8 awesome application of diodes in circuits.

[@amolchagassilva7249]

I always wanted to learn electronic engineering, but because of money issue i took mechanical. Now i want to fulfill my dream of learning electronics practically just like how we create machines mechanically, and YOURS is the only channel which i have found right on the dot. Amazingly and calmly explaining. you got all the tools and components in the background, i wish you all the very best, and always aspire to be like you. Would be an honour to be in touch with you.

[@LambdaTechnology]

A fantastic video for the hobbyists, and a great refresher for the professionals. Easy to follow, concise and very well executed. Thanks for sharing this and spending your valuable time creating this content 👍

[@elewizard]

Thank you too, for watching the video and writing such a encouraging comment 😃, so nice of you

[@jeffmoden4332]

I don't often comment on videos and I'm not one to "subscribe" but had to do both on this one because it's obvious to me that you love to teach and both your visual aids and the order of revelation of your simple explanations are, IMHO, impeccable. VERY WELL DONE, good Sir!

[@elewizard]

It is an honor for me that you spent your valuable time writing a comment for me ​thank you for supporting me ❤️

[@SteveRaynerMakes]

I felt the same.

[@WynneGarnie]

This fellow is a legend, detailed explanation, and friendly teaching. Well done

[@elewizard]

Thank you dude for your warm and encouraging comment 😃

[@androiduploadsutube]

Thanks!

[@elewizard]

Thank you so much ❤️❤️❤️❤️

[@damienmilk3025]

Yours is one of the best electronics tutorial channels on KZbin. Thanks, subbed.

[@elewizard]

Thanks for the sub!🥳

[@SteveRaynerMakes]

A lot of information here` explained very well.

[@elewizard]

Glad you liked it❤️😃

[@sananjabrayilov5349]

Man, glad you are back. Have seen your different videos about electronics (open collector, microcontrollers). Hope you'll add back them all. Subscribed already

[@elewizard]

Thank you for sub. I have face an issue with my MCN and because of that I have created new channel, I am going to add old videos along with new videos

[@Denyzyne]

Very helpful! I sure hope my diodes won't mind being in my circuits now! ✨😃

[@elewizard]

😂

[@jungleb]

your content is amazing, you are my new teacher. thanks

[@elewizard]

Happy to hear that! 🥳

[@dimitrioskalfakis]

good presentation. minor nuance though: at about 6:00 in the example of reverse circuit protection you referred to using a schottky diode but the symbol you used was that of zener ;-)

[@elewizard]

Thank you for noticing the point. Sharp lines are presenting zener diodes and curvy symbol presents schottky. 👍

[@dimitrioskalfakis]

@@elewizard well, an S and a Z are still different (inverted) whether you use curvy or sharp lines.

[@mustafaiqbal89]

Thank you so much for making a thorough overview on diodes! :)

[@elewizard]

My pleasure!❤️

[@CableWrestler]

Subscriber number 26 here! Just found your channel. Great content - thank you for taking the time to make this video.

[@elewizard]

Welcome dude. Thanks for sub 🥳🥳🥳🥳

[@utube321piotr]

Outstanding channel, thanks for taking time to share information.

[@elewizard]

I appreciate your kind words. Thank you for taking time to comment ❤️❤️

[@billporter149]

Excellent presentation of diode capabilities and common usage.

[@elewizard]

Many thanks!

[@Q80100]

You are awesome in the end of video 😂😂 Also your videos really useful , liked and subscribed

[@spyghetti]

This channel is great, I'm consuming each video at an alarming rate.. please keep it up, your examples and explanation is superb.

[@elewizard]

Wow, thanks!

[@mohammedalathari9635]

Hello, great video, thank you. Good to see you back, I was sad to see you disappeared from youtube! Where are the older vids?

[@elewizard]

I had trouble with my MCN. This is my new channel and I am going to add old/new videos here

[@smilingdog2219]

I have so many questions about the magic of circuits and you answer a few. Thank you.

[@elewizard]

I will answer 😉more in next videos

[@tanner1985]

I appreciated the style of teaching, subscribed! Greetings from Italy

[@elewizard]

Glad you liked the video, you arr most welcome my Italian friend 😊

[@startrek416]

very clear explanation, it is good to collect knowledge in one lesson, well done

[@elewizard]

Glad you liked it!

[@brucehatch6415]

Used, 3 t05 cans with 12 diodes in each(closest to identical as you can get) 1/2 of each can were used to pass + and the other half of the can passed - placed between 2 opamps. Out of one opamp +/- to Input of the next +/- the delay caused by the two18 diode strings gave us the ability to do limiting and compression on audio

[@mikepanchaud1]

Nice video. It's interesting to connect a piezoelectric sounder to the output of the infrared receiver. You can hear the pulses and hear differences between different brands of remote!

[@elewizard]

Yes that is nice. But the sound fifference is not because of band difference, it is because of the difference in the code the remote sends. IR remote controllers are my favorite, I will do projects with that as soon as possible

[@tgetvtips]

Looking forward to your next video 🙂

[@brianwood5220]

You have a great channel, I have learnt a lot watching you. Thanks for sharing.

[@elewizard]

Thank you for watching

[@MuliokelaLubinda-c7r]

Good presentation sir. Keep it up.

[@elewizard]

Thank you, I will

[@Fin_nish_usr]

Respect for you. Your channel helps me to learn about electronics. You have a new subscriber.

[@elewizard]

You are most welcome my friend, I am proud of having audience like you 😃

[@aijaz4441]

Your explanation is amazing. Please make more videos on understanding electronic circuits and with emphasis on what each component does in the circuit.

[@elewizard]

Thank you dude. Will do 👍

[@marcelogouveia9614]

Man, thank you for this great vídeo with all the basics 👌 We (except the haters) all greatly appreciate your time and effort!

[@elewizard]

I appreciate that! Thank you for supporting me ❤️❤️❤️

[@yangranay8102]

The usage of Diodes is quite clear in someways, may I get the link of the video that you've just mentioned at 7:37 about the battery backup charger?

[@msg1956]

Excellent explanation..! I appreciate your hard work..!

[@elewizard]

It's my pleasure

[@VeraBulatovic-s3b]

Mr. He said, You got him.

[@lsambrexi6173]

WAW!! It was the most beautiful coincidence when I met your channel.❤

[@elewizard]

You are most welcome , cheers 🥂

[@abdulsami7042]

Excellent. Many thanks.

[@elewizard]

My pleasure!

[@ServiceOrchestramegastore]

you are a great teacher. thank you for shearing this knowledge.

[@elewizard]

Wow, thank you so much. Thank you for being here 😊

[@ServiceOrchestramegastore]

I like the positive mood you brings us with you...🙂 @@elewizard

[@mdamanotullahfahadi7772]

Thank you so much for excellent presentation and informative videos. I have already subscribed.

[@elewizard]

Thanks and welcome ❤️

[@sastrydasigi7010]

Great video. Thank you very much!

[@elewizard]

You are welcome!

[@ThomasJagielo-ek8nq]

Glad your back!

[@elewizard]

Thank you dude❤️

[@mikex691]

This is EXCELLENT!!!

[@elewizard]

Thank you so much

[@RobytheFlorentine]

Very very good video. Thanks

[@elewizard]

Glad you liked it!

[@ambition112]

0:00: 🔌 Diodes are versatile components that can rectify current and have various applications in circuits. 4:30: 🔌 The video discusses various applications of diodes, including rectification, reverse polarity protection, and connecting multiple power sources. 8:52: 🔌 Diodes can be used to reduce voltage in a circuit and as flyback diodes in relay circuits. 12:17: ✨ The use of diodes and zener diodes in circuits to eliminate spikes, regulate voltage, and protect against overvoltage. 16:45: 📺 The video discusses different types of diodes and their applications, including the use of LEDs for remote communication. Recap by Tammy AI

[@GeRoNiMo-m4v]

Thank you very much for all the knowledges..appreciate it!

[@elewizard]

My pleasure!

[@معكتاب]

I was looking for the all uses of components because I am suspicious of one or two uses for each component, and I am glad to see this channel and from the beginning I subscribe the channel 🙏🏻

[@elewizard]

Thank you for subscribing the channel. Keep watching 👍

[@MarineElectrical]

Very good and informative video! Thank You!

[@elewizard]

Glad it was helpful!

[@KarldorisLambley]

another fantastic video, I've been making notes.cheers!

[@elewizard]

Glad you like them!🥳🥳🥳🥳

[@KarldorisLambley]

@@elewizard tbh for this sort of stuff you are better than Mehdi, the way you list things, to make note taking easy. whereas, and please don't be offended, medhi is more entertaining to watch. (don't think i expect you to start zapping yourself!)

[@elewizard]

@@KarldorisLambley thank you for your feedback. Yes I know, mehdi is an artist more than an engineer 👍 It is quite normal to get more views

[@KarldorisLambley]

@@elewizard pah. more views? means nothing, popularity is over-rated. this sounds bad but i think most people have dreadful taste. he may get more views but you have taught me far more. why do you not have patreon or that buy a coffee thing? i'd gladly give you a few quid. and wow. yesterday you had 6.8k subscribers, today is 7k. congrats!! that is nearly 3% in one day!

[@elewizard]

Yeah, my progress is fine. We are going to create big community 🥳

[@jerson8146]

Awesome video. New subscriber here.. Please also make video discussing applications of inductors.

[@elewizard]

Welcome aboard 👍 I will make it as soon as possible

[@bikashdas4078]

Knowledgeable video.

[@elewizard]

Glad you think so!

[@stalwartekwere2157]

Best video man ❤❤❤❤

[@elewizard]

Thank you so much 😀

[@xila8861]

I am learning , that's good.

[@elewizard]

Very nice, keep watching 👍

[@ianuragaggarwal]

Diodes are very talented devices 😊

[@simbakali]

I have subscribed immediately! Let’s wait for the next insightful videos. Bless you.

[@elewizard]

Awesome! Thank you! New videos are coming soon

[@simbakali]

@@elewizard Thank you so much 🙏As a beginner, I want to understand what is bandwidth of a signal. I have googled but can’t find a simple explanation of how bandwidth related with hertz.

[@pheymee88]

4 things on my mind to add: 1) LEDs can drop up to 2-4V, depending on its colours! The bigger the band gap, the "colder" the colour and bigger voltage drop! 2) I never heard of flywheeling diode, do you mean flyback or freewheeling? :D 3) I'm missing the explanation of the flyback diode - it's dropping that peak voltage because it allows the coil to "decharge" through itself (to absorb the inductive current kickback), making a nice peak current "circle" flow between the diode and the coil, instead of your circuitry. 4) I'm surprised you didn't mention opto-isolators alongside with LED transmission devices, those are my favorite type of power protection devices!

[@elewizard]

1-i mentioned the voltage drop capability 2-yes flywheel is used 3-correct 4-i can't mention everything, I have to ignore many other items to keep the video length acceptable

[@EI.01]

Sir i have being following your channel, but i can't find Your old channel anymore what's wrong with it, i do love your videos

[@elewizard]

I had trouble with my MCN and because of that, I have created a new channel. I am going to add old videos along with new videos here.

[@gidomareyt]

I like your video, i like the circuit to charge battery

[@elewizard]

Thanks for liking.

[@kjuirteerdserty9618]

excellent explanation

[@elewizard]

Glad you liked it!

[@mctoddhikvision6189]

nice video,, can you make a video about replacing diode on solar panel?

[@elewizard]

Thank you so much for your suggestion. I will consider your suggestion

[@edwardchance2543]

Thanks for sharing subscribed

[@elewizard]

Thanks & welcome

[@drtidrow]

Another application is to use the reverse-bias junction capacitance for adjusting the frequency of a tuned circuit - varying the reverse voltage varies the capacitance, which can then change the frequency of an oscillator. Varactor diodes are specialized for this purpose, but the effect can be demonstrated with pretty much any reverse-biased diode.

[@BillAnt]

A full wave rectumfryer never gets old as an electronics joke. lol

[@elewizard]

😂

[@Enigma758]

I have a basic question I was hoping you could answer. Normally, a resistor is used along with the diode to limit current. However, when used as a rectifying diode bridge, I normally do not see any resistors being used to limit the current. So my question is, in that case, what limits the current? Is it only because they are high current diodes and therefore don't require any external current limiting? Thanks!

[@elewizard]

It is because of the power supply. The output current of power supply is limited, so you have to use a diode with a current rating higher than the power source. Then the power supply can't deliver current needed to destroy the diode. I hope you got the answer ❤️

[@Enigma758]

@@elewizard Yes, thanks. So in general, if the diode rating exceeds the current delivered by the circuit, then you don't need a current limiting resistor.

[@tgetvtips]

Your efforts sharing this valuable info are greatly appreciated. ❤

[@elewizard]

My pleasure 😊

[@sadaasivomkm9994]

Neetest work Shop

[@waltermelyon4300]

In forward bias setup, if you pass negative current through the cathode side of diode will the diode pass the negative current through the diode?

[@elewizard]

Passing negative current means drawing positive current, so ye answer is yes

[@RixtronixLAB]

Well done, nice video,thanks for sharing it with us :)

[@elewizard]

Thanks for watching!

[@surajmandal_567]

Hi i wanted to know that how circuits are designed. How do engineers know where to put a capacitor, resistor or inductor. I think its an advanced topic but a simple explanation will do enough.

[@elewizard]

It is not easy to answer your question. But if i try ro answer your question in a very simple way, they learned from books which are written based on experience and knowledge. In my opinion, all of these sciences and knowledge are coming from experience.

[@LapNguyenthi-f6q]

I love it ❤

[@elewizard]

Thank you for watching 😊

[@vinicus508]

It’s not wrong to say it’s very simple because it is! It’s the easiest silicon based component to make. But being simple is what makes it powerful. All silicon based components have diodes or diode like stuff in it

[@elewizard]

Exactly 💯

[@MrJam1858]

Great video friend!! Did you used to have a different channel? I remember watching a video from you about capacitor applications that was extremely informative amd helpful. But the video is no longer available says KZbin.

[@elewizard]

No, I don't. My last channel is not available because of the issue I had with my MCN. 😑 I am going to upload old and new videos here 👍

[@walt5507]

At 7.42, you mentioned a video on charging a backup battery setup, and I am most keen to see that, but I can't find it on KZbin . Can you direct me to that one please? Great videos btw.

[@elewizard]

I said in one of my next videos, the video is not published yet. The video is going to publish in 10 days

[@anontoakanda5847]

Sir, I am from Bangladesh 🇧🇩. I recently search your channel but could not find. Today Got you❤️

[@elewizard]

So nice of you. I had trouble with my MCN and because of that, I have created a new channel. I am going to add old videos along with new videos here.

[@sayedhassanphysics8491]

🌺🌹 Excellent 🌺🌹🌺

[@elewizard]

Thank you! Cheers!🥳

[@sienervanrensburg6644]

How do you read the code printed on zener diode should you not be able to get the data sheet for the diode? Would appreciate it for the assistance as I feel that all my research to my question is leading to no answer and thus I hope that you will be able to assist me. You're explaining on components and examples are the best that i have seen and even advise my colleagues to watch and subscribe to your channel.

[@elewizard]

You need a microscope to read tiny printed text on the diode, then search for 'SMD zener diode code table' on Google. You will reach many tables that map the smd code to device name 👍

[@specialservicesequipment393]

So I can use a ZENER diode to block current in a circuit when the voltage is below the zener diode voltage?

[@elewizard]

Yes, you can

[@Belginator]

I did not know S and Z rule and have worked in electronics for many years, thanks

[@elewizard]

Glad it was helpful

[@nimaebrahimi6475]

6:02 good explained

[@elewizard]

Thank you😊

[@EngineerView]

3:32 that's a bridge rectifier

[@amobiikegwu8241]

Wonderful tutorial! As you rightly mentioned that zener diode can be used to protect the circuit from over over-voltage, can it protect an ac voltage? Can it take care of under-voltage?

[@elewizard]

No, It can't protect AC or under voltage 👍

[@marcelogouveia9614]

You can use a "Voltage dependent resistor" AKA: Varistor

[@Book_worm_1999]

Make similar video for coil inductor

[@elewizard]

Will try

[@faraday2803]

nice channel!

[@elewizard]

Glad you enjoy it!

[@feedmytv]

radja + lep, just saying, can you do the driver?

[@johnedwards315]

Hi and thx for your effort. I wish someone would make a video on how to find/calculate value etc for real life situations for us ignorant enthusiasts. Let me explain. I am using lots of buck converters - boosters and lithium solar chargers. I use bear modules for cost and flexubility. In their instructions are mentioning not to reverse polarity and put a diode etc. How do I find which diode? how do I calculate values? I have clamp meter and accurate multimeter. No more fancy bench instruments. I do not want to become an electrinics engineer just solve everyday little problems in laymans terms. Any help or direction much welcomed. TNX

[@onyxfn3183]

عالی بود استاد

[@elewizard]

Thank you dude

[@johnfiott]

I really enjoyed this video and have now subscribed. One question though - Re the induction motors, why do you usually see a capacitor across the terminals and not a diode? Or do they serve different purposes?

[@allensmithphotography]

They serve the same purpose. To protect from high voltage spikes, but they do it slightly differently and at different price points. If the manufacturer can get the capacitors cheaper than the correct size diode, they'll use the capacitor. Because the diode would have to withstand a potentially high voltage and current spike that would make them more expensive.

[@elewizard]

Good question! The answer is not simple to describe. In next week's I will upload a video about capacitors and their applications. One of experiments I will cover this subject 👍

[@colinbatey7876]

An induction motor needs a rotating magnetic field to operate. On a single phase motor a extra separate winding connected in series with a capacitor gives a phase shift or timing difference between two windings causing the resultant field to rotate and this causes current to be induced in the rotor and the rotor will turn. Nothing to do with spikes.

[@allensmithphotography]

@@colinbatey7876 that's an ac inductance motor. The original referred to a DC motor

[@colinbatey7876]

It did, but the question said induction motor which as you say is an AC motor.

[@umesh.kumar.naik278]

Good evening sir... Very nice video.... What happened with your other channel... I really missed u and your video... Lot of ❤ from odisha, India

[@elewizard]

High dude, I missed you too. I have faced an issue with my MCN and because of that, I have created a new channel. I am going to add old videos along with new videos.

Anyone know what would be oscilloscope banditech/samples if I would like to see and keep testing (able to see what what is happening) these at home with these diodes (and possibly some NAND /transistors) ? On this video looks like it is 100Mhz Oscilloscope, that would be pricy for just learning and small tests. Thank you

[@elewizard]

Yes the oscilloscope in the video is 100 Mhz but for these experiments a 20Mhz would be enough

[@elewizard]

Yes the oscilloscope in the video is 100 Mhz but for these experiments a 20Mhz would be enough

Oh thank you 😊, 20mhz is affordable

[@HOLLYWOODlosANGELES]

*Votre chaine est formidable pour l'amateur que je suis, je m'abonne.*

[@elewizard]

Welcome aboard ❤️

[@danylipsker]

Thank you again for such a broad explanation and clarity❤

[@elewizard]

Glad it was helpful!

[@HighDesertOffgrid]

I would prefer you show me how to build 8 useful devices with diodes.

[@elewizard]

Maybe in next videos

[@amobiikegwu8241]

Sir, I got your feedback on the question that I raised. I commend you for it. You used 1N4148 as a flyback diode in an indictive circuit instead of a power diode such as 1N4007, Why? I think that 1N4148 is a signal diode and used in a circuit that requires high switching speeds. Please, refer me to your videos on Operational Amplifier and how one can use it to compare AC voltages. Thanks.

[@elewizard]

There is no need to use power diode there because voltage and current is not much high, actually power dissipation is low then we can use 1n4148 or other diodes there. I will make a video about OPAMPs as soon as possible 👍

[@amobiikegwu8241]

@@elewizard Thanks so much for your feedback. I am looking forward to seeing your video on OPamp.

[@VeraBulatovic-s3b]

Mr. Exist applications to switch his lasers, maybes calls Spectogram or Spectrum, something with Hz, I almost put him down long times ago. He want to kill himself, gives for us that he want to stop. Thank You.

[@TravisTellsTruths]

Thank you

[@elewizard]

You're welcome🍻

[@kmalnasef1512]

what happened to the old channel? I saw all your videos long time ago but here it looks reuploaded! is this a new channel? any way I subscribed and waiting for you to Explain more electronics and more concepts good job my friend

[@elewizard]

Hi, yes this is a new channel. I had trouble with my MCN and because of that, I have created a new channel. I am going to add old videos along with new videos. Glad you are here

[@vsab786]

Thanks

[@elewizard]

Thank you too for watching ❤️

[@Dionisiosaucedo-t4k]

I'm new to this. I'm an electriian. But I have a question

[@elewizard]

You are most welcome. Ask your question in a new comment

[@spudhead169]

There is another way to reverse polarity protect with a diode, that's by placing a regular diode in reverse bias across the power input so long as your power source is fused. Connecting the power backwards would pop the fuse before the diode burned.

[@elewizard]

Yes, exactly. And then the user have to replace the fuse or sometimes the user think that the device is broken.

[@spudhead169]

@@elewizardIt's not a particularly good solution. It's just something that is sometimes done.

[@elewizard]

@@spudhead169 no, you didn't. 👍

[@spudhead169]

It used to be done quite a bit with car audio equipment, but not so much these days due to some folk wiring directly to the battery in reverse, so no fuse inline. The best reverse protection is really the p-channel mosfet approach. Very little loss.

[@elewizard]

@@spudhead169 There are so many approaches, each of which has its own advantages and disadvantages.

[@arp_catchall]

Thanks for the video. Can you please in the future remove the "bleep" sound? Hurts my head.

[@elewizard]

OK, In new videos I will remove that sound. Bad news is I have few videos ready to upload and there are beep sounds on them

[@arp_catchall]

@@elewizard No worries since they are already made. Thanks for your consideration for the future.

[@03_abdullahdzulfikar51]

Greattt😅

[@03_abdullahdzulfikar51]

Please explain inductor

[@elewizard]

Will do👍

[@prattacaster]

You must save your project!!!!

[@umerstar]

Is this your new channel. What happened to your older videos

[@elewizard]

Yes, this is new channel. I had trouble with my MCN and because of that, I have created a new channel. I am going to add old videos along with new videos here.

[@dunckeroo1987]

Solar cell is a diode. If you put power into solar cell it will emit deep red light visible in camera. Diode can be used to protect relay contracts from REMF from a heavy DC inductive load when contracts open. The diode absorbs the energy that produces momentary arc in relay contracts.

[@elewizard]

Yes, exactly. Thank you for your comment

[@d614gakadoug9]

A diode is not always the best choice for contact protection with an inductive load - or for protection of the driver of a relay coil. A simple diode acts more-or-less as a short circuit across the inductor when the contacts open or the driver turns off. That means that it can take substantial time to discharge the energy stored in the inductor. Often that is not a problem, but sometimes it is. For example, a diode across the coil of a high-power relay not only delays the opening of the contacts but it slows the opening once that actually begins. That can lead to increased arcing of the contacts, shortening the life of the relay.

[@dir2002usable]

Very strange things happens at time 3:38-3:39 . Suddenly the circuit transformed to something quite different that it was a moment ago, but there was a perfect oscillogram. I have an idea what difficulties author experienced . Likely it was the ground which is common for both channels. It is very sad that the author didn't clearly show how he resolved that.

[@elewizard]

Yes, you are right. But I think it was not necessary to explain what exactly happened, because my goal is to teach the concepts not the experiments. However, your comment shows that you are experienced 👍

[@gkdresden]

You can also use silicon diodes als switches for low voltage ac signals. As long as the ac signal is lower than the forward voltage the signal is blocked. When you now add a dc voltage to the ac signal, which is higher than the forward voltage, the ac voltage will appear behind the diode on top of the dc voltage. Using 2 capacitors before and after the diode you can switch the ac signal on and off. You can also use a full wave recitifier to switch between a current sink to ground and a current source from the positive supply voltage a point in your circuit whos voltage is between positive supply voltage and ground. you just need to connect one of the ac inputs to your circuit point and the other between ground or positive supply voltage. The current source and sink are connected to the dc outputs of the rectifier. In this way you can make a 555 astable multivibrator whos output switches the current source and sink to the capacitor point which gives a precise linear voltage ramp, which can control other circuits (for instance a vc oscillator or a vc PWM generator).

[@elewizard]

Thank you for your comment. I will cover these items in updated video of this.

[@d614gakadoug9]

Diodes as signal switches suffer from nonlinearities, so they are not always useful. They are good for switching RF where the signal amplitude is quite small and a bit of distortion is tolerable. It is important that the DC bias be applied from a source that is reasonably high impedance relative to the signal path impedance. In RF circuits this is usually accomplished by means of an inductor in the DC path. A properly designed current source or sink also works (an ideal current source or sink has infinite output impedance; practical ones don't but can be very good).

[@gkdresden]

@@d614gakadoug9 yes, you can use a full wave rectifier (4 diode bridge) to switch a current source or a current sink to a load by control voltages. And the currents can be different or you can modulate them by use of voltage control. I have used such a circuit for charging and discharging of the capacitor in a 555 astable multivibrator by exit voltage control in order to make a very precise voltage to pwm converter.