Push On - Push Off Transistor Switch
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- เผยแพร่เมื่อ 4 มิ.ย. 2024
- A simple example of a three transistor circuit that turns on and off with a single momentary contact switch. Check out this website for over 100 circuits with transistors!
talkingelectronics.com/project... - วิทยาศาสตร์และเทคโนโลยี
Here you have a very interesting very sensitive circuit and the transistors Q1 and Q3 together may be looked upon as forming a thyristor, which is rather a tricky device to switch off, once it is on.
The surrounding resistors which you included, tame the thyristor effect and that is the only reason you may switch the combination of Q1 and Q3 off. It is not easy to design this circuit.
The action of Q2 is ingenious to say the least . All I can say is that it is a sensitive circuit to switch off as anyone handling thyristors would know. Congratulations, for even if it does not work reliably, I assure you that you did very well in choosing those resistors to enable you to bring on and off that tamed thyristor!
I would say that you need that capacitor at the output, so that Q1 will remain momentarily on to keep Q2 on to keep the voltage low on the capacitor C1 to ensure the charge on Q3 is depleted to switch it off. It is not an easy circuit to design and each set of three different transistors will need their own particular tuning, I do not think that this circuit can be repeated for any three transistors without retuning the resistors . Well done, for a self taught gentleman.
Nice rundown on how a great many pieces of electronic equipment, receivers / transceivers get their "solid state" turn-on and turn-off. Many use this type of circuit, others use a dedicated small IC.
This setup is invaluable. Ive been running this through a sim to learn how to setup my own circuits and i also had to fudge the numbers. In doing I've learned how to control the amperage and that one component has a cascade effect. The biggest factor of the latching however is the cap. In my sim it had to be at least 60uf to start being stable. To really gasp how latching works it is essential to break this circuit into its individual circuits. I also recommend debouncing on any switch component. One cap and 1 ohm resistor in series tied parallel to the switch. Now if i can just figure out how to control and understand the charging and recharging part of these circuits ill be well on my way.
Thanks for the link. Will be very helpful for analog design in the future.
I changed R7 value to 1k ohm and it works very stable. I can turn the circuit on and off as fast as I can rapidly push the SW1. I added an PNP transistor as a switch to the output of this circuit to operate a small load relay. I am using 2N4403 PNP for Q1 and 2N3904 NPN for Q2 & Q3.
I love this! Thank you SO MUCH! used this circuit for an LM386 bass boost toggle!
Excellent!
if I replaced the switch with an op-amp comparator then put a guitar signal on the op amps + input would i get a squarewave octave down effect?
This circuit works fine with a few changes. Connect output to a 150-250 Ohm Relais to plus and parallel use LED with 1k resistor in line to plus. If LED with 1k resistor allone is used for demo replace R2 by 100 kOhm (R2 is critical). Also use R3 with 22 kOhm instead of 10kOhm. A smaller capacitor of 100nF vor C1 may work as well. The circuit turned out to work very well from 0°C to 50°C, resistant to humidity, very low power consumption. Thanks for this well designed video.
That cap is acting as a debounce filter and stops the oscillating of the circuit while you are pressing the button
No, the cap behaves like memory latch to decide whether it'd open /close in the next pressure sw.
@@alexlo7708 The OP is referring to the "mystery cap" that was added to stabilize the circuit.
Shamus is cute. Thanks for the link! I was just having trouble with transistors today, and I was definitely looking for something to experiment with to refresh my transisting.
Am I seeing correctly, a capacitor connected between the negative terminal of the LED and the supply? When I do that the light turns on after pressing the switch, but then cannot be turned off.
what is the output voltage for led. Can i operate the whole circuit on 12 volt and also can switch on off 12 volt relay in place of led
Thank u... muy bueno pero cual es el consumo.? or what power consuption?
where is output +ve? and how much out put current?
Thank you for the video.
Fabulous! Great little circuit, and Seamus too! Liked and subscribed!! :)
Simple and Nice video
Great vid, thank you!
Many thanks for the shared link..
OK. I decided to make the circuit all over again since I saw this video again. I made a few modifications. It now works just fine. I'll post a video.
electronicsNmore Can you do that? Não where is The vídeo?
@ one year later, here are the videos : th-cam.com/video/vNpryyroaWQ/w-d-xo.html and th-cam.com/video/o9yV-katMdg/w-d-xo.html
Great videos. keep it up.
Nice little circuit. It's working.
PS. Great the cat at the end ;)
In one state Q1 and Q3 are both in saturation and in the other state Q1 and Q3 are both in cutoff.
Assuming an open load, that is nothing attached to the output:
In the saturation state the output, the collector voltage of Q3, should be around 0.2 volts or so. In the cutoff state the output should be around +9 volts.
Assuming the output is attached to a RED LED as shone in the video:
A RED LED has a typical forward voltage of 1.8 volts.
If Q1 and Q3 are in saturation, the output voltage is around 0.2 volts and the LED is off.
The problem I can see arising is when Q1 and Q3 should both be in cutoff. The LED is providing a current path around Q3. Current can flow through R2 and R4 and the LED. This will produce a voltage drop across R2 which will start to bias Q1 and turn it on. Because R2 is such a large pull-up resistor it takes only a very small current through R2 to produce a voltage that will forward bias the BE junction of Q1.
The output of a circuit like this is not very good at sourcing current. The current it is trying to source interferes with it's own operation. The output of this circuit could be buffered before driving an LED. If you are trying to do your design exclusively using discrete transistors you might try a saturated transistor switch using a transistor with a very high Beta. The output voltage of this circuit should be almost +9V. This is probably high enough to turn on a field effect transistor which would not load down your circuit at all since the Gate draws no current.
Those transistors you drew in on the whiteboard are fairly high gain for BJTs. Most really common transistors like the 2N4401/4403 and 2N3904/3906 are low gain (Hfe). Could seriously mess up the circuit if you subbed with low Hfe... also that website shows powering the circuit from 12V instead of 9V. Could also matter. The spot where you put the 0.1uF cap is kind of a weird place to put it and I don't think it's helping really as you can see at 2:15 What values for everything did you use?
I'll have to revisit this one...
can i use a 12 v power supply and i it possible to turn on a 12 v globe bulb in full brightness
What is the purpose of Q1and the output - thing?
You may find the circuit a bit more stable if you use a MOSFET as Q3, Your main pull down capacitor "C1" should be a bit higher value too. Something more like 33 mics or so. 22 to 47 is about the best working range depending on preference. I feel fairly sure that you'll find the circuits' behavior more to your liking if you follow my advice...
Hello. I am looking to build a similar thing, but with some caveats. I want the off action to require holding the button for a few seconds. I also don't want an RC oscillation if I keep the button held. Can anyone help, or would I be better off using something like an Arduino to make this happen?
any ideas how you could make a circuit where you have 2 or 3 on's and 1 off? so one push is on1 two push on2 third push off?
You're describing a counter? Where the first switch operation gives an 'ON' condition and the 3rd operation gives an 'OFF' condition?
The quickest way to build this would be using a CMOS 4017 decade counter in conjunction with a single transistor LED driver stage. You could select any number of counts up to 10 whereby the ON condition would be maintained until the next sequential count would switch the driver stage OFF. (the decade counter outputs can be routed via diodes)
THANK YOU SIMPLE CIRCUIT
I'm a novice. I'm looking for a way that when my makeshift switch is pushed on for a split second, the circuit it initiates carries on for 5 seconds (for example). Can anyone suggest an idea please? The main circuit is 24v.
Your videos are cool, they're varied and interesting without getting bogged down in masses of theory.
The volume in your video is a bit quiet though.
that was a great book in description.
Thanks man.
i have been trying to find a way to store on and off values (0 1) but every video only showed the circuit and not explaining at all. Sometimes they do explain, but i need something to dumb it down a bit. Thanks for the help :D
buen dato el de esa pagina....... Gracias!!!
What replacement transistors did you use? I can't get the circuit to work :( The LED is always on, pushing the button only causes a flicker. I've tried using 2N3904/3906 and S9014/9015 with the same result. Interesting thing though is that if I disconnect R6 and the base of Q3 before connecting the battery, and then reconnecting them after power is on, the LED would stay off until I push the button the first time, but after that it will never turn off again.
same issues here. Just built the circuit 3 separate times and doesn't work, or rather, very briefly.
Thanks!!!
Do someone know how to build a circuit where u can use one push button for starting 3 relais? (first push, relais 1 ON, second push, relais 2 ON, 3 push, relais 3 ON.
Thanks in advance, and thanks 4 this vid and the website Hacka.
The capacitor decouples the mixed signal(AC and DC) at the output. This is why caps are used on the outputs and inputs of bjt amplifiers.
I have on off by connecting to leads using 55 all working. But instead of touching the wires together to turn of as switch like to use a transistor but can't get it working any help?
I use 12 volt input then the circuit is work or not
when we opreat it on main 220v ac through transformer it turns on/off by main switch of the power supply
thanke u Dr
please can u make one Circuit of free light
Yes, as an electronics enthusiast, this was the circle what I needed for a long time.But, can't we do that with just one transistor and a few resistors, etc.And is it possible to do this with just one part like a triac? One guy said the name of a different switch type name and I bought that switch.Yes, it was a push button switch.When I pushed once and take my hand back, the lamp was on.When I pushed again it was off.But I was surprised to see that that switch was doing the job mechanically.
This same type of circuit technique can be implemented very reliably with two CMOS inverters, 2 resistors, a capacitor, plus an N-channel MOSFET and resistor to drive the LED.
Re the 0.2 uF capacitor placement from Vcc to the signal path, it's usual to decouple digital circuits from their power supplies with an electrolytic cap of c. 22 uF and a ceramic cap of 0.1 uF across the Vcc and Earth pins on an IC.
I'm not sure you've managed such a decoupling by slightly unorthodox methods (i.e. The wonderful, "I tried it and it worked," method of designing which all inventors use), but I suppose it's possible. My (analogue only) electronics training was in the seventies
Wow, splendid professor. - Can you replace the key with Condenser Mic
can this be adapted to 3v input?
transistors have 0.6V drop, so 3V should be fine.
is that a momentary contact switch?
try adding a 100nF capacitor from the "right side" of the switch in the schematic to the ground, this helps debouncing the switch which i think causes your troubles.
PARABÉNS! GOOD GOOD
CMOS are more stable but also more expensive. I was just saying something about the MOSFET though. It really does make a notable difference. As per cost effectiveness I'd leave the rest the way it is.
How would one have 2 'latching' switches, such as using the original to power on the circuit and switch number 2 to latch it off, resetting the circuit for the capacitor to refill?
I would assume a SW2 would ground out using a diode, but where would it go, between R3 and the collector of Q1?
I know this video is ages old, still good and I thank you for sharing. You had a great camera for 2011!
Joshua Nulton I know it has been a long time since your question... Look up SR flip flop using transistors. That will give you 2 button operation.
Next step: build 2 of them and have a button that copies the state of the first one to the other! Thanks 🙏
Agreed. I do use a 9 volt battery sometimes. That power supply is shit. :)
4017 (decade counter) you can use it for 9 relays. there is tutorials on youtube. there is reset option to use only number of relays that you want. On out pins you use transistors to power the relays because relays can sometimes kill IC. there is sch on net you just have to adjust it...
Good simple useful circuit. Excellent video. I love felines too.
Cheers from Indonesia
I'm not sure what you're talking about now. A circuit like this has an RC oscillation if you hold down the button. It's visible because it takes a few seconds to happen. If you hold down the button the LED will switch on and off every few seconds. This applies to whatever load, not just an LED.
Seamus? Seems more like "shameLESS" to me! Anyway, great vid, and an interesting circuit! I'll have to try that one out!
Congrats for your video, one thing could you be so kind to adjust volume please!?
Yeah, Talking Electronics is cool. I have some ov the original hard copy magazines. Hail Colin! :)
Haha, cute cat
He is a Doctor House of electronics!!!!
Very cute kitty.
Its what is called debounce,
google it to find out more about switch debounce.
So this is a or just like a flip-flop IC? Am I right?
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If you replace the BC557 (PNP) with a BC547 (NPN), it will not work. The NPN would have incorrect voltages on the pins.
What's mysterious to me is how is the LED connected? It's not shown in the schematic drawing. I would add another transistor to deliver more current to the LED without loading the circuit.
BTW, my previous said Schmitt trigger (CMOS), I really meant to say hex schmitt inverter (CMOS).
I built this same circuit and it does not work. The circuit is initially on, and when I press the switch, it turns the output off and back on for a few microseconds. The PNP transistor is on all the time, therefore recharging the base of Q3. I see that your using 9v instead of 12v, but it doesn't make a difference. Anyone else having same issues?
even it did not work for me
You can use a D latch to do that too
Great videos, but this circuit is no good. It is unstable just like you showed in your video. I tried several times to breadboard this, and all attempts failed. I can get it to turn on, but only one time it went off. Tested with different voltages also. All components were exact and tested OK.
أحسنت حياك الله
It looks like you are just using the added cap as a decoupling cap which would keep the voltage across the LED steady and not cause the bugginess
like number 1kkkkkkkk nice video! thanks very informative
What is your input voltage?
Maybe try decrease the resistance values so you sink a little more current to run the switch. Your circuit drawing does not match your test unit. Because you cant run that led light on 9v. You may need a higher voltage or lower resistance. For average NPN PNP transistors, 5v will make life a lot easier.
9v is on the circuit drawing, try that voltage, and line 5~ or 6 little 1.5v leds up in series to take the 9v, then test again.
nice thanks
change R3 to a 220k resistor and it will work without the cap
From Colombia, thanks for your information, that's how it worked for me
Looks like R3 should be of a bigger value, voltage drop at base is less
Than .7 volts needed for the npn transistor Q2 to turn ON.
as others have mentioned I would guess that the capacitor acts as a debounce...
ne555 pin 5 on pin1(gnd) 0.1mf and pin 1 to pin 8 also 0.1mf sometimes it not needed sometimes it is... depend of power supply...
Hi. How old are you?
51 when I did this video, 60 now.
Cute cat
I saw this video accidentally after I posted the Video "Push On Push Off with Siemens" by PLC khuong dao
U Welcome.
Cool cat. what is his name?
photogenic looks :)
Could it be that your transistors are knockoff transistors? They are quite common and can really mess up your circuit.
Might be cause of the capacitance of the breadboard
Thumbs up for the cat
Nice cat
Audio is really bad. Any chance of cleaning up, filtering and re-uploading?
i need a circuit that Works by keeping the push botón pressed and goes out a one sec signal
Google that along with 555 timer and you'll find a solution
they are fond of you either
Wow that seems far more complex than I would have thought; there's got to be an easier way to do it.
Cute Cat.
Related is Dave Jones' "Simple soft latching Power Switch" v=Foc9R0dC2iI
No, the RC oscillation has nothing to do with switch bounce. It happens when you hold the switch down, while anyone would know there is zero bounce when it's held down. Switch bounce lasts only milliseconds. Still, there would have been no way to make what I need in a small circuit. I ended up paying someone to write me a PIC program.
Acting strangely because of button bounce? Pressing a button actually causes many open/close states for a few microseconds while the contacts bounce. That's my guess.
The Ceramic Capacitor Eliminate the AC current that escape from the power supply ....
ruel de guzman
Zeynep
Make sense
yeah but if you dont use 0.1mf on + and - Ne555 can go crazy to...
No matter how many different times I breadboard this circuit I can never get it to work.