Back-to-back diodes?????

[carbonzit]

Saw something posted over in another thread here that has puzzled me for a good long time. (Pardon my relative ignorance if it shows!) It's a pair of diodes connected back-to-back.

What????

Doesn't this just create a ... a short circuit?

Since when does this
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not equal this?
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(or at least this, R being equivalent to the 0.7V forward drop of a SI diode)
**broken link removed**
?????
Now, I'm not a complete dummy. Obviously at DC this would essentially be a short circuit, so it must have something to do with AC signals, possible dependent on frequency. Can someone enlighten me (and perhaps others) what this highly non-intuitive scheme does?

 

[audioguru]

Two back-to-back diodes do nothing when the AC signal across them is low at about 1V peak-to-peak or less but they suddenly conduct when the signal level is about 1.2V p-p or more.
It makes a lot of fuzz (distortion) in a guitar circuit. It makes a good voltage clamp to prevent an AC signal from exceeding 1.2V p-p or 1.4V p-p.

 

[carbonzit]

Two back-to-back diodes do nothing when the AC signal across them is low at about 1V peak-to-peak or less but they suddenly conduct when the signal level is about 1.2V p-p or more.
It makes a lot of fuzz (distortion) in a guitar circuit. It makes a good voltage clamp to prevent an AC signal from exceeding 1.2V p-p or 1.4V p-p.

So they behave almost like an ac zener? (I know, not really, but they sound functionally similar.)

So this behavior is due to the ~0.7 V forward voltage drop of the junction (for Si: ~0.3 V for Ge), correct?

 

[KeepItSimpleStupid]

Basically it's a clap at +0.6V and -0.6V. One place you will see this a lot is across the inverting and non-inverting inputs of an OP amp. In most circuits, the difference is supposed to be zero. It also helps overload recovery.

You can also see this in certain scopes or meters as part of the protection circuitry.

 

[Roff]

Basically it's a clap at +0.6V and -0.6V. One place you will see this a lot is across the inverting and non-inverting inputs of an OP amp. In most circuits, the difference is supposed to be zero. It also helps overload recovery.

You can also see this in certain scopes or meters as part of the protection circuitry.

If you read "clap" as "clamp", it will make a lot more sense.

 

[KeepItSimpleStupid]

yep. Cheap keyboards on expensive computers.