The Transistor Switch, Module 1

It's a common-emitter (CE) transistor switch, using an NPN. See how to do it. -- PJ Allen --

*** The point is that the "5V", in practice (in case anybody doesn't get that), should be a logic signal, of course. The LED and its resistor could be swapped for a relay (a coil, and a free-wheeling_diode), and then you have a new world of options. Maybe that'll be "Module_2? ***
OK, here's what -- Send me an email and if there's some interest then I'll go ahead with "Mod 2" using a relay and so on.

Category:

Science & Technology

Tags:

• transistor
• breadboarding
• BS2
• basic stamp

[vusiliyK]

I just dont get it. Why should I use a transistor as a switch instead of a regular toggle switch? What are some applications where using a transistor is more beneficial/convenient than a toggle switch?

[2N2222A]

@vusiliyK -- First this was intended solely as a tutorial for a 'friend', how to get the wires right and test the circuit "manually", but it took a life of its own. Of course it makes no sense to hop a wire on/off, it would/should be connected to a microcontroller, a low-current/logic output, which would take it HI/LO. Instead of one LED you could have several in series or parallel, many; or a relay coil/s; or a solenoid; buzzers -- you get the idea, now. Hope that helps.

[adrian17cy]

so it is controlled by a 5v input and the main power supply is a 9v battery, yes?

If i want to use a 12 v input what resistor size should i fit best? thank you

[2N2222A]

@adrian17cy: Ic = (12V - V_led) / R. We'll assume 10mA (Ic) is desired and we'll assume a V_led of 2V. So, 10V / 10mA = 1000 ohms [1K]

[madamerotten]

Do you happen to have a sister named "2N2907A?"

[2N2222A]

@madamerotten Yes, it's true. We started seeing less and less of each other, just holidays, with the advent of ICs; it really affected the act, the Class_B days. Sad really, that's "progress" for you.

[almouloudi]

@vusiliyK You could instead of putting the wire to switch transistor use a LDR to change resistance to that when it light on you'll light the LED or a thing else and everything can be reversed there .

[newcptv]

THANKS! Earlier I was lost in what i should connect it to but now I know how to! :D Thanks!

[madamerotten]

@2N2222A :)) LOL

[2N2222A]

Sometimes you need to "pull down" the Base, so that it doesn't "float." So, a 22K (10k to 47k) resistor from Base to Ground should do it.