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Constant current circuit diagram

Hi everyone,

I’m going to make a constant current circuit that can be used for many
purpose with very wide current range. The max currents are 0.2, 2 or
20mA, you can choose by a switch.

I don’t know the English name of machines those are just constant
current circuit, so would you let me know those names?

Several weeks ago I wrote that I had finished to design the final
diagram and maybe been able to release it soon. But I had no chance to
buy some parts to make and test it, and I don’t know when I can even
now. So I’ll release the diagram only for get advices or opinions from
those are familiar to electronic circuits. THIS DIAGRAM IS NOT A FINAL

This circuit is designed to be comparably simple, cheap and precise.
Would someone watch and let me know any advices? The diagram can be
seen on web page The battery
is about 18V or more.

There are three sections enclosed by boxes. Those are “battery alarm”,
“Max current set” and “ammeter” sections. I decided to use a cheap
voltmeter instead of an ammeter because the cheap ammeter is not
precise and the precise one costs high. The OP amp (This may be a
Japanese name, the triangle amplifier in the diagram) is LMC660. I
don’t adopt FET instead of transister because FET is too difficult for

Now I’m also having advices by professionals and veterans to improve,
so the diagram may be changed without notice.

Thank you, Takashi Tomoeda @Takashi_Tomoeda1

Hello Takashi Tomoeda,

I am impressed by your work and wish you well. Please excuse me for
offering an alternate idea at this late date but I can say that I
have built several of these with good success. The original is still
in service after many years without ever having a glitch or fault.

To this end, I offer you the paper and design to be found at which is from the Lapidary
Digest web resource (main- ). There are
several other plating references in the Lapidary Digest Archives that
you may find of interest. All back issues are on-line for
downloading, This use of this is free to the public
(publication of is per conditions of Hale Sweeny, LD

We have worked for several years with free-shaped lapidary and use
electro-forming as our primary tool to create integral bezels. You
are very correct that current measurement is the expensive part of the
process. The power supply is trivial, any 3A 12v DC unregulated unit
will suffice. The regulator must be custom made but the parts are of
minor cost. It is required to measure 1/10A per square inch and, for
my work, I need currents regulated to two significant figures as low
as 15ma. Only a digital ammeter will suffice for this and I find a
(USA) Radio Shack #22-163 is excellent… but costs (about) $90. The
device shown in the LD delivers from 14ma to 2.5A in two ranges and
only a meter with the this minimum precision provides my necessary

Good luck to you with your project.

…George Butts <@George_Laurie_Butts>