#400 USBProtector

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

Build

Notes

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.

Schematic

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

Construction

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:

kit_parts

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

USBProtector_build_front

USBProtector_build_rear