# RF choke vs bypass capaxitor

Discussion in 'General Electronics Chat' started by yuvi1, Mar 6, 2014.

1. ### yuvi1 Thread Starter Member

Feb 1, 2013
37
0
hi guys,

can someone explain what is the difference between RF choke and bypass capacitor ? i know that we use capacitor to pass AC to ground , and i know that we use RF choke (coil) to block AC signals , so what is the difference and how can i know when to use each one .

thanks !

Last edited: Mar 6, 2014
2. ### Papabravo Expert

Feb 24, 2006
11,132
2,173
I have two questions for you
1. What is the impedance of an RF choke as a function of frequency?
2. What is the impedance of a capacitor as a function of frequency?

3. ### yuvi1 Thread Starter Member

Feb 1, 2013
37
0
i know that the impedance of the choke increase with the frequency , and the impedance of the capacitor decrease with the frequency in order to pass ac to ground .

but how the choke block the AC ? what are the considerations to use a capacitor and GND , and not to use RF choke ?

4. ### alfacliff Well-Known Member

Dec 13, 2013
2,449
429
chokes have resistance, in high current aplications, they might drop too much voltage. the best is to use both if you really want to get rid of stray ac or rf signals.

5. ### Papabravo Expert

Feb 24, 2006
11,132
2,173
So choke in series with a power rail will pass DC and low frequencies while blocking high frequencies -- right?

6. ### alfacliff Well-Known Member

Dec 13, 2013
2,449
429
it depends on the inductance of the choke. the higher the inductance, the lower the frequencies it will block. unfortunatly, that means more wire which means more resistance. or a (usually) ferrite core, which you have to choose the ferrite mix to determine the frequency also.
if using inductors and caps together, watch out for resonance, strange things can happen if you hit a resonant frequency, the impedance could go way up or way down.

7. ### yuvi1 Thread Starter Member

Feb 1, 2013
37
0
thanks a lot guys !