How to test 2N6027 (SILICON PROGRAMMABLE UNIJUNCTION) - Page 1
Forum section: electronics / projects

author: sdancer75
author_rank: Frequent Contributor
timestamp: June 12, 2020, 05:38:15 pm
content: Hi,Is there any way to test out of or in the circuit a 2N6027 PUT with a multimeter? In diode mode (off the circuit), I have 0.7V between Gate(+) and Cathode(-).My problem is that Anode to Cathode is always ON.Thanks

author: Ian.M
author_rank: Super Contributor
timestamp: June 12, 2020, 05:56:01 pm
content: Its effectively an anode-gate SCR. With the anode positive, and the cathode negative, it should pass no current until a trigger current >5uA is drawn from the gate. If your DMM's diode check range goes up to several volts you can use that to test it connected to its anode and cathode. It should initially read as open circuit. It can be triggered by briefly connecting a 10K resistor between the gate and the cathode. It should then conduct with a forward voltage of under 1V, and remain conducting until you break the anode or cathode circuit. Due to its high sensitivity, you may need a high value resistor, say 100K, between gate and anode to prevent false triggering during handling.

author: sdancer75
author_rank: Frequent Contributor
timestamp: June 12, 2020, 06:19:45 pm
content: Quote from: Ian.M on June 12, 2020, 05:56:01 pmHi, and thank you for your answer.Here what I did. I used the diode mode with the red probe connected to the anode and black probe connected to the cathode . No conduction.I connected a 9V battery negative (-) to the cathode and instantly touched the red (+) to the gate. I had conduction (anode-to-cathode) of about ~0.7V.Question: It supposed the PUT's gate it behaves as a voltage threshold, which means that anode-to-cathode should have more than 9V to conduct in the case as the gate to cathode had already 9V from the battery. That's the theory at least I have read. Am I wrong? So, why it is conducted while the anode-to-cathode had no more than 3-4 volts from the diode test multimeter?Regards,

author: Ian.M
author_rank: Super Contributor
timestamp: June 12, 2020, 06:50:53 pm
content: I hope you had a minimum of a 180R series gate resistor to limit the gate current, otherwise you may well have damaged it.I did say you might need a high value resistor from gate to anode to prevent false triggering.Operating as a PUJT (rather than as a SCR), it triggers when the anode goes significantly positive (typ. 0.7V) with respect to the gate, while the cathode is negative with respect to the anode. N.B when it triggers, all three terminals internally conduct, so the gate supply *MUST* have enough series resistance to keep the gate current under 50mA.If still in doubt try the first test circuit on page 3 of its datasheet:http://www.unisonic.com.tw/datasheet/2N6027.pdfWith a 9V supply and a 100nF timing capacitor it should oscillate at approximately 20Hz.

author: sdancer75
author_rank: Frequent Contributor
timestamp: June 15, 2020, 05:38:58 pm
content: Quote from: Ian.M on June 12, 2020, 06:50:53 pmOk, I tested the following schematic but the LED stays always ON instead of blinking.

author: Ian.M
author_rank: Super Contributor
timestamp: June 15, 2020, 05:54:12 pm
content: Try a red LED with a 100R resistor in series with it, as blue LEDs usually have a Vf of around 3V, which doesn't leave much headroom for the PUJT to operate with only a 6V supply. If that doesn't fix it either your PUJT is bad or you've confused its gate and cathode pins!

author: sdancer75
author_rank: Frequent Contributor
timestamp: June 15, 2020, 06:14:29 pm
content: Quote from: Ian.M on June 15, 2020, 05:54:12 pmI have a bunch of 2N6027 and all behave the same way. I doubt they are all bad. The battery I connected is 9V and no 6V but is metered about 8.8V.I connected also a RED LED with 150Ohm resistor in series, nothing changed. I am really really confused of what is going on here. Also, I connected the PUJT like the datasheet I found and you linked in a previous post.

author: Ian.M
author_rank: Super Contributor
timestamp: June 15, 2020, 08:10:09 pm
content: Where did you get the 2N6027 PUJTs from?

author: fuzzoli
author_rank: Regular Contributor
timestamp: June 15, 2020, 10:23:16 pm
content: Last week I just received my ebay stash of 2N6027s! I was actually stunned that they are still available!@sdancer75, what will you be using them for?-Frank

author: nuno
author_rank: Frequent Contributor
timestamp: June 15, 2020, 10:35:03 pm
content: I played with 2N2646 in my childwood... good memories.I bought some of these 2N6027 sometime ago and I assembled a basic circuit, but I can't remember which circuit exactly I assembled, but it worked.

author: Ian.M
author_rank: Super Contributor
timestamp: June 15, 2020, 11:00:45 pm
content: I had a certain fondness for thePhilips BRY39which is a four lead PNPN device, with both the anode gate and cathode gate brought out to pins, suitable for use as either polarity of PUJT or as a small SCR with either anode or cathode gating. Unfortunately its long discontinued and ludicrously expensive NOS from reliable stockists.

author: sdancer75
author_rank: Frequent Contributor
timestamp: June 16, 2020, 02:43:15 pm
content: Quote from: Ian.M on June 15, 2020, 08:10:09 pmhttps://www.ebay.com/itm/10PCS-2N6027-6027-TRANS-PROG-UNIJUNCT-40V-TO92-IC-TOP/172821744346?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

author: sdancer75
author_rank: Frequent Contributor
timestamp: June 16, 2020, 02:44:40 pm
content: Quote from: fuzzoli on June 15, 2020, 10:23:16 pmHi,From eBay too.https://www.ebay.com/itm/10PCS-2N6027-6027-TRANS-PROG-UNIJUNCT-40V-TO92-IC-TOP/172821744346?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

author: Ian.M
author_rank: Super Contributor
timestamp: June 16, 2020, 02:56:13 pm
content: So there's a medium chance that they are fakes, probably something else that's dirt cheap in the same TO-92 package, remarked.Using a meter with a diode check range, with the remaining pin not connected, a PUJT should read as a diode between anode and gate, anode positive, and open circuit between gate and cathode in either direction. It should read open between cathode and anode, with cathode positive. As we discussed earlier, it should either read open or under 1V between anode and cathode, anode positive, depending on whether or not its triggered.If two unused ones fail those tests, you've got fakes. Two pins conducting and a diode junction to a third pin suggests they may actually be JFETs.

author: sdancer75
author_rank: Frequent Contributor
timestamp: June 16, 2020, 03:28:34 pm
content: Quote from: Ian.M on June 16, 2020, 02:56:13 pmHi,As you can see by yourself I can read diode only when Gate (+) and Cathode (-) is connected. All other combinations are open circuit.

author: sdancer75
author_rank: Frequent Contributor
timestamp: June 16, 2020, 03:43:45 pm
content: GM328 recognized this as a thyristor. I will give it some tests to verify this.EDITED:Yep, it works like a normal thyristor.I connected the Anode to meter red lead, Cathode to black lead, and set meter to diode test. Then I shorted the gate to Anode instantly, and the meter showed 0.7V just like a thyristor.

author: Ian.M
author_rank: Super Contributor
timestamp: June 16, 2020, 03:50:44 pm
content: That explains why the PUJT test circuit wont work. A small SCR (thyristor) can act as an 'inverted' PUJT: Turn the whole test circuit upside down, keeping the positive supply at the top, (and also keep the LED with the correct polarity), and hook up the fake '2N6027' using the pinout from your tester, cathode to where the test circuit anode was and visa versa.

author: sdancer75
author_rank: Frequent Contributor
timestamp: June 16, 2020, 03:57:40 pm
content: Quote from: Ian.M on June 16, 2020, 03:50:44 pmThanks, Ian for your time.I lost my time with this....I bought them, just to play, nothing important or a repair job, but I couldn't leave it before I get a serious explanation of what's wrong with this thing.Best Regards,

author: madires
author_rank: Super Contributor
timestamp: June 16, 2020, 03:58:49 pm
content: The GM328's firmware (most likely a k-firmware) doesn't seem to have the PUT check enabled, but the OSHW firmwares (k and m-firmware) both support PUTs. For the k-firmware uncomment WITH_PUT in the Makefile.

author: sdancer75
author_rank: Frequent Contributor
timestamp: June 16, 2020, 04:04:21 pm
content: Quote from: madires on June 16, 2020, 03:58:49 pmThanks,Yes, I have the k-firmware (all other firmwares I uploaded, were not compatible with this PCB) but in this specific case, it seems that GM328 was correct. The PUT was actually a thyristor.

author: Ian.M
author_rank: Super Contributor
timestamp: June 16, 2020, 04:59:03 pm
content: You'll probably find your SCRs are *FAR* less sensitive than a real PUJT, so need much lower resistor values in the test circuit.Here's a LTspice sim using a Littelfuse EC103D1 400V 0.8A sensitive TO-92 SCR as an 'inverted' PUJT. I started from the 2N6027 test circuit, flipped it, then reduced resistor values till it oscillated.

author: SilverSolder
author_rank: Super Contributor
timestamp: June 17, 2020, 12:50:19 am
content: Don't forget to raise a case with eBay and get your money back for the fake components... teach the scammers a lesson!Typically they won't ask you to send them back (they would have to pay for it and it isn't worth it to them).I've seen this movie a few times now...

author: sdancer75
author_rank: Frequent Contributor
timestamp: June 17, 2020, 07:36:06 am
content: Quote from: SilverSolder on June 17, 2020, 12:50:19 amUnfortunately, eBay does not keep the refund or open request option for more than 3 months..... but I will try to contact them directly for fake components.