Question for electronics geniuses.

I have a 36V DC power supply that provides +36V and Ground. Is there some EASY way of getting +/-18V and Ground out of this?

I was sure I saw this done somewhere, but I'll be darned if I could find it. Would appreciate any help.

aside from cracking it open and removing/replacing some parts, I can't think of anything. I wouldn't trust a step-down (resistor, etc.) of that size.

Well, you could take the 36V line, and connect it to both the device needing 18V and to a resistor hooked to ground. The resistor will need to be equal in resistance to the object needing the 18V. You can find this by dividing 18 volts by how much current it draws (in amps) when connected (should be able to find this somewhere). The resistor will have to have a power rating of at least (18 * current drawn in amps). I'd go for more though.

Here's a quick and dirty schematic:
               |----------- <device> ------- <ground>
               |
+18V  o---|
               |
               |----------- <resistor> ----- <ground>

JigPu

I was trying all afternoon to stay out of this one.
Using a resistive bias setup, the voltage presented to each tap will depend heavily upon the device(s) connected to them having a fairly "static" current draw. If the current draw varies, the voltage is going to be all over the place. If the device(s) have varying current demands, I do not see a "good electronics practice" solution for you, but then I do not consider using the +12V and +5V lines to achive +7V as a "good electronics practice" either, so take it for what it's worth.

73, Hoot

Thanks for the suggestions guys. I can see that I need to get a bit more specific in what I'll be doing (although it may not help much )

I'm trying to power a run-of-the-mill 471 op amp. The op amp needs +/- (9-18)V for power and the signal needs to run between the positive side and ground. Here is a schematic of what I'm building (almost all the way at the bottom of the page). This diagram calls for +/- 9V and ground, but I need higher voltages, so I'm going to use +/-18V and Ground. The problem is that current demands are going to change as the feedback resistance changes.

I can see that there is no EASY solution, but just though I'd ask. Thanks again yall.

P.S. I came up with a dirty solution. Using two small 15V batteries hooked in series. This way the center connection is ground and each end will give me +/- 15V.

Why didn't you say so? Running a 741 is a piece of cake. For $5 you can ge a DC-DC converter that puts out +/- 15V at .8A each with 36V input. it's about the size of a matchbox. They have other DC-DC convertors and a plethora of cheap power supplies.

http://www.allelectronics.com/cgi-bin/category.cgi?category=200&item=DC-27&type=store

73, Hoot

Great idea, thanks Hoot.