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Voltage Filter

  1. Dec 26, 2014 #1
    I'm working on a circuit involving an incoming audio signal via a 3.5mm headphone jack. The circuit cannot handle voltage spikes greater than 4 VPK. Is there any sort of IC, or circuit that allows voltage under 4 VPK to pass through, but filters any voltage over 4 VPK to exactly 4 VPK? The only way I have come up with is to use a micro-controller that samples the incoming audio signal every 50 microseconds and perform the calculations to limit any voltage over 4 VPK. It'd be much easier and cheaper if I could use some sort of IC or circuit to filter the voltage instead of using a micro-controller.

    To be clear, I am not trying to filter based off of frequency, I essentially want any incoming audio signal greater than 4 VPK to essentially "platue" at exactly 4 VPK. So if the incoming signal has 3 VPK, it passes into the circuit as 3 VPK. If the incoming signal has 5 VPK, it passes into the circuit as 4 VPK.

    Also, sorry if this is a simple question. I'm about halfway through my EE degree, but I can't seem to figure out a way to do this besides using a micro-controller.
  2. jcsd
  3. Dec 26, 2014 #2


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    Staff: Mentor

    You would use diode clamps or a transistor with base multiplier resistors to clamp at your 4V level.
  4. Dec 26, 2014 #3
    Thanks so much for your reply. After researching clamping/clipping circuits, I came across this circuit, which I believe is very similar to what you're describing, however it uses an op-amp.

    I continued my research further to see if anyone had used a clamping/clipper circuit for audio, however I ended up finding this Wikipedia page about consumer and professional audio line levels. It turns out that consumer audio has a VPK of 0.447 V, and pro audio has a VPK of 1.736 V. It looks like I won't ever have to worry about the voltage peaking higher than 4 VPK anyways!
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