BJTs as Transistor Switches | AddOhms #10

Transistors are electronic switches that are used to control things that would kill an Arduino, Raspberry Pi, or Beaglebone.
Support on Patreon: / baldengineer
There are two major types known as a BJT and MOSFET. This is part 1 of a two part series, which looks at BJTs first.
Learn what they are and how to use them.
Show Notes:
www.addohms.com...
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#transistor #bjt #electronics

[@TrentSterling]

Dude I've watched so many videos on transistors and mosfets (lots of 'big' youtubers in electronics) - but your visualizations and descriptions are the best I've found! Nice job man!

[@PinkeySuavo]

Too fast for me even though I kind of know this stuff already

[@DigGil3]

Mother of God: an actually useful explanation of the transistor! You, sir, are among two other people I've found on both IRL and the whole internet that actually tells how transistors work without rambling about "Holes" and "Electrons" and quantum magic.

[@borisjevic6338]

Totally agree! A breath of fresh air! I am totally getting it now. Others bire you with way to much theory and equations, that you loose the plot. This guy gives you very simple formula and how and where and why it is used!

[@edwardfanboy]

How transistors work: Quantum electrons mumbo-jumbo. How to use them in your circuit: This video.

[@noeltrimm7216]

It's a long time since you've posted this comment, but could you link/tell me where the other two explanations are, if you remember? I'm still having trouble grasping the concept, thankee.

[@mostafashorche3105]

@@edwardfanboy اهنگ‌ اگرین

[@mostafashorche3105]

‌

[@tobes9074]

Fantastic Video! As a studying engineer trying to demystify what the hell I do with a transistor this video is amazing! I'm so sick of hearing about pnp/npn, holes, CE configs etc. How do I apply it!? Subscribed.

[@SunsTo7]

Just use your imagination for pete's sake these are tools to preform work with.

[@RealDealHolyfield2099]

Fantastic video editing and graphics. They both help support a clear presentation. I like this channel. Thanks for the video!

[@Calslock]

This 4 minute video explained principle of transistor to me better than 3 years of uni and countless hours of other yt videos. Thanks!

[@liumander]

Are 1mA and 100mA the maximum of current allowed before it starts to become a risk for the transistors? Also, if the a certain voltage and currency goes from B to E and another from C to E there's an increase of the total voltage or current from E to forward?

[@gprgprgprgpr]

This video is good as a quick overview about BJT as a switch, but lacks many important details, so not suitable for building bjt switches in practice. Relying on actual value of beta is very bad design.

[@reeseyme9613]

excellent tutorial, with the added animations make it easy to understand....

[@aubreymartin435]

Excellent, understandable and perfectly clear video, Brilliantly done! Thank you so much!

[@emperorsfinest]

Very good tutorials, teachings indeed. However, i think it will be better if you can make a real circuit including the component in the tutorial. That makes things a lot clear (at least for me) when components are in action.

[@brnmick]

very nice explanation! (currently studying electrical engineering and i thought this very insightful - especially the explanation for using a suppression diode)

[@LHJARS]

never put a power source ( f.e. a battery ) between base and emitter as in the beginning of the clip. That is not a good idea...

[@mikewezyk]

Fantastic and very informative video, Thank you so much!

[@ChannelPica]

Great transistor lesson,big 👍 from new friend

[@B1TCH35K1LL3R]

Real good videos! Thank you very much! Helps for electronic engineering students like me! Greetings from Mexico.

[@bryand6811]

i cannot thank you enough for making this video! i've been trying to figure out for months how bjts work and i just had my "uhuh!" moment after watching your video. i couldn't figure out how to connect the more pictorial diagram for bjts to the schematic and the animation you included just solved that problem. really, thank you so so much!

[@norlure]

Bryan D, ...define....."uhuh".....lol

[@swedemake5571]

This helped me to understand. Wery good video. Thanks. 😊

[@andrewezzat9227]

please can you tell me how did you know that IB =1 mA ?

[@CHistrue]

I think it was an example.

[@wouldbabyhitlerkillyou4217]

Helpful video but correct me if I'm wrong, I thought the data sheet said the "beta" would be 70 at 1ma, not 100? 100 was for 10ma from base to emitter?

[@AddOhms]

Beta depends on the collector current not the base current. Both temperature and the voltage drop from collector to emitter can cause it to be different as well. It varies on such a wide range of conditions that it is difficult to state a single value. However, for a 2n3904, 100 is a common number that is used.

[@FourthWayRanch]

can you use it just as a momentary switch that connects a microcontroller pin to ground?

[@RixtronixLAB]

Nice video, well done, thanks for sharing it with us :)

[@DelbertWagner]

I am building a miniature garage for my great grandson . I have miniature 6 volt gear motor , that I am using to open my garage door with reversing switch . Having problem figuring out limit switches to stop it when it goes down and up . I can limit up and down but that shuts off the electricity to make it go the other direction . I am building a miniature . Any help would be much appreciated . Thanks in Advance

[@phd3333]

I have to echo the positive and very accurate comments made about your video training style. It really makes things real and approachable. I like the suggestions of useful components to use in circuits like your idea of the suppression diode with part number provided. You are awesome--keep it up.

[@tangofan4u]

Thank you for a quick intro to transistors. In your example you connected the motor to the collector. Would it be okay to connect it between Emitter and ground instead? What would be the difference between the two?

[@triplexSch]

Bernhard Kohlhaas I was wondering that as well - could somebody explain?

[@udithkumarv734]

'The code's more what you call guidelines than actual rules' Hector Barbrossa

[@mee-gionee-]

where can i learn short-cut form (like VIO, HF, IC and IB)?

[@james77011]

@time 1:55 How did u calculate 1ma of current of u only had the voltage and not the resistance?

[@AddOhms]

I didn’t. I just picked the value.

[@md.sharifulalam6980]

Great video and good explanation

[@clems6989]

I love the little tidbits of knowledge. Such as the Vcc origin's.....

[@james77011]

Did the 3.3v applied at the BASE cause the the transistor to turn on? And by it turning was the 100Ma of current allowed to flow from COLLECTOR to EMITTER?

[@the2d]

I liked your video as soon as you said BJ transistors instead of BJT transistors.

[@Chupria]

Why did you pic "100" for the Current gain from the datasheet. I don't understand that part. There were other numbers to pick from. Why the 100?

[@bald_engineer]

Good question. The reason I picked 100 is from experience with a 3904. There is a range of values which depends on the voltage drop from Collector to Emitter and then how much current is flowing through the collector. Also notice that the range is from a *minimum* value to a maximum value. So even if your conditions show 30 on the data sheet, its likely going to be higher anyway.

[@randomcontent7703]

I would like to make a 24V pulse with a width of 300ms with an Arduino to give the logic low/high. Is it possible to use a bjt or MOSFET as a switch which the logic low/high is fed into?

[@AddOhms]

Yes

[@l3yonk408]

Very nice explanation and with pictures simplified for understanding Thank you with regards

[@evamg21]

Here I was trying to build a transistor switch for my raspi withouth ever having learned how a transistor even works (or I did and it's just been too long ago). So thanks for your help!

[@donpixote3321]

such a clear and concise explanation that makes me wonder what sort of people would thumb it down. Idiots that can't understand probably.

[@leonamferreira8053]

Thanks so much for your explanation!!! It was soooo easy and clean to understand it!!!!! I love it!

[@WoonCherkLam]

Thanks for the (very) clear explanation! :)

[@malukodafaka]

Great video ! Maybe you can make a portuguese subtitle for i send to my friends in here on brazil. Thanks !

[@tomaszdabrowski5087]

Easy and cleared explained. Good luck with your job. I will cross fingers.

[@jorgemix123]

Hey there I have a problem, I have an integrated C.I. PT2272 6-volti want to control relays of 6v but it seems that the output of integrated does not have much power that the integrated output is down 5 volt to 2 volt and the transistor is not saturated that I could use transistor I used the built-in 548 bc is supplied with 5 volts but the relays are supplied with 6 volts is something like what you did in your circuit thanks for help,

[@cristianpopescu78]

What a great video, full of practical Informations!Thanks!

[@mooblu8837]

Im a newbie if transistor act as a switch w/out human intervention then which of the component send signals to turn on and off the transistor or stop supply and closing current to the base without a switch Enlighten me thanks

[@AddOhms]

First, please use punctuation. Your question is very difficult to understand. The source of what controls the transistor can be many things. An Arduino IO pin, a push button, another transistor, a sensor, or anything that can supply (and change) a voltage.

[@stanrock01]

I went through transistor theory back in the 80s. I have never really understood it until this video! THANKS!

[@khoinguyenquang2649]

wonderful! Many thanks!

[@josephtan4663]

What are the advantages or disadvantages of using a mosfet to say drive a flyback over using a bjt? Thanks

[@squalazzo]

is the AUDIO TO 11 a reference to The Spinal Tap? :D

[@AddOhms]

+squalazzo Yup. :-D

[@hamzabendi9751]

1:54 , 1mA is flowing from B to E, and then u said when that happen we get 100mA flowing from the collector to the emitter. what i don't understand is from where we get that 100mA current? i mean the collector isn't connected to anything, so it's like an open switch. great videos by the way, keep it up!

[@AddOhms]

+Heisen Berg It is implied that the collector is connected to a supply.

[@hamzabendi9751]

Hmm, as i think about it, my question was really dumb haha, i'm new to electronics. Thank you :)

[@calirific3503]

Pretty valid question, I was missing that too. While I knew he probably meant to add a PSU. A video for beginners shouldnt imply stuff which make things vague. Other than that one of the better videos on using transistor in practice.

[@mmitza]

Hello. I want to make a transistor switch for a high power LED that consumes 700 mA. The switch will be controlled by a 5V Arduino. I made the current source by using a LM317T. I am between using a TIP29C BJT and a IRF510 MOSFET. What would you recommend? Thank you.

[@AddOhms]

mmitza The 510 may be overkill, I'd go with the TIP29C.

[@johnlim9979]

May I know what software u used to present your drawing ?

[@AddOhms]

+John Lim After Effects. Well, that’s what I used today. This one was done in Motion 5. #14 is when I switched to AE

[@greengohm]

Hands down best explanation! And the practical examples make it even better!

[@CrisDFF30917]

Dear AddOhms, just one question, Is the bjt transistor completely unstable to temperature? I mean without an emitter resistor or a heatsink Collector Current will keep getting bigger even if the initial one is around a few milliamps?

[@AddOhms]

Yes. Their gain is temperature dependent. It’s why I rarely use discrete transistors as an amplifier. I’ll use an op amp instead.

[@H-Visage]

I'm not an electrician, just a hobbyist but man, your videos are so well done, quick, and easy to understand! Keep up the AMAZING work!! 💖

[@caelsprute8233]

how can I use this to cut the voltage in 1/2 for my slot car? the track is 14 volt. I have a car that is max speed and powered directly by the track, no controller. I want to cut the speed in 1/2 and then it can drive itself around the track w no controller.

[@AddOhms]

You could use a transistor to power the track. Control the transistor with a PWM signal. At 50% duty cycle, the effective voltage would be cut in half. If you create the PWM with an Arduino or even a simple 555 circuit, then you could control the speed.

[@mikeyz8775]

Im trying to make a led blink rapidly with a pnp.

[@Revendir]

Great stuff! Thank you!

[@rioaditiyono8442]

Can I use BJT to replace motorcyle relay? The voltage is 14.4V. I got so many relay and cable that I need to simplify. Not really sure about the amperage, but I guess is around 7A or more.

[@AddOhms]

7 Amps would probably require a PowerBJT or a MOSFET. No matter what transistor type you pink, you'll likely need to heat sink them. If the signals are pure DC, then a solid state transistor is an option. However, if they are AC, then no, a simple transistor will not work.

[@rioaditiyono8442]

@@AddOhms thank you so much for your reply. It's a full wave DC with 2 phase stator. I already tried the circuit with 10K resistor, a T-10 socket LED bulb and a 12V 10A adaptor on a breadboard, and the BJT seem fine, no heat on the BJT and resistor. I'm going to test the circuit again on my bike tomorrow. I'll tell you the progress.

[@rioaditiyono8442]

@@AddOhms The collector current turn out to be very low, it's unusable. I use a combination of C945 and 2N5601since I only have positive signal. Any suggestion what MOSFET should I use to get those 8A pass through completely?

[@jorgemellooliveira9611]

Ótimo South of Brazil

[@Alexandria197]

just don't hook it up backwards or you have a little firecracker LOL.

[@matias25162]

If motor needs 6V and you've a 6V battery, the transistor doesn't polarize i think. You need a Vce to make it work, right?

[@AddOhms]

There will be a small voltage drop across Vce. But if the transistor is saturated, it will be very small. A 6 volt motor does not need exactly 6 volts to operate.

[@miketony2069]

Clear and concise . Thanks!

[@djtoddles8750]

1:45 I've always wonderd what the CC meant in VCC, now I know!

[@abdullah927-e6g]

Yep

[@technical5880]

am adicted to this channal.

[@ibrahimhussain3248]

I do understand that there would be voltage spikes but, how does the diode in parallel to the motor protect the transistor from voltage spikes?

[@AddOhms]

The diode isn’t for spikes. It provides a path for the collapsing magnetic field.

[@bitpilot79]

You have one of the bests channel here on youtube.

[@jimadams2473]

Very good video my brother... Excellent!!! Thanks

[@amunkc]

hi, can I make reset switch for microcontroller using a transistor instead of push button ......?

[@AddOhms]

Yes

[@user-su5sq5ib3i]

thanks for the clear concise explanation

[@herminigildojakosalem8664]

How about if the transistor were PNP?

[@99GAZI]

Have you considered doing a tutorial on the operation and interpretation of characteristic curves of FET transistors?

[@AddOhms]

I wrote an article on MOSFET curves here: www.element14.com/community/community/element14-presents/workbenchwednesdays/blog/2019/08/07/reading-mosfet-curves. And I did a video on the Miller effect here: kzbin.info/www/bejne/mKjCi3yvmpedbJY

[@giovanni5396]

thankyou great video

[@stanbekker]

Finally, somebody drops some math... Finally got the concept, thank you!

[@rithotyn]

I had also been struggling with that. All the videos seem to be "dive right in" which is fine if you want to mirror the exact setup but if you wanna experiment, you've no theory to do so.

[@-.......................-]

So I need to use a resistor onto the base in order to limit the current to 1mA? Right? I'm confused lmao

[@AddOhms]

Yes

[@tobeelou2609]

great video, would you also happen to have one on the functionalities of an IGBT?

[@AddOhms]

+Pierry Louis No. I haven’t worked with IGBTs much. I understand them to be basically a BJT driver for a MOSFET, in a single package. That’s as much as I know about them.

[@tobeelou2609]

AddOhms oh alright, thanks for the heads up. It's just that you really explain things pretty well and I saw it on the video.

[@jeffreykennedi4489]

Hello, can anybody explain why in 3:50 the consumer(fan) is connected *before* Collector, instead *after* Emitter??? What's the difference if any?

[@AddOhms]

NPNs are usually used as a low side switch, which is what that circuit is showing. More information here: www.baldengineer.com/low-side-vs-high-side-transistor-switch.html

[@larrybud]

@@AddOhms I'm not sure that link really answers the question, since you discuss the difference between NPN and PNP. In your link, in both the NPN and PNP examples, the load is at the collector.

[@bashiraftab5466]

Very good job for basic electronics

[@AliKiani7887]

Really nice video, thanks.

[@iliag1]

Please do a video about PnP transistor as well as current amplifier

[@ilaserbia]

Even shorter and much more useful guide than GreatScott! ones. Thanks!

[@rithotyn]

2:34 "the amount of current the transistor will ALLOW from the collector to the emitter" So does this mean that if the current draw between the C and E was say 20mA for a single led, but 1 mA was being provided to the base, that up to 100mA COULD flow between C and E, but that only 20mA would? Or would it be 100mA and blow my led?

[@AddOhms]

You still need something to limit the LED's current. Which, in most cases, is still going to be a resistor. You COULD design a BJT circuit that limits the current by varying how "open" the CE junction is. However, it would require feedback and be more expensive than just using a resistor.

[@rithotyn]

@@AddOhms yea I meant that there was a resistor in series limiting it to 20mA if it was without a transistor. So with a transistor in that series circuit, what would flow, 20mA or 100mA if B = 1mA and the beta is 100?

[@AddOhms]

up to 100 mA. but BJTs and their beta are not stable. They change for a variety of reasons which is why you'd have to use some form of feedback to use them as the current limiter.

[@phamxhoang]

What can be happen without diodes ? I searched "voltage spikes" but couldn't understand exactly what is that and consequence of that

[@AddOhms]

The voltage and current generated by the motor's "back EMF" can destroy the transistor. The diode dissipates the EMF's energy: kzbin.info/www/bejne/n3zUo6h5jtqWZ7M

[@OnlyNeed1Shot]

Great tutorials, thx for the effort you put into these vids. I'm in the middle of a few projects but haven't started using an ICs yet. With the info you have shown here in your tutorials, makes my circuit building a bit easier....and I can stop releasing the factory installed smoke in some of my components lol. A quick question, when would you decided to use relays over BJTs or MOSFETs? Or vice versa...

[@AddOhms]

+OnlyNeed1Shot Relays are good for very high current DC and all AC. You almost always need a transistor to drive a relay's coil from a microprocessor.

[@OnlyNeed1Shot]

AddOhms ok makes sense. Thx again. I have a few AC projects I'm working on with transformers, fans, Motors and such.....but no ICs, so I'm trying to design a control circuit using the components I scavenged from many electronic appliances I have torn apart. Needless to say I have fried a few components while testing my circuits. Maybe I'll try and design a small DC circuit on battery to control the activation of the ac circuit via relay activation.

[@Integrelle]

Soooo, its just a switch for higher Current applications?

[@AddOhms]

it is one application for a transistor

[@pcpatel01]

Nice tutorial. Could you please guide me, I need your help in understanding how to convert 230v dc to 230v ac using transistor.

[@AddOhms]

You need to build an inverter.

[@pcpatel01]

@@AddOhms inverters are 12v 24v or 48v. I have a power bank of 230v dc can I use mosfets to convert dc to ac without an inverter?

[@rjmunt]

Have you got the PNP video up someplace? Thanks for the content.

[@shubhamnayak9369]

Awesome videos man... Waiting for more such videos

[@dakshatapatil8226]

Hello as transistor is made of two diodes can you explain me transistor in terms of diodes

[@AddOhms]

It’s made of diode structures, not diodes.

[@dakshatapatil8226]

@@AddOhms if collector base diode is in reverse biase then how the current is flowing from collector to emitter because is not conduct in reverse biase so how current will flow? Is there modes of operation like saturation mode and cut off mode i want know when transistor used as a switch???

[@AddOhms]

I can't make sense of what you're saying. There isn't an actual diode between the collector and base. The unique combination of the PN junctions in the same substrate is why transistors get the "transistor effort" and discrete diodes do not.

[@frankreiserm.s.8039]

This was a very understandable lecture! Thanks

[@vasu26akkala]

just one word awesome, I was looking for these tutorials quite a longtime.

[@lispnik]

Nice explanation, but I was so hoping to get an insight into PNP BJTs, and what the point of them are.

[@AddOhms]

Something I plan to cover later. A quick generalization is that NPN sinks current while PNP sources current. So you'll often see them used to switch "on" a path to ground. While a NPN will be used to switch "on" a path from the positive supply. They're very popular in differential amplifiers and can be used in push-pull amps used for audio.

[@QAhkam]

Very good tutorial. Thanks for sharing

[@gengisk1987]

Muy buen video, regards from Oaxaca Mx.

[@mungelectronics7601]

good

[@eaglehigh-h3e]

Fantastic

[@LucasGuanes]

Very nice video! Keep them comming!

[@hakandemir3244]

Can somebody help me i watched so many videos but i dont understand it. I set on a breadboard wires connected to the led but i want to swith it on and off so i have buttons but do i need a transistor?

[@AddOhms]

For a single LED, there's no need to use a transistor.

[@hakandemir3244]

AddOhms i watched other videos now i understand but now i need to know which transistor i need. I need NPN but if i want to buy i see 2n2222 transistor but idk how i calculate. I have 9volt batterij connecting to 3v led with 220r resistor what transistor do i need to buy?

[@AddOhms]

It doesn’t matter. Any NPN will work fine.

[@isaacgarcia518]

I'm confused as to where you found that base current. I see you use 1 mA to find the resistance value but how do you know it's 1 mA? is that just a set value that this particular transistor uses?

[@AddOhms]

It isn't found anywhere, it is determined by how much collector current you want to flow. Divide that value by the transistor's beta, and that tells you the minimum base current required. So in this example, I wanted the collector current to be 100mA and I estimated the beta to be 100. That means I need at least 1mA of base current. From there I calculated the value of the base resistor (3:33).

[@enricoricci6072]

+AddOhms Hey could you explain how exactly transistors are used as a amplifier I still don't understand.. Is it from dropping the resistance from collector and emitter? I have heard it explained but it never makes sense .. I love your vidz btw!!

[@DigGil3]

+Enrico Ricci As shown on this video, you actually have an amplifier already: you input a little current (1mA) and it outputs a larger current (100 times amplification). It's a current intensity amplifier. Nonetheless, you usually want a voltage amplifier, so most BJT amplifiers have the transistor in place of a voltage divider's resistor. The transistor will act like a variable resistor and thus the output voltage will vary from minimum to maximum supply voltage. It's not that simple, but I think I gave you good introduction.

[@larrybud]

@@AddOhms I think the confusion is that your example was in reverse order. At 1:58 you started with 1mA at the base, then proceeded to point out the BETA for 10ma in the datasheet.

[@smartdesignengineering]

Sir how can i turn on and off irfz44n mosfet using bc547 transistor ??

[@AddOhms]

search google for “bjt mosfet driver”

[@smartdesignengineering]

I have Searched on google but did not find any solution

[@VinayKumar-nm2hv]

could you please explain the Note #1 that why we need diode in reverse?

[@ALSmith-zz4yy]

The simple explanation is, it's to protect the transistor from 'Back EMF (Electromotive Force)'. The motor is an inductive load meaning it has inductors, also known as coils. When the motor is on, coils store electrical energy in a magnetic field around the coil. When power to the motor is disconnected this magnetic field collapses. That generates an EMF that can build up to quite a high voltage in a direction which can destroy the sensitive PN junctions of the transistor. The diode, oriented as shown, will block the flow of this harmful EMF.

[@larrybud]

@@ALSmith-zz4yy Wouldn't the diode also protect the circuit incase the motor was spun by hand? Spinning it manually will create current.

[@yarnew-old3828]

Best