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Author Topic: So I've burnt my 3.3v output...  (Read 1075 times)
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I was experimenting with the my Arduino Mega 2560 and I think I must have done something terribly wrong because the 3.3v is no longer working. When I connect an LED and a resistor to it, it just flashes dimly for a split second and turns off. With the 5v output, there are no problems.

Ahh yeah, and there was this burning smell....

So, if I wanted to supply an SD card reader that takes 3.3V as a power input from one pin, would it work if I use a voltage divider circuit?

Also, any other options? I've tried to connect to the RX but it only seems to work momentarily. I don't need many 3v outputs, just one. I'd like to avoid an external power supply. Thanks
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No on the "voltage divider" idea.

The only partical practical work-around is a separate off-board 3V regulator.
That could be done many ways, but, still, there's no way around it.
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Daveste,
You could replace the 3.3 v regulator, if you like soldering SMT parts, that is.
If you need help finding it, then it is probably beyond the scope of your (present) abilities.
A TO92 LM33 regulator with a .1uf cap on the input, and a 10uf electrolitic cap on the output should run an SD card, but I would check. They can use a lot of current to write.
See the datasheet for the regulator for simple circuits to wire it up.
regulator: http://www.digikey.com/product-detail/en/LP2950-33LPRE3/296-31455-1-ND/3505910
TomJ
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Dave,
Here's an smd one, http://www.digikey.com/product-detail/en/SPX3819M5-L-3-3/1016-1248-ND/2411180  (it's between the crystal and the 2560). Knowing my tendency to reply before I research enough, you should check out that it would work.
TomJ
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are you sure ur sd card thingy doesnt have a built in 3,3V regulator?
Where would u power it from otherwise?

Mine has a regulator but no level shifters (cheapest possible on ebay), means csi mosi and whats not r connected to 5V i/o of arduino. Using voltage dividers for these lines it works like a charm.
« Last Edit: March 28, 2013, 03:54:31 am by lax123 » Logged

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Quote
No on the "voltage divider" idea.

Why?
One of the more stupid ideas.
Why, because the current drawn by an SD card changes as it operates and therefor so does the voltage you are feeling it. Just because some crap design happens to function for a short time is no reasion at all to think it is fine. It will not work on other cards or when the card ages or over any great temprature range, or at any great speed.
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ive seen people use those crap designs which use 3,3v for power, but only 5V for i/o and it works for them, so using a voltage divider to get into the 3,3V range for the i/o to arduino u still think its that problematic?
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Changing a 5V logic output to 3V3 with resistors is fine because the load you put on the lower resistor is high impedance when compared to the lower leg resistor. It will slow down the signal edge but generally works well at low speed.
However when it comes to power it is another matter. Generally the lower leg should take at least ten times more current than you are drawing from the load. So if you want to use very low resistor values and burn a lot of current then at a push you can but I would not recommend it as a viable option in this day and age.
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yea sorry, after i wrote that post i realized its wrong and modified the post before i read yours. all those cheap sd modules on ebay have a 3,3 Vregulator but no lvl shifter. Id believe davstes module has one too, otherwise how would you connect them on a regular basis to your 5V usb, if its not a arduino sd module.
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Daveste,
You could replace the 3.3 v regulator, if you like soldering SMT parts, that is.
If you need help finding it, then it is probably beyond the scope of your (present) abilities.
A TO92 LM33 regulator with a .1uf cap on the input, and a 10uf electrolitic cap on the output should run an SD card, but I would check. They can use a lot of current to write.
See the datasheet for the regulator for simple circuits to wire it up.
regulator: http://www.digikey.com/product-detail/en/LP2950-33LPRE3/296-31455-1-ND/3505910
TomJ

I've just checked and locally, I couldn't find neither the regulator, nor the LP2950. ebay.co.uk don't seem to ship any either. If I can't get them from there I can't get them :/ Sparkfun have exorbitant shipping to my location, and amazon have them available at $0.70 each with $60 shipping. Ugh, I might as well buy two new arduinos at that price...

Are there any other alternatives left?

Edit:
I've found this: http://www.ebay.co.uk/itm/LM3940IMP-3-3-National-Semiconductor-V-Reg-LDO-3-3V-3940-Sot-223-3-/140938501670?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item20d096de26
It's input voltage is 5v and the output is 3.3v. Is it what I'm looking for? I'm going to pay £7 (around $11) for one of them. Seems a bit overpriced but looks like my only option.
Also, what voltage does the capacitor have to be?
« Last Edit: March 28, 2013, 06:05:47 am by Davste » Logged

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davste, what kind of sd card reader do you have? are you sure it has no built in regulator?
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I'm pretty sure, yeah. I also need to connect other stuff to the 3.3v, like an NRF chip. Can't really do much without the 3.3v.
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Is there a way to achieve this with diodes by the way?
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OK! I think I found a good one:
http://www.ebay.co.uk/itm/AMS1117-Regulator-Output-Output-3-3V-/221183098345?pt=LH_DefaultDomain_23&hash=item337f8a3de9

"Input 4.7V – 10V
Output 3.3V"

Nowhere near as expensive as those LM chips...
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Yes that look fine.
If you fill in your location on your profile maybe we could help more in finding you a source of supply.
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