I am a bit stumpped! I need 700-750mV regulated

[large_ghostman]

Hi,
First off I did have a sort of working solution and used some diodes and a resistor divider to drop 3.3V to around 700mV, the problem being the room this is in dosnt have heating and the diodes changed the voltage slightly. I have a HP power supply that will happily give me exactly 400mV at any current upto 5A, but that ties up my best PSU for a while.
I need to have a stable Voltage of between 400-750mV MAX, I cant go above 750mV (actually not true I could push to 790mV but thats pushing my luck). I would like anywhere from 500mA to 1A in an ideal world, its for an electrolysis cell and the voltage cant go above 750mV. in a perfect world I would like 400mV, anyone know of a suitable regulator? I have 3.3V and 5V lines to power it.
the reason why its critical is this.

I am running at buffered pH4 and would like to stay inside the CuCl bit, if I need to I can go into CuCl2 but dont want to get anywhere near 800mV as that starts to leach out the gold, this is for using salt and sodium acetate buffered with acid for dissolving copper from gold plating, yes I could use aqua regina or hydrogen peroxide with it but the idea is a environmentally safer way. So any ideas how to make a voltage regulator that stable under different temperatures? Worse case scenario I can do without the electric but it speeds up the process a fair bit.
Thanks

 

[KeepItSimpleStupid]

I can get you partly there: https://www.ti.com/lit/ds/symlink/lm10.pdf

It's a really old part, but still available even in the new packages.

 

[MikeMl]

So get a temperature-stable precision-voltage-reference that makes a higher voltage, and then use a resistive divider followed by a voltage follower if you need some current.

 

[crutschow]

Linear Technology has a number of voltage regulators that go down to zero volts, such as this.

 

[large_ghostman]

Thanks the linear technology part looks like the jobby, I will get one this week. 1.1A!! in a tiny package like that, I havnt looked at there stuff for ages.

 

[Les Jones]

If you have a negative voltage supply available you could use an LM317 and connect the reference terminal to the slider of a potentiometer that went between - 0.55 volts (1.25 -0.7) and - 1.25 volts. You could could regulate the negative supply using an LM7905 and set the voltages at the ends of the potentiometer with fixed resistors. One to 0 volts and one to - 5 volts. I would suggest using a fairly low value potentiometer. (Say 470 ohms or less)

Les.

 

[large_ghostman]

Its a ATX PSU the ned side is pretty low current, I will give the LT part a try it might be handy for a few other things. But thanks for the sugestions

 

[ronsimpson]

I would get the LT3080 in the TO220-5 package. You will have about 2 watts lost (depending on current). Heatsink

 

[large_ghostman]

For what they cost (samples ) I might try both out, I have some heat sinks so that should be ok

 

[AnalogKid]

That is such a weird little part. I keep looking for an excuse to design it into something.

Rule of thumb for TO-220 heatsinks: At two watts dissipation and no heatsink, a TO-220 package will remove the fingerprint from your thumb.

ak