disconnect load while charging using a single TIP120 ?

[despictable_g]

Hi all,

As this is my first post I would first like to thank the arduino community for all the contributions. Arduinos are so cool

I have a CS background but know next to nothing in electronics, so please pardon the possible stupidity of my question.

I'm building a portable device. Its main components are :

• an arduino pro mini (16mhz 5v with 5v sensors)
• a single 18650 protected roaring lion.
• a module with a TP4056 with discharge protection which looks exactly like this one : TP4056 - Micro USB 5V 1A Lithium Battery Charger with Protection [TP4056-Protection-Modules] - US $1.20 : HAOYU Electronics : Make Engineers Job Easier
• a dc-dc "booster" regulator to feed my arduino with 5v
• a ON/OFF switch

When I ordered that TP4056 based module I was thinking that I would be able to use its OUT pins while charging, but according to the above website it looks like I can't do that. ("Important! Disconnect load when charging")

The problem is that the potential users of the device I'm working on might forget to turn off the device before charging.

=> How can I disconnect the load when there is some current through the IN pins ?
I have a TIP120 lying around. Can I use it to build a NOT gate and use the output of that gate to feed the load ?

Best regards,

[strykeroz]

That's quite a restriction !

The first method that comes to mind is, so long as you're using the input terminals rather than the USB on the charging source side, to add a 2P2T switch such that the input is only connected in one position and the load is only connected in the other.

If you're using the USB for the power input you won't be able to isolate it without probably removing it off the board, and injecting the switch between it and the existing pads where it is now.

Cheers !
Geoff

[despictable_g]

strykeroz:
The first method that comes to mind is, so long as you're using the input terminals rather than the USB on the charging source side, to add a 2P2T switch such that the input is only connected in one position and the load is only connected in the other.

Thanks for the answer!
Yes such a button should exist but it has downsides :

• As you mentioned I'll have to use another usb connector or desolder and fiddle with the existing one.
• Finding and ordering this button.
• The on/off button I'm using has a potentiometer builtin that I'm using to control a volume. It will make that 2-in-1 feature useless.

I just did a test with that TIP120 as a NOT gate. It's still drawing current when the output is 0. I guess transistors are not relays (see, I'm that bad at electronics)... I guess a real relay with a default "ON" state should do the trick too.