Similar to this question, I need a replacement for a programmable unijunction transistor [PUT]. Specifically, I'm trying to emulate the behavior described in the 2N6028 datasheet. However, I would like to build my own from normal transistors rather than buying one.
I found this page on the Makezine forums where someone asked the same question. This links to this page on edaboard which includes a schematic, but I'm not sure what the OP means by "two base B1 B2" or whether the following schematic:
indicates that I need exactly those particular transistors or if I could substitute in other bipolar transistors (e.g. BC548B).
This is a curiosity, I am not saying that it is a functional project, but I am instead interested in attempting to build a component out of others. I may learn something, I may not. I look forward to finding out. I'm working through the Make: Electronics book, and several of the critical beginning experiments call for a PUT. I am aware that PUTs are old, but I'm interested in this as a curiosity.
Best Answer
I'm also working my way through the book "Make electronics" by Charles Pratt. I also stumbled on the PUT at experiment 10. The circuit simulator I'm using icircuit, based on this circuit simulator applet but it doesn't provide a PUT component, although it's a really great simulator.
I tried the first proposed alternative above (1 transistor PNP and 1 transistor NPN), but it doesn't give reliable results on my simulator. I guess ordinary transistors don't always behave as ideal/simulated transistors.
Consulting the book "practical electronics for inventors" from Paul Scherz, I think i found a good alternative to the PUT with the MOSFET N channel:
Please note that for the MOSFET (enhancement) n-channel, the positive voltage must be at the gate (G) and not at the source (S) as it is the case for the PUT.
I took a a printscreen of the result in my circuit simulator applet. It seems to work all right.
UPDATE 23/08 : In the end, it happened that the idea of replacing the PUT with a MOSFET (enhancement n-channel) in experiment 11 of makes electronic from Charles Pratt was a dead end. A valid alternative is a 555 timer. See following post.