Battery charge complete LED indicator - Page 1
Forum section: electronics / projects

author: kian0079
author_rank: Contributor
timestamp: June 08, 2024, 09:43:11 am
content: Hi all,I am working on a project where I use a single 4.2V lipo battery. My circuit uses an inbuilt lipo charger IC (MCP73831) that already comes with STAT pin where I can connect an LED to it. The LED lights up when charging and turns off when completed. Due to certain constraints, I am do not wish to put an LED on my circuit board. The circuit board is charged from a 5V source (a separated charging circuit board that provides 5V output - 5V and Ground). It is possible for me have the charging status indicator on the charging circuit board instead? Hope to get some insights on how the circuit should look like. Thanks in advance!Cheers.

author: ArdWar
author_rank: Frequent Contributor
timestamp: June 08, 2024, 02:16:50 pm
content: Sensing your supply current? So when it's sourcing more than MCP73831 charge termination current then the other end must be doing some charging.

author: tooki
author_rank: Super Contributor
timestamp: June 08, 2024, 05:22:06 pm
content: Quote from: kian0079 on June 08, 2024, 09:43:11 amIt sounds to me like you’re simply asking if you can locate the LED off-board. If so, that’s trivially easy: just connect the LED to the STAT pin through the needed resistor to Vin.Also, please clarify, ideally with diagrams, exactly what is what. In your text, you talk about “my circuit”, “the circuit”, “the charging board” (which sounds like it might be a power supply board, not a charger), “my circuit board”, so it’s really unclear how many boards there are, what’s on each, and who designed each of them.If my suspicion is correct, and what you want is to have the charge status LED on the power supply board, then you just need another wire connecting the STAT pin, and somewhere you need the resistor.

author: kian0079
author_rank: Contributor
timestamp: June 09, 2024, 12:56:48 am
content: My apologies for the confusion. The block diagram for my setup is show in the image below. I have a charging dock circuit that connects to multiple devices. I cannot put the charging indicator LED on the microcontroller board and I only can have 2 wires (5V and Gnd) going into each of the microcontroller boards. Hence I am hoping to have a some extra circuits that I can put in the charging dock circuit for indicating that charging is completed with an LED that go off when charging is completed.Quote from: tooki on June 08, 2024, 05:22:06 pm

author: tooki
author_rank: Super Contributor
timestamp: June 09, 2024, 07:17:32 pm
content: Why can’t you add a third wire back to the charging dock from each MCU board? That’s all you’d need.Short of much more complex systems of measuring current, that is by FAR the easiest way to do it. That or moving the charging IC itself to the dock board and instead disconnecting the battery and MCU from the charging circuit itself.Bear in mind that with current monitoring, it’d be comparatively difficult to have an LED that can differentiate between a finished charge and a disconnected MCU board.Edit: photo of block diagram saved below so it doesn’t go missing if/when that third party image hosting dies. It’s always better to just attach images here.

author: kian0079
author_rank: Contributor
timestamp: June 10, 2024, 12:31:02 pm
content: Unfortunately the MCU board have all been designed without charging indicators and it uses a 2pin magnetic connector for charging. My only choice is to add the charging indicators on the charging dock.I presume I would need a current sense amplifier with its output cascaded to a comparator? Then the output of the comparator should be 0 when the charging current drops to 0?Quote from: tooki on June 09, 2024, 07:17:32 pm

author: tooki
author_rank: Super Contributor
timestamp: June 10, 2024, 12:39:51 pm
content: In practice, I’d tell whoever is in charge “can’t be done, the signal is on the MCU board”.The problem with current sensing is that you don’t knowwhatis drawing the current: is it the charger IC? Is it the MCU and its circuitry? Those look the same to a comparator.

author: Zero999
author_rank: Super Contributor
timestamp: June 10, 2024, 06:30:15 pm
content: If it's not possible to redesign the MCU boards then you're stuffed.The only way to do this, without modifying the connectors is with a wireless or power line communication system, which would need to be added to the MCU boards and charging dock.

author: ArdWar
author_rank: Frequent Contributor
timestamp: June 11, 2024, 04:07:29 am
content: Since your options are going to be suboptimal anyway, it's time for crazy ideas.Looking at table 5.1 in MCP'31 datasheet. You can bodge a NMOS across the input supply, controlled by STAT pin. When charging is complete it will hopefully crowbar the shit out of your power supply. Letting you know charging is complete. Hope it got good output protection and safely trip.What could possibly go wrong, right?