Constant Current Source

In this video, I describe a constant current source used to drive the LED backlights of a LCD.

[@ThanassisTsiodras]

Thank you, Craig! Useful circuit to know about, and very nice and clear explanation of its inner workings.

[@benthere8051]

Thanks, Craig. That's a very useful circuit. The two silicon diode voltage source is much better than a zener diode because the low voltage zeners are hard to source and only available in a limited number of voltages.

[@Yorumcu63]

Great video

[@ovalwingnut]

That was down right magical, as I try to wrap my head around "constant current". Thank you 👍😁

[@craighollinger9972]

The circuit is "constant" within limitations, as I showed in the video, but is useful otherwise. Keep studying basic electronics, you'll get it in time. Thanks for watching.

[@cateyenebula]

Just what I needed to drive my DC optocoupler with an AC input. I just need to add an additional diode and I'm set. Thank you for the excellent explanation and demonstration!

[@craighollinger9972]

Glad I could help.

[@shvideo1]

What a great circuit and so well explained. Thank you also for the component part numbers in your circuit. Great work.

[@craighollinger9972]

I'm glad you found it useful. Thanks for watching!

[@M0NTVHomebrewing]

Thanks! Great explanation. Very helpful.

[@wasiuadeleke6869]

Thank you for your explanations

[@mokus8643]

nice clear job thanks...good teacher skills...cheers to you

[@craighollinger9972]

Thanks for watching.

[@zainaabdin]

Thanks....Simple. explanatory. useful. practical

[@craighollinger9972]

Thanks for watching!

[@dd0356]

thank you very much. very clear video. greetings from india!

[@craighollinger9972]

You are welcome. Thanks for watching!

[@user-vp9wi1nk5k]

Legend brother

[@ziadfawzi]

Thank you so much.

[@craighollinger9972]

You're welcome!

[@konstantinosvafeiadis4548]

Is it a good idea to put a trimmer (rheostat) of ~47ohm in series with the 68ohm resistor, in order to have a variable brightness on the backlight? Thank you very much for sharing your knowledge.

[@craighollinger9972]

That would work if you could find something that low in value.

[@mark8664]

I prefer using an NPN transistor. Those PNP's give me a headache :)

[@deepakroy82]

i need ur help

[@christianurgese]

What does happen decreasing source voltage ?

[@craighollinger9972]

The circuit is quite simple, so not perfect. The current will change slightly as the source voltage changes (up or down), but it's pretty constant. That's the whole point of the circuit, constant current.

[@horacewonghy]

voltage regular + series resistor = constant current

[@MrBobWareham]

could you use an NPN instead of PNP

[@craighollinger9972]

Yes, you can. Basically just turn the circuit over but keep the diodes pointing toward ground. The device you want the constant current to flow through now gets connected between the positive rail and the collector of the NPN transistor.

[@MrBobWareham]

Thanks for that

[@cancaonegro]

Same question as you! :D

[@carbonosilicio5318]

Good explanation, you have very nice and soft voice always constant and clear but, if i may sugest, use some sort of a soft matt on the table in order to avoid those clicks and pops of the hard objects while moving them. It would help alot for some of us with sensitive hearing. Thank you.

[@hamaraapnaboutique5888]

hindi m do

[@labanchege5261]

Was the first four minutes really necessary it makes tge video boring

[@craighollinger9972]

When I find something boring in a video, I just use the slider and move ahead.