Using a Transistor as a Switch

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This tutorial shows how to wire a transistor as a switch. This is useful when you want to power a large load using a small physical switch.

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    Popular Comments:

Eugenio Rodz . 2019-04-06
Excelente, muchas gracias !
121 2 . Reply
ali behrouz . 2019-03-19
why didnt you select 5 for beta?
121 2 . Reply
ali behrouz . 2019-03-19
thanks it was great
121 2 . Reply
ali behrouz . 2019-02-11
I have searched several times on the internet without any I say it is the best explanation fpr this topic, thanks kind man
121 2 . Reply
Noah Alessi . 2019-02-06
This is not a transistor acting as a switch
121 2 . Reply
gyan mishra . 2019-01-08
Why always a base resistor is needed to make the circuit work??? Why it don't work without it
121 2 . Reply
Mwaura Bapeter . 2019-01-03
Well explained.thsnks
121 2 . Reply
Rude Professa . 2018-12-29
Your protoboard circuit had the Resistor output going to the EMITTER and the Lamp output going to the BASE.
121 2 . Reply
Msz Zsm . 2018-12-28
can alternate current be used for the Base emitter current
121 2 . Reply
TheEtbetween . 2018-11-08
I wish Professors could make it so easy. Thanks
121 2 . Reply
Klyze . 2018-10-08
hi there, i found this explanation very usefull for solving a little problem that i have.

I made a simple circuit with this video help and maybe, if you dont mind, could give me some feedback ot tips to improve it.


A bit of context first:

1 - those 3 leds represent a 5V RGB LED STRIP with COMMON ANODE(+), its a very small and low power strip 2 cms (+-) btw.
P.S: those led strips have 4 terminals, (5+)(R)(G)(B)
2 - those two 5v power sources are separated (exactly like in the schematic) and only switch 1 or switch 2 is ON at all times, both are never on at the same time
(altough in the circuit is possible but i could not find a switch like that in the website list)

The objective is basically:
- if switch 1 is on (therefore 2 off) green led will be ON and blue off
- if switch 2 is on (therefore 1 off) blue led will be ON and green off
(red will be always off so its irrelevant)

More context: I have a PCB that if i press a push button, the PCB switches between MODE A and MODE B (and does stuff) but it has two 5v terminals (lets call them A and B), Represented by the two power sources on the left, originally for two leds, i want to connect a led strip, but the problem is the led strip has common ANODE and not a common CAthode. :|
This is why i need a circuit like that.
Can i use two Pn2222A transistors and a couple 1k resistors and call it a day? :)

Thanks in advance!
121 2 . Reply
J34365 . 2018-09-26
Is that fuse..?
121 2 . Reply
INDIAN NSG . 2018-09-08
Why was the transistor even kept in the circuit, if you push the switch, the light glows, what did the transistot do??
121 2 . Reply
rain go uy . 2018-08-28
i cant get why you use switch button...if you use transistor as a switch? and i think transistor is still a current enhancer...
121 2 . Reply
χυδαίο ποτάμι . 2018-05-25
what kind of transistor is this ? pls tell me!
121 2 . Reply
Алкан Бензолов . 2018-05-24
Оль информэшьень ю кен файнд инъ дата щит оф дэ транзистаръ
121 2 . Reply
Алкан Бензолов . 2018-05-24
Ай ляйкь йоръ прононсюэйшьенъ
121 2 . Reply
John Michael Stock . 2018-05-09
At 1:05 Why did you pick the 20 value from the datasheet and not 5.0 or an average?
121 2 . Reply
Lonely nl . 2018-04-22
sir can you explain how our ac soldering iron working .Without any transformer .
121 2 . Reply
Lou Fazio . 2018-04-06
More like a relay.
121 2 . Reply
Paco S . 2018-03-30
God app thanks
121 2 . Reply
Avyakth B Puthran . 2018-03-25
Why to use transistor as switch when we can us a mechanical switch
121 2 . Reply
Rishabh madan . 2018-03-14
121 2 . Reply
Darren Krebs . 2018-02-11
Doesn't ib = Beta*ic only in the active state? why is he using this formula when he wants saturation?
121 2 . Reply
THE GAMES FUNplay . 2017-12-22
we are using a switch to make switch.
what a great invention
121 2 . Reply
Bo Fiddley Diddley InTheMilkyWayTwinStars . 2017-12-18
This is more like a transistor used as a remote switch
121 2 . Reply
Perfect Parts . 2017-11-06
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TheJavaSync . 2017-10-21
And ... What's your Power Supply inside?? That's cool PSU
121 2 . Reply
Somnath Dey . 2017-09-19
If I use 5 Volt for base voltage and 12 volt for load voltage then while calculating resistor value for base then V= 4.7 (5 - 0.7) volt . Am I correct ?
121 2 . Reply
Ammisaddai Arciga . 2017-08-24
Really good one, thanks. But, you really need to improve your english pronunciation, it is really bad.
121 2 . Reply
TheNormalGuy E . 2017-08-11
Then what the fuck is the use of the transistor if you still need to press the switch.
121 2 . Reply
Owat Thorne . 2017-07-24
can you connect the lamp before the base and collector is connected so it goes dim and bright?
121 2 . Reply
TheJavaSync . 2017-06-13
sir, leme ask You, how if use PNP transistor?
121 2 . Reply
sesha chary . 2017-06-11
very educative thank you
121 2 . Reply
{BK}Pepo12 . 2017-04-18
hablas español verdad, se escucha en tu acento al hablar en ingles
121 2 . Reply
Alexandre Contant . 2017-03-30
it seams too many people don't see the point of the transistor when there is already a switch in the circuit. Guys this is an example to show you the switching action of the transistor. You need to apply voltage( well current for BJT) to the base of the transistor to turn it on. Whenever there is voltage, the transistor allow current to flown from the collector to the emittor (NPN BJT only). It might seams like there is no practical design for this circuit if you see this as 2 switches using the same voltage. However, if you play with very high voltage, you could connect a very low votage on a switch and the base of the transistor. Then you could put 120/240 volts on the other side to turn on an apliance without risquing to hurt yourself playing with high voltage. Think about a computer or a TV that is connected to this kind of voltage but the switch to turn it on could literally be licked without killing yourself (still dont do that!!! there is some appliance that have a 120v switch). Long story short, you could have a mechanical switch operating at 1.5, 3 or 5v and turn on/off stuff on the other side of the transistor with lethal voltage. The other use without a mecanical switch and by using only the transistor for switching would be by turning the switch logicaly. One example would be to hook the base to a pin of an Arduino and putting the pin high or low in the code. You would then open the transistor switch on or off accordingly. As an example, if my arduino detect (using other component of course) that it's dark in the house, it could trigger a function that will set the pin where I connected the base of the transistor to high. Doing so could open a light inside the house, if such device is along the current path past the emittor. If I put the same light on the side of the collector, I would turn it off. Hope it helps giving you an example where you could use an additional switch or not.

To summarize, if you put a mechanical switch, there is still a point of using a transistor for switching, but you'll need some kind of interaction. If you want to automate the action of your transistor (as as switch), you'll need something to feed the voltage to the base like a microcontroller, the output of another transistor and so on.
121 2 . Reply
saboor saboor . 2017-03-25
i don't know much about electronic. I don't see the point of having a transistor in the circuit because he is controlling the circuit with a switch...he push the switch the light comes on and he push it again and the light goes off...so what does the transistor do in here??? if he is turning it on and off with is hand...
121 2 . Reply
Ahmed Shaikh . 2017-03-20
Sir 1 my project Helpe Requst Plz sir Connect Email Adress send me .......
I M Create A Project
121 2 . Reply
kenny ball . 2017-03-16
the only thing wrong with this i think is ur breadboard doesnt resemble ur drawing so its a little confusing and the base pin on the left just trips u up
121 2 . Reply
MEndeavour . 2017-02-21
You are manually turning it on and off LMAO
121 2 . Reply
TheAmazeer . 2017-02-12
what is the use of transistor in this case ? you don't explain the switch function which is also the title of the video..
121 2 . Reply
syphou seng . 2017-02-12
please tutorial shows how to wire a fet as a switch
121 2 . Reply
Herlan Ramos . 2017-02-10
Why the transistor is necessary?
121 2 . Reply
drout . 2017-01-29
i did the same circuit but without the transistor. I inserted the switch in place of the transistor, connecting one terminal to the red wire and the other to the black wire.
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ibble kibble . 2017-01-02
for that matter why not just jump the lamp to the switch then to a power supply? the transistor is useless in this application.
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Santosh Debaki Krishna . 2016-12-26
Thanks for sharing.
121 2 . Reply
Erick Lopes . 2016-11-30
What if you replace the resistor for a potentiometer?
121 2 . Reply
Charles Tan . 2016-11-24
Why does he keep saying coolant?
121 2 . Reply
DIYmetric . 2016-10-30
thanks !
121 2 . Reply
B Dutta . 2016-10-14
why is the lamp taking more current when in a transistor circuit than when hooked directly to the power supply..shouldn't it be the opposite?as the transistor puts some extra resistance.
121 2 . Reply