Urgent: Need help in Power Electronics and PIR sensors

[fskhan]

I am working on a project and nearing its deadline and still stuck in
few problems ... can anyone help out?

I needed a transil diode for my circuit protection and I am having
trouble acquiring it (surprising! isn't it) and for time been I am
doing it with a Zener but I know it wont be enough when it get tougher
i.e. when a high voltage transient gets in... so can anybody suggest me
a solution or alternative. I actually needed SA5.0A unipolar transil
diodes but can anyone suggest any other having same
characteristics(like 600W 57Amps 5.8V clamp and 6.8V breakdown) or a
zener perhaps would do?

can anyone tell me if I could use a VDR (voltage dependent resistor)
instead of a MOV(metal oxide varistor)

one more thing.. does any one know a triac or like wise that requires
low triggering current like 1 or 2 mA and PIR (pyroelectric infrared
sensor) thats cheap and easily available

 

[El Zorro]

(1) You can get SA5.0A from the distributor Digikey (www.digikey.com)
in DO15 or axial package from Littelfuse, ON Semiconductor or Diodes
Inc. The have stock now i just checked it. It takes a few days once
you´ve made the order and the price is quite good even if you order a
few samples.

(2) I have always heard VDR (voltage dependent resistors) to be another
name for varistors (variable resistors).

(3) Whether you can use a standard zener or not instead of a TVS diode
depends on the lines you are protecting and what you are protecting
them against. If they are high-speed lines (i.e. communications) then
you shouldn´t use a normal zener in general because of its higher
capacitance as compared to that of a TVS. Also a TVS is much faster
(typ 1ns). But if the only problem is the power capability then I
can´t think of any big problem because when we say a 600W TVS it
usually means 600W during 1ms or that order of magnitude.

(4) I don´t know of any triacs with gate currents lower than 10-20mA
at all operation temperatures but there may exist. This current
decreases with temperature so be careful to ensure proper operation.

fskhan ha escrito: