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High voltage NOT gate Answered

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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lemonieBest Answer (author)2011-05-05


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?

L

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iceng (author)lemonie2011-05-06

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

A

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GenAap (author)iceng2011-05-15

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?

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lemonie (author)iceng2011-05-06


Looks right to me, that's helpful.

L

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seandogue (author)2011-05-07

A simple Mosfet relay can be used for the purpose.

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gmoon (author)2011-05-06

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...

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AndyGadget (author)2011-05-06

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?

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iceng (author)2011-05-05

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.

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gmoon (author)iceng2011-05-06

Right on.

A single NPN in a common-emitter setup is inverting...

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Jayefuu (author)2011-05-06

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.

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iceng (author)2011-05-05

When ThrgRreatS deems to answer my early questions.
I will show him an emitter follower driver stage for his LED array.

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iceng (author)2011-05-05
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Re-design (author)2011-05-05

use an electronic relay. They are available in a very small package.

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