Tuesday, March 31, 2015

USB Ports and High Voltage Power Supplies

Customer Inquiry on a High Voltage Power Supply

VMI recently received an inquiry regarding a high voltage power supply powered via a USB connection.  We had to decline the design because it wasn't a good fit for unrelated reasons, but it got us thinking about USB ports.

USB Power Delivery

This particular application's output was about 10W, which, come to find out, is the maximum limit for the +5V power delivery via a USB connector, as defined in the USB Power Delivery Specification [1].  From a design point of view, it's not recommended practice to run at the maximum rated power.  I'm reasonably sure the PD specification has some built-in margin, but one never knows.  It might be that one instance where the maximum really is the maximum.  Maybe if the output power was 5W or 7W......

Information Credit

The USB PD specification was finalized in July 2012, and has since been revised.  The intent was to provide uniform charging of lap tops, tablets, cell phones, and other electronic devices, and was largely due to a collaboration between industry giants.

High Voltage Power Supply Idea

It's an interesting idea - to power a high voltage power supply via a USB connection.  It is probably totally do-able, given the right parameters.  Here's a potential block diagram.  It is definitely food for thought.

  1.  "USB 3.1 Specification". Retrieved 2014-11-11.
  2. http://commons.wikimedia.org/wiki/File:USB-Connector-Standard.jpg
  3. https://en.wiki2.org/wiki/RF_connector
  4. http://en.wikipedia.org/wiki/USB#PD

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