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Diode usage to protect tweeters


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Good discussion on the use of diodes in tweeter protection circuits and how they work. One poster claims they work better than fuses.

Nobody's mentioned it yet, but they protect via clipping the waveform.

[There may be an "UT, oh" in the approach.... :P ]

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Nobody's mentioned it yet, but they protect via clipping the waveform.

[There may be an "UT, oh" in the approach.... ;) ]

Paralleled zener diodes connected anode to cathode connected across a tweeter will not form a class of circuit known as a shunt clipper or clamper. When the applied voltage exceeds the reverse breakdown voltage of the zener, it goes into the conduction band. The problem is that when it is forward biased it will conduct like a regular diode shunting the signal to the tweeter. This can be seen in the tutorial below;

http://www.electronics-tutorials.ws/diode/diode_7.html

This device is best used for establishing stable reference voltages in power supplies and is a valuable element in a voltage regulator. A series resistor is needed to limit the current through it. A better choice is an MOV. This is a true clamper. But it has the disadvantage of effectively short circuiting the amplifier if the voltage exceeds the breakdown voltage. The best circuit design would be to use a current limiting series resistor with an MOV and that combination in parallel with the tweeter. This will avoid damaging both the amplifier and burning up the MOV. The MOV voltage should be carefully selected to take into account the voltage drop across the current limiting resistor and the maximum voltage the tweeter will see. Here's a tutorial;

http://www.littelfuse.com/data/en/Applicat...note_an9767.pdf

Here are some offerings;

http://search.digikey.com/scripts/DkSearch...+oxide+varistor

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They are not in parallel, rather, series connected in inverse polarity. ;)

That should work. One will be forward biased and the other won't conduct until it reaches its reverse breakdown voltage. I think a current limiting resistor in series with them is still necessary to keep them from burning up and from short circuiting the amplifier.

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