Zenner Diode Clipper

  • #1

Main Question or Discussion Point

HI.

I am using Piezo Electric as a AC voltage source which gives voltage spikes of around 35V little current because the impedance of the material is verry high, I would like to clip this voltage to 22 Volts i have seen that a 2 x 22V zenner diodes can be used back to back is thie right or will i need a different value zenner for the negative?

also can anybody tell me what rating of diodes i will need?
 
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Answers and Replies

  • #2
berkeman
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HI.

I am using Piezo Electric as a AC voltage source which gives voltage spikes of around 35V little current because the impedance of the material is verry high, I would like to clip this voltage to 22 Volts i have seen that a 2 x 22V zenner diodes can be used back to back is thie right or will i need a different value zenner for the negative?

also can anybody tell me what rating of diodes i will need?
Yes, back-to-back or nose-to-nose Zener diodes make an effective bidirectional clamp. Since the source impedance of your source (the piezo) is high, you probably do not need any series resistance.

If you want the clamp voltage to be 22V, you can use either two 20V zeners or two 22V zeners. The forward diode voltage drop adds to the total clamp voltage, obviously. :smile:


EDIT -- OH, whoops. You edited your post since the last time I read it. Now instead of resistance, you are asking for what rating of diode to use. Since your currents are small, I would think that a small 400mW rated diode would work.
 
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  • #3
Thank you I have ordered some 22v zenner diodes in which I will use tomorrow.

I tried to use this before but this didn't work I assume its because I used a series resistance thus making my over all impedance very high which pretty much stopped my circuit from working. I will simple try using this back to back with no series resistance and see what result I get. Thank you
 
  • #4
jim hardy
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Check your zeners when you get them - some zeners use an internal second junction in series for better temperature performance . If you find that yours won't conduct when forward biased to their reverse breakdown voltage, you can use them in parallel rather than in series.

old jim
 

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