Diode Basics

[mark_3094]

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

 

[dknguyen]

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.

 

[Mikebits]

You left out my favorite diodes. PIN diode and Varactor diode.

http://www.electro-tech-online.com/custompdfs/2009/03/pin_diode_handbook.pdf

Varactor or varicap Diode :: Electronics and Radio Today

 

[solis365]

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]

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]

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]

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]

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.

 

[colin55]

Some corrections to diodes.doc

 

[mark_3094]

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

 

[mark_3094]

Can the diode conduct when there is less than 0.7v across it?

 

[smanches]

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)

 

[colin55]

It will allow a very small current to flow when the voltage is as low as 200 - 300mV

 

[Sceadwian]

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