Hi, I'm polarizing with a zener.
How much capacity must the capacitor have in parallel to the zener .. to silence it? ..please..
I would like to stay away from the audio band of course ...
many thanks 😀
How much capacity must the capacitor have in parallel to the zener .. to silence it? ..please..
I would like to stay away from the audio band of course ...
many thanks 😀
Look up the Zener incremental impedance R at the operating point, then use the formula
f = 1 / (2Pi x RC) by choosing the frequency f at say 20Hz. The C value will be fairly large.
If the Zener is used as a reference voltage and does not need to have a low source
impedance, instead just follow the Zener with an RC low pass filter. Then required C
will be much smaller since the R can be much larger.
f = 1 / (2Pi x RC) by choosing the frequency f at say 20Hz. The C value will be fairly large.
If the Zener is used as a reference voltage and does not need to have a low source
impedance, instead just follow the Zener with an RC low pass filter. Then required C
will be much smaller since the R can be much larger.
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Just be sure if the zener is used as a voltage reference, that the series R is not big, compared to the circuits resistance of the transistor, IC, or tube that uses the reference voltage.
Otherwise, the voltage drop across the series resistor will lower the final reference voltage.
Otherwise, the voltage drop across the series resistor will lower the final reference voltage.
Note that zeners are many orders of magnitude noiser than any other active device you are likely to encounter. The ESR of the capacitor is often the limiting factor in the noise that gets past the capacitor.
Say the zener dynamic impedance is 10 ohms, the capacitor ESR is 0.1 ohms, then you cannot attenuate noise more than 40dB with that setup, irrespective of the capacitance, and that may not be enough to bring the noise down to the noise floor. If you want the capacitor to reduce the noise by 40dB at 20Hz you'll need 80,000µF too!
However string an RC circuit off it (10 ohms + 10000uF) and it'll perform way better, (-80dB ultimate) and the original cap can be reduce to 10000µF too for the same -40dB at 20Hz
Its common to use LEDs for small voltage references in amps these days as they are not noisy like zeners.
Say the zener dynamic impedance is 10 ohms, the capacitor ESR is 0.1 ohms, then you cannot attenuate noise more than 40dB with that setup, irrespective of the capacitance, and that may not be enough to bring the noise down to the noise floor. If you want the capacitor to reduce the noise by 40dB at 20Hz you'll need 80,000µF too!
However string an RC circuit off it (10 ohms + 10000uF) and it'll perform way better, (-80dB ultimate) and the original cap can be reduce to 10000µF too for the same -40dB at 20Hz
Its common to use LEDs for small voltage references in amps these days as they are not noisy like zeners.