I want to design a safety circuit for a battery powered device which measures human body impedance. It is intended to be powered only by an external battery pack (5V) via a USB cable. But I want to make sure that even if device is connected to wrong power supply by mistake (e.g. a faulty USB charger leaking 230V), the user is safe. I am also limited in PCB size. What kind of circuit or IC should I look for this purpose? I couldn't find any regulators that can tolerate such high input voltage.
Electronic – User safety for battery powerd device against misuse of power supply
biopotentialpower supplysafety
Related Solutions
Many novices seem to want to measure the current output capability of power supplies by setting their meter to read current, then connecting it directly across the power supply terminals. YOU MUST NEVER CONNECT AN AMMETER DIRECTLY ACROSS A POWER SUPPLY Doing so will cause very large currents to flow, and may permanently damage the meter, power supply, or user!
If you keep the meter in voltage mode, and are careful to not short the test leads or power supply wiring, you should be able to measure the supply voltages without any hazard.
Many PC power supplies (and other switch-mode supplies) require a minimum load to operate correctly. Be sure you have a suitable load connected during your tests (or any time the supply is on.)
Cover your USB connector with a pre-cut piece of Kapton tape that glues down on the top and folds over the sides and back, like so:
The photo is from Sparkfun and this article describes the solution in more detail.
Best Answer
You need to study isolation. If you put a USB connector on the device, you'll need two means of patient protection, 5kV of isolation, and 250V working voltage to be medically safe. There are isolated DC-DC modules available. All of this is contained in IEC-60601. Study it. People are killed by designers that don't follow the rules.