Author Options:

substituting capacitors Answered

I was designing a board that uses a bunch of the same chip and all of the inputs require a capacitor. For example lets say I have 10 identical chips with identical setups. Instead of having individual capacitors for everything to ground (except for the outputs) can I combine all of the ceramic capacitors and use a couple of bigger electrolyctic capacitors? So lets say I can have 1 capacitor for all of the identical inputs instead of 10 smaller ceramic ones. But for stuff like timing do I need individual capacitors?



10 years ago

The way you describe the setup, you'd be tying all the inputs together, and I don't think that will work. And if it's decoupling caps to gnd, I'd say no. But until we know bit more about the chips, etc....hard to tell.

ok I'll be more in dpeth this time. Basically I'm making a battery charger that chargers 6 individuals batteries (each comprised of 3 cells). The input of all of them is 5 volts. attached to each input to ground is a 1 uf capacitor. If I have 10 of those chips running, can I have one 10uF electrolyctic (or ceramic, but I might not have that value in ceramic) capacitor instead?

Here is an explanation.....kind of: IF the capacitors are linked "in parallel" normally, then you could possibly get away with the larger cap since they would have their values added together. There may be problems with behavior however, as ceramics do not behave exactly like electrolytics.

Caps in series however, the formula is much like that for resistors in parallel.
For instance, the formula for 2 caps in series would be CT = C1 * C2 divided by C1 + C2

yeah, they're in parallel, I was just checking, I'll probably end up using ceramic caps though, 10 uF isn't that bad

It's worth experimenting with a single substitute... But if they are decoupling caps, then the capacitance is present just to draw off higher frequency noise. Substituting more capacitance probably would change the cutoff frequency. So also try it with 1, 2 or 3 ceramics of the normal value (decoupling caps are sometimes required to be very physically close to the IC--if so, maybe all are required.) Again, just guessing.

I'm still very much an electronics noob, but I'd think it would depend on the circuit.