PUT Programmable Unijunction Transistor, how they work.

[oz2cpu]

Programmable Unijunction Transistor,
if you like to know how a PUT works ??
I finally figured it out today 🙂
feel free to look here:
https://youtu.be/WyaoWMIgkiI
super short explainer video

[SeanB]

Yes have used those in the past, mostly in light dimming applications. Very interesting devices, and they are actually still available, and cheap as well. Not quite in the dozens per cent range, but a few cents each, or by me 4 ZAR.

[oz2cpu]

the actual device i mention in the video 2N6027
it is still available from mouser, and is a few $ if you like to play with it.
is a low power signal level kind of part, used to trigger bigger parts that handle the power you need,
and its gate polarity is the other way arround, compared to SCR and TRIAC,
that is why i found it interesting to play with PUT and to explain it, since no where i looked online,
no videos, revealed the important gate polarity and what terminal is its refferance,

the parts you mention for light dimmers, are TRIAC
they are like an SCR, but double, so they can be used for AC

[BILLPOD]

Good Morning Oz2cpu,  Thank you for this video, (very well done).   You have triggered my memory to a point back in the late 1970s.   Back then I was in school,
(adult night classes), and I now remember learning about these, briefly.   And I found one in my collection of 'rare & unusual devices'.  I'm going to spend some time reproducing the circuits in the video.  Thanks again.

[SeanB]

the actual device i mention in the video 2N6027
it is still available from mouser, and is a few $ if you like to play with it.
is a low power signal level kind of part, used to trigger bigger parts that handle the power you need,
and its gate polarity is the other way arround, compared to SCR and TRIAC,
that is why i found it interesting to play with PUT and to explain it, since no where i looked online,
no videos, revealed the important gate polarity and what terminal is its refferance,

the parts you mention for light dimmers, are TRIAC
they are like an SCR, but double, so they can be used for AC

No, used unijunction transistors to trigger a triac, using the UJT  as phase angle control, with it having a slowly rising voltage feeding the UJT.

Similar to this in fig 2

https://www.chemical-ecology.net/papers/aesa83.htm

Though it did not have that complex LDR assembly, just a simple RC and diode to have a slow ramp feeding the emitter, though it did have the 2 transistors gating the UJT power so as to synchronise it to mains zero crossings.

[HwAoRrDk]

Only time I have ever come across a PUT in the wild is in a heating system pump over-run module from the mid-1980s that I was trying to repair. The module's job was to make the pump run for a couple of extra minutes after the heating was shut off. I tried to reverse engineer the circuit to figure out how it worked but couldn't figure it out, mostly due to this weird, unfamiliar transistor that at the time I couldn't find any good information about. So I had to take a trial-and-error approach with replacing obviously or potentially bad components. Luckily it was just a couple of bad caps and a burnt resistor. All the while I was hoping it wasn't the PUT that was faulty because the only place I could find that stocked a replacement was Mouser USA, which would've been a rather expensive purchase for just one part.

[oz2cpu]

thanks for the link Sean, yes that is exactly a PUT cool idea to make a light dimmer
adjusted by how much light you have in the room :-)

to HwAoRrDk, that is exactly why i feel i had to make the video,
no one wanted to reveal in any online material webpages or videos,
how the gate voltage is controlled, polarity, or in relation to what of a PUT
that important information was needed for my power supply repair,
I show a schematic bite of it, in the end of this video, i was able to repair the unit :-)