481 IC (although it might be considered a sepic topology as well). Typically in a boost topology, you put a diode before the output capacitors so they don't drain backwards. I want my circuit to be more efficient since I'm wasting lots of power through the diode.

Here is a bit of my schematic. The DR pin switches on and off quickly, allowing the inductor to build its magnetic field when M1 is closed, then briefly deliver a high voltage as the magnetic field collapses when M1 is open. In all the following schematics, pin 1 of M1 leads to ground. enter image description here I've only just started learning about PSU's and I don't know if my idea(s) will work. My first idea was to replace D1 with an N-MOSFET: enter image description here My logic behind this was that when the voltage is positive, the gate can be charged and allow current to flow, but when the voltage wants to flow backwards, the gate will be pulled to ground and stop any reverse flow.

My second idea is to use a P-MOSFET:enter image description here

My logic behind this is that the gate can be tied to the drive pin, so when M1 is open, Q2 is closed and current can flow forwards. But when M2 is closed, Q1 is open, which should block any current from flowing backwards to ground.

Do either of these ideas work? If not, where are the flaws and how can I fix it. If they both work, is one preferred over the other?

edit. I just noticed the incorrect polarity of the diode in Q2, please take note.

  • 5
    \$\begingroup\$ Look up the term "synchronous converter". That might get you a step in the right direction. \$\endgroup\$ – Hearth Oct 26 '19 at 2:39

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