High voltage NOT gate

I am creating a circuit and I need a not gate to run 20 3v 20mA LEDs. The only problem is that to run all of those LEDs (4 series circuits in parallel, if that will help) I am using 18 volts (2 9v batteries in a series). My circuit is compact (,think fitting inside an Altoids container) so a relay wouldn't work. So I need a high voltage way to make a not gate. I can read schematics if that will help you explain it, but I do need you to mention the ohms of the resistor. Thanks a million!

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lemonie6 years ago

Logic gates should be used for logical functions, not direct power-switching.
Either you need a switch to run 20 3v 20mA LEDs, or you need to connect the logical NOT gate to one.
Relays can be small, power-transistors come in small packages.
Show us your circuit please?

iceng lemonie6 years ago
All ways respond to plz :-)
Here is the circuit but no values until TheGreatS chimes in.
Wont you please say how many inputs etc, you want to use, Please

GenAap (author)  iceng6 years ago
I only need one input. This circuit works great! However I don't see a switch anywhere in here. Is the 'logic stage' were the switch would go, or would you attach it to B on Q2 and leave the other transistor?
lemonie iceng6 years ago

Looks right to me, that's helpful.

seandogue6 years ago
A simple Mosfet relay can be used for the purpose.
gmoon6 years ago
Use four small NPN switching transistors.

2N2222 transistors are dirt cheap, and conservatively can handle 400mA (that's half the max rating of most). Depending on how you configure the LEDs and current-limiting resistor, you should be easily able to keep the current draw on each string of five to way less than 400mA.

Or try two 2N2222s, or some other multiple, just so you keep well within the specs.

As icdng pointed out, an NPN in a common-emitter circuit is inverting....

They are small, too. Keep the 2N2222s separated inside your case, or epoxy the to the tin for some heatsinking...
AndyGadget6 years ago
Just give me a bit of clarification here, will you.
Do you want a HIGH level on the circuit output to turn the LEDS ON or OFF?
iceng6 years ago
You need to say, what kind of not gate ( also how many inputs ) ??
NAND = NOT AND ( takes two to tango :)
NOR = NOT OR ( anyone will do :)
NOT = INVERT ( 1 => 0 ) ( 0 => 1 )
You see, a plain NOT gate is a single NPN transistor.

gmoon iceng6 years ago
Right on.

A single NPN in a common-emitter setup is inverting...
Jayefuu6 years ago
I agree with everyone else, use a relay. These Omron ones come in a nice small package in 5 or 12V, they'd fit in an altoids tin:

5V link
12V link

OR, you could use an LED driver. It would have an enable/disable pin and regulate the current to your LEDs, meaning they could last longer. I've not used one before so you'd need someone else to recommend you a suitable one.
iceng6 years ago
When ThrgRreatS deems to answer my early questions.
I will show him an emitter follower driver stage for his LED array.

iceng6 years ago
Circuits 4 U.

Re-design6 years ago
use an electronic relay. They are available in a very small package.