I am using a USB Power Bank as a Power Source for my Arduino.
It is very convenient since the Power Bank gives 5v like my Arduino Nano needs,
but there's a small problem.
When I view the Voltage coming from my Desktop Computer via a USB Cable, it looks like this:
As you can see, almost perfectly flat.
When I view the Voltage coming from the Power Bank, it looks like this:
I assume it's coming wavy like this, because the internal battery in the Power Bank is 3.7v,
and then it goes thru a Step Up circuit..
If I want to flatten the voltage that I get from the Power Bank,
should I only add a big electrolytic capacitor parallel to the power source?
Or do I need any additional component(s) besides the electrolytic capacitor?
Should I do something to limit the current that the big capacitor takes?
It might be critical especially in the beginning, when the capacitor is empty and then connected to the power..
The circuit is indeed working with this power supply,
yet for the sake of learning and improving, I would like to straighten it.
Also the price of a capacitor is not high at all, so why not?
It's just important for me to do it right,
because I remember that capacitors can pull high current on the beginning,
so just sticking a big capacitor might not do good (or even do bad), so I prefer to consult with people who know electronics as a profession..
Do you know the IC used for your step up, e.g. is it an MC34063A. Most boost converters will current limit to protect itself and the capacitor as well. The MC34063A has a lot of ripple like the scope image you posted shows, it runs at a lower frequency and is not current mode controlled. My project uses the MC34063A, so I've become aware of its weakness. The current mode control method is like a current limit auto adjustment, it should allow the voltage mode control to turn on the switch with each PWM cycle so the ripple is less (at partial load). The MC34063A lacks current mode, it only has voltage mode, so it waits until the voltage is low and then enables the switch. The power moves like a bucket line, and the MC34063A only moves full buckets. However with current mode control the amount in each bucket can be reduced.
LarryD:
If the power supply is a switching type, this ripple is normal.
Yes I know..
Yet I want to learn how to improve it..
(as I said, the arduino works, but learning how to improve it is interesting for me)
ron_sutherland:
Do you know the IC used for your step up, e.g. is it an MC34063A.
Well, the USB Power Bank is closed, and not with screws but with heat,
so unfortunately I cannot open it and have a look...
mauried:
If you do add a capacitor make sure its a low ESR type designed for switch mode power supplies.
Thank you for the tip.
I remember the term ESR - it's the internal resistance of the capacitor.
Why would it make a different here if the capacitor has a minimal resistance?
Wawa:
If you're not using the analogue inputs for measuring things, I wouldn't worry too much about it.
So the analog readings are most affected by power source ripple?
hmm, makes sense.
Wawa:
Smoothing caps on a (boost) converter could upset voltage regulation.
Not wise to add too much capacitance.
A better way is an LC filter.
A 47-100uH inductor (with low resistance), a 47uF LowESR electrolytic cap and a 100n film cap.
Hi Leo
Thank you for this circuit.
are all these 3 components connected parallel to each other?
or the 2 capacitors are parallel, and the inductor is in series to them?
The inductor is used in series.
An inductor has a high impedance for high frequencies, and is almost 0ohm for DC.
The caps are on the Arduino side, to ground.
They short the remaining high frequencies to ground.
An electrolytic cap is better at medium high frequencies, and a film or ceramic cap is better at very high frequencies.
Google LC filter.
Leo..