MOSFET - Off after a delay

MOSFET - Off after a delay
In this video we use the charge discharge cycle of a capacitor as a timer. When you press the button, the gate of the FET goes high and it switches on, while at the same time it charges the cap. When you release the button, only the charge left in the cap keeps the gate open, and when it discharges fully, the FET is switched off. You can have delays from minutes to days...
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[@rdpoulson]

This was really great! Please keep making more of these type of instructional videos - loved it!

[@dominicdima7305]

Very helpful, Thanks for the upload. Watch all the content, typically as you release it, and enjoy and learn from everything so far. However, Classic Circuits You Should Know tends to be my favorite and as far as I can say as of now, the most educational that I've learned from. Thanks again keep up the awesome work. You've really turned my attention to electronics and I thank you for that Paul. Great stuff to know, awesome hobby, and the community so far seems great too.

[@felixruiztorrez5192]

Thank you for this circuit. My understanding of this circuit is, when you press the button, you charge the capacitor, then when you release the button, the capacitor get discharged on the resistor because there is no current flowing between G and S terminals, so all the current goes through the resistor. The MOSFET is acting in the saturation region as a current source because (V_GS-V_T) is smaller than V_DS.

[@kingshahzad78]

Thanks for making this video dear. You have solved my tonnes of problems. Love You

[@rhoniandjeff7453]

since ive never taken any courses or training of any kind, this is such a wonderful find. I love this. thank you.

[@learnelectronics]

Welcome, please watch all you like and email if you have any questions. [e-mail]

[@rhoniandjeff7453]

@@learnelectronics awesome man, thank you for making yourself available.

[@marktiger4613]

Great video I am a older guy that loved working I my garage on old cars but I hurt my back and and I am still working my full job but at the end of the day I go out to the garage and can't do anything so I bought a soldering station and going to get some parts and kits to keep myself busy thank you for your service and for your channel and information now I just need to figure out what to order for a beginner with no parts or kits and where to order

[@learnelectronics]

May I suggest my Amazon shop? Check out this page from learnelectronics www.amazon.com/shop/learnelectronics?ref=inf_own_learnelectronics

[@marktiger4613]

@@learnelectronics thank you that's great

[@AsbestosInhaler-f6r]

Thanks Paul. You and the Art of Electronics book have thought me considerably more than my College course on electronic engineering have. Once again thanks

[@learnelectronics]

Wow, thanks

[@ricardordz7538]

Great content man, i'll use this circuit for a self filling water bowl for my dog and see if it helps for when i'm out of the house

[@friedmule5403]

Again a video I needed, and at the right moment:-) I did make a delay, but only using a cap across positive and negative, follow by a resistor on the positive rail. It make the LED, fades in and out on push of the button.

[@learnelectronics]

Sounds great!

[@oscarpeters1351]

Im using this circuit for my garage lights, thanks a lot!

[@bassome3000ify]

i must say i love the knowledge and experience u share with us. also like the Classic Circuits knowledge u share. small note/question, at 5:02 the second graph, are we not doing the opposite? i.e. with the resistor make the capacitor discharge slower? i.e. less sharper. thx!

[@idiotwithasolderingiron]

The resistor is pulling current to ground discharging it faster

[@TheEmbeddedHobbyist]

The graph has slight issues, there is not resistance to limit the current while the capacitor charges up when the key is pressed. so the voltage rise should be almost vertical and stay there without the 1M resistor until the cap self discharges. the 1M resister gives you a defined discharge path so you can control the discharge rate.

[@eval1035]

very simple but it is really usefull.

[@Taran72]

Yes, very useful! To see the application of something you studied with formulas....it always is. :)

[@deankq4adj125]

Great video, really enjoy you sharing with us!! Keep up the good work my friend!

[@peterlethbridge7859]

Brilliant. Thank you.

[@HelmutTschemernjak]

Great video, I love this simple things. This should bring over the message to many students/attendees.

[@learnelectronics]

Im glad you likes it. Thank you very much.

[@devanesanandrews3488]

this is fantastic, Would you explain how to calculate the Mosfet on off deadly times with oscilloscope

[@baldrickdaisy8982]

Thanks once again Paul. Love the classics 👌

[@drocles]

Love your channel, thanks for being so dedicated to education!

[@learnelectronics]

Thank you

[@keithking1985]

i like those croc clips, do ya have them long Paul?? these are great i bet loads of people will start to learn new stuff giving the situation were in. and stuff like this is always cool to see.

[@dukeeod1650]

A very simple circuit that can in very handy I could also use an LDR in a separate circuit so when the LED goes out the LDR functions as a dark activated circuit. Oodles of applications, thanks

[@vojtadanda5932]

Super video. You should make the on after delay circuit

[@learnelectronics]

Coming up....

[@Electronzap]

Very cool circuit!

[@georgechambers3197]

Very cool circuit. I really like this series, keep them coming. 😁 Thanks for the video!

[@learnelectronics]

How you been buddy?

[@georgechambers3197]

Pretty good here. We're pretty isolated anyway so distancing isn't a problem. How about you other than the tooth? How's the family, the boy mom and your sister?

[@vlader7515]

Damn love you man was looking for this 🤣

[@rw2897]

While this may sound like I am joking but have you ever thought of writing a book? The simplified way in which you explain things, to me, are extremely helpful. You can explain in minutes what reading an entire chapter doesn't do.

[@learnelectronics]

I have thought of it, but I cant sit still long enough.

[@mohamedvahed1008]

Hi, very well explained.can the switch be a toggle switch.but does the same work? Basically 1 want to use this circuit to switch on a item with a car ignition switch and it will supply 3 sec on and then off. Once the the IGNITION is switch off and then on will do the same.

[@LitesLAB]

This was great Paul! My little one has a moon light on her wall that uses this exact circuit! Nice to see it laid out like this. Thank you :) Did your vid on Pots get taken down?

[@mikeburton8687]

This is cool circuit, really enjoyed this something I can understand

[@bertspeggly4428]

Good video. Where do you get that capacitor kit? Thanks

[@MrBobWareham]

Very good video where did you get your box of caps, please

[@samuelchamberlain2584]

Yes I have used this circuit for outside lights befor also it should work for extract fan boost etc . It has a nice soft off behaviour.

[@michaelpadovani9566]

Different take on the 555 delay, I like it!

[@learnelectronics]

Glad you like it!

[@simuk]

What would you change to make the LED go completely off instantly, rather than "fading" off as it shows in your video? So the LED is either completely off, or completely on but not a state between those two.

[@jonelectronics510]

You can add a Schmitt trigger to get a clean logic switch between the filter and the gate.

[@jeepingneatus]

Could I use this type of circuit to turn a DC motor on and have it shut off after just a couple seconds? I am trying to do a delay off in a very confined space. This seems like one of the most simple (and space saving) delay off circuits I have seen.

[@khwezimngoma]

Awesome guy, between yesterday and today I learnt a lot from you, you got a new subscriber with a bell and a like.

[@learnelectronics]

Awesome, thank you!

[@stevesfascinations1516]

Love your video. Thanks for such a good explanation. Thumbs up (already subscribed).

[@electronicdanuma7067]

Good

[@excitedbox5705]

These are the most useful videos. I am working on a website where I will have a DB of these types of circuits. Knowing these circuit building blocks is what will ultimately allow someone to design their own devices instead of just reconstructing other peoples works. If anyone has any good resources for where I can find more of these it would be a great help.

[@kalikatz2382]

I built the same circuit for the dome lights in my car. So when I close the doors, interior lights stay on for a few seconds. That was over 10 years ago. 😀

[@tusaisix]

Very nice circuit. Can it work if i remove the button and stays always connected. I want to make it work when i give it constant power supply and then the circuit turn off but the power supply stays connected until i cut the power off and reset itself. Please (you or someone else) give me an answer even if it can't be happen.

[@electronic7979]

Super 👍

[@barthsmusic9515]

Hi, thanks for the post. I have the 2 problems: 1. Not al 12V is available on the output and 2. the output current drops when it's counting down (=when de current on the elco is decreasing). Is it possible to make it stop in 1 step insteat of going down in output current? Best Regards, B.

[@GORF_EMPIRE]

A nice circuit for reset timing in a computer.

[@vladimirhromis8759]

if u put resistor on the input of the capacitor you can make the turn-off time dependent on time that it has been turned on for . I guess .. :D

[@abhayraj695]

Iam using similar technique....a low pass circuit for creating an on time delay for gate

[@ku4nz]

Good job. Only 20K to go.

[@learnelectronics]

Fingers crossed!

[@mirceanicolaepop3707]

A Schmidt trigger in series with the gate would have helped avoiding the dimming.

[@antonypilepich8947]

Thank you, Simple timing like this I have built in the past (with NPN switching transistor) I've put a resistor along the base line for delay. Is there some Mosfet reason for putting the resistor gate to earth?

[@learnelectronics]

The resistor speeds up the discharge of the cap.

[@TheEmbeddedHobbyist]

Antony, the NPN transistor is a current controlled device. it needs current to flow into the base for it to turn on. so the discharge time of the capacitor between the base and emitter controls the on time, to modify the on time you change the discharge current by changing the resistance between the cap and the base. The fet is a voltage controlled device when there is only current flow in to the gate at the start as the gate capacitance charges up. after this the fet can stay on all by itself, the capacitor is much large then the internal gate capacitance and with the 1M resistor to ground gives you more control of the timings.

[@majorkuso6720]

coud you calculate the approximate discharge rate with the cap and gate to source resistance Rgs?

[@waynegram8907]

PAUL, make a YT lesson about FETS miller plateau. How to measure the miller plateau and how do FETS have a miller plateau

[@pulesjet]

I just spent $90.00 on SSR Solid State Relays to switch Solar Panel Voltages between uses-es. Following up explain Thermo Heat Management of the Mos Fet.

[@TheJavaSync]

Can it replace led with relay?

[@weerobot]

Yes...Delay Circuits...Pantry Lights..

[@jonelectronics510]

It would be a good idea to place your RC filter into a Schmitt gate so you don't run the mosfet into the linear mode. With an led the load would not be an issue but if you used that with a higher amperage it would heat the mosfet up as it switches off . Maybe that would be an interesting video to scope the gate with and without a Schmitt to get a clean on and off switch? Thanks for the video as always Paul ;)

[@learnelectronics]

Thanks, that's a great idea

[@radius.indrawan]

+1 on this for future video. :)

[@jotarojoestar1399]

how do you do this for p-channel mosfet? for high-side switching

[@jeffvenqueleir2036]

nice

[@chancefears1759]

What about a circuit that will turn off after a few seconds after power is supplied continuously?

[@gapadad2]

I gotta ask, what kind of pen is that?

[@yassirbenmessaoud4587]

Very nice circuit Could you make a circuit about h-Bridge

[@learnelectronics]

I did about 2 years ago

[@MrBrechtD]

where did you get the capacitor box? seems like a good thing to have, big range

[@RoBBz2000]

see ebay from China

[@learnelectronics]

It's in my Amaxon shop: Check out this page from learnelectronics www.amazon.com/shop/learnelectronics?ref=inf_own_learnelectronics

[@contemporiser]

can you show the simplest way to make timing independent of how long the button is pushed?

[@learnelectronics]

It is. You only need to press and release the button.

[@contemporiser]

@@learnelectronics Yes, but it seams to me that as long you keep the button pressed, the light is on. What if you want to make sure that the time will be shorter than you could control with your finger. To trigger a relay in a spot welder for example.

[@fuchsfalke5063]

to get rid of the fading out i assume an Zener-Diode a bit below VCC would do?

[@jonelectronics510]

Use a Schmitt trigger on the gate

[@dukeeod1650]

Can you make it to turn on after a delay? As usal great video, Stay healthy and safe

[@learnelectronics]

Yep, I made a video on that...

[@dukeeod1650]

@@learnelectronics thanks I must have missed it. Take care.

[@hvdtoorn]

Hey, just a quick question, can't really see on the board on my phone, do you need a current limiting resistor on the led or is the mosfet sufficient?

[@learnelectronics]

There is a resistor soldered to the cathode of the led.

[@hvdtoorn]

@@learnelectronics I see! Thanks

[@vernonraines3002]

Would love to use this to drive a relay. Have a battery charger for drills that I always forget to shut off for a day or two. Wonder if this would work?

[@learnelectronics]

Yes it would

[@vernonraines3002]

Any idea how to tie a relay coil into the circuit to control 110v?

[@NullaNulla]

Could use this to drive something like a porch or driveway light or a time out on my radios lol. I tried to make similar with a different tran and got a different effect where switching by a tap from + resulted in a perma power on till tapped with - which resulted in a power off. It's a trans I got for my UPS that went BANG and smoked ... one of these trans was missing it's hat after that. HOPING it was just the trans ... hoping.

[@learnelectronics]

As long as you dont exceed the power rating of the FET you can drive whatever you want. Put in a big cap and remove the gate to ground resistor and you can have delays that last days!

[@NullaNulla]

@@learnelectronics yeah think the idea is use this circuit to drive a relay to power on/off whatever you're doing. I understand some electronics principles but have a hard time still generally speaking with certain things (biggest reason I'm still needing to upgrade my ham call). Out of curiosity what was the resistor put in place for here? Extra drag on the cap?

[@jonelectronics510]

@@NullaNulla to discharge the capacitor else it would never discharge due to the high impedance of the mosfet gate (well it would discharge eventually, there would be leakage in the cap and gate etc).

[@georgestephens3513]

Like to see one with short turn on delay.

[@learnelectronics]

Soon

[@RespawnRestricted]

Could I sub in a different mosfet ?

[@learnelectronics]

Sure just dont exceed the power rating

[@jakub2190]

MOSFET is a bit of overkill for LED dont you think?

[@learnelectronics]

The LED is an example load. Replace it with whatever you need.

[@BrucesWorldofStuff]

Wow, I could hook up a infrared module and a bigger led with a 2200 uF cap and have it turn on in the bathroom when I walk-in and no more bright light at night... :- D Then It will turn off after I leave... Nice! LLAP

[@bblod4896]

Possibly the same design used on dome lights in automobiles.

[@johanponin1360]

What about the reverse ? a capacitor delaying the gate ?

[@learnelectronics]

Soon

[@yigityildirim8974]

What’s the ratio between the capacitance and the on time in seconds

[@jonelectronics510]

5RC. But nothing in this circuit is linear (bar the resistor) so timings won't be that accurate.

[@peterdavidson3242]

Is there a formula for this specific circuit to calculate the time on based on all three variables, voltage, resistance and capacitance? Could you add into the "down below" so it's viewable to everyone without having to read a reply to my comment?

[@jonelectronics510]

5RC will give you the discharge time, however, bare in mind the VI curve of the capacitor and LED is not linear so it will fade slowly then just go out. Similarly the response of the mosfet is not linear so that too will affect the result.

[@WatchesTrainsAndRockets]

Thanks. I have been looking for a way to do this. The only thing is that I wanted a square wave output. To that end, I played around for a while in everycircuit and came up with this: everycircuit.com/circuit/4959474069274624 My description reads "Pressing button turns on blue LED. Stays on for the delay time delay determined by the RC timing with the on/off threshold set by the voltage divider. This makes the switching a square wave. Red LED is directly controlled by the RC circuit, so it starts to fade as soon as the push-button is released. The blue is at full intensity until the circuit times out." Ypu can fiddle with the settings by clicking on a component, then click on the wrench symbol in the lower left and move the dial that appears on the right. The green line in the graph is the RC circuit; the purple is the input to the mosfet gate controlling the blue LED.

[@rsactivescience2647]

Can we use 12v battery

[@learnelectronics]

Sure

[@Tolderian]

Buuuut…. What if you want it to go off while holding the button?

[@Bernhard_V]

Something else I miss about a "switch" like this: What's the current through the FET when it's off?

[@jonelectronics510]

Current only flows through the FET when Vgs is above Vthreshold of the FET. When it is below that then no current will flow.

[@Bernhard_V]

@@jonelectronics510 "No current" is not possilbe. It is a FET-Transistor, not a switch. This question is important if you operate a circuit with batteries.

[@jonelectronics510]

@@Bernhard_V very true, I was simplifying for educational purposes.

[@maxprophet2401]

First on, off after delay, woohoo, life complete, circuit not