The stuff of Kryton

An eclectic selection of technology with some cookery

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USB Charging ports – Part 2, Design my own?

Possibly not a good idea, not sure I want to see what airport security would think of my taking a home made USB Power Supply Unit (PSU) on a plane. I’ll do this as a thought exercise.

Working on the principle of the old Engineering adage of “Quality, Time, & Cost, pick any two” and the market is flooded with “Time and Cost” examples I’m going with Quality & Time. I.E. I want to be reliable, course few issues and be quick to design because I don’t want this post going on for pages about winding an inductor.

Custom PSU Specification:

Travel requirement:

• Compatible with voltages
• 100-240V (Japan to Australia)
• 50-60Hz (EU & USA)
• Compatible with world plugs / sockets
• Class II Earth
  • Earth connections are not ubiquitous or vary greatly.
  • “Europlug” CEE 7/16
  • German
  • French
  • Italian
  • Swiss
  • NEMA 1-15
    • USA & Canada
  • JIS C 8303
    • Japan
  • IEC 60320 C8 inlet
    • Change leads per market
    • Limits power to 250W in 100V markets

Main switching element:

• Mains element comes with CB report
  • Better able to introduce to global markets
• EMC
  • Radiated & Conducted emissions class B
    • A device under charge is only going to add noise so lets start with Class B and make the systems integrators life easier.
    • Yes I could specify Class C but this needs to be achievable to meet the “Time“ requirement.
  • Surge, dips & trips passed
    • I want this device to survive on dodgy supplies.

Outputs:

• 2x USB A 2.0 Output ports
• configurable D+ / D-?
  • Apple 2A to charge Apple kit quickly
  • USB DCP for every one else!
  • Needs some kind of circuit to configure this.
• Current limits
  • Apple 2A should be 2A
  • USB DCP
    • Most I’ve seen is 1.4A Sony CSC
    • Spec permits more, 2A to match Apple seems sensible but I’ll leave this open for wiggle room.

Potential parts:

IEC 60320 C8 conector

• PCB mounted so no internal wires
• PTH mount for strength
• Suggested: Schurter 6160.0009
• Hight 17mm needs to be checked regards enclosure & hight of other components

AC/DC power regulator

• Off the shelf module
• Offers good EMC performance
• CB report for grater market access

Suggested: Recom RAC20-05SK/W Hight 23mm Current limiter for each output (Needs more research) Dual output Monotonic power turn on

Short circuit protection

Suggested: STMicroelectronics VNLD5300-E Further design analysis needed is Apple 2A or 2.1A?

Dual USB A 2.0 conector

PCB mounted so no internal wires PTH mount for strength D+ / D- need to have Less then 200mΩ for USB DCP Suggested: Würth Elektronik 614008235023 Contact resistance under 20mΩ so 40mΩ max for D+ / D- on this conector Hight 16.7mm needs to be checked regards enclosure & hight of other components

Resistors for Apple port

• 43.2K x1 Yageo RC0100FR-0743K2L
• 49.9K x2 Vishay CRCW010049K9FREL
• 75.0K x1 Vishay CRCW010075K0FREL

Low Current so small SMD case 01005 viable Operating voltage 2.7V max so still OK for 01005 Further thoughts

The design seems feasible to build electrically although without an SMT line I’m not sure I’d be able to fit the 01005 devices by hand so would probable go for 0805 or even PTH. I’ve not done a great deal of analysis of the current limiter chip and would look at this aspect a lot more closely prior to committing to a PCB. Again I may also go for a PTH chip to enable hand soldering. The mechanical design would need a lot of consideration as the AC/DC module is much taller than the connector.

/ license

Keywords: ELECTRONICS TECHNOLOGIESTAGS: IEC60320, USB