HOME Schematics Discover Forum Hobby Corner Dave's Circuits Electronic Resources Book Corner Contact Info

What the World Needs Now -- AC to DC Power Supply with 40KV Isolation

Previous Issues
This request came from a company who needed an unusual power supply.  They required a low power DC supply assigned to a high voltage power supply, which was elevated above earth ground by 20KV.  The power supply needed to be connected to the 20KV supply.  They said that their circuit performed some logic function and communicated to a computer through an optical fiber interface.  The logic circuit could operate using a voltage from 2 to 3 volts and only needed a couple milliamps of average DC current.  The kicker with this system was that to insure no arcing, they wanted the supply to be able to withstand 40KV with respect to earth ground.  Wow!

The usual method to generate a low power supply with good isolation is with an iron core transformer or a ferrite core AC to DC converter.  But, those systems usually only provide a few kilovolts of isolation.  Getting isolation to 40KV would almost be impossible with a magnetic approach.   I think one way to do this job is with an optical approach.  The method I have in mind is illustrated below.

An array of infrared LEDs is positioned on one side of a thick piece of clear 3/4 inch thick Lexan plastic sheet.  Light from the LEDs would shine onto an array of inexpensive solar cells or photodiodes on the other side of the plastic sheet.  Since the company said they only needed 2 to 3 volts with a few milliamps to perform their logic function, then only 4 to 6 solar cells would be needed.  Surprisingly, a good photodiode has a light to electricity conversion approaching 50% if it is illuminated with 900nm infrared light.  This infrared wavelength matches the peak response of the typical silicon device.
The LEDs would be on one side of the thick plastic insulator and the solar cells connected to the 20KV source would be on the other.  Iím pretty sure that this amount of plastic will hold off 40KV and maybe a lot more.  At 40KV, any electrodes would need to be at least 2 inches away to insure no arcing through air.

August 2011

Page 1 Back
Good Idea
gone Badly
What the World
needs Now
Wily Widget

Imagineering Ezine    Discover Solar Energy Dave Johnson & Associates Faraday Touch Switches

 About Us   |  Advertise on DiscoverCircuits.com   |   Report Broken Links  |    Link to DiscoverCircuits.com  |   
Privacy Policy

Discovercircuits.com endeavors to credit original designers.   Please alert us by eMail so we can
delete links to material that have been copied without your permission
.   Thank you.

© Copyright of all original material on this website is the property
of David A. Johnson, P.E. (Dave Johnson & Associates ) unless otherwise noted.  

Linking is ALLOWED but COPYING any content or graphics to your web site is EXPRESSLY PROHIBITED.
All material is provided "as is" without guarantees or warranty of any kind, either expressed or implied.