Diodes - explanation please?

[igorbog]

Hi
could you please explain when I use each type of diodes and what are important parameters for each diode type:
Schottky Diode
Zener Diode
PN DIode
SCRs & TRIACs
I'm looking for a short explanation. Thanks

[Rerouter]

Schottkey diodes have a very low forward voltage drop, they are good in clipping circuits (if external diodes clip the signal before the internal ones, your device wont need to shunt any current through it, also are good for higher efficiency rectifiers, (lower drop means less wattage for given current)

zeners give a stable voltage drop when given a stable current source, far better than a resistor divider, worse than modern reference IC's, though when around 6.3? - 6.4V? has nearly no temperature offset, and at other voltages can be used in temperature compensation, as most follow a rather static charachteristic, though with way they go, i have also forgotten,

as for the rest, lack the knowledge to summerise,

[mariush]

Watch these:








  (and the following videos in playlist explain shottky diodes and so on)
 
Should explain a large part of your questions and requests.

[Jovian]

You may find this link useful:

http://www.sparkfun.com/tutorials/212

Regards,
Jovian.

[Jovian]

As for SCRs and TRIACs,
Basically and SCR is two transistors an NPN and PNP in the following configuration:

when the SCR is "off" only a small leakage current will flow through it. however when the gate is activated (sufficient positive gate current) then TR2 starts to turn on, as it does that TR1 starts to turn on too, this feeds more current into the base of TR2 and so the cycle goes. This means that if the gate current is removed the SCR remains latched "on". To turn off an SCR the anode current must be reduced to below a value called the minimum holding current (I_H).
As for TRIACs they are basically SCRs for AC, essentially just two SCRs in parallel anode to cathode with the gates joined, so that it can operate in both directions.

SCRs are commonly used for crowbar circuits, motor controllers, high power AC rectification.

This may help: http://www.allaboutcircuits.com/vol_3/chpt_7/5.html

Regards,
Jovian