Latching Circuit npn/pnppnp

[cjdelphi]

While waiting for the thyristors....



I built this, simulator says it works (using a 2n222 (generic npn) and a 2n44?? (Generic pnp)

In real life, it fails to work...



After an hour or so i gave up and tried the above circuit (simply moved the feedback point to the base of the npn)

This works, but i don't understand why the first circuit fails (if you get some free time, give it a try)

It's a self latching circuit, touch gnd via the 1k on the npn it goes off, supply a pulse of vcc, the LED comes on, basicslly a thyristor... it has me stumped as to why the first circuit fails but works on a simulator :/

 

[Alec_t]

i don't understand why the first circuit fails

The top transistor is upside-down. It shouldn't work in the simulator unless the sim is modelling reverse breakdown.

 

[Arouse1973]

The simulator will work and so will the circuit in real life. The transistor doesn't care which way around the emitter and collector is connected. It will just have different component value requirements for it to work. This includes max reverse voltage and gain considerations. This is probably why it's not working in real life.
Adam

 

[Colin Mitchell]

"I built this, simulator says it works"

That's why the simulators are so reliable.
If you need a simulator to work out if a circuit will function, you don't know anything about electronics.
You would be an ideal person to employ at $230,000 per year.

 

[cjdelphi]

Yeah, originally the pnp was the right way round, i must have accidentally hit the reverse icon (flips it)

I flipped it back, the gain is working now on the sim, it's also possible i made the mistake of copying it into the breadboard

6am right now, thanks, i'll try it out later on and get back