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Transistor for supplying ground, I think mine are way overkill

blackcats

Oct 14, 2016
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Hello guys,

My knowledge is growing everyday and the more I work on this project the more I learn that I was going way way over on components since I didn't have a firm grasp of everything. This leads to my next question.

I have two transistors in my design that supply ground source for 2 LEDS that are on 14.8v.
I am using STP16NF06L for this task.

It works great, I have the UNO controller wired straight to the gate on it no resistor send. Works flawlessl will turn on the 14.8v circuit and the led in it turns on and off like it should.

Now that I have learned more about components I have found a 60v 16a mosfet that costs .69$ is way over kill on this design. I have check the current draw on the 14.8v side of the mosfet and it only draws 50ma when the led is on.
Now the part I need help on, what kind of transistor should I look at I know its going to NPN and I know it can be a low AMP rated one but I don't know what to do to get a drop in replacement for the boards I already have made. I look at some NPN and they say .5v so 5v would be way to high going into it from the controller.
PN2222ATFR is one that I was looking at as I see it a lot in circuits. It also looks to have the same layout that I'm already using all though I don't know if it needs to have a resistor or not on the base.


Thanks for all your guys help.
 

Harald Kapp

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Nov 17, 2011
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I know its going to NPN
Why? The STP16NF06L you currently use is an NMOS FET, not NPN. An NPN will not work without a base resistor.

I look at some NPN and they say .5v
0.5 V what? Am I right in assuming Vbe? That's where the base resistor comes into play. You may want to read more about "using a bipolar transistor to turn a load on and off" in our ressource section.

While a bipolar NPN will work fine in your application (with base resistor!), you can find suitable MOSFETs using a selector guide as for example this one. This distributor is probably not the least expensive, but you can use the table to find a suitable MOSFET and then search for good prices elsewhere.
Other distributors and manufacturers have similar selection guides / tables.
 

HellasTechn

Apr 14, 2013
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How about a general purpose NPN with base resistor ? like the BC337.
 

AnalogKid

Jun 10, 2015
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How about a schematic so we can evaluate your question with some information?

ak
 
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