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:
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:
|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.
Recommended construction order:
- top-side components:
- TVS1, next to Q1
- SMD passive components
- REF1 and Q2
- bottom-side components:
- D1, D2
- USB plug and socket
Credits and References
- Complete kit for the USB Port Protector - writtten up in Silicon Chip May 2018 p57
- μArt - a similar protection project but intended for UART applications, available on crowdsupply
- SK153 DIODE SCHOTTKY 30V 15A
- CDSOD323-T05S TVS DIODE 5V 13.5V
- AN431AN Shunt Voltage Reference
- ECH8102-TL Bipolar (BJT) Transistor PNP - high-current
- SM2T3V3A TVS diode
- BAT54S SCHOTTKY DIODE ARRAY
- ARRL Hands-on Radio (Vol 2)
- ARRL Hands-on Radio (Vol 2) Experiment 120: Power Polarity Protection
- ARRL Hands-on Radio (Vol 2) Experiment 121: Transient Protection