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Project Notes

#400 USBProtector

Building the Silicon Chip USB Protector which demonstrates various methods of reverse-polarity, over-voltage and over-current protection.



I picked up the Silicon Chip USB Protector not so much because of need, but because it is an interesting study in a range of over-voltage and over-current protection mechanisms.

The project is written up in Silicon Chip May 2018 (p57), with the kit and supporting materials available online.

I just saw μArt on crowdsupply, which is an interesting project with similar protection mechanims but intended for UART applications.

ARRL Hands-on Radio (Vol 2) also has good coverage of these topics. See:

Circuit Description

I made a quick transcription of the circuit in EasyEDA for the purpose of getting a little more intimate with the circuit.


At it’s core, the circuit is a pass-through of the USB power, ground and two data lines (D+, D-). It then adds the following protection mechanisms:

Component(s) Protects Description
PTC1 Vcc over-current Resetable, handling moderate over-current without needing replacement
Fuse Vcc over-current Reacts faster to very high currents than PTC
D3 Vcc reverse polarity Limits Vcc to -0.55V. Potects PC-side from peripheral-side reverse voltage which should cause PTC or fuse to trip
Q1, REF1 Vcc clamp Active protection from over-voltage that may not trigger over-current. Reaction time relative slow
TVS1 Vcc clamp Passive over-voltage protection that is also fast-acting
D1,D2 D+/D- clamp Over-voltage and reverse-voltage clamping for data lines
TVS1 D+/D- clamp Transient voltage supressor for data lines

The circuit includes two LED indicators:

  • LED1 is simple power indicator, always on when Vcc powered
  • LED2 turns on proportionally to the degree of voltage clamping being applied


The kit primarily uses SMD components, but reasonably large packages and not too cramped so I decided to hand-solder rather than bust out the hot air. the parts are conveniently provided taped up and labeled on a sheet or paper:


The PCB had one error in the silk-screen. The lower component marked “10k” is in fact the 47kΩ resistor between Q1 and Q2.

pcb_front pcb_rear

Recommended construction order:

  • top-side components:
    • Q1
    • TVS1, next to Q1
    • SMD passive components
    • REF1 and Q2
    • LEDs
    • D3
  • bottom-side components:
    • D1, D2
    • TVS2
    • F1
  • USB plug and socket




Credits and References

Project Source on GitHub Project Gallery Return to the LEAP Catalog

This page is a web-friendly rendering of my project notes shared in the LEAP GitHub repository.

LEAP is just my personal collection of projects. Two main themes have emerged in recent years, sometimes combined:

  • electronics - usually involving an Arduino or other microprocessor in one way or another. Some are full-blown projects, while many are trivial breadboard experiments, intended to learn and explore something interesting
  • scale modelling - I caught the bug after deciding to build a Harrier during covid to demonstrate an electronic jet engine simulation. Let the fun begin..
To be honest, I haven't quite figured out if these two interests belong in the same GitHub repo or not. But for now - they are all here!

Projects are often inspired by things found wild on the net, or ideas from the many great electronics and scale modelling podcasts and YouTube channels. Feel free to borrow liberally, and if you spot any issues do let me know (or send a PR!). See the individual projects for credits where due.