Sign In


Forgot your password?

Create Account


#281: Bipolar Transistor Switching Time Measurement

#281: Bipolar Transistor Switching Time Measurement

In this video we explore the good, bad and ugly aspects of switching time measurements on bipolar transistors (BJTs). We find that the switching time measurements (rise time, fall time, delay time and storage time) are all highly dependent upon the test circuit and test conditions - and that these conditions are not standardized by any particular device type of manufacturer. Notes for this video are here:


List your electronic components at

Tags: transistors

About the Author


  1. Date: April 13, 2018 at 07:15
    Author: AcctistaZ

    Sir, I am an electrical engineering undergrad and i give you standing ovation on your every video. You've helped me understand many concepts and i consider you one of my lecturers. Keep up the good work!!!

  2. Date: April 13, 2018 at 08:26
    Author: Dennis Lubert

    This also means that with sawtoothish drive waveforms you can shorten the storage time while still having a square wave at the collector. This may come in handy at some times where you want to minimize pulses to spread out

  3. Date: April 13, 2018 at 09:30
    Author: Philippe

    Hello Alan,
    thanks for these precise explanations abour switching time. Great video. What kind of wire do you use for your homemade probe connector?

  4. Date: April 13, 2018 at 09:39
    Author: Philippe

    I found the answer in the #111: How to make a high performance oscilloscope probe socket.

  5. Date: April 13, 2018 at 12:02
    Author: Mahmood Mammoth

    Hi Alan,
    thanks for such informative video.
    I have a question, when you were testing the RF diode and measuring the rise and fall time, I think you have to zoom in more horizontally as the scope relies on the horizontal resolution to give you an accurate rise and fall time. it would interesting to see what they would be on 400ns or 200ns per box scale if you still got the setup up and running.

  6. Date: April 13, 2018 at 14:25
    Author: jonka1

    You are very good at this. Thank you for wanting to do this for us all

  7. Date: April 13, 2018 at 14:28
    Author: Danish Native

    The differences in the generic house types is quite revealing. Some makers probably don't do much extensive testing if at all. Guess you get what you pay for especially when it comes to speed and quality.

  8. Date: April 13, 2018 at 15:01
    Author: kubeek

    you should show how long the storage time is with 0V turn-off drive

  9. Date: April 13, 2018 at 22:09
    Author: Mc Flapper

    Thanks a lot. One more detailed look inside an interesting electronics chapter.

  10. Date: April 14, 2018 at 00:06

    Thanks Alan! Another area of misty understanding gets blown away by the clear breeze of reason 🙂 I'll definitely be building one of these. Are the switching times pretty consistent among batches of transistors of the same type?

    Sorry, one more question; is the switching time, particularly thinking of the on time, what gives rise to the propagation delay in TTL ICs?

  11. Date: April 14, 2018 at 00:41
    Author: tohopes

    I was hoping you would show without negative base voltage, just going back to 0v.

  12. Date: April 14, 2018 at 09:33
    Author: Tom Biskupic

    Very cool thing to experiment with and again a really nice, well explained video. One question though – do the parameters vary much between transistors of the same type? So will two different 2N2222 transistor exhibit about the same times?

  13. Date: April 14, 2018 at 21:06
    Author: Kevin McEnhill

    How fast would the fall off be if you didn't drive the switch off negative?

  14. Date: April 15, 2018 at 18:23
    Author: Tom Anderson

    It would be interesting to use these measurements to derive the SPICE models parameters for the part. If done correctly, the simulation should match the measurements over a wide range of conditions. Too bad the manufacturer's don't do this (correctly) for us. The procedure is in "Modeling the Bipolar Transistor" by Ian Getreu, and in the ICCAP software from Keysight EEsof.

  15. Date: April 15, 2018 at 18:48
    Author: drumrboynoid

    Wow! Thank you very much for this tutorial. Please keep them coming.

  16. Date: April 16, 2018 at 16:37

    Very good, I would expect to get this education at a higher level of college. My thoughts on this are that many transistor circuits used as a switch to take the load off of a microcontroller, or in some other similar circuit, won't matter much. But when the circuit involves much more complicated switching times that correlate with switching times elsewhere in the same circuit, that is where the selection, and tweaking of control parameters of each stage are important. The testing you are doing can be turned into a book of practical transistor data. You can simplify what each testing parameter means, and list the transistors in or of best to worst for that particular test. I would buy a book like that. In most cases, simple transistor circuits can work around any common transistor, but even those have their limits. Usually those limits are in power handling, and how fast or slow they are isn't of much concern, as long as they go off, and on with no noticeable delay. Other circuits involving audio, have requirements about low noise, and that is another area that can be tested. Thanks for the excellent way you explain things in great detail.

  17. Date: April 17, 2018 at 08:55
    Author: Roger Onslow

    Nice video Alan. Have you considered a follow-up video showing how to speed up the switching by using various techniques such as Baker clamps, parallel cap across base resistor and proportional base drive? RBSOA explanation would also be nice to see.
    Its almost a lost art nowadays with high speed MOSFETS.

  18. Date: April 17, 2018 at 22:11
    Author: JT Mott

    I fully agree with all of the positive comments. You are certainly a 5 star and/or Gold content provider on YT. Thanks for all your time and dedication!!!!!!!!!!!!!

  19. Date: April 18, 2018 at 04:24
    Author: Davy Oneness

    Thank you very much for this visual. You did this BJT set up with a basic common Emitter circuit, I would really be interested in seeing it also done in a Common Base, and also a true Common Collector (reverse mode) set up if you can have the chance. Thanks again, and keep up the excellent work!

  20. Date: April 24, 2018 at 08:01
    Author: cMaXeJIJIo

    Hi, Alan!
    I have finally received my first ever HAM license on Sunday and wanted to give you a big thanks, since I consider you to be one of the people who inspired me to take up the hobby!
    Going down memory lane a little, I had first found your channel because I wanted to find a video on scope triggering just before I bought my first scope. A Tektronix 2235, by the way(Yep, I'm one of the family, too, lol). That was in November last year. And then I watched those seminars on scope applications with antique radios that you had hosted and it all went down from there haha!
    Anyways, I wish you many healthy, productive and fun years ahead!

  21. Date: April 25, 2018 at 06:05
    Author: Ron Jones

    I love your scope probe connection. I will do a similar thing on my next project. Love your videos and excellent presentations. 73

  22. Date: April 25, 2018 at 19:35
    Author: Vince I

    Hi Alan, someone asked me what exactly does "PAD" stand for? Passive Attenuation Device? Or something else? I looked in the ARRL handbook and interestingly there isn't a definition in there. Thanks as alway, Vince.

  23. Date: May 1, 2018 at 03:44

    Hi Alan, sorry to be a pain, but I wondered if you (or your subscribers) know of, or have a way of finding out, what a recommended replacement would be for RT1010 (NTC thermistor, 7.5 Ohm, 10% – I think 7A) on the A2 regulator board of the 24XXB 'scopes? There are two, the smaller, inboard one is not a problem, as the SG200 (5 Ohm, 5A) is still produced.

    There is one p/n for it in the 1989 Service Manual for the 2465B/2467B (75DJ7RK5-RO-220), and a Tek p/n in the 1993 edition (307-0350-00). The closest I've found so far is a 7 Ohm (within 10%) 10A part, but it is quite a bit larger and radial rather than axial.

    There is a gap at the junction of the leads and encapsulation of the old one, and the cold resistance has shifted upwards (I'm guessing moisture ingress thru the gap has caused this) to just under 10 Ohms. I could dry it out and re-seal the leads with very low viscosity epoxy, or use the over-sized part I found, but I'd really like to get a new part, closer to spec as it's in there for current inrush limiting on start-up.

    I totally understand if you are too busy, but maybe one of your viewers has the answer.

    I think I may have an addiction problem developing, though. I've got a 2465B n its way, an Ex-Sony Gmbh. owned one with a Tek cal sticker on it from '09. Happy days!

  24. Date: May 2, 2018 at 04:46
    Author: BrendaEM

    Good and informative video. Thanks. I've been aware of MOSFET's gate capacitive issues, but your video has taught me bipolars aren't perfect either.

    The test was interesting, but would most applications use negative voltages to pull a transistor low to deplete it in switching application?

    When you mentioned that there was little of a test setup, I immediately thought of level shifting from 3.4v to 5v, or vice versa.

    Driving an 30ma LED from either a Raspberry PI's 3.3 paltry "general purpose I/O" pins or driving one or more LED's from an Arduino 5v pin would be an interesting response time test. I am not even sure if a PI can even power most opto-isolator/couplers, safely.

    An Arduino can handle an LED from a pin, but not more than one. For current draw LED's 20-30ma seems like a nice current draw for a test, though biasing aside most Arduino people just use a 1K resistor for current limiting because they close enough, most people have them, and when you are holding a hammer, everything looks like a nail. : )

    Thanks again!

  25. Date: May 3, 2018 at 01:23
    Author: TrickyNekro

    Well the BJT performance in switching is generally very depressing, you almost have to be desperate to use them (see IGBTs) 😛

  26. Date: May 10, 2018 at 17:31

    Your capacity in delivering such well-structured and detailed tutorials, covering both the theoretical and experimental aspects is truly amazing. We are really grateful. Would you consider making a video on demonstrating and measuring the characteristic impedance of a transmission line and/or coax cable and its dependence on frequency?

  27. Date: June 3, 2018 at 10:02
    Author: dlinnoedlinnoe

    Great video as always! Thank you very much.
    Also it would be interesting to see Ts & Tf times without negative bias, just 0V at the base. I think Ts will incease by ?50% or so. Still I'd think it's kinda missing in the video.
    But again, it's great anyway.!

  28. Date: June 16, 2018 at 10:18
    Author: Filip Štirn

    Hello. I didn’t know on which video should I ask this question: for uni project I want to make something with using lora rf module, microcontroller and gps module. I don’t want to use arduino so I want to make my own board. But I have a lot of problems currently with electronics knowledge. Is there any way you recommend me which videos should I watch for that purpose or which websites should I visit to learn and make that board asap. I would be very grateful because curreny I am searching and searching for days and I dont find nothing usefull that would help me. And time is clocking too fast haha. I have some basic knowldge of how parts works (resistors, capacitors etc.) but I still don’t know how to make something usefull out of it. Like how to connect those “bricks”. Thank you!

  29. Date: July 9, 2018 at 14:04
    Author: Mike Dodd

    I'd like to see a germanium transistor — though I guess it would be somewhat redundant. I would have to say this in one of the most interesting vids I've seen. It is so fantastic, really no words can really say.

  30. Date: August 18, 2018 at 13:59

    It would have been interesting to see the switching speed vs temperature, like get a hot air gun or better yet an adjustable soldering iron so you can look at the relationship between temps and operating speeds.

  31. Date: September 3, 2018 at 00:54
    Author: Matt Hollands

    Question: When the drive voltage went from negative to zero volts, right at the end of the sequence, you can see a llittle gulp of current on the base. My best informed guess is that that is the capacitance of the base being charged up from -ve to zero. Is that correct?

Leave a Comment