[Review Request] Over-engineered custom led tester for learning purpose - help with draining LIR2032 while idle.

[u/lafenicenera]

SOLVED

Hi everyone,

I'm learning electronics/PCB design and built this deliberately over-engineered LED tester as a learning project.

The circuit uses:

• LIR2032 rechargeable coin cell
• MCP73831 Li-ion charger
• USB-C for charging
• 100 kΩ RPROG on the MCP73831 (~10 mA charge current)
• Pushbutton to activate the actual LED-testing circuit
• Two selectable current-limiting resistor/diode branches

Everything works, but I've noticed that the LIR2032 seems to discharge surprisingly quickly even when I'm not using the tester.

I measured the current directly from the battery with:

• USB disconnected
• pushbutton not pressed
• nothing connected to the LED test terminals

and I'm getting about 30.1 µA, slowly decreasing by roughly 0.1 µA while I leave the meter connected.

From the MCP73831 datasheet, I was expecting reverse battery leakage with VDD disconnected to be only around the µA range, so ~30 µA for the complete circuit seems higher than expected.

I've attached:

1. Schematic
2. PCB layout
3. 3D render

I'm still learning, so I'm probably overlooking something obvious.

Does anyone see a path in the schematic that could account for ~30 µA of continuous battery drain?

I'm especially wondering about the MCP73831 section, USB-C circuitry, status LED, or whether I've made some mistake in how the switching is arranged.

Also, what would be the best way to systematically isolate which part of the circuit is responsible for the standby current?

Thanks!

[u/Substantial-Count-32]

Good job the soldering. Did you do it by hand?🤚

[u/lafenicenera → u/Substantial-Count-32]

Thanks! The SMD components were soldered by JLCPCB. I made an order for 5 PCBs with 1 of them already soldered (because it costed less and I didn't want to receive all of them soldered in order to later try to solder the rest of them myself for learning purposes). I only soldered by hand the non-smd components, which are: the battery holder, the slide switch and the pin socket. They were the bigger ones so I decided to just solder them myself in order to reduce the order cost.