LM338 as negative voltage regulator?

I'm trying to build a big beefy power supply with this old harrison console supply I have here, and I'm looking at the LM338 regulator. I've read that this can be used as a negative voltage regulator but I can't find any info on how to do this. Ideas?

Kevin

have a look at this

http://www.tcaas.btinternet.co.uk/jlhesl.htm

:wink:

I'm curious about the performance of these arrangements. Is there any difference with respect to output impedance, regulation, load transient response or stability in comparison to a "true" negative regulator?

Samuel

This is a question rather than a statement.... don't you lose the short circuit or overload protection features if you use them this way ?

[It is lurking in the back of my mind that someone told me this once].

Colin
www.audiomaintenance.com

Hi!

The PSU schematic proposed here doesn't have any tracking circuitry, which is a serious shortcoming if the PSU is to be used in the console. Why not use a Soundcraft or AMEK PSU design? Those are quite simple and reliable.

Samuel,
there are no significant differences beetwen this design and the one that uses a "true" negative regulator, IMO. Except .... there is no "complementary" negative regulator for the LM338 (not to my knowledge).

Colin,
all regulator features are preserved with this topology.

Regards,
Milan

There are no significant differences beetwen this design and the one that uses a "true" negative regulator, IMO.

Click to expand...

So why are there negative regulators then..?

The PSU schematic proposed here doesn't have any tracking circuitry, which is a serious shortcoming if the PSU is to be used in the console.

Click to expand...

By "tracking circuit" you mean tracking of the positive and negative voltage, right? Why should this be needed for a console?

Samuel

[quote author="Samuel Groner"]

There are no significant differences beetwen this design and the one that uses a "true" negative regulator, IMO.

Click to expand...

So why are there negative regulators then..?[/quote]
IMHO you'll need separate secondary windings, a center tap for gnd will not work.

[quote author="Samuel Groner"]So why are there negative regulators then..?[/quote]

For example, they allow you to build simple designs such as the one in the picture below. :wink:

By "tracking circuit" you mean tracking of the positive and negative voltage, right? Why should this be needed for a console?

Click to expand...

If one of the rails is down for any reason, channel strips may (and usually do) draw excessive current from the remaining rail.

Regards,
Milan

[quote author="Harpo"][quote author="Samuel Groner"]

There are no significant differences beetwen this design and the one that uses a "true" negative regulator, IMO.

Click to expand...

So why are there negative regulators then..?[/quote]
IMHO you'll need separate secondary windings, a center tap for gnd will not work.[/quote]

So to use two of the LM338k in a bipolar supply, I need two separate windings, 20-0-20 won't work?

[quote author="Baltimore"]So to use two of the LM338k in a bipolar supply, I need two separate windings, 20-0-20 won't work?[/quote]

Yep.

Do the right thing....I made this for my summing box, but instead of using three terminal regulators I kept it discrete and brought it up to +24/-24V. This design works very well. Obviously you can choose any of the 78xx pair for voltages up 15V, 18V, 24V. And add current boosting transistors to satisfy your desires.
Case closed.


analag

Analag

What power rating should the resistors have ???

I don't know the power rating for the resistors, but this circuit was taken from here :
http://sound.westhost.com/project30c.htm

While 3055 are pretty slow devices, there is some voltage gain in that configuration. I would be tempted to add a compensation cap from bases to unregulated rail on both, for some insurance against oscillation.

JR

[quote author="keefaz"]I don't know the power rating for the resistors, but this circuit was taken from here :
http://sound.westhost.com/project30c.htm[/quote]

Wow...

[quote author="analag"]
Wow... [/quote]
Hey forgive my newbieness :grin:, but this page has a lot of informations and I thought it was adequate to give the link.

Analag, thanks for the link. I think I'll be building something like this.

Kevin