Why the base resistor in Darlington transistor circuits? With demo

You will often see a resistor connected from the base of the second (driven) transistor to ground (or emitter) in Darlington circuits. This video explains one reason why this is done.
NOTE: when talking about the Darlington transistor gain calculation, ignore the resistors in the diagram as they will reduce the gain.

[@JohnAudioTech]

On topic content starts at <a href="#" class="seekto" data-time="98">1:38</a> if you don't want to watch my intro. Ignore the resistors in the diagram when I discuss the gain calculation.

[@ufohunter3688]

When is it better to use a Darlington like TIP120? It has the resistors built in. That built-in resistor, is even 120 Ohms like you explained. Can you please do a series on Darlington differential amps input stage, and the use of Darlingtons in Audio applications.

[@willyrivero470]

Don't worry man. I'm also an animal lover. Keep doing what you do.

[@noelj62]

This explains why an off-delay timer that I've built a while ago does not have a linear timing every time it's activated. Thanks John.

[@reptiloidx8942]

HELLO THERE . THERES A TIP142 NPN TRANSISTOR IM TRYING TO USE IN MY ONE TRANSISTOR SOUND AMP . SO TELL ME HOW THE CIRCUIT WILL LOOK LIKE ??? THANK YOU

[@Tetrakan]

I

[@edwardbartolo6382]

You explain like an experienced teacher. Well done! Today, I learnt something new from you. Thanks.

[@aurthorthing7403]

Thank you, John. This helped me understand some missing links. I play bass guitar and I have been trying to find some new and inexpensive circuits to boost certain tones... as well as some inexpensive DIY preamp circuits that aren't too complicated. I really hope you and Snickers have a good start to the new year and thanks again.

[@fbach2100]

I always wondered about the purpose of these base-emitter resistors embedded in an ULN2003, now I understand. Thanks a lot John !

[@myenjoyablehobbies]

Very nice and imformative explanation, and demonstration. I learned a lot watching this video. Thanks.

[@tectalabyss]

Hi John.. Very well explained and I would like to see more videos like this one. Happy Birthday Snickers. Has always I Liked,Shared and added to Playlists. And the Ad played this time. All my best. Bobby

[@boonedockjourneyman7979]

Great stuff. Definitely do more. KZbin is full of BS EE videos. Nice to see someone really good on fundamentals.

[@jeetlodaya775]

Wow just discovered your channel ! Great video 🙂👍👍

[@TrystansWorkbench]

John & Snickers - glad you got my Christmas card, it's great to see it arrived. Whoohoo. I wasn't sure what to send you, but I guessed you might have some fun with the MPSA14 darlington transistors. The other thing is a "Digispark compatible USB attiny85" (it's a bit random, but was the other next flattest thing I had to mail to you!) Snickers is doing great at 12 years old. I found the your vid on the base resistor very interesting - I hadn't realized before that it was to combat the effect of B-E capacitance - and you demonstrate well how that capacitance becomes more of an issue at higher frequencies too. It would be interesting to see how the Darlington transistor MPSA14 behaves too - as it doesn't have a base resistor internally so it should behave pretty badly at higher frequencies I'm guessing.

[@JohnAudioTech]

Hi Trystan. Thanks again for the goodies. Those MPSA14 Darlingtons have high gain of up to 20,000. I'm curious to see if they leak. Some Darlington transistors have a B to E shunt resistor around the first transistor to help keep it off otherwise the circuit will pass a bit of current even with the base open.

[@SianaGearz]

Ha, i was thinking "Is that a Digispark..."

[@saarike]

Thank you for interesting issue and explanation with test!

[@DiscoverRajivVlogs]

You are awesome brother thanks for your kind tutorials.

[@phenome4973]

Great video! Learning alot from your videos, could you do a more in depth video on the darlington configuration

[@hugoribeiro8281]

Nice explanation :)

[@martinpaap7739]

In depth video would get a like from me!

[@lordjoshuarobindumbleton275]

I would love a more in-depth video too, such a great teacher!

[@stuartmp1974]

Me to. Yes please

[@shantk7378]

Love the ending!

[@SciPunk215]

Great video !! That incandescent lamp brought back memories of my childhood. Funny how the old socket board is all yellowed. I'm sure you don't really care about that. But have you ever seen a KZbin channel called "The 8-Bit Guy"? He restores old computers and consumer electronics. He's done a lot of experimenting with yellowed plastics and he shows some techniques for getting them back to their original color... more or less. (Just a random comment, has nothing to do with the actual content of this video.)

[@JohnAudioTech]

I occasionally watch "The 8 Bit Guy" and have seen that video.

[@kalusovsky]

It would be nice to see how to set quiescent current to ab class output stage that consists of two Darlington transistors (as a one piece).

[@mexicanmoustache8180]

Thank you!

[@willyrivero470]

Great videos! Love to watch them. Say hi to your kitty. I myself have a small doggy that is with me in my lab all the time, his name is psycho. He doesn't like cats though...sorry. Man I feel tech today.

[@KarlAdamsAudio]

Excellent. I'm curious as to the change in input current when the resistor is added - i.e. exactly how much gain was traded away to get the improvement in turn-off speed.

[@JohnAudioTech]

I'd have to take measurements but you give up a lot of gain. With the 120 ohm resistor, around 5ma is shunted through it which is a lot more needed to drive the second transistor with the 80ma lamp. I could have tried a higher resistance at the possible cost of speed.

[@TheScottytr6]

Nice vid! I'm curious how that resistor affects the overall gain of the darlington pair.

[@wongyoketheng679]

Does darlington circuit boost up AC current gain or DC current gain?

[@makingsense2268]

I have precisely the same Radio Shack Experimenter's Kit! Mine isn't so yellowed on the board, though. :-)

[@iblesbosuok]

Snickers, I want to pet you Cheers from Indonesia

[@abhijithalder4567]

can u make a video...to calculate the value of the resistance needed in details. ....

[@subStuff]

This capacitance is like a capacitor has been placed between the base of 2nd transistor and ground, right?

[@williamhazelwood8288]

Hi John i enjoy your videos, i have a request is it possible for you to do an ab output stage design tutorial?

[@HillsWorkbench]

He has done a few already, such as kzbin.info/www/bejne/j4XQnnmvf6-EmaM you just have to dig back a ways. A few on my channel too BTW, see my Cat Killed Tiger series. Hey John, how about a playlist for your B and AB videos?

[@michaelmarini3123]

Lovely Kitty...!!!

[@jamest.5001]

nice kitty soft kitty little ball of fur !

[@rich1051414]

Soft kitty, warm kitty, little ball of fur. Happy kitty, sleepy kitty, purr purr purr.

[@carlfranz6805]

OK. Just f2f the top of my head and when I get home ( a couple of weeks) j may try this... What if instead of a resister we used Shotsky diode?

[@RexxSchneider]

Then the power transistor would never conduct, because the Schottky diode would clamp its base-emitter to a couple of hundred millivolts and it needs around 600mV to turn on.

[@mr.amp0076]

New clamp meter.... Awesome

[@valdarmort]

it's there to enhance the bass

[@HillsWorkbench]

Yeah, should have remembered the devil of the collector to base capacitance, especially in power transistors. Reminded me of an older video you did on Baker Clamps: kzbin.info/www/bejne/mpPMYWh7naaJjLs

[@tseckwr3783]

4141? vs 4140

[@uK8cvPAq]

FEELtech, is that a meme reference?

[@steveone]

I reckon they meant to call it "FIELDTECH" but spelt it in Chinglish .

[@tinkerwithstuff]

Given that the BNC ground has 110VAC (or 230VAC in europe) on it, you could guess why it's FEELtech indeed. Reportedly not much power behind it, coupled through a capacitor in the internal switching PSU, but one guy reported actually feeling something, lol, and then investigating, bringing this issue to light.

[@RobynTapps]

The usb thing is an FTDI chip

[@SianaGearz]

Nope.

[@bigbread9000000]

As a postal mechanic I ask people not to send objects in plain envelopes(send as a package), as these object may get jammed in mail processing equipment and not get to their destination in one piece!

[@TrystansWorkbench]

I do apologize. Sorry. Consider me told off. The items were taped to the inside of the card, but I imagine that's no guarantee that they won't break out and have a party in your mail sorting machinery.

[@bigbread9000000]

Sorry, didn't mean it in a way to tell you off!! lol just trying to inform people that it is a crapshoot if the letter with an object inside, makes it through the machine.

[@kevinlivingston9563]

Trystan's Workbench 🤣🤣🤣 Yeah I’ve learned that the hard way. Their machines are something like a football launcher with rollers pressing down and spinning it through, flattening out any humps.

[@ladronsiman1471]

Therehould be two resistors .one in each transistor

[@Vidya1939]

TKQ

[@BuzZ.]

First