Old 03-03-2011, 04:33 AM #1
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Default LM1117 Driver Question?

Hey there, everyone. I recently got my parts from Mouser and DigiKey and I have been working on a micro, Aixiz-sized driver for a couple of hours now.

For some reason though, even though it's all wired up and it *should* work, my test-load reads about 353mV => 353mA, but I am using a 3.3Ohm resistor and I get the same reading when I use a 10Ohm resistor! Why isn't it working?

Anyway, here is how my board is set up (it is all on a 3x7 through-hole board... imagine 3 holes by 7 holes and it should make sense).



So why won't it work? What's wrong with it?

Is something wrong with the LM1117?


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Old 03-03-2011, 04:19 PM #2
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Default Re: LM1117 Driver Question?

How many diodes are in your test load, what is your supply voltage, and what is the power rating of your resistor?
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Old 03-03-2011, 08:43 PM #3
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Default Re: LM1117 Driver Question?

I have the Rkcstr driver (which is switchable between 4 and 6 1N4001s), and I just stuck a little 1/4W SMD resistor on the pads, but it didn't start smoking or anything when I connected the testload.

My supply voltage was slightly lower than 6V, probably around 5.8V. But, I set it up to be using the "red" diode setting, and it still read the same.
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Old 03-04-2011, 01:06 AM #4
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Default Re: LM1117 Driver Question?

Mm - I discovered something else.

When I disconnected the resistor from my test-load, and I hooked up my driver with a 10Ohm resistor on it, and then I put my DMM on ammeter and measured the amperage across the area where the resistor used to be, I get about 350mA, and then after about 2 seconds it drops to 124mA. Doesn't that sound right? 1.25V drop from the driver, so 10 Ohms = 125mA, correct?

Anyway, is that an accurate way to measure the output of some drivers (or at least mine)? And why did I get that boost of 350mA at the beginning? Cap discharge?
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