Constant Current Sources (Interactive!) - Simply Electronics Basics 9 

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A transistor in saturation condition can act as a constant current source so the component constant current source in the video can be replaced by a transistor

The simplest constant current source would be a BJT. A current transformer wouldn’t exactly work the same without rectification and filtering, plus it isn’t practical for this application. Good question though!

you can buy a constant current driver the same way that you would buy a battery. They are pretty common components.

Without having to make anything, benchtop power supplies with voltage and current control knobs and set to run in constant current mode will be the most efficient current source for experiments. A ballast used in fluorescent lighting fixtures is a current source. A specifically sized transformer can be used as a current source. Resistors are current control devices.

yes, and also you cannot even connect one diode to a voltage source like that, unless you make sure that the voltage source is current limited, otherwise you will burn the diode as its current does not increase linearly, itwill draw more and more current with just a little increase in voltage over it's voltage threshold.

You are almost right : the V-I curve of R LED is radically different from a G LED which is radically different from a B LED... see lednique.com/current-voltage-relationships/iv-curves/ I would guess that a 60 ma constant current source would be divide amongst the diodes as I]red ~46ma ; I]G ~ 12ma ; I]B ~ 2ma further the current will continually divide differently as real LED heat up .

This problem is irrelevant here, but in general you are 100% right

I guess they could have chosen incandescent lamps.

Someone’s a Debbie downer

Seems like trap to make people comment on video, there is no way a channel creator could made such mistake for real

Red LED would light up first and burn out in seconds(half a minute at most), if it fails open all other will burn out subsequently(though blue one may stay lit depending on it's voltage drop, depending on maximum voltage of constant current source), if it fails short it would either way have voltage drop of less then 1 volt and no other LED will light up

That's my question as well, if you get a chance to explain.

You are right. Therefore it's not smart to connect the LEDs in parallel. When the LEDs are connected in series on a current source, you are sure all leds pass the same current. Even if the forward voltage of the leds is different. This is most likely for leds with different colors. By the way,never connect leds directly to a voltage source. A lead has no linear relation between voltage and current. Once the voltage is slightly larger as the forward voltage of the led, current rapidly increases. So with manufacturing deviations, temperature diverenses,... it's impossible to maintain a steady current through the led, using a voltage source without resistor to limit the current.

You're Welcome! Another coming very shortly :)

me me again thought that too

EveryCircuit program allows you to show "electron" flow or "Conventional" flow . This is because at one time it was believed that electrons would flow from Positive to Negative. So all schematics and circuits drawings were arranged that way and it became sort of a "Standard". So since so many schematics were drawn that way it is still used that way when drawing circuit diagrams. Some programs allow you to switch between the two just for personal preference. In all reality it does not matter which way it shows that it flows in these Circuit Simulators because the end result is the same. As long as the circuit is closed electrons will flow no matter which way they are shown. Its just personal preference mostly. Depends on how you were taught.

But what about integrated circuits, which cannot handle the size of a resistors, there we can use constant current sources .

the point is that when using constant current sources the LEDs are connected in series.

You bet I will :)

+Simply Electronics Great... Wating for it... 👍👍👍😃

@@ankitpatle1996 5 years later. You can stop waiting, the last video was 4 years ago with no more on cc circuits.

you imbecile

That's just one problem with this video. Constant current drive is for LEDs in series, and if he insists on doing that, he still needs one resistor per LED. Even if the LEDs were the same as he states, that would still be true due to manufacturing differencs.

That is the convention. When Benjamin Franklin discovered electricity, he had no way of knowing in which direction electricity (electrons) flowed so he arbitrarily chose positive-negative. Everyone just went with it. When we later realized this wasn't the case, rather than change the convention, we just stuck to it for convenience.

@@TriplekilzTk1 Yes, but in his previous videos the current was running in the "correct" fashion, neg to pos. So why the change?

@@rosshollinger8097 Perhaps so that the people that watch the video aren't confused when they find that a majority of engineers follow the convention. In any case, he should have provided an explanation.

da man ,all solar panels will have a higher voltage with no load. If you have a 12V 100Watt solar panel, it will be 12V with. 100 watt load in full sunlight. My guess is that when the buck puts a load on the solar panel your voltage is dropping to 12v or lower and most buck converters need 3v to 5v more then what they are set to, so when the solar drops 12v under load the output from the buck will drop to 7v or turn off tben the voltage on tbe solar goes up the buck turns on and the voltage drops again causing it to cycle. Hope that helps.

he used a site called EveryCircuit.

thanks. could you plz tell me how to make the animtated current flowing presentation?

JERRY ONG ohms law, resistance (forward voltage of the led) in the led

Thank You! The active component would be something like a linear current regulator or switched-mode current regulation IC. Active components are "Active" because they rely on having a feedback loop so that they can monitor output and respond/compensate for any change.

Rahul Maurya icircuit

@@oscarpeters1351 Thannkkkkk youuuu!!

Yes, ohms law equations. If you know the current and the resistance you can calculate the voltage. With any 2 of these variables you can calculate the third. In the circuit you're referring to we actually know the current and the voltage, but not the resistance of the diodes. So you'd have to work out the resistance of each diode to be able to calculate why the voltage dropped from 3V to 2.95V after adding a diode. Check out the first video in this playlist.

This bothered me too so I did more research. The constant-current source must decrease voltage because adding a 4th diode *decreases* total resistance in the circuit. Resistance is calculated as: (resistivity * wire length) / area Adding a new diode increases the Area the current flows through, so resistance is effectively *decreased* in the circuit. Hence lower voltage required to keep the current constant.

Chidurala Jeevan kumar dont need to be grounded, because it goes directly back to the source in this diagram

We are supplying 3 volts, so all the LEDS will be supplied with 3 Volts

Thanks. Btw, I really like your videos, simple, short, straight to the point! Keep it up :)

You're Welcome :)