6V power supply

I have a project that needs to pull power from an existing 6V system. I know 6V is shaky territory for Arduino boards because the regulator likes more than that and it's too much to put directly in. I probably won't be using a board anyway, I'll probably mount a 328 on a perf board.

But what are my best options for getting 5V out of 6V? LDO regulator? What's a good one?

If all you are trying to do is get a 5V fixed regulator with less than 1V of dropout, there are many options. Just looking around I found this:

http://www.ti.com/product/lp2954 http://www.newark.com/texas-instruments/lp2954it-nopb/ldo-voltage-regulator-5v-250ma/dp/41K6619

$1.26 at Newark. But it does suck having to order cheap parts and they paying the shipping on it.

Linear and Micrel have several too, all more expensive.

The onboard LDO drops <= 1volt. So you could feed +6volt directly into Vin.
Not into the DC socket, because that drops another 0.6volt because of a polarity protection diode.
A cheap solution would be two (1N4004) diodes in series to drop 1-1.2volt.
Provided the 6volt supply is stable and clean.
Leo…

Wawa:
The onboard LDO drops <= 1volt. So you could feed +6volt directly into Vin.
Not into the DC socket, because that drops another 0.6volt because of a polarity protection diode.
A cheap solution would be two (1N4004) diodes in series to drop 1-1.2volt.
Provided the 6volt supply is stable and clean.
Leo…

The 6V is well regulated. Is the diode solution really viable? That feels like a hack to me.

Wawa:
The onboard LDO drops <= 1volt. So you could feed +6volt directly into Vin.

Not according to the data sheet you can’t. It says

with a maximum dropout voltage of 1.2 V

And the 5V fixed voltage regulator is specified at

(Vin=7.0V,Iout=10mA,TA=25°C)
(Vin = 6.5 V to 12 V, Iout = 0 mA to 800 mA)

Is the diode solution really viable? That feels like a hack to me.

A typical silicon diode will drop voltage ~.7v. If a hack is not wanted, get a 5v power supply. They are cheap and common.

zoomkat: If a hack is not wanted, get a 5v power supply. They are cheap and common.

But they generally need a 110VAC outlet, and this I do not have. I only have 6VDC available.

I think I will just find an LDO regulator.

Had a look at the datsheet of a typical onboard 1117 LDO. Drop is ~1volt at ~300mA. And ~0.8v at a typical 100mA. And yes, 1.2volt when you want to draw 500mA at 20degrees below zero. Two diodes works fine. Arduinos also run on drooping USB supplies. If 1.4v is too much, a 1N4004 and a 1N5819 (schottky) in series will drop 1.1volt @100mA (measured!). Supply is not that critical, unless you want to measure analogue things accurately. This Pololu buck converter is another option. Dropout is 0.25volt at 200mA. Leo..

Diodes work just fine.

Delta_G: But they generally need a 110VAC outlet, and this I do not have. I only have 6VDC available.

I think I will just find an LDO regulator.

I'm with you on the LDO, but keep in mind that if you are making a bare circuit in the end and using an ATMega328P, it is speced from 1.8V-5.5V. You have a big voltage window to play in, depending on what other circuits you are going to interface to it (note you will have to use a slower crystal as you get closer to the lowest voltages). Arduino runs it at 5V only because some decision had to be made and that is the hobbyist voltage of choice

JoeN: I'm with you on the LDO, but keep in mind that if you are making a bare circuit in the end and using an ATMega328P, it is speced from 1.8V-5.5V. You have a big voltage window to play in, depending on what other circuits you are going to interface to it (note you will have to use a slower crystal as you get closer to the lowest voltages). Arduino runs it at 5V only because some decision had to be made and that is the hobbyist voltage of choice

You mean I can just power the thing at 3V3 and call it a day?

3.3V for 8 MHz. If you want 16MHz, you need >=3.8V. How about a 4.5V regulator for up to 800mA? http://www.digikey.com/product-search/en?FV=fff40027%2Cfff80182%2Cc0004a&k=regulator&mnonly=0&newproducts=0&ColumnSort=0&page=1&stock=1&pbfree=0&rohs=0&quantity=&ptm=0&fid=0&pageSize=25 Or something similar, 4.75, 4.8, just to yourself some margin to regulate down from 6V. Example: http://www.digikey.com/product-detail/en/MIC5201-4.8YS/576-1252-ND/771721 Vin needs to be >= Vout +1V, so 6V in & 4.8V out would be fine, at up to 200mA. Do you need more than that?

Nope. All it's gotta do is be able to send signal to a couple of NPNs driving a pair of MOSFETs toturn on a couple of little motors. I don't need a huge amount of current for anything.

Well that sounds easier than trying to get 5V. If Arduino can run on 4V5 so can everything else involved.

My arduino has an ethernet shield attached, and is powered from my netbook. The voltage on the arduino 5v pin is 4.32v. I’ve also seen the arduino operate for a short time with~8v indicating on the 5v pin. This is an old Duemilanove which appears to be fairly rugged.

@zoomkat, What is the netbook output voltage when the Ethernet shield is not attached?

I'm surprised 8V didn't kill the '328P, with its Absolute MAX of 6V for VCC. Same for the FT232. Bet the Power LED was a bit brighter!

Bet the Power LED was a bit brighter!

That is what prompted me to see what was going on. I had a 12v battery connected to the external power jack at the time. Some issue with the on board voltage regulating system (9v connected resulted in ~7v). I then connected the 12v to an 7805 regulating chip connected to the 5v pin and everything was back to 5v.