Battery managment problem

In a project, I use the MCP73831 battery charge management controller. You can see the schematics below.

Problem is, if I use it as it is, I have a voltage drop-out on a 1n5819 diode and this regulator lose some noise. If I remove it and bypass it, it works. Sort of. There is no noise. But that LED is not turn on as bright as it should. Can’t say if it charges the battery at all.

If I connect it with the 12V/3A power supply, my LiPo battery is charging. When charged, LED will turn off. If I remove this 12V powering it, my setup will work.

But, if I just plug my battery, without 12V powering it, That LED U22 on LM2596 will turn on and I get a magic smoke from MCP73831. Something is wrong, and I can not see what.


Hi, @who_took_my_nick
Welcome to the forum.

Please read the post at the start of any forum , entitled “How to use this Forum”.

@who_took_my_nick circuit.

Where did you get the schematic, did you look at application data for the BMS IC?

Tom… :grinning: :+1: :coffee: :australia:

I have read this article, but not sure what I did wrong.

MCP7383/SE5218 part I use in a bunch of my projects and it works fine with LiPo batteries. Although, it is powered with a USB power adapter. Or PC USB. And it works fine. Not a single issue.

LM2596 I use in a bunch of projects when I need a 12V power supply.

This is the first time I use them combined. I have a drop-out on 1N5819, but I must have some protection there. Yes, I looked at the datasheet for everything here for days. I haven’t seen anything that could help me solve this out. Only that cap C14, that should be 4.7uF. If that makes the problem, I will eat the whole reel.

Where I get this schematic? Not sure I understand. This as it is, I made. I didn’t invent hot water. Maybe out there someone else made the same. Who knows… It is not important.

Which diode? D1 D2 D12 etc
Which LED? U22 LED8
What is the voltage of Vbatt?

It would be clearer if you connected everything together rather than rely on net names,.

Where does the 12V come from?

Thanks… Tom… :grinning: :+1: :coffee: :australia:

It is part of a larger project, with 4 sheets.

However, I said I am talking of 1N5819, which is D12. That line goes directly to an MCP73831. Stat LED is the one that shows is it charging or not, it is LED5. 12V comes from a 12V/5A power supply. Huge one. The battery voltage of LiPo is 3.7V. It is charging with 4.2V.

Sorry if I was not clear enough. Thank you for your effort. If any info needed, please tell me.


What do you mean “drop out”?

When it is in circuit.
What is the voltage on the cathode of D12 with respect to gnd?
What is the voltage on the anode of D12 with respect to gnd?

Tom… :grinning: :+1: :coffee: :australia:


Try adding the 4.7uF and a 0.1uF between Vin and Gnd at the 73831.

Have you got decent earth wires/tracks?

Tom… :grinning: :+1: :coffee: :australia:

By a drop-out I mean, I have a 5V before the 1N5819, and 4.81V after it.

There is a single one 10uF.

I just made a change to a PCB. I added those caps as on the datasheet.
Traces are 0.5mm. Both.

Will see in a 10 days.


That is a normal volt drop across a schottky diode
1N5817 and 1N5819 are part of a group.

In fact your measurement is lower than the spec.

Tom… :grinning: :+1: :coffee: :australia:

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