I like the "drive bigger trucks over the bridge until the bridge falls down" method of circuit design.

The 2N3904 says to the 2N3906, "nice package". The 2N3906 says to the @2N904, "nice legs". That's an example of a "complimentary pair". But when the 2N3904 says to the 2N3906, "you complete me". Now that's a complementary pair!

Yes, an engineer can put together a design to nominal/typical parameters without a simulator. However, SPICE and other tools are useful, if for nothing else, to check the tolerances of the devices in the design. While any engineer can get a prototype working in the lab, the usual requirement is to produce good yields through manufacturing and reliable products in the field. Part variation is expensive and time consuming to verify in the lab, but tools like SPICE and other simulators, as well as mathematical tools, can calculate extremes and determine margin relatively inexpensively. This can also check for violation of maximum characteristics, such as your overcurrent situation. Since in my career with many companies and being responsible for many products, I was always tasked, as part of the requirements, to create reliable and manufacturable systems, and I would have had to fire any engineer who would not simulate or calculate the variations. Luckily, I never had an engineer working on my team that did not know how to prove his work and seek to do just that. My first six years of my career was mostly spent fixing and cleaning up the empirical designs that other people pretending to be engineers did before me. I have a low tolerance for low quality work, because it costs my company a lot more than any savings because engineering did not take that extra hour to verify it. Tools should never be a crutch, that is true, but the right tool should be used to do a job right. If you are doing analog design, SPICE is easy to learn and often the CAD tool chain can create the deck for you. There are free versions of SPICE that work for many uses, but if your project supports it, licensed tools often have some worthwhile advantages. In digital design, simulation is also useful, but I also suggest trying formal methods as well, wherever you can fit it in schedule. Most designers and managers underestimate the value of verification, but it helps preserve schedule and budget and produces better results as long as you have people on the team that know how to get the value from it.

If you use two diodes on the input to bias the transistors, the crossover distortion will be very small. If used with the op amp, it will be phenomenally small. With the op amp but without the diodes, you will still get noticeable distortion.

Be careful that the popular BC547/8/9 have the opposite pinout (swap C and E). Always check datasheets from a semiconductor manufacturer not random webpages.

Always good to review the basics. Thanks.

It will eventually fail. At high temperature, the dopants migrate faster and it will fail sooner. At high temperature beta increases to the point of instability and it will be on until cooled even without base current (thermal runaway).

Nice quick vid i enjoyed it! Thanks

Your tutorials are great !...more please....cheers.

IMSAI Guy, I want you to know that you are my FAVORITE electronics channel and how much I appreciate your dedication to producing educational, entertaining and high quality videos on really interesting and relevant topics. You actually do things like I or some other experimenter or engineer might do them at their electronics workbench. Thank you for this treasure trove of goodness you have and continue to provide. That said, this episode in particular spurred me to post this comment because transistors are such a fundamental part of the world of electronics, and related circuits are so easily accessible to us all, that I wanted to ask if there is a possibility that you could do a series covering the various implementations of BJT, FET, JFET, MOSFET etc characteristics and circuits, going into as much detail as possible. I personally have been fascinated by transistors since I was a kid, and 50 years later, that fascination has not waned. It’s nice to see how you go think about things and solve problems in general, would be great to see even more specifically on transistors. I know you covered some of this in your past videos, but a refresher with maybe a new twist would be AWESOME. Once again, THANK YOU for your dedication and GREAT WORK!

APPRECIATED. YOU REMINDED ME OF MY ENGINEERING DAYS IN UNIVERSITY OF ENGINEERING AND TECHNOLOGY, LAHORE, PAKISTAN OF 1974-1978.

Since last week, I'm playing with a portion of a circuit that Roland used in a very famous synthesizer. Transistor, Fets and mosfets are quite more complex than just switching. Also the transistor totem pole arrangement is pretty special, there pretty much no current usage on the base. Both transistor cancel each other out on the base, pretty amazing, like you would be using a mosfet / fet.

Looks like you'll need to add a bias circuit to get past the dead zone when switching between high side and low side. Sure the op-amp can mask some of it but for audio, you need it.

Excellent! Thank you.

Amazing channel.

You can heat sink those to92 packages to get a bit more power out of them. I have used a binder clip for that. You can also bend them over and glue them to the ground plane to remove quite a bit of heat. Also I think the die is thermally more bonded to the collector lead, so keeping leads short and having a large collector copper pour can also act as a heat sink.

Like what you said about rules of thumb when quickly prototyping.

The way I remember the pinout for these is that the shape is a C, not a D. So from looking down on the C, the top of the C is the collector. The base is the middle, and that leaves the emitter as the remaining pin.

Good explanation :) Pretty amazing what op amps can do.

As soon as you drew in the 50ohm load at 4:15, I jumped on the calculator and thought this is going to get interesting. Time to sit back and wait for the smoke to escape :)

Nice idea for AGC

At 12:00 There's no "sometime" about it. You either need to read the datasheet and do the maths and make sure at worst-case you're within limits for voltage, current and dissipation, or you've read the datasheet and done the maths so many times that you have a feel for what's reasonable. There are not "two schools of thought". There's a sensible middle way between creating a spice model for every simple circuit that you've built a thousand times, and just sticking any old voltages and resistances into a circuit to "suck it and see" with no prior expectation of the outcome. And if I was the R&D manager and I saw you just sticking any old circuitry together that was bound to fail, I'd fire you.

I can remember using but can't remember what for. A transistor lockin amplifier perhaps

Interesting video. I have 1 thing to point out. You are the first person that I've seen using an HP. I really love using RPN.

How do you figure the voltage and current of the 3906?

I'm fiddling with a design for a big-output-capacitor-less audio amplifier (eliminating the highpass effect w/ the speaker as well as an extra 6dB) that push-pulls the speaker with inverse-phased class AB stages like this (TL084 is my op amp) and I'm using just 2N2222s (basically a little beefier 2N3904) and 2N2907s (lil' beefier 2N3906) and even though they're just little TO92 signal transistors they're actually surprisingly good at filling a room with sound.

Please suggest another complimentary pair with a higher power capacity. I've considered these two to replace proprietary power design transistor because they share high hfe's. I can't locate other transistors with similar abilities. How do I search without reading every data sheet?

hi, I have trouble understanding how both PN junctions can be shorted in the bases, in some other circuits I see they use 2 external dropping diodes in the bases. can you elaborate?

Dude, your dissipation calculations are (slightly) off. With he load you measured about 3.8V across the load. That would give you a current of about 75mA. The voltage drop across the transistor was 12-3.8=8.2V. Therefore the power being dissipated by the transistor was 8.2x.075=615mW. Jus' sayin'. But it's close enough to AMR to cause real trouble.

These 2 are plentiful in my stock. Also 2N7000

Cool calculator.

Who just happens to have a 51Ω resistor lying around? ;)

0:45 For 3-leg components (transistors in this example), I'd recommend just skipping the 1 2 3 pin numbers and go straight to simply memorizing EBC (for common examples like these). To help clarify thoughts, does anyone use pin numbers for diodes, or straight to Anode and Cathode ? Polarized capacitors, easier straight to + and -. I'd suggest that pin numbers only add value for a larger number of pins. In this case, they make memorization arguably slightly more difficult.

I always wonderd about this: There are two types of to92 packages: The one with straight leads and one with bend outwards leads. Which do you recommend for breadboarding? And is there a reason why there are two types?

BTW, emitter arrow direction: NPN = Not Pointin' iN, PNP = Pointin' iN Please. You'll never forget.

As with the other comments adding base diodes would help a little by biasing the transistors on and negating base emitter drop, could also get it to oscillate. I was curious was to how much the base voltage was changing due to current in the through the potentiometer. You didn't mention if it was a 470K pot or a 100 ohm pot, obviously not 100 ohm.

1:58 Why are no base resistors required? Is it because there is a load? What if there was no load, would the transistors be damaged?

Classic

I always first design using rules of thumb using good old pen and paper, but before I built it I also do a spice model. Why? Especially important for stability analysis. E.G, the circuit you drew of the fb for an amp? How do you know that the parasitic capacitance of the transistors will not affect the fb, even make ringing with the parasitic inductance of the wires? Right, spice model. Before you build. Always. Rules of thumb are nice, but nothing compares to a good spice model 🙂.

This video is going to get the 2N2222(A) / 2N2907 fanboys riled up. 🙂

Something to keep in mind is that the maximum power dissipation rating on the datasheet, is at 100% duty cycle. If this arrangement would have been used as intended, each transistor would have around 50% duty cycle and could handle that current easily without overheating. There are actual charts that show this on some transistors, but I was unable to find one for the 3904/06.

5:27 11.4V÷51Ohm= 0,235294118 Amp. that's quite a current consume for these small boys not using a resistor on the base of them. What would you do? since the HFE is 100 average, if you need 100mA, you need to limit the base current to 1mA, correct? Did you try the Falstad simulator, it quite correct and good, buy a Moog Filter clone diy kit, build and simulate it, if will respond the same.

U would want a focused product 4 this though, right! so what will this generic circuit go in? good luck! mad scientist engaged!

You're going to need a bigger transistor.

Sorry, I don't get it. Why wouldn't you play around with anything but the simplest circuit in Spice before trying to build it? It's not perfect, and it's no 100% substitute for real world component experience, but it'll still teach you a lot. It'll allow you to mess with amplifier biasing and gain before even warming up the soldering iron. Maybe I missed your point.

You are limiting your decision to function of a device to last as long as possible ... that's not something to consider in a missile guidance ... so it is telling what industry you worked in ... I'm just saying sometimes macgyverneering is good enough and fits the bill ... planned obsolescence is a thing that surpasses the binary thought process.

Spice shy? Why? Back in the 1980's (and early 90's) ... more than 30 years ago (a hyperbolic infinity in semiconductor design and modeling) ... back then, Pease, and his cronies, had their good reasons. But in the last decade, at least, I can't think of an undergrad (and especially a grad) EE school where the labs don't start with SPICE simulations, and even more specialized simulation packages, before going to the lab to build. Maybe in the EE School of Old Farts,, they're still just stuffing breadboards. Dunno. Seems like small businesses, run by old farts, might be doing the same. But if you want to work in analog design, and even with discretes, and you're SPICE shy, then get a job as a plumber's apprentice. (You'll probably get a job faster, and keep it longer.) Seems to me, someone's been out of school, and a job, for a long time.