Self activated transistor?

[fuzic]

I've lately been trying to set up a simple circuit with a transistor, where when power is connected to the base, some portion of the emitted voltage is channeled back and fed back into the base to keep the transistor open.

So far I've had no luck.

I tried to put together a flip-flop last night but that seemed to just short circuit and heat the transistors to unhealthy levels.

I'm mostly curious as to whether the circuit described above is even feasible, so that I can start looking in another direction if this can't be done.

Thanks for the help, and sorry for my ignorance.

 

[Nigel Goodwin]

You mean a latch?, turn it on and it stays on? - you need two transistors, one NPN and one PNP - wire them to make a 'silicon controlled switch' (PNPN or NPNP) - it's a standard circuit.

 

[UTMonkey]

I don't know about feeding back to keep the transistor on, but won't an SCR do this?

 

[jpanhalt]

I don't know about feeding back to keep the transistor on, but won't an SCR do this?

https://en.wikipedia.org/wiki/Silicon-controlled_rectifier

Aren't Nigel's suggestion and an SCR essentially the same thing, except the SCR is in one package.

 

[dknguyen]

Yeah. One is an actual SCR, and the other is the theoretical circuit model of an SCR using BJTs- brought to life in the most literal sense. Is an SCR actually built the same way? I was under the impression it was slightly different somehow.

 

[Nigel Goodwin]

Yeah. One is an actual SCR, and the other is the theoretical circuit model of an SCR using BJTs- brought to life in the most literal sense. Is an SCR actually built the same way? I was under the impression it was slightly different somehow.

An SCR is made on a single piece of silicon - two transistors are on two seperate pieces (fairly obviously). SCR's tend to be high power, transistors tend not to be.

 

[jpanhalt]

Is an SCR actually built the same way? I was under the impression it was slightly different somehow.

SCR's are made by General Electric exclusively, as I understand it. Other companies make thyristors -- another pearl from Wikipedia. John

 

[Dean Huster]

Last time I taught the material, silicon-controlled rectifiers and triacs were both members of the thyristor family. Has history changed on me again?

Dean