Making a portable rechargeable lithium LED lamp

Thread Starter


Joined Mar 21, 2015
I am making an LED rechargeable torch/lamp. I have an off-the-shelf charging circuit (see below) with micro usb to charge the battery and my question is this: Can I use the lamp whilst charging or do I need some extra circuitry? The charging circuit, when attached to a wall socket/USB adapter, outputs about 4.1V at the battery terminals, this is slightly higher than the nominal 3.7V of the battery and so the first problem will be that I will be over-powering my LEDs, this could be managed with a voltage controller so my main concern is that the extra load on the circuit, from the LEDs (100 to 300mA), will mess up the charging of the battery, possibly confusing the charging chip or maybe stopping the charging by robbing most of the available current....

Thanks in advance.

I am using this charging circuit to charge the battery:


Joined Aug 21, 2008
Generally speaking (writing),

If the charger can provide enough current for the LED and to charge the battery then charging and use can be simultaneous and not affect each other.

If the charger cannot provide enough for both at the same time, the battery will be charged with whatever "surplus" current is available after the LED's load is subtracted from the charger's capabilities.

The above assumes that the output of the charger, the LED load and the battery's load are all steady direct current. Pulsing etc. makes the assertions above less accurate.