EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: yalect on July 11, 2017, 10:50:01 am
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Hello,
I would like to ask you I want to choose capacitor for transistor amplifier input and output.
please, can you led to me how I can do that or what's formulas and conditions?
Thank you
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For the input cap, use the input impedance and calculate the CR divider for a reasonable cut-off frequency, say 20 Hz.
For the output, make an assumption about the minimum impedance of the load and do the same calculation.
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Hello, thank you for your reply
what do you mean by the CR divider for a reasonable cut-off frequency, or can you give formula or example?
Thanks
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Commonly called a "High pass RC filter" or maybe a "first order passive high pass RC filter. The R is the input impedance of your next stage, while the C is your coupling capacitor.
Lots of good info out there, such as:
http://www.electronics-tutorials.ws/filter/filter_3.html (http://www.electronics-tutorials.ws/filter/filter_3.html)
With the corner frequency Fc=1/(2*pi*R*C) being the one of interest to you.
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Hi,
thank you for your reply but what's a simplest way to determine The appropriate value of coupling capcitor (input and output) ? considering the input impedance of the amplifier if we know that Extracting that impedance is something complicatedand.
thank you
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Well, if you can't compute it or estimate it, you can only measure it or simulate it with something like LTSpice. I would think it would be fairly trivial to measure it by inputting a signal from a signal generator via a resistor, and measuring the signal on either side of the resistor with a multimeter. Just make sure the frequency of the signal is within the multimeter's AC volt frequency limit.