# High voltage, low current fuse-type device?

#### DMAERO

Apr 21, 2014
1
Hello,

I'm looking to use a device that would function as a fuse. However, I need a device to withstand high voltage (~5 kV), but to limit the current to ~40 mA. I've found fuses that can limit in the mA range, however the max voltage is in the V range. I've also found high voltage fuses, however they limit in the A range. Does anyone know of anything that would work for my specifications?

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,510
What is the source of the 5kV? Assuming you use some sort of lower voltage (ac or DC) to drive a circuit which generates this, perhaps you can limit the input current to this, and hence the output power.

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,510
Another option is to place an optocoupler set up as a current sensor (or indeed any other type of current sensor which has the required isolation) in the output and then to additionally regulate the maximum output current.

The simplest version of this is simply an optocoupler across a resistor so that at 40mA the required Vf for the optocoupler (say 1.8V) is exceeded (this would be a resistor of approximately 45 ohms. In a practical circuit you would probably do something a little more complex than this (for both performance and protection), but that's the general principle.

5000W at 40mA -- that's a fair amount of power.

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