power supply question

[sal_park]

Hi,

I've got a power supply situation that I could do with some help on. I'm powering a raspberry pi (5v, 400-500mA) from a powerbank (http://www.clasohlson.com/uk/Clas-Ohlson-2600-mAh-Powerbank/Pr386941000 rated at 5v 1A).

Anyway I want to be able to cope with the situation when the power coming in to the powerbank is removed. The powerbank will then take over and supply the 5V, but there is a 100ms gap where the voltage drops to around 3 volts which causes the raspberry pi to crash.

Question is, what kind of a circuit can I place inbetween the powerbank and raspberry pi to fill in this 100ms gap ? I know which end of a soldering iron to hold, but I'm not an EE.

So, any pointer are welcome as I'm a bit stuck 

sal

[Kjelt]

A huge elco or goldcap capacitor is needed.

[hushaoxin]

Add a Super capacitor between the powerbank and raspberry pi, That's OK!

[danadak]

You can calc the capacitance. See attached.


Regards, Dana.

[TheAmmoniacal]

http://www.ebay.com/itm/2-PINs-Super-Capacitor-Button-Type-5-5V-1-5F-Ultra-Capacitor-2pcs-/272225538535

These should be more than enough

[Kjelt]

But I would choose a decent brand of goldcap like Nec or similar.

[Ammar]

Your load is effectively R = V/I = 5/0.5 = 10 ohms. You want to smooth over 100ms, so say you want a time constant of 3 times tau for your capacitors. tau = R*C. Looks like you might need about 30mF.

Try a 47mF or higher super cap. Then put a few electrolytic caps in parallel (several hundred microfarads), and then a ceramic 0.1uF cap. Super caps tend to have high ESR and probably will not be able to deliver pulses of current. Hence, the extra types of other caps.