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Diode Basics

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mark_3094

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The attachment is my notes for diodes and how they work.
I'm not so sure if I've got the right idea, particularly with zeners.

Would anyone be able to have a look and tell me if I've got it right or not?


Thanks
 

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  • Diodes.doc
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Zener diodes are designed to survive the breakdown (within limits) and breakdown very predictably (predictable breakdown voltage).

I didn't read anything after the first 3 bullets of zener diodes.
 
I just skimmed, but seems pretty good.

have a look at the I-V curves for diodes, especially zeners. they helped me understand - when a Zener is in breakdown, its slope is VERY steep. This means that for a LARGE change in current (vertical), there is a SMALL change in voltage (horizontal), which is why they are good regulators.
 
Look at the datasheet for a 1N4148 diode. It does not suddenly conduct when its forward voltage is 0.7V. The graph shows that current and temperature affects the forward voltage.

At a current of 1uA the forward voltage is only 0.275V at room temperature.

Why do you say that diodes have a maximum reverse voltage of usually only 50V?
Look at the 1N4148 and the 1N4007.
 
If you bias it properly a diode can actually be used to amplify. You just have to bias it precisly at that knee point where it goes into conduction.
 
If you bias it properly a diode can actually be used to amplify. You just have to bias it precisly at that knee point where it goes into conduction.

How so? Please elaborate. I don't get it...
 
Not great amplifier mind you! Diode's have a linear region during their pass from non conducting to conducting, you can bias the diode with a fixed voltage and capacitivly couple an external signal into it. Distortion is horrible though, not particularly useful, though I've heard some crystal radio makers use a bias voltage to increase sensitivity.
 
Misread some information on that one. It should have been 'Diodes have a maximum reverse voltage, usually around 50v or more'

I missed reading the 'or more' part

Thanks
 
No, a diode will not conduct until it's forward voltage threshold is crossed. Typically .7v. LEDs are higher (1.0-2.0v) and Schottkys are usually less (~.3v)
 
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The current is so small in all but the rarest of conditions you can ignore it.
 
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