Changing a transister tester circuit - Solved - Page 1
Forum section: electronics / beginners

author: t1d
author_rank: Super Contributor
timestamp: November 13, 2018, 09:20:25 pm
content: I would like to take the switch out of the circuit. The circuit will remain open, until the transistor is applied to the socket, in the correct orientation. When the transistor finds the correct orientation, the circuit is closed, the LED lights, the transistor is proved and it is identified.As the transistor is moved from one position to the next, it will be exposed to incorrect power, until it reaches the proper position. Is a small dose of incorrect power (3v3) likely to significantly stress, or damage, the transistor? I am sure that it is not recommended, by the manufacturer, but, from a practical stand point, is it truly an issue? Don’t all testers work this way, by some manner?Proposed Transistor Tester InstructionsFor unknown transistors...Attach the battery. Orient the face of the transistor toward the NPN side. Apply the transistor legs to the top three socket spaces. If the LED does not illuminate, move the transistor legs to the lower three socket spaces. If the LED does not illuminate, move the transistor to the PNP side.Orient the face of the transistor toward the PNP side. Apply the transistor legs to the top three socket spaces. If the LED does not illuminate, move the transistor legs to the lower three socket spaces.If the transistor type is known, from the start, just test it on its type side.When the LED illuminates…If it is facing the NPN side, it is a NPN transistor. Take note of the alphabetic code coinciding with its legs. This is their pin assignments.If it is facing the PNP side, it is a PNP transistor. Take note of the alphabetic code coinciding with its legs. This is their pin assignments.If the component does not cause a LED to illuminate, in any of the tested positions, the transistor has either failed, or the component is not a transistor.Alphabetic CodeE = EmitterB = BaseC = CollectorE = Emitter

author: newbrain
author_rank: Super Contributor
timestamp: November 14, 2018, 12:22:44 pm
content: Most general purpose transistors will survive the voltage and currents at play even if wrongly connected.A couple of thoughts:If you remove the switch, you'll have to disconnect the battery in some other way (manually?), as the1117-3.3can draw as much as 10 mA with no load: this kind of load will kill a standard alkaline 9 V battery in very short time (a couple of days).Even following your instructions, the pinout identification is not 100% guaranteed.The pinouts of, say, TO92 transistors are pretty much random,CBE, EBC, ECBat least.Every time a PN junction is correctly polarized across 1-3/4-3 on NPN side or 8-6/5-6 on PNP side the LED will light, even if the transistor is not correctly connected.Bonus comment: For the love of symmetry, I'd have used a common emitter configuration on the PNP side, too

author: t1d
author_rank: Super Contributor
timestamp: November 14, 2018, 12:44:56 pm
content: These are really superb insights, Newbrain; thank you.Quote from: newbrain on November 14, 2018, 12:22:44 pmIt is good, to confirm that.Quote from: newbrain on November 14, 2018, 12:22:44 pmOkay, the switch stays.Quote from: newbrain on November 14, 2018, 12:22:44 pmIt is not intended to be advertised, as a precision device. I really just made it to give them away, when introducing myself, at MakerSpace-type functions, etc. That is why I named it the "Handshake." There is room on the back, for contact information.Quote from: newbrain on November 14, 2018, 12:22:44 pmI love symmetry, in design, too. At least the PCB layout has some elegance, IMHO. I did not design the circuit. It's just a common one, found on the web. :-)One small improvement might be to use a 2x4 socket, for the IC socket. That would save a little PCB real estate.Thank you, for your help.