How do I amplify .11 mA to 500 mA?

Hi,

I'm working on a project to drive an IR LED pulsed at 500 mA from an arduino board connected to a touch-screen display. For reasons I'm not entirely clear about, but I think related to the amount of power the display is drawing, I'm only able to get about .11 mA at +5V from the pin driving the LED. Using that as input to the base of a PN2222A NPN transistor, I can switch about 13 mA. I had thought if I connected that output to the base of another NPN transistor, I could draw the appropriate current through the LED, but when I do this, I cannot measure any current running through either transistor.

What am I doing wrong? I feel that I am missing something fundamental. Any help?

Thanks in advance,

-Pete

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I just like to make stuff.

Without performing an actual circuit simulation it is difficult to make specific suggestions.
In general, a PNP type transistor is used as a 'source', while NPN type transistors 'sink' current from a load.
Along this line, you could set up a PNP transistor to supply current to your IR LED. Then devise some way to get the output pin to drive the PNP transistor gate at a sufficient level.

Are you are able to draw a sketch or provide a schematic of your problem .... to clarify the situation?

Here is one possible solution ...

Pete,
It will be nice to know more. 0.11mA is very small, you should get more like 11mA. Is there a pull up resistor on this pin? (47k)?

If the two NPN transistors are in a Darlington configuration then 0.1 mA into the base of the first should easily get you 500mA from the collector of the second. But there's clearly something wrong if the pin can only provide 0.1mA. You need to resolve that issue first.

do you have a schematic of the circuit coming out of the pin in question?

Thanks, the Darlington configuration was what I needed. I am now able to get 500 mA out of the circuit.

The .11 mA question still remains, but I will post that on the AdaFruit forum, where I got the touchscreen.

Thanks for the help!

-Pete

about current

I have a similar problem..I have a current output of around 45mA...i need it to be 1 A...is it possible so such a amplification....And about the darlington..do u know the circuit...because whenevr i tried it....the transistor just stoped working

Prav1091 said:

I have a similar problem..I have a current output of around 45mA...i need it to be 1 A...is it possible so such a amplification....And about the darlington..do u know the circuit...because whenevr i tried it....the transistor just stoped working

Click to expand...

Again, post a schematic - a single transistor should be all you need though, and the previous poster shouldn't have needed a darlington either.

For an example, check the hardware for my PIC IR tutorial.