# AC Coupling

Discussion in 'General Electronics Chat' started by RadioRental, Sep 3, 2009.

1. ### RadioRental Thread Starter New Member

Sep 3, 2009
3
0
Hello all,

Great forum,

Can anyone tell me how you work out what size capacitor you use to ac couple circuits. I assume its to do with the frequency but how do you work it out?

Also i was how do you know when to use polorised and non polorised caps? Can they be interchanged if the same value?

sorry for all the questions i am only beginning to learn electronics.

Thanks

2. ### GetDeviceInfo Senior Member

Jun 7, 2009
1,571
230
you will want to calculate what impedance you wish to introduce into the circuit. Your formula of Xc = 1/ (2Πfc) will help you determine the meaure of capacitance.

Polorized capacitors are typical of the electrolytics. You should use them with DC values. I've had firecracker action with reversed electrolytics.

3. ### kkazem Active Member

Jul 23, 2009
160
27
In a pinch, one can use electrolytics as non-polarized caps by doing the following: You need two caps, each double the value you need. Put them in series either plus-to-plus or minus-to-minus. The series caps will cut the value in half to the desired value, and it makes the series caps non-polarized.

The calculation for coupling was covered by GetDeviceInfo, except how do you know what impedance you need? You will actually want to calculate the cap impedance to be at least twice the input resistance or impedance of the circuit you're coupling it to at the lowest frequency of interest. If not, tou will get your input signal cut down at the lower frequencies.

Regards,
Kamran Kazem
kkazem