Re: I need more power!

I assume a ULN2003 will give you what you want,
however in a similar situation I would probably find me a pile of SOT-23 logic level FETS instead. Go to Fairchild Semi and look around for SOT-23 logic level FETS. Finding good 3.3 ones is slightly hard. Best to find a 2.5v one and use that so you know it is fully on.

Hawker


On 3/20/2007 10:38 AM, The digits of MattWilson.6185@xxxxxxxxx's hands composed the following:
Hi!

I am trying to design a printed circuit board with quite basic
functionality. (My first one!) The main part of it is taking pulse
width signals, passing it to buffers which then goes to LED's.

The system voltage is 3.3v with a power supply of 3.7v

I took the LED's to the lab and ran some tests on them. When you give
them the appropriate voltage, around 3.5v they draw 20mA of current.
So naturally I assumed at around 3.3v they would draw somewhat less,
right? WRONG! they draw upwards of 40mA.

I can't find a single buffer that will give me more then 100mA per
chip, with a max of 50 mA per pin at 3.3v. There are ton of chips
that would work if I could supply it with 4.5 source, but the max
voltage from the battery is 3.7v.

I've looked at using the buffers to power a transistor but with my
limited math skills the transistor won't turn on because I need to
give it more than 3.3v! everything seems futile without more
voltage. There has to be a way to draw more power (current) from a
source without increasing the voltage!

Any suggestions at what I should look at?

Thanks a ton!

Matt

.

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