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Comment by bschwindHN | Hacker News Reader

I needed to remotely power cycle some USB devices. These "smart hubs" are hard to find and I couldn't get the results I wanted on any hardware I had, so I made a PCB with a solid state relay on the 5V line - problem solved.

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Why a solid state relay rather than a MOSFET?

Transistors generally can't switch significant currents effectively. Also, they can't latch.

Uh, citation needed? A typical MOSFET is abundantly capable of switching several amps of current, orders of magnitude more than you'll find in a USB system.

Also, an SSR (whether MOSFET, IGBT, triac, or SCR based) doesn't latch either. Only some esoteric mechanical relays latch.

I had a similar requirement to OP, though my USB hardware was fine, it was a third party device that would sometimes fail to connect when the system restarted. A watchdog reset of the uC trivially reconnected my hardware, but I resorted to enabling/disabling the AHCI driver to force Windows to re-enumerate USB devices to get that to be reliable.

I was misinformed. Thanks for the correction.

Solid-state relays provide isolation between the control circuit and the load, which makes it easy to deal with voltage differences between those circuits, which happens frequently when there is some distance between them. Those relays can be built with MOSFETS or other doped semiconductor switches.

It was conceptually simpler to design for me, I'm not an electrical engineer but an SSR seemed like the most surefire way to make sure the circuits were isolated, and operation is really simple to reason about.

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