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can a pnp transistor conduct ground signal?

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poolman966554

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hi all! got a (hopefully) easy question here..

ive been playing around with my arduino 2560 with plans to build a led cube, and have been using some 2n3904 to manipulate ground layers..

can a pnp control ground too?

I realize that a pnp requires a voltage drop to close circuit, but was wondering if i could use one if i wanted too, to close a ground loop.

Thanks!
 
Really have no idea what you are referring to. What does a PNP transistor have to do with closing a ground loop (whatever that means)? Post a diagram of what you are talking about.
 
ok i understand that is a very vague question.. sorry for that.

on the fly, no schematic available.. best i can describe here..
lets say i have a simple 3x3x3 led cube, that wired common cathode per Layer.. 9 pins to anode.
im using the base of npn to "let" a layer light.

my friend (whos a coder) asked if i could make a pnp transistors work to close a ground circuit.

Not sure what benefit he has in mind, but, im just learning how to write c++ so im pretty green to all of this. Thanks for response!
 
ok i understand that is a very vague question.. sorry for that.

on the fly, no schematic available.. best i can describe here..
lets say i have a simple 3x3x3 led cube, that wired common cathode per Layer.. 9 pins to anode.
im using the base of npn to "let" a layer light.

my friend (whos a coder) asked if i could make a pnp transistors work to close a ground circuit.

Not sure what benefit he has in mind, but, im just learning how to write c++ so im pretty green to all of this. Thanks for response!

Edit: just occurred to me he may've meant coding for a common anode? make any since?
 
Why don't you post a schematic to explain everything?????

I am guessing that your NPN transistors are emitter-followers that have a voltage loss because they are not a good switch. You do not show anything that limits the current to the LEDs.
OR maybe your "layers" have their common cathode connected to the collector of an NPN transistor??

A PNP transistor is a "high side switch" and its collector goes high when its base goes low with a series current-limiting resistor. The anode of an LED connects to its collector with a series current-limiting resistor. The logic must be reversed.

The power supply voltage for the emitter of the PNP transistor must be the same as the power supply voltage for the Arduino.

I also have no clue about "to close a ground circuit" whatever that means.
 
I'm going to assume that "to close a ground circuit" means to switch the negative side of your LEDs to ground. I will further assume that you are using PNP transistors to control the 'positive' ends of your LED matrix, and want to use the same part on the negative end. This task is very easy to do with an NPN transistor. And, while it can be done with a PNP, doing so takes a special drive a fully on switch.

To turn on a PNP transistor you need to drive the base negative with respect to the emitter. Not just from where the emitter is at to begin with, but where you want the emitter to be when it is closed (conducting current).

So, if the collector is at ground, and you want the emitter to be near ground, you will need to take the base voltage level from your positive supply voltage (when off) to a voltage below ground,(-5V?) when on. Doable, but not easy.

The best parts for the job are PNP for the positive end, and NPN for the negative (ground) end.
 
I'm going to assume that "to close a ground circuit" means to switch the negative side of your LEDs to ground.


That it correct.. sorry for the lack of proper terminology.
guess it turns out the bunch of npns on hand are best to accomplish my project. Thanks!
sorry for the bother
 
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