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Saturday, June 17, 2017

Powering Orange PI Zero with a Power Bank

You might ask yourself why wouldn't it work?
I asked myself the same question when I saw the tiny thing won't turn on, or worse, turn on and freeze all the time.

The answer lies in the way power banks work and some of the power converters, as well as usb power supplies.

In the good old days when you wanted to take a power source like 220v or 110v and down convert it to 5v, you would use a transformer, then a rectifier and lastly filter out the noise with a capacitor and optionally an inductor. This works great and if used on audio applications the noise is inaudible or very close to it (at least not from the power source) but the biggest drawback of this method is weight, high power transformers weight a lot.

These days there is a need to make things smaller and weight less and so we have all sorts of switching power supplies and as their name implies, they switch the power on and off to achieve the same goal.

In general there are 3 types of switching power supplies:
- step-up, also referred to as boost converters where the input voltage is lower than the output.
- step-down, also referred to as buck converters where the input voltage is higher than the output.
- buck-boost converters where the input voltage can either be lower or higher.

In my particular case it is step-up converter from a Lithium Ion battery so 3.7v - 4.2v up to 5v

But lets look how bad it is

If you look at the ripple size, it pretty much covers the whole voltage output range, a very fast ripple but still.

Looking at the Orange PI Zero, there seem to be another relatively large inductor next to the USB connector where power comes in:

Which led me to believe another type of switching is going on the PI and common sense dictactates that two switching power supplies without some type of smoothing or filtering is a bad idea.

So I decided to experiment with a small 220uf capacitor and solder it straight on the power bank

And voilà !

124mv !

But the best part is, its actually working and stable.

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