Constant Current Source with BJT Transistor

[@electroquests]

Thank you! Very well explained!

[@pileofstuff]

I've been meaning to play with constant current supplies one of these days. Thanks for the head start.

[@GadgetReboot]

remember to use a good quality breadboard instead of those cheap eBay ones, I lost at least four hours debugging the wrong part of my set up.

[@BobWa43]

Thanks, good video with clear illustrations and explanations.

[@henrikjensen3278]

It is often a good idea to do power calculations for led drivers, with 10mA you will seldom have problems, but at 50mA and a small transistor you might have problems. Other ways to make simple current generator is JFET and constant current diodes

[@DrexProjects]

That's cool. Who knew? You did. Thanks.

[@electronic7979]

Helpful video I liked it

[@andymouse]

Great stuff, I'm quite into this fundamental stuff at the moment, it's interesting how much I have forgotten...cheers!

[@GadgetReboot]

Yeah I need to fill in the blanks that have crept up on me over the decades. One thing I learned in this experiment - ebay breadboards can't be trusted for signal integrity. Until I switched to a proper breadboard, current was jumping all over the place!

[@andymouse]

@@GadgetReboot Massive problem, I'm doing small current stuff to and it's practically impossible on cheapy boards. Maybe a breadboard review ?

[@GadgetReboot]

yeah it’s similar to the problems I have with test leads that have alligator clips on them and they are poorly made so they build up resistance and you try to use them to provide 5 V to a circuit from a power supply and you’re getting 4.1 V and then it jumps to 3.7 V, I wonder if it’s possible to easily measure or demonstrate breadboard connectivity issues. Something to put on the list. lots of videos out there take apart the cheap breadboards and show the contacts are poorly made and it’s easy to see why it’s hard to shove components into those but I don’t know if anyone’s demonstrated connectivity issues and reliability.

[@newburypi]

Good one👍 Well explained and demonstrated.

[@Lionel_Walder]

Toujours au top tes explications

[@MarcRidders]

I learned a lot, thanks for the video.

[@TheEmbeddedHobbyist]

Nice video, now we need to move on to the current mirror and the long tailed pair. ;)

[@GadgetReboot]

I was going to do current mirrors but the whole thing was starting to get too long, but that saves more for another day!

[@aurthorthing7403]

Sweet. I've been thinking about building a similar circuit to improve cheap LED flashlights. Something to tame it down while squeezing as much juice as possible out of the batteries.

[@johncoops6897]

Then DO NOT use this kind of circuit (with series resistor). You lose light but the excess power just gets wasted as heat (in the series resistor). If you want maximum juice from the batteries to be converted to light, then use a proper LED driver. If you want control, use PWM. Don't use "linear" type drivers - you want a high quality switching controller, Buck to step down, or Boost to step up..

[@david96110]

So if they asked me to design a 100-µA current source i would need to set my Ie to that value ??

[@hugobracamontesbaltazar]

Good video! Regards.

[@GnuReligion]

Some blue LEDs will light up with very small currents ... sometimes far less than 1mA. The BJT mirror configuration can be a convenient to globally trim constant current to a series of loads. www.allaboutcircuits.com/uploads/articles/current-sinking-and-current-sourcing.jpg

[@GadgetReboot]

I remember regularly using around 2 mA for surface mount LEDs in designs but I don’t think I’ve had one less than 1mA, now I want to investigate that, maybe see if I have any already in my collection of surface mount and through hole. One thing I did notice recently with my through hole red LEDs, out of the same batch I got on eBay, some work fine and some look like they are only operating at about 1/3 brightness in the same circuit so that’s weird, I think I have to go through and do a quick audit and just throw away the weird ones. A few months ago I was researching current mirror circuit configurations but now I can’t remember a few of the things I learned, need to start over. i’ve never used them before and I can’t remember if they need matched transistor pairs or something else might have been a critical parameter, maybe I’ll get it the breadboard and see.

[@WistrelChianti]

By jove, I think she's got it!

[@sauravti]

That's fucking helpful video thnx for it😭😭😭😭😭

[@GadgetReboot]

I should make more like that. Useful building blocks for bigger projects.

[@sauravti]

I will wait for it