I need help with configuring an scr with discrete components..i have tried it so many times using npn and pnp transistors but it never works..
Is it not practical?

 

Please help me out

 

The configuration is correct. What exactly "doesn't work"?

 

The configuration is correct. What exactly "doesn't work"?

It doesn't work as stated...it is on already even without an initial gate trigger..

 

It doesn't work as stated...it is on already even without an initial gate trigger..

What happens if you connect the left hand end of the resistor to ground instead of the 4V supply?

 

Thats the gate terminal connected to vcc via a switch in series with a resistor..so how am I suppose to send a signal to the gate if connect the other end to ground

 

Use a double throw switch so that end of the resistor is connected either to the supply or to ground. If you leave it disconnected then the leakage current may be sufficient to trigger the 'SCR'.

 

Use a double throw switch so that end of the resistor is connected either to the supply or to ground. If you leave it disconnected then the leakage current may be sufficient to trigger the 'SCR'.

Can i get a diagram please

 

it is on already even without an initial gate trigger.

It is permanently triggered in the circuit you show, because the 'gate' (the base of the NPN transistor) is connected to the positive supply through a 1k resistor.

 

Can i get a diagram please

Here's an easier solution to the problem. Connect another 1k resistor from the base of the lower transistor to ground.