Question for you experts

The quest for my part sourcing is still going on, bringing to me so many questions that need answers. So here’s my question to you guys, because your preparation is far far better than mine:

talking about the tantalum cap, what if I use a 1uF cap instead of the indicated 10uF?

Please, give me a simple answer, I’m still trying to understand but sometimes I need an hand.

Thank you all.

Its to small to be really helpfull.

But you can go completely without (the word optional is even printed on the PCB), should be no problem with a reasonable dimension of your wallwart (+500mA).

basically, the 10uF can store 10 times more energy than the 1uF. if for example a cap has to smoothe a pulsation then the effect increases with higher capacitance. like in a psu for higher currents you increase the F value. but that’s very generally spoken, not necessarily related to the use here at this place in the circuit. in other words i don’t know!

Thank you guys for your answer.

Let’s see if I get it: a capacitor stores the current just like a little can; it can release the stored current in case there is a drop in the tension of a circuit. In the Shruthi’s power line it is possible to have drops which are well handled by a 10uF cap, while a 1uF cap is a “too small can”.

Am I right or am I telling crap?

Then the next question is: why a tantalum cap? I read they have a more accurate and stable capacity while have a lower loss of current, but is it strictly necessary or it can be substitued with a ceramic one? (I know it is marked as “optional” on shruthi’s board, I’m just trying to understand more).

It depends… referring to your picture the capacity is the volume of the can , now it depends how fast you can get the water in and out. Tantalum caps have a “big hole” so in your picture the water can very fast flow in and out - and thats whats needed when you have fast transients. Luckily nowadays there are next to no nasty Transients on the powerlines and if your wallwart is a good one (that shurely has some caps in it, too) the chips (1054, 7805, 7905) + caps on the board can well handle the Shruthis needs alone - as long as no solar storm comes around. If you have a tantalum cap - fine. If not it will work without. Its like triple topping ond the double cream on your supersize icecream .

If you plan to drive your Shruthi from a DIESEL generator in an Brazilian Favela you’d better go for a Tantalum Cap but hey - then you have obviously other problems then gettin the right cap. If you want to replace it with a ceramic one its a waste of money because a ceramic cap has not the needed specs - it will work but it wont make your PowerSupply better.

Tip: Put a Dollar under your Pillow, maybe the Capacitor Fairy will bring you a Tantalum . .

So it’ not a matter of capacity, but how fast you can handle the transients.

Thanx fcd72, now everything is more clear.

Its a matter of Both. If its fast but to small you can only buffer halfway . . . or put it another way: you don’t just need a fast car, you also must drive like hell :wink:

Yes, of course… I was thinking at the difference between tantalum and ceramic caps both with the same capacity (10uF)… in this case it’s only a matter of the car type :smiley:

yes, the one is a Lada Niva whereas the tantalum is more the Alfa 8C type…

Olivier explained it in some other thread earlier. the reason why he chose a tantalum cap in parallel to an electrolytic was to obtain lower ESR, because that’s what tantalums are also very good at.
i haven’t looked for the thread but you should be able to find it, it’s been just recently and that’s what i remember.