Basic Transistor with Arduino. Is this accurate?

[CrossRoads]

Wiring diagram is still not correct.
Want to use N-channel as a switch to connect "bottom" of Light to Gnd.
Low value resistor prevents too overcurrent into MOSFET gate capacitance.
Large value resistor keeps MOSFET off during reset state when IO pins are floating.

[Bittsen]

I haven't tried anything yet. THis is all still theory because I don't have the correct transistor in my possession yet.

In your example, however, you show to be switching the ground. My application won't be able to do this as my applications are going to be mostly automotive.
As most know, automotive is a passive ground system where the entire body of the car is the ground. There's no easy way to put the switch on the negative side so most switching goes on the positive side.

In your example the gate appears to be activated from a negative source, is that correct? If so then adding a resistor from the gate to ground seems like it would trigger some activity in the transistor.

Or am I seeing it wrong?

I do see the benefit of a drain resistor on the gate though. It would assure a true zero if it's important that the gate stays zero in an "off" situation.

[Bittsen]

This is exactly why I'm posting.

Telling me I have something wrong doesn't help. Telling me how to fix it would help.


Do transistors not trigger with a positive? Or is positive not going to flow through a resistor?

What's the deal?

[larryd]

I don't know why people, like you, feel it's necessary for a hobbyist to learn engineering to be able to build a simple circuit.

This is why. . .

[CrossRoads]

So you want "high side" switching vs "low side".
N-channel is not good for that.
You need P-channel to go between 12V and the "top" of the load - and that requires an extra transistor because the Arduino can't switch 12V on/off.
I posted that diagram earlier in this topic. A pullup resistor to 12V keeps the P-channel off, a high into the NPN base turns the NPN on, which pulls the P-channel gate low to turn it on.

You need a copy of my book - it covers the basics like this.

[runaway_pancake]

No, the transistor turns on when the Gate goes positive.
You cannot source current from an N channel MOSFET.
When did we start talking about cars?

Ha,
I have been playing with a p40NF0 all morning. By playing with it I mean I've been picking it up and trying to figure out if it would be right.
I think I have a few of these laying around.

THis is all still theory because I don't have the correct transistor in my possession yet.

Come again???

[CrossRoads]

See Reply #5 again, covered this before you got off into the Darlington discussion.

[runaway_pancake]

Here's your drawing rendered rightwise (attached).

[CrossRoads]

Yes, for N-channel. See Reply #5 for P-channel & high-side switch.

[Bittsen]

No, the transistor turns on when the Gate goes positive.
You cannot source current from an N channel MOSFET.
When did we start talking about cars?


Come again???

The transistor I was "playing with" is different than the one I put in my drawing.
Your drawing makes complete sense if I'm switching the negative.

I have been looking for a solution for, primarily, car applications the whole time. ALl of my drawings have been to switch the positive side. It appears there was a misunderstanding wbout that and all the suggestions have been centered around switching the negative side.

It's frustrating because whenever I put a Pchannel somewhere someone says I need a Nchannel. Then I get a handful of advice that's completely the opposite of whatever I just learned.

Then some people come in and call me a fool (not in so many words).

If I wanted to switch the negative then it's not an issue. But everything I'm working on is built around a positive 5V digital output from the arduino.

I will look again at post #5

[CrossRoads]

We keep ending up on N-channel as that is what you showed in Reply # 27, even posted part of a datasheet there.

[runaway_pancake]

The transistor I was "playing with" is different than the one I put in my drawing.

I think it is the same as that in my example.

Then some people come in and call me a fool (not in so many words).

Not by me.
Anyway, just leave it go.

If I wanted to switch the negative then it's not an issue. But everything I'm working on is built around a positive 5V digital output from the arduino.

So has everything that I have showed you.


You changed the context to "cars" and "high-side switching" all of a sudden.

[runaway_pancake]

It'd be nice if you'd be so kind as to stay "online" till this gets sorted.

I'm going to turn it over to CrossRoads.

[Bittsen]

Crossroads-

This is why I glossed over post 5 (and because I was reading about Darlingtons.

[larryd]

http://forum.arduino.cc/index.php?topic=61308