Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Polarization Problem

Status
Not open for further replies.
I do feel like i am bashing my head against the wall here.

1) a SCR is a latching device with DC power and can not be turned off via the gate, if so something is wrong.
2) the leds on the output (K) side of the SCR Can not make the gate sensitive or turn the SCR on, if so something is wrong.
3) the SCR can only switch on when + power (5v+) is applied to the gate, when power is removed from the gate or the gate goes negative the scr will remain latched on, until the load is removed from the output (K) or the supply is disconnected (A) then the scr will switch off and remain off till the gate is activated again with 5v+.
So yes the leds on the output of the scr can hold the scr latched on ONLY after the scr has received a 5v+ signal to the gate and not before.

Please try this test circuit to help solve the problem, note i have removed the 15 ohm resister and placed a 2200 ohm (2K2) resistor in the gate supply from the opto, as well as a 330 ohm resistor in the led supply to the opto.
Also note i have also removed 1 led from the output side of the SCR (K) as the 2nd led allowed a current path to supply the first led, the existing led should be on when the SCR is off, and the led will go off when the SCR is on.

Wire it EXACTLY as i have drawn it and it should all work the way these components are meant to.

Please do this test to help us help you.

Pete.
 

Attachments

  • PYRO test circuit.jpg
    PYRO test circuit.jpg
    119.1 KB · Views: 134
SA,
The SCR probably won't latch on with no load. I don't think the fuse is really there for the tests.
It probaby did latch with the other circuit with 45 ma load.
 
Last edited:
Hi Ronv,

Yes i agree the SCR wont latch without a load so maybe use a light globe for testing in the place of the fuse.

Ronv do you agree the test circuit i posted should work?

The SCR should latch until the fuse blows then it will unlatch, unless the fuse wires short out.

Pete.
 
Hi Ronv,


Ronv do you agree the test circuit i posted should work?

Pete.
Hi Pete,

Yes, You are going down the same path to confirm each stage is working.
I was going to have him put the led on the output of the opto after I confirmed the driver was sinking current.

Ron
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top