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Diode Basics

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mark_3094

New Member
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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dknguyen

Well-Known Member
Most Helpful Member
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.
 

solis365

New Member
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.
 

audioguru

Well-Known Member
Most Helpful Member
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.
 

Sceadwian

Banned
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.
 

Mikebits

Well-Known Member
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...
 

Sceadwian

Banned
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.
 

mark_3094

New Member
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
 

smanches

New Member
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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Sceadwian

Banned
The current is so small in all but the rarest of conditions you can ignore it.
 
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