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# Clock conversion of dc to ac

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#### syedhamzaali

##### Newbie level 3
In quartz crystal, a piezoelectric crystal is used. Which is either pressed or released when a dc voltage is applied. But in quartz crystal a dc voltage produces a clock, which is in fact caused due to continous vibration. How can continously vibration is produced?
And y it is not produced in piezo electric material? (I AM CONFUSED)

The crystal flexes when DC is applied but does not release until the voltage is removed. To make it oscillate it is necessary to add a circuit to remove the voltage or reverse it's polarity to make it release and flex again. How fast it flexes is decided by the crystal cut and size which is why it can be used to control the frequency of oscillation.

If you see a crystal oscillator module running from DC, it has the additional circuitry inside the package, it isn't just a slab of quartz.

Brian.

You are indeed confused.

A crystal has two terminals and is used as part of an oscillator circuit to determine the frequency, the crystal usually has an AC voltage imposed on it by the external circuit which sets up a mechanical resonance that the external circuit amplifies and outputs, typically the crystal is placed in the feedback circuit of an amplifier so that it the whole thing is self sustaining as long as there is power for the amplifier.

Now there are (usually 4 pin) modules that combine the crystal and the other components needed to form an oscillator, these are sometimes incorrectly referred to as crystals, but these take DC power and give you a nice high level clock output....

HTH.

Regards, Dan.

Sir can you refer any material regarding it. Because I don't know any ac input in my wrist watch, i just put a very small dc cell. Yes sir I read your last line too about dc input. But I need good material for it.
Regards

An oscillator circuit is powered by DC but it outputs an AC signal. The quartz crystal in your watch is part of an oscillator circuit.
Look in Google for Crystal Oscillator Circuit.

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