EEVblog

[@MostFolkCallMeOrangeJoe]

EEVblog Please do more videos like this, showing how circuits are developed, I learnt so much from it. I like it,

[@mrquint15]

+Adam Harrington +EEVblog yes please! this REALLY helped me grok a few things. would love to see more like this one. Thanks for keeping this going!

[@markuscwatson]

same!!

[@freezxify]

It's seems hard to find proper circuit development tutorials around. This one was perfect!

[@Justsquareenough]

ditto

[@happyhippr]

This channel is solely responsible for getting me hooked on electronic circuit design

[@LazerLord10]

Just in case you were wondering how much this saves... I got a parts list for what he drew whipped up in digikey, and this is what I found: 3A toggle switch = $1.76/unit at 200 item price break (min quantity) 200 units = *$352 total* I will assume the 200 unit price break for the rest of these numbers and surface mount components except for the push button. If the minimum quantity is higher, I'll include that cost. 5,000 100k resistors = $6.46 (4,400 not used) 250 1M resistors = $7.99 (50 not used) 200 22uF capacitors = $16.86 200 30V 3.8A P-channel MOSFET's = $35.00 200 Dual NPN transistors (2 transistors, one package) = $25.90 200 Through hole momentary push buttons = $15.18 Total price = *$107.39* Less than 1/3 the price! And I didn't even try to make things better by trying to minimize the number of different parts.

[@the_atomic_kebab]

Yes, but you must consider also the operation cost. The pcb must be manufactured, the electrical components must be placed an soldered. If you are gonna place this components on a pcb which already is designed to be in your system, the influence on the operation cost for this feature is almost insignificant. Anyway, the final price tag is still below.

[@ohmslaw6856]

Well, that's the problem.. your buying off digikey haha

[@CXensation]

Try expand the calculation by comparing the pcb cost, pcb assembly and fitting vs Drilling a hole for the toggle switch, soldering leads to the switch and fitting the switch Yes - I do consider the electronic solution done with other electronics fitted anyway. As a former PTA engineer I learned to avoid any extra manual assembly cost on the production line.

[@thekaiser4333]

You forgot to factor in 200 breadboards at $2 a piece...

[@fifaham]

As you go higher in production count the end cost may worth it, because the robot machines can populate all those parts in 3 seconds and the addition of the PCB is almost negligible. It is good alternative however.

[@tuxthemagicpenguin]

Living in the US I had never heard the phrase "half a bee's dick" before. I burst out laughing. Thanks Dave!

[@jeetenderkakkar7570]

Laughing

[@Necrocidal]

I'm from UK. I'm learning a lot of awesome Aussie slang from this channel.

[@victordss]

Important: if you have a capacitor on the output, the comportment becomes erratic. It will not latch off anymore (will turn off only while switch is closed), and oscillation becomes unbalanced.

[@shamsheralamraja]

Hi Dave, I have a slight improvement on the circuit, move the capacitor to collector of the T2 and remove 1 M resister from base of T2, connect both bases togater and put switch between the collector of t2 and basses. replace 100 k resister with 650k at collector of t2 and vcc.works just fine , no more ocilations, hold the switch as long as you want

[@jozeftorok6667]

Works great, thank you very much !!!

[@renatokristic8800]

This works great :)Thank you :)

[@JK360noscope]

Anyone have a diagram for this? Is the capacitor in series with the collector of t2 or between collector and ground? Intrigued...

[@mrstevesmall]

Jacob Kon between collector and ground

[@keldsor]

How about an explanation WHY it works ... is it as "good" as the original concerning current in OFF state ?

[@CuentaSpam23]

13:37 "My product never has bugs. It just develops random features."

[@BlackXeno]

Interesting the 1337 timing... like "1337" slang on Reddit. Creepy coincidence...

[@play_sports_and_read_books]

@@BlackXeno what doe sit mean?

[@BlackXeno]

@@play_sports_and_read_books en.wikipedia.org/wiki/Leet

[@TechsHelpingHand]

Bob Ross of electronics

[@padmanabhaprasannasimha5385]

Happy little accidents.

[@ddandrews825]

Your channel is damn good. The way you describe things from simple to complex can rival the best tech school teacher out there. I am learning things I've never bothered to learn, all thanx to your channel. Cheers.

[@daviddaigle4841]

Absolutely agree

[@Jono6671]

wow I'm a complete noob and know nothing at all about transistors, but this video was still very helpful. thanks!!

[@EEVblog]

Yes, it will usually be cheaper, cost it out yourself. It's not just about cost either. Sometimes you want/need a soft switch instead of a big clunker mechanical toggle.

[@fernanmady1861]

Beautiful. Simply beautiful teaching.

[@MB-st7be]

Just here for a bit of nostaligia for when Dave's videos were actually about circuits! Now they're all mail bags and teardowns, like every other channel :(

[@EEVblog]

Please show me a simpler design for a discrete soft latch power circuit. There are many reasons to use such a circuit, not just cost.

[@ReactanceIsFutile]

For anyone wanting to simulate or build some of these circuits as Dave goes along, remember that BJT transistors realistically require either a pull-up or pull-down resistor in order to ensure their default state. For example, in this video, at minute 4:00, this circuit would likely actually start in the ON condition without pressing anything because the base of Q1 (the PNP) transistor is not guaranteed to be held high, and is likely close enough to ground, it will start conducting, causing Q2 to fire turning the circuit on. If we use 100K-Ohm resistors everywhere to keep current low on the base of the BJTs, a weaker pull-up is necessary on Q1 simply to ensure the base is high on startup but can be easily overcome by the ON switch, grounding the base. For this pull-up, simply connect a 1M-Ohm resistor between the collector of Q2 and the emitter of Q1.

[@δωμάτιομελέτης]

You are right.... In reality this 4.00 circuit will be pretty unstable.... We just have to use a big resistor between the collector and base to ensure that the base of Q1 remains high enough not to turn on randomly.

[@Vulpusvulpes]

Youare actually right, I tried to make the circuit at 4.00 but turned ON by itself and the ON sswitch seemed to be doing nothing at all. I will try with your suggestion again

[@MlokKarel]

Would I read this earlier, I would save myself some 8 hours of building and simulating... 😂 On the plus side, I am able to simulate this circuit in CircuitJS, TinkerCad AND Ltspice... 😅

[@ZillaYT]

I tried to build this curcuit (using a breadboard for now), but my LED that I connected at the output (drain of MOSFET) just stays on when I toggle the switch. If I leave the switch on, I do see it blink. What could I have done wrong? I've double-checked my connections. I did use a NDP6020P instead of the IRF 9110

[@brettski74]

I quite liked the circuit at www.mosaic-industries.com/embedded-systems/microcontroller-projects/electronic-circuits/push-button-switch-turn-on/latching-toggle-power-switch - see figure 3. two MOSFETS, 3 resistors and a cap.

[@SeanStrongman]

This is great, i already know , that i could use this circuit in my project , thanks Dave!

[@linuxguy1199]

Is there an auto dislike bot on KZbin because every one of your videos has roughly the same amount of dislike and it's almost every channel on KZbin all having about 30-100 dislikes so wtf???

[@EEVblog]

Jeremiah Lowe There is a core group of people who thumbs down all my videos, some within minutes of uploading. They haven't even watched it yet. I don't know about other channels, but I have a core group of haters!

[@ElectronicMarine]

EEVblog that's how you know you're doing something good :)

[@linuxguy1199]

EEVblog i knew itd be something like that btw do you know any cheap power supplies like under 50$ mine broke and idk why it was a computer PSU anyways

[@superdau]

Almost all videos have approx. 1% downvotes. That's the "standard". Less downvotes than that is either a video on a small channel or what you could call "exceptionally" good. A higher percentage means you either said something controversial or just too much stupid/boring stuff.

[@olaostehvel9763]

EEVblog You're pretty harsh sometimes and some people really don't like that. Me on the other hand I would give thumps up for the sole reason of being able to speak clearly even if it means to bash people who deserve it. Well that is if I could get myself to use the (dis)likes buttons at all. I believe they are made for immature people who actually beleive quality derives from how many likes one gets. Even though enormous amount of proof points in the opposite direction, stupid people (which includes most of the human kind) still cling to the lie. You are doing a great job teaching electronics and I hope it is enough money for you to keep on making videos until death. If it was something I would like to see more of it would be rf. Maybe even a simple DIY spectrum analyzer just to crack the nut about it being so hard. You are a great teacher and you would know how to make so called hard stuff simple to understand. Against, I really appreciate your videos.

[@andrewferg8737]

Built your circuit over the weekend. Had to adjust the bias a bit for a 12V supply, but the circuit worked very well. Thanks for sharing! Would you be able to explain how to replace the push button with some sort of pulse trigger circuit? I tried a few ideas with some small success, but nothing stable. I would like to integrate the latching circuit with a motion sensor circuit...

[@matthehat]

"Half a bee's dick" KZbinr phrase of the week

[@ElectroRestore]

Can you build that same type circuit for 120VAC -> to power a 100W light bulb on and off -> with a one button -> using no additional power supply than the mains 120VAC?

[@gernoteyssler8296]

It's a really good idea! Thank you! Remarks: 1) for the second transistor use a NMOS --> no big capacitors needed 2) use a resistor from basis to ground for the first transistor - helps against leakage current 3) If the battery voltage is more than 15V ... 20V, most of the PMOS don't like this and go to the semiconductor heaven.

[@VK6TT]

re pt 2 - i had issues with the filter cap of the downstream circuit bleeding back through Q1 turning it back on. A 680k resistor as suggested solved this

[@AdrianCarter_Oz]

There is.. but not for a buck. One option I recall seeing a few days ago: LTC2955 from Linear Tech: about 4 bucks, and still needs a couple resistors and a separate reg with a shutdown pin (like an LT3008). So right back up there with the cost of a mechanical switch...

[@Mr_Meowingtons]

OMG i have been looking for some thing like this... i would like to see you doing more projects like this..

[@dtewksbury]

If you don't want it to oscillate, then I would imagine a simple Parallel RC network in series with the switch should do the job. Maybe something like 1M and 10nF ? This time constant would determine how long the switch needs to be released, before it will result in a toggle. The cap must charge before the 22uF gets to the transistors VBE, otherwise it will still oscillate.

[@dtewksbury]

I think I was a bit fast in posting that. If the node on the delayed transistor has a fast enough fall time it will still turn it off. It would be a balancing act with the first 100K resistor. It might still work though.

[@m1geo]

"Half a bee's dick" hahahaha

[@ryanoconnor7957]

I love that half a micro-amp is half a bees dick in Australia.

[@SeanBZA]

Careful in humid environments with leakage..............

[@mathewk2961]

FYI for those novice, such as myself, who are building this soft latching switch. I had been working on making this switch work for over a month. I'm using all bjts. I tried different resistors, different capacitors, and different types of bjts. I could not get it to latch off. As soon as I let off the momentary switch the light came back on. Holding down the push button I could get it to flash like Dave's but it would not stay in the off position. Finally I went back to original components and then it dawned on me, after viewing Dave's video a couple of dozen times, the LED I was using was not a sufficient load. I put in a 1/2 watt 2200 ohm in parallel with the LED and viola! It's working! Thanks Dave.

[@0x8badf00d]

It may be the leakage current. I've witnessed a thyristor made of jellybean BJTs turn on by itself due to leakage.

[@CorruptName1]

I like this one better. And who doesn't have a 555 timer laying around? kzbin.info/www/bejne/laa1loaXmdVggaM I'm not sure if it draws current when off though. If so, it's probably only "Half a bee's dick" worth. Lol. I like the 555 timer method bc it doesn't start in "ON" state. Though this may be preferred for some people.

[@evgenysavelev837]

Congrats man, your video is now offered as a first result when looking for a soft on/off circuitry. This must mean something.

[@TheCod3r]

First comment in 2022 😄

[@SatyajitRoy2048]

I don't know who's clicking dislike button on this nice piece of video.

[@deliandiver6579]

Hello! What about softlatchin' of 3 power rails: +/-12 and separated +5 ? How to sync them in one switch?

[@peterd6927]

+Delian Diver Maybe you could place some mosfets on the load of that circuit, where each one switches a different rail? I think you might need to reverse Vdd and Vss for the -12V so that 0V is on Vdd. I'm not sure exactly, but just an idea. With the right components and arrangement it might work.

[@zwz.zdenek]

I'm disappointed. I'll just take the liberty to throw the jellybean rule out of the window based on economy and employ a CMOS divider/counter. Then just one resistor, one cap (those just to smooth out the button input) and an output transistor and Bob's your uncle! No blinking, no residual current (which you forgot to fix in your design), an option to make several ON modes in sequence... and the price will be the same!

[@ilike600baud]

Sounds interesting! I know nothing about that kind of circuitry (sounds like logic!). Please make a video on a design concept and give us a walk through! Especially of the power-on sequence capability. Then throw a couple part numbers in there so novice people can get up and running! It'd be great!

[@GRBtutorials]

Or just use an MCU if you already have one (very probable), a pushbutton, and a MOSFET. Problem solved for a few cents!

[@Wren6991]

How are you setting the initial state of that counter after power on?

[@johnfrancisdoe1563]

Luke Wren Also, I doubt his CMOS chip has as tiny standby current as the circuit in the video. Video circuit standby is dominated by C-E leakage in the left BJT.

[@Wren6991]

@@johnfrancisdoe1563 that's true! I have one major problem with Dave's circuit though, which is its sensitivity to bleed time of the system load. Large output capacitance and small load -> 2N3904 becomes biased again and doesn't switch off. I think any circuit where you try and be clever and use system load as a switching element can have this issue. My current favourite circuit involves a latch built from a dual inverter IC, e.g. 74LVC2G04. They cost around the same as a small-signal transistor, leak around 4 uA, and give you clean switching every time. I think the lesson might be "if you want a latch, build a latch" :)

[@MrTriac]

You didn't get the idea, it's about saving energy. The NE555 would draw current from the source either the output is in 1 logic state(ON) or 0 logic state(OFF). Even the CMOS version(LMC555) draws a little amount of power. This one draws current only in ON state, which could be an advantage in some applications such as battery powered/portable apparatuses/appliances.

[@markk4409]

So instead of using an on/off switch, add 6 more components to an on/off switch and you now have an on/off switch! Did he really say "Half a bee's dick?"

[@IvanIvan1974]

...and don`t forget the Christmas illumination when you hold the switch.

[@magicponyrides]

You can't really be this dense.

[@IvanIvan1974]

magicponyrides What do you mean exactly?

[@RWoody1995]

IvanIvan1974 he means the point of this is that its cheaper to implement because it means you don't need a beefy switch and can use an elcheapo switch without blowing it up :) if you were just joking it didn't work, this is text its hard to tell so you should expect those reactions from people :)

[@IvanIvan1974]

megaspeed2v2 I don`t even know if he wrote to me. His reply is not directed to me. BTW, I use switch system like this too, I implement it a little bit in a different way but actually it`s quite similar. (without Christmas illumination)

[@rainbowsalads]

i was thinking to use this latch circuit post multiplexer. microcontroller >multiplexer > optocoupler > soft latch circuit.

[@BobD1001]

Dave, as always your tutorials are the best around! Your videos have taught me more than many of my electrical engineering classes. Thank you!

[@myfelipe95]

Thanks Dave, very good video! Can i change the resistors values? i'd like to build it without needing to go out to buy those 100k.

[@power-max]

I paused the video at near the beginning, and I tried to make a own solution to this, and I came up with the EXACT same solution you did! LOL (I just used 1K resistors in LTspice instead of 100K and 1M ones.)

[@organizedfromwithin2525]

Power Max While the NPN transistors are ON, you'll be drawing 100x more current through both of your 1K resistors than if you used 100K resistors, stressing them more. For production, you'd probably want higher reliability, thus higher resistor values.

[@power-max]

downthetube within Well it was a simulation, I often use the 2N2222 transistor in LTspice in such a way it ends up dissipating many hundred watts. Not an issue! I often use TO220 transistors when prototyping stuff, as they are more difficult to destroy. However the disadvantage is that more base current is necessary for bias the transistor, and consequently I will end up using low value pullups for the bases. For small signal transistors and darlingtons and stuff, you are correct.

[@organizedfromwithin2525]

Thanks - I was just mentioning some obvious improvements as a design philosophy. Guess I'd have to look up datasheet for 2N3904 to see how much margin is left when increasing from 1K's or decreasing from 100K's. Another issue is power budget or allotment on the input power form. Of course, how one makes these compromises and reiterations in design are largely dictated by an overall product specification, implementation, schedule, budget, and all the "ilities". The video is a fun, nicely explainable circuit. cheers!

[@renelefebvre53]

very simple, very clear, very usefull. I have a lot of push buttons and this is the features I look for. Dave, you are the BOSS !

[@kkeinob]

The bad thing is that the FET is ON after plug-in. Who want to have circuit activated after plug-in? If then you do not need this circuit at all. I think if you add BE resistor to the transistor on the left should solve the plug-in problem. The voltage at the resistor should be lower than 0,5 V assuming the leak current from FET. As it was explained by Trunov Michael bellow.

[@EEVblog]

a) The clock pin would need to debounced anyway. b) A J-K flip-flop that uses a whole chip with dozens of transistors? Egad! c) it's another BOM item. But with jellybean transistors you might already have some of these in your design.

[@DaffyDubzFPV]

LMAO is it me or does he say "Half a Bee's dick" at 15:48

[@t1d100]

Bread Board Success: I built Dave's circuit and it worked. Things to note: - I used a 5Vsupply. - I used an IRF9Z24N P-MFET. - I used a 47uF e-cap. Dave spec'd 22uF, but actually used a 47uF on his board. I like the button press timing of the 47uF better. - I used a red, SMD LED with a 1K resistor, for the load. - Dave's circuit starts in an on state, when power is first applied. To me, this is a problem. Say this is on a stereo and the power goes off/on in the night. The stereo is going to startle you awake . However, for whatever reason, mine does not start in the on state. Lot's of fun, Mr. Dave = Thanks!

[@bob4analog]

Tap on the white board...Yes! Very good, mate!

[@kmuns4]

Commenting again because this is that good. This is the first video by EEVblog I've watched, but communicating the thought/development process of a circuit is what I've been searching for since my undergrad years! Extremely impressed. And delivered with an Australian (?) accent? Amazeballs, and Bob's your uncle.

[@trunovmichael]

I tried the circuit @04:00 with BJTs, but without the buttons. On 'out' I had a resistor followed by a lit LED. In theory it was supposed to be off. Apparently, there's a thing called 'transistor leakage'. It means even when a transistor is in cut-off state, some current might still go through (micro-Amps in magnitude, I guess it varies among the different types). I suppose it could be ignored if applied to load, but when it's connected to a base of another transistor - it gets amplified, then it feeds the first transistor and we end up with fully activated circuit. I hope this comment will save people about half a day of puzzled head scratching. In the end it was fun to find that out, probably I should have added a "Spoiler alert" in the beginning :)

[@martinwestermeyergondonnea84]

OMG I LOVE YOU, i thought i was just dumb

[@dharmikbhavani7272]

just add one small capacitor between emitter and base of a PNP transistor and it will work as theory describe.

[@Vulpusvulpes]

If referring the circuit at 4:00, just add a 1M resistor between the emitter of PNP and the collector of NPN.

[@leochang222]

​@@dharmikbhavani7272 it works well!! thank you

[@jjoeygold]

How about stability of the switching circuit during Vdd and load transient behaviour?

[@MrXerotom]

does this work on 12v to power up a relay?or what i need to change?

[@EEVblog]

KZbin stats stop for a day or two at around 300. This is deliberate. Stats only return to normal after maybe 4-5 days.

[@smbrob]

Great tutorial Dave. Maybe you should do this more :-)

[@markuscwatson]

Does anyone know of any good resources for learning some common/basic transistor circuits like this?

[@gorillaau]

"..And for those that hate me tapping on the whiteboard." Ha ha. Nice line :-)

[@EEVblog]

It's the inherent flip-flop nature of the circuit. Nothing to do with switch bounce, which of course there is none when the switch is held down.

[@Robonza]

If understand this correctly. If you had a power cut then this thing will turn on the device. Can you modify it to start up in the off state?

[@0x8badf00d]

Uh. This doesn't start up in the on state. The gate of the *P*-MOS is pulled up and the transistor that pulls it down has no base current before you press the switch.

[@rbhis000]

@@0x8badf00d Uh. It can start in the on state. You're clearly missing something in your highly simplified response. Don't be a shit.

[@jeffreypetree7163]

Thank you mark

[@teuton8363]

why not replacing the 1M by a 100k (and 22uF cap with a 2.2uF) so that the BOM gets smaller?

[@0x8badf00d]

Check your math. The time constant would be a hundredth. If you go down in resistance, you'd need to go up in capacitance.

[@omsingharjit]

Can you help me .. There are Two type of Toggle on and off circuit are available on the internet one using 555 and other from 3 transistor in both latch circuit one switch is used to on and off the Circuit and the current flow in the circuit is bidirectional mean current goes in one direction when push for turning on and Vaise versa . So the problem is , i can't activate this circuit using External Signal or using Transistor because the way it works . I tried connection ldr in place of push switch in order to Fool the circuit by simulating as Push switch so i can on or off using external light powerd by sensor signal but no success . Do you have any idea ?

[@ernststavroblofeld1961]

My secretary is bi-polar too. And she works as a soft latch switch like a beauty. Almost telepathically. Bingo! Thanks for the inspiration.

[@marionetadelplaneta]

Ernst Stavro Blofeld does she has high input impedance if you know what i mean ?^__^

[@ernststavroblofeld1961]

marionetadelplaneta She does, but that is none of your business.

[@marionetadelplaneta]

Ernst Stavro Blofeld what's so private in asking if someone is friendly?

[@ernststavroblofeld1961]

marionetadelplaneta I signed a nondisclosure agreement.

[@PhilXavierSierraJones]

I have a question. Can I replace MOSFET with generic transistor? It's hard to get parts here by small quantity.

[@teadrinkingilluminati9173]

Phil Sierra You should be able to as long as its pnp

[@skoue4165]

Really liked the video and I can see some good reasons to do this but not sure cost would be one. You can get a ten pack of latching pushbutton switches rated at 1 amp off Amazon for $8 US and a 30 pack of mystery spec ones for $6 US. Now the ability to be able to switch it off automatically could be important for some things so? Nice to know how to do it though and I love that you explain the why's as you go.

[@164Qvier]

Can I also switch the ground with this circuit? If not, can you suggest another circuit which can...

[@LostInLeiden]

Why does it start ON and how can I get it to start OFF instead?

[@DeadBugEngineering]

Pretty cool circuit, will try this one out in one of my next projects. Switching the power off looks nice and clean but there's a weird negative voltage spike when switching the power on (at 15:23) of approx. 250mV. Does anyone have an idea what's causing that spike and how to prevent it? I'm not nitpicking, just being curious.

[@necro_ware]

I guess, I'm too stupid. I was trying to rebuild this circuit, but failed miserably. So I went back to the very first schematics with the two bi-polar transistors and one switch, to better understand, where exactly I made a mistake. Unfortunately, I already fail there, as soon as I connect the base of the NPN transistor to the collector of the PNP one, it instantly switches on and grounds the base of the PNP transistor. The switch is actually out of the game. I guess, I took wrong resistors? I'm using two resistors with 470 Ohm, 2N3904 and 2N3906 transistors. An LED is connected to the "output" to see if something happens. If anyone has a suggestion, please enlighten me :D

[@usertogo]

Brilliant mate! The only two things I see are, that you have to add a Zener diode if you up the voltage, and the load can switch on due to output voltage, so if you drove a dc motor for example a touch on the axis could get it spinning under power! Anyhow Dave I want to work with you on another brilliant open source circuit ! How do I contact you?

[@shanemitchell735]

Didn't even notice he was tapping on the white board, too focused on the circuit.

[@EEVblog]

It means a common and widely used general purpose device. The kind you would have in your parts draw.

[@WistrelChianti]

Great! I actually understood it this time :D (been away learning things)

[@zwz.zdenek]

Just posted a response to this video here: kzbin.info/www/bejne/gWTLmXSCrK18fZI

[@Chewbacca651]

Did he say the One Hung Low factory in China 1.15? pmsl

[@SeattleRingHunter]

Yep and he also said practically "0 u Amp... half a bee's dick" LOL

[@m3chanist]

Great video, you have a natural design sense (could actually call that a feature) rofl. Cheers mate, I'm shamelessly ripping off your circuit for my project as I type. Top work.

[@andribiotico]

Nice!! It works fine!!

[@PlasmaHH]

In the BJT only version at 4:25 isn't that depending on the load being of low enough impedance to not switch it on when power is applied? I would say that due to parasitics when power is applied (and nothing is on VOUT) there will be a bit of current flowing through the PNP to the NPN collector capacitance, causing a tiny bit of current to flow through the right resistor to the NPN base, turning it on. Only when there is sufficiently much of that current drained through the load, the NPN base can never reach enough voltage to turn on. This seems to be a problem when the load is an LED, which means not much current can flow there until it turns on, causing the NPN to turn on, causing it to latch into on state. Putting a cap from the base of the NPN to GND (10n or so) would somewhat help here, though introduce a minimal time for the button to be held

[@organicelectrics]

+Dennis Lubert +{MLP} Rainbow Dash I have experienced the same effect, the LED is initially on and stays on unless the button is held down and the circuit oscillates. I tried placing a capacitor at the base of the npn transistor like Dennis described which only delays the LED returning to a fully on state after pushing the button. Dave doesn't specify voltage range for this circuit, but I have tried 3, 5, and 6V. I'll keep playing with it to see if I can get it to as a latching switch.

[@kellyq1234]

Can somebody help, my circuit is allmost the same except irfr9120 as p-mosfet and bc846b as switching transistors. My circuit don't turn off after press second time switch

[@KrotowX]

Tried to make this on breadboard and spectacularly failed. Load (12V 1A motor) runs straight after circuit is powered. No reaction on button press. I used 18P06P P-MOSFET and SS8050 NPN BJTs though due to lack of other types here.

[@rsattahip]

An engineer talking like a cost accountant, how sad. I like things that turn off without any doubt. (smile)

[@trebushett2079]

Yes, bloody stupid if you ask me. Give me a proper switch any day!

[@usertogo]

I want to plainly challenge you to a beautiful open source circuit for an individual cell Lion charge and discharge protector, that can bridge the cell out of the circuit - so if a cell is full others get a better share of the incoming, - when its empty or over current, it is bridged out of the circuit while the stronger ones try, or all signal defeat and completely short out all cells in a series! You know I want a circuit that can make a high voltage chain of mixed batteries!

[@diymicha4905]

Hello, I've bread boarded this, but it keeps toggling around ON. If I stay on the button. If I just tap the button, it switches off very shortly, and coming back on again.,.... Any suggestions?

[@slaznum1]

Thumbs up for tapping on the white board.

[@leslievalmadre5086]

Coming very late to this Video by Dave and having trouble making it work as expected as the LED stays on at 7v and goes immediatley off at lower voltages. In looking at Dave's breadboard set up am I totally off base when I think I see the T1 transistor Emitter leg connected directly to the Mosfet Gate when in the schematic it should be the Collector leg connected to the gate? Main problem in my setup is I cant get my hands on a IRF9110 and am using instead a IRF9540 which has a Vgs that is just too high for the low voltages I am using.

[@kurtrowland5587]

I'm sorry. Half a bee's what?

[@EEVblog]

I got tired of it, and didn't see any value it added.

[@alexgrasic]

Two things... 1. If I up the value of the capacitor, would u be able to hold the switch for a longer period of time without the light pulsing? 2. Could I add a relay into the mix to use this circuit to control a light on 230/110VAC?

[@CollinBaillie]

Dave, this may "fall on deaf ears", but I reckon each video should have a topic on the forums created, and a link added to the description of the video. It'd be handy to jump straight to any discussion around the topic covered, and the search function on the forum sucks. Older videos like this could have any existing topics linked, if none exist, no link necessary. But mincing forward, you think you might do something like this?

[@ambassadorkees]

Nice. The only problem being: Switches on with initial power supply. That can be a safety issue in some cases.

[@ashmcgahee6389]

Great explanation and walk through, very solid final circuit! Thanks! I ended up using a DMG3415U, which you can put a couple of amps through at RDS(on) of ~40mohms, and still about the same RDS(on) as the IRF9110 at small loads. Definitely still taking recommendations though if you have a better one - there are a ton of P-Fets out there to try and compare.

[@MD-qz6gk]

Can i do it with logic gates ????????? Pleaseee answer meee !! I need it !! I have got some AND - NAND - OR and NOT logic gates? Can i make it with NOT logic gates for examples??

[@Stinktierchen]

I know thats an old video but that solution is most certainly not cheaper than a cheap switch :P I am not a professional.. I guess this makes sense when switching stuff with high current flow that needs a soft start to prevent high initial current flow and high spikes compared what would happen if used a physical hard switch that would allow a harsh initial current rush. I am talking as a hobbist. Where I have to take into concideration of lots of planning and soldering for a single project doesnt make it work for me. A switch is much more logical and practical in any way. I cannot speak for commercial products. For personal it makes no sense at all. You get 5 switches on Ali for 1.5€. And then I dont need to wire and solder a small PCB just connect the pins of the swtich and thats it.

[@levarg91492]

Can someone please explain the pros and cons for using BTJs vs. MOSFETS for the latches? It seems to me you are just throwing away current through the BJT bases.

[@luhaisisameng2769]

irossoul92 1956a

[@platinumystic]

Hi, I'd like to use this circuit on a mains voltage 220v before the step-down transformer. I'm powering an audio amp, I built a crude power supply but I don't want to have to use a toggle switch turn it on or off. I can't find anything on the net that explains how to build a soft starter with one button

[@thecool2328]

EEVblog, i kind of like this circuit. Can i use 2N2222 or BC547 instead of 2N3904. It kind of avialability here in my shack.

[@chikopl934]

Please help me! I have to use this circuit 160x because im building battery testing machine. Is there any 8 channel integrated circuit? I need a name of the chip. I have searched internet many times but i only can find non latching switch integrated circuit. Please help me, thank you

[@techalyzer]

Does not work. At all. All components are tested and measured. Output remains at about 0.5 V at all times.

[@FutureAIDev2015]

If you wanted to use all FETs, what would the schematic look like?

[@YugoZex]

It's easier with 4017 IC Decade counter one or more transistors depend on what you use it for + resistor + diode and el.capacitor and there you go... Every time you trigger it it power another pin also there is a reset pin to limit it on 2 or 3 or 4 pins so every time you trigger a push button it power another pin so if you limit it on 2 pins and put transistor only one one pin, when you pres second time it will power pin that is not connected to anything or Red Led just to tell you in what stat it is. and then first pin is turned off. When you press another time it will power first pin and green led and switch off second pin and there you go... I know this is old video but it works.

[@sadafjarah5583]

How is the key to the PB with the PB. What does the circuit change: a clear mode means 1, a moderate mode like the flashlight that blinks and the third place is zero. Can you guide me?

[@Frankey2310]

OK, now I'm trying to rework this using a N-channel power mosfet (i.e. as a low-side switch). Fuck, is this even doable?

[@abdulbasyirmohddahalan3374]

Hi.at first i do not understand the process.after a while i notice that the collector is generating negatif charge when conducting.when base to ground will turn off the transistor.so the collector will provide negatif to the base to make the system turn off.the 1 m ohm i think can use diode as well as i think to prevent from short circuit to ground ( in respect to this system maybe vin is the ground). Well a brillian idea.