1. Home
  2. Electronics Design
  3. How to drop 2-40V down to 1-1.5V?

How to drop 2-40V down to 1-1.5V?

Hi, I've run into a problem that I have worked on for quite a while. I was trying to find an inexpensive way to drop a 2-36V source down to around 1-1.5V. I had done it with a zener and a LDO voltage regulator before to drop sources from 5-18V, until I found a particular source that had 36V. I had been using the zener to drop the higher voltages down to a range that my voltage regulator could handle. However, when I tried the same circuit on the 36V source, the zener drew too much current causing the source circuit to "misbehave". The source is a DC source and the less current I draw to drop it down the better. The source isn't a battery and has some output impedence (which is why I used the zener), but depending on the product I test on, the voltage varies between 2-36V.

Is it possible to do this inexpensively? I am not an expert by any means but have done the best I can researching on my own and trying my own solutions. Any help is much appreciated.

Thanks, Gabe

Reply to
Gabe
Loading thread data ...

As with all power supply questions posted here, I'm going to have to ask: How much current do you need coming out (at 1.5 V)?

Reply to
mc

try something like this for your preregulator for the LDO.

formatting link

use a current limiting diode (1n5299) instead of the resistor to provide about 1mA constant current.

Chose a transistor beta large enough to handle your currents. If biasing a zener cause erratic operation it doesn't appear to be much available current.

Reply to
Mook Johnson

I could probably get away with around 2mA but 5-10mA should be plenty.

Reply to
Gabe

Reply to
happy

And how efficient does it need to be?

One approach is to use an LM317 voltage regulator, which, I think, outputs

1.25V if you use it like a 7805 (no resistors, sense pin directly connected to ground).

Another is to build a current source -- say 10 mA -- and drive the current through an infrared LED, which should give 1.6 V across the LED, or a pair of silicon diodes, which should give 1.2 V.

Reply to
mc

Thanks guys,

I'll have to order some samples and try them out... I think both will work. I think the sites I had searched didn't have a regulator that could handle the spread in voltage (at least not cheaply), and I didn't know about the current limiting diodes. I'm a software guy, but I think I have chosen the wrong field as I am fascinated by electronic design... so all I can do is tinker for now!

Thanks again!

Gabe

Reply to
Gabe

normal diodes can be used to limit voltage, but there are (or were) diodes out there that limit current.

or maybe a JFET could be used...

--+-[50R]---. .----+--- 1.2V | | | | | ---- | | ^ | | | | | V | `---------[100K]--+-->|-->|-- ground

Bye. Jasen

Reply to
jasen

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.