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I just made my buck converter, this is gonna used in MPPT project. I use simple buck converter in this project.

My problem is when I connect battery to output of buck converter, then electricity is flowing to the input of buck converter.

I tested to connect my LED to the input, then the LED was on. Why was that happening? No voltage is being used to supply gate of my MOSFET. So the leakage is only from output to input, not input to output.

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  • \$\begingroup\$ Is this a synchronous converter? I'm guessing it is, as that would explain the behavior of power flowing in reverse. Could you post a schematic of the buck converter? \$\endgroup\$
    – Math Keeps Me Busy
    Commented Apr 2 at 4:44
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    \$\begingroup\$ We can't know why current went in reverse if you don't show the schematics and components used to build it. \$\endgroup\$
    – Justme
    Commented Apr 2 at 4:53
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    \$\begingroup\$ Besides your "issue", does the circuit work otherwise? \$\endgroup\$
    – MOSFET
    Commented Apr 2 at 5:15
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    \$\begingroup\$ @MathKeepsMeBusy even if it's asynchronous, he would have the same problem that you're thinking - the high-side body diode conducts right through the inductor regardless if the low-side switch is a diode or fet. \$\endgroup\$
    – MOSFET
    Commented Apr 2 at 5:20
  • \$\begingroup\$ My buck converter was doing good to control the voltage down. I’m using asynchronous buck converter \$\endgroup\$
    – tabun
    Commented Apr 2 at 8:45

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My problem is when I connect battery to output of buck converter, then electricity is flowing to the input of buck converter.

Here's a typical buck regulator from this site: -

enter image description here

It's a synchronous buck regulator (the lower MOSFET replaces a diode) but that is irrelevant to your problem. Look at the upper MOSFET (HS) and notice that there is a diode in parallel with it. That diode is inside many commercial MOSFETs whether implemented inside a chip or, as an individual part. It is called the body diode.

Notice that the diode will not conduct when the input supply voltage is present and higher than the output voltage but, it will conduct when the input voltage falls below the output voltage.

That is what is happening here. Maybe these green arrows will help you visualize the current flow: -

enter image description here

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  • \$\begingroup\$ I think this is exactly that happening to my circuit. By the way, i'm using async buck converter but, that's should be the problem here. Now i'm thinking to use a diode to block the reverse current or a 5V relay to cut the input. Do you have another solution to this problem sir? \$\endgroup\$
    – tabun
    Commented Apr 2 at 8:51
  • \$\begingroup\$ @tabun a diode is the simplest solution but, you lose a diode drop and that affects efficiency (if important) when running normally. I'd be thinking about adding a P-channel MOSFET so that when the input voltage falls below the battery voltage, the PMOS deactivates (not dissimilar to how a reverse voltage protection PMOS is used. You would need a low power comparator though to help you achieve this (beyond the scope of this Q and A session). \$\endgroup\$
    – Andy aka
    Commented Apr 2 at 8:52
  • \$\begingroup\$ Now I’m confused, where should i put the diode? On output side or input side sir? Does it matter ? \$\endgroup\$
    – tabun
    Commented Apr 2 at 9:06
  • \$\begingroup\$ I'd use an input side diode. \$\endgroup\$
    – Andy aka
    Commented Apr 2 at 9:10

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