bypass capacitors inquiry

[robismyname]

I understand what a bypass cap does - suppress DC signals with ripples.

But how does the bypass cap work?
Is the amount of suppression caused by the bypass cap based on the charge and discharge time of the capacitor using t(tau)=R*C?

 

[zx_sa]

The bypass cap (or decoupling cap) is effectively a low-pass filter. It offers a short circuit path to ground for high frequencies.

Yes, you can calculate the capacitance based on Tau = RC. In this case you can pretty much use the Thevenin equivalent resistance that the capacitor would see in the circuit.

But, it's more common that rule-of-thumb values for bypass capacitors are used. For example, you will use a 100nF cap when you deal with noise of up to 1-2MHz.

 

[robismyname]

But, it's more common that rule-of-thumb values for bypass capacitors are used. For example, you will use a 100nF cap when you deal with noise of up to 1-2MHz.

This link suggest 3 caps in parallel with varying sizes. Is this overkill? Or is there a real need to do this?

**broken link removed**

 

[dipnirvana]

well use of multiple caps in pareller may kill your design by the "anti-resonance" . use should always do some simulation b'4 putting it in your design .

 

[zx_sa]

I can't say that I've seen using three caps in parallel as being common practice. However, two caps are used in designs which are noise sensitive. These caps will be different values so that each filter a different frequency range.

Looking at your link, this is what they suggest. The third cap that they suggest would go on the output of your regulator / power supply. The other caps will general go right next to the power pins of the ICs in your circuit.