PUT Programmable Unijunction Transistor, how they work. - Page 1
Forum section: electronics / projects

author: oz2cpu
author_rank: Frequent Contributor
timestamp: August 01, 2024, 08:18:49 pm
content: 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/WyaoWMIgkiIsuper short explainer video

author: SeanB
author_rank: Super Contributor
timestamp: August 01, 2024, 09:23:34 pm
content: 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.

author: oz2cpu
author_rank: Frequent Contributor
timestamp: August 02, 2024, 09:01:26 am
content: the actual device i mention in the video 2N6027it 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 TRIACthey are like an SCR, but double, so they can be used for AC

author: BILLPOD
author_rank: Frequent Contributor
timestamp: August 02, 2024, 01:48:17 pm
content: 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.

author: SeanB
author_rank: Super Contributor
timestamp: August 02, 2024, 04:51:54 pm
content: Quote from: oz2cpu on August 02, 2024, 09:01:26 amNo, 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 2https://www.chemical-ecology.net/papers/aesa83.htmThough 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.

author: HwAoRrDk
author_rank: Super Contributor
timestamp: August 03, 2024, 03:03:49 am
content: 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.

author: oz2cpu
author_rank: Frequent Contributor
timestamp: August 05, 2024, 02:48:28 pm
content: thanks for the link Sean, yes that is exactly a PUT cool idea to make a light dimmeradjusted 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 PUTthat 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 :-)

author: oz2cpu
author_rank: Frequent Contributor
timestamp: October 01, 2024, 08:12:17 am
content: I just released a video about a power supplycontaining this PUThttps://youtu.be/0-c-puwGHjkthe video show and explain the mains frequency phase chopped pre-regulator with the PUTand two SCR and large inductor,i also show a rather funny problem, my inductor saturates randomly on first positive or negative phase pulse,and then it stay like that until next power on, i think the inductor is not perfectly designed for the job.