"let's quickly slap in the previous transistor before we set our LED on fire"

The gain varies a lot from one transistor to another (of the same reference) and with current, temperature, Vce etc... The only thing that matters is the datasheet and the minimum guaranteed gain in it. Also when calculating resistor values during a circuit design, it's better to use a conservative value. Measuring a transistor and then building a circuit based on that is the first step for a bad day.

Two things you can't depend on when desigining with a transistor: - current gain ('round 200 when you must) - base-emitter voltage ('round 0.6V) If you are doing something that needs some precision always include a trimmer!

I would say keep in mind the traditional BJT is both a current *and voltage amplifier.* I recently configured one for high input impedance in contrast to the source, and still achieved very high voltage gain. About 300mV input AC signal, and 3.6 vac output. Bias resistors being 1 million and 100K for my divider. In contrast, running a very lossy 1.8K and 150 ohm divider, I was only achieving 4.0 vac, but obviously my current gain is massive. *It does go to show that BJT's still have excellent voltage gain when configured for high impedance.* That impedance is only about 100K, *but my source is on average 15K.* The MPSA13 and 14 obviously give me a lot more current gain, but working with guitar signals my focus is on voltage gain. I've gotten lazy with the math, but will start again soon. It's been 11 years since I was last in school for engineering lol.

Im only 2 years into learning electronics. Great video. TY so much!!

13:00 There's another very important information to look for: the maximum power dissipation. 0.625W is not much. For example with 10v Vce the maximum current is not 200mA but 62.5mA !!!! This is with an ambient temperature of 25C. If it's in a box during summer, it could easily be 50C. With a derating of 5mW/C it's 125mW less ie 500mW max so a current of 50mA. 1/4th of the claimed 200mA. Be careful!

For higher current requirements I like to use AO3401 and AO3406. They have very low on resistance and switches Amps in small sot23 package

Your lessons are priceless! If possible, about the calculation of the transistor switch and the amplifier stage lesson. Thank you.

Thank you for this.

A trick for young players for all types of ICs is their wattage rating. All/Most IC have a maximum wattage rating that is well below their maximum volts rating times their maximum current rating. If you max out both the volts and amps, you are going to cook things.

Thank you.again

I don't think I heard you mention what what the hFE actually stands for. Apologies if I missed it. You described it well, but for those interested, what I found for the definition of the letters is: hFE is an abbreviation, and it stands for "(h)ybrid parameter (F)orward current gain, common (E)mitter", and is a measure of the DC current gain of a junction transistor. I learned it as beta or the greek B symbol and had to relearn it as hFE. Actually I'm old enough that we learned tube theory first and then about the new kid on the block - transistors. FETs were mentioned as an interesting device that might pan out some day :-)

Glad to see a transistor.lesson and that you are taking a break from the Japanese scope... I look forward to seeing traces on the CRT some day...& no hurry. And that is hasn't caused too much of a loss of sleep... When HFe is wrote in little caps it implies an AC beta or cuurent gain...and I know you knew that... I am forming a little creation and will send a tiny description.... Have a great day. We used the MPS-A13 by the boat load... I will look up the MPSA14 to see whatever subtle difference it has with is little brother... It seems like there are too many choices out their and Motorola and others were never afraid to do a slight redesign for their customers and find a new niche. I think my Motorola Power datebook was the fattest out of all of them..... With so many choices ....some classics seem to be prevalent..... Maybe familiarity with the EE played a role... I wonder the single most popular transistor ever sold would be a ???

I have a suggestion for a new video. Have you heard of diode steering/ORing to power a load from 2 batteries? Basically put both batteries (or supplies) on same ground, and give each of them a diode between their positive and the load. If the batteries have the same voltage, it should be switching rapidly between the two, the faster the diode, the faster the switching, but i'm a bit skeptical about that part of it, so I'd like to see that on scope.

Whenever I buy IC's or Transistors I always download the datasheet for them, even if they are replacement parts for something broken.

Nice videos, i really appreciate. I have a question regarding transistors: from what i get, some transistors are better for liniar applications (like amplifiers) while others are better for switching. Can you give us any informations as to what models of low power bipolar transistors would be best for switching, please ? I've been working alot with BC547 and lately i realised i actually don't know if it's best for liniar, switching or if it's an average transistor. Thanks alot

Good video. I would like to see a video on DC coupled amplifiers, for, um...a function generator (ducks), perhaps something with TIP120s/TIP125, for a handful of watts, at most. Perhaps a simple Op-Amp front end, with adjustable bias, likely not the LM358, which suffers from crossover distortion. A dual-rail 15c or 18v power supply would be nice, perhaps with some of those "capacitor doubler" pass transistors. Perhaps a regulated power supply for the bases of transistors. Perhaps the out of band frequencies highs could be pulled down with caps. But of course, I have no idea how to bias any of this, and there is very little information on DC-coupled amplifiers out there. ~ On MOSFETs, I tend to put a 10k pull-down resistor on the gate to make sure the capacitor nature of its gate is well drained. I don't know if the 2n7000 suffers from this, but some MOSFETs won't shut down in any reasonable time without it. I seem to remember Afrotechmods draining one with his fingertips. [For Arduinos, a $1.65, IRL640A logic-level MOSFET with a t0-220 case, works pretty nice, up to 200V / 18 amps. Of course, 100 or 1K resistor current limiting should be used between the controller pin and gate. The IRL640 Rds is something in the milli-ohm range, which is okay for a logic-level MOSFET. For inductive loads, a helper diode in the flyback configuration is a good idea. I have been working on a circuit using them with optocouplers, when I noticed that because of the optocouplers made the MOSFET spend so much time in linear region, it became quite hot with PWM at 12v and 1A, over 10Khz. I experimented with just an LM358 Shmitt trigger, and then Comparitor, but the LM388 slew-rate was too slow--also keeping it in the linear region. So, I found some optocouplers with built in Schmitt-triggers, the H11L1M series, which I hope will allow, which I hope will be at least 16kHz PWM. Well, see.... I was even tempted to test the SN74LVC245AN class device bus transceiver as a schmitt trigger, because the square waves that come off of it are so sharp you could cut yourself on them.]

On Mouser, for 2N3904, the price for one unit is 7 to 10 times what you quoted. Some manufacturers are cheaper; but, there might not be stock. You have to buy 1000s of them to get them for 5 cents each.

Thank you. Great information that really helped me. What would you say is the iconic TO-92-style Darlington Pair Jellybean Transistor? The one every hobbyist should have in stock to learn and play with? The MSPA14, or something else?

Hi - Would you drive your car flat out every where? - Then why do you drive the LED at Max Current and shorten it's working life? - Also what are the components to the left across both top and bottom of your bread board supply rails they are not in your circuit drawing?

If you do saturate that transistor, Forward current through the LED should warm it up ! Max I(fwd) for most LEDs around 20mA…

The higher current spec is for the 7002 device. Andy

Where can I get those nice clip on leads, moreover the end that attaches to the multimeter with standard spacing?

measure the hfe while warming the top of the transistor

note you have looking at Absolute Max ratings,...

1 ohm on resistance is nothing to write home about. It seems the through hole T0-92 style package is responsible for the relatively high on resistance, and relatively low continuous current capacity. TO-220 packaging has better performance; but it's harder to use in a breadboard. If one goes to a surface mount package, higher currents and lower on resistance are significantly better. In terms of buying a few to a dozen units, the price for the better performing SMD devices is about the same. Use a PCB adapter for breadboarding with them.

1)Thanks & 2)Question ,,,Thanks for super videos mr.ImsaiGuy :-) ,,,Question: Is it really a 100ohm, and not a 1kOhm in series with the LED on the breadboard? >..Just asking because it seems the LED survives with over >80mA (according to the video's calculation with the 100 ohms series-resistor) ..standard led's have 10mA to 20mA nominal current-requirement, pluss-minus some few mA's. //Thanks again for sharing video's to the Diy's&Engnr people. //br from norway.

what current does your little box test the transistor at?

Very good and timely for me. Thanks. I'll repeat you demonstration with the parts and gear I have handy. I would recommend that you upgrade your little component tester. This guy explains the upgrade: kzfaq.info/get/bejne/Z6qKetpexL-yY4U.html 73