Trying to build a current limiter.

Thread Starter

woozycactus

Joined Jan 4, 2021
80
Hi, so I'm new to this forum and I'm sorry if I'm not posting in the right place. I am kind of new to building circuits. I am trying to build a current limiter for a one watt led. I have been searching tutorials and designs for some time and everyone i find is about 5mm leds. My main issue is i have a assortment of transistors and every design i find say you must have this one transistor but a different one on each design. My first question is, how do you choose which transistor to use? I under stand how the design works in a way but not sure what parts to use in my situation. I have not decided exactly what I'm doing yet but its either going to be one or two 1watt 3-3.4 volts 300-350ma led. Any insight on how to build this and what resister and transistors to use would be great. I am planning on using either a usb power supply if possible or a 12v supply.
 

dl324

Joined Mar 30, 2015
12,929
Welcome to AAC!
My first question is, how do you choose which transistor to use?
It would be helpful if you posted a schematic for the current limiter you have in mind.
I am trying to build a current limiter for a one watt led.
Do you want a current limiter? Or a constant current source?

If you use multiple LEDs and brightness matching is a concern, you'll want to drive them with a constant current source.
 

bertus

Joined Apr 5, 2008
21,453
Hello,

You can use a constant current source to drive a led:
Constant current led driver DC.png
An other option is a dedicated driver for leds, like the ZXLD1360.
See the datasheet for a schematic and information on how to set the current.

Bertus
 

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Thread Starter

woozycactus

Joined Jan 4, 2021
80
Welcome to AAC!
It would be helpful if you posted a schematic for the current limiter you have in mind.
Do you want a current limiter? Or a constant current source?

If you use multiple LEDs and brightness matching is a concern, you'll want to drive them with a constant current source.
sorry it is a constant current circuit and something like this. attached
 

Attachments

Thread Starter

woozycactus

Joined Jan 4, 2021
80
Hello,

You can use a constant current source to drive a led:
View attachment 226747
An other option is a dedicated driver for leds, like the ZXLD1360.
See the datasheet for a schematic and information on how to set the current.

Bertus
so this was my point with finding designs... I have a TIP120 but i do not have a 2N2222. Will it only work with that transistor or are their options?
 

bertus

Joined Apr 5, 2008
21,453
Hello,

Almost any other NPN transistor with a collector current of more than 1 A can be used for the TIP120.

Bertus
 

Audioguru again

Joined Oct 21, 2019
3,317
Why not look at the difference between a TIP120 power darlington and a little low power 2N2222 on their datasheets??
Their base-emitter voltages are VERY different and the TIP120 has a metal tab that can be bolted to a heatsink.
 

crutschow

Joined Mar 14, 2008
27,463
question is, how do you choose which transistor to use?
For typical low frequency or switching applications, the main considerations are the voltage and current ratings which should be at least 25% higher than the maximum it will see.
I have a TIP120 but i do not have a 2N2222. Will it only work with that transistor or are their options?
A TIP 120 is overkill and a Darlington type, so is not a good substitute for a 2N2222, but just about any small NPN transistor should work as a replacement depending upon the current and voltage requirements, e.g 2N2219. 2N3904, BCW60 etc.
 

Thread Starter

woozycactus

Joined Jan 4, 2021
80
For typical low frequency or switching applications, the main considerations are the voltage and current ratings which should be at least 25% higher than the maximum it will see.

A TIP 120 is overkill and a Darlington type, so is not a good substitute for a 2N2222, but just about any small NPN transistor should work as a replacement depending upon the current and voltage requirements, e.g 2N2219. 2N3904, BCW60 etc.
the schematic he showed was using both. as i was replying i have the tip 120 but not the 2n2222. So basically their is no different between npn transistors except the ratings?
 

Thread Starter

woozycactus

Joined Jan 4, 2021
80
Hello,

Almost any other NPN transistor can be used in stead of the 2N2222.

Bertus
that's what i was trying to figure out. i know about resisters and caps and diodes but not a lot about transistors. so basically the difference it the rating? As for npn transistors i have 2n4401, 2n3904, pn2222 and 8050.
 

crutschow

Joined Mar 14, 2008
27,463
so basically the difference it the rating? As for npn transistors i have 2n4401, 2n3904, pn2222 and 8050.
Yes they all basically operate the same, but with different ratings for polarity (NPN and PNP), voltage, current, power handling, and operating speed.
The 2N4401 is a PNP type.
The PN2222 is the same as the 2N2222 except for package type.

The data sheets for the transistors will tell you what you need to know about each type.
If you want to learn about transistors, then learn how to read the data sheets.
 

Thread Starter

woozycactus

Joined Jan 4, 2021
80
well thank yall for the help. This sets me in the right direction. Thanks for the data sheet. Its alot easier than looking up each one.
 
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