If you are working on a portable electronics project, or in a remote place where you can’t bring your bulky bench power supply with you, then powering your circuit becomes quite challenging sometimes. To power our projects we often use Lithium ion or Li-Po batteries. These batteries are convenient to use because they are small, rechargeable and often come in various shapes & sizes. But the issue with these batteries is that most of these batteries are rated for 3.7 volts and a maximum of 4.2v. Now for our application we generally need either 3.3v or 5v because typical microcontrollers and sensors work on these voltage levels. So in order to get the right voltage you either need a buck converter or a boost converter. Then we also need a charging circuit to charge the battery. So all and all you need some additional circuitry in order to use this kind of batteries.

At this point you might think why should we bother with all these and why not just use a powerbank then. It’s portable, can output 5 volt also it’s rechargeable. And yes, we could use a readymade powerbank to power our projects but there comes another problem. You see, those commercially available powerbanks require a minimum holding current typically 100mA to stay on. Now if you use deep sleep in your circuit to save power then the powerbank can no longer work properly. Because in the deep sleep stage the microcontroller consumes very less amount of current which usually falls under the minimum required current of the powerbank. And thus it turns off automatically after some time as the device enters into deep sleep. 

So keeping these things in mind I started working on this project to make a trusty portable power supply unit that can power my projects uninterruptedly. 

Let’s have a closer look at what we have in this circuit. We have separated outputs for 3.3v, 5v and an adjustable voltage output which basically fulfills most of our power related demands. We have both USB type-C and micro USB port for charging. It runs on two 18650 li-ion batteries which gives us about 5000 mAH of battery backup.