Understanding a 555 w/ SCR circuit.

Thread Starter

Wendy

Joined Mar 24, 2008
23,415
OK, this is a spin off of this thread...

2 led timed circuit

It is funny, what the OP needed was actually much simpler than what I came up with. However, I came up with a circuit that shows how a basic SCR works.

I'm thinking of using this for one of the articles. I'd like to understand when something don't go the way I think it should. The first circuit doesn't work on the alarm/red light, the second does. I'd like to understand why.




 

gerty

Joined Aug 30, 2007
1,305
Looks like the Sonalert is shunting the led, maybe the fact that it's polarized has something to do with it. I don't know whats in the driver circuit for them.
It's probably something simple that'll make us slap our foreheads.
 

Thread Starter

Wendy

Joined Mar 24, 2008
23,415
Actually R5 is the same part on both, I just forgot to update the schematic. If you look at the print it is 330Ω.

It doesn't appear that an "SCR" is being utilized in the posted schematic.
Please advise....


You may review:

http://en.wikipedia.org/wiki/File:SCR_symbol.svg
Review this and you will see the connection...

http://www.allaboutcircuits.com/vol_3/chpt_7/5.html

Thanks Bertus, I hadn't realized the difference. Subtle, but there. I needed to trigger on the negative side of the pulse.
 
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