# Please Read! Any suggestions on how to make a current limiting circuitry?

#### Hooriya

Joined Oct 4, 2015
5
I am a student of Electrical Engineering and I am currently working on a biomedical device which stimulates a human arm through functional electrical stimulation technique. Now for instance, if something gets damaged in the circuit due to which a large amount of current starts flowing then, the human arm can get damaged. So, I want to make something like a breaker myself which will break the circuit right then.
I considered using a fuse but the problem with a fuse is that it will allow the current flow through to arm atleast once before cutting off the connection.
I want to make a limiting circuit that has a low foot print so that the device doesn't look too large. Could you please give me some suggestions?
Any help will be appreciated.
Thank you!

#### wayneh

Joined Sep 9, 2010
17,405
One solution: Include a low-ohms shunt resistor in the circuit, say 0.1Ω, rated for whatever wattage is appropriate for your circuit. While operating, there will be a small voltage drop across this resistor. You can set a comparator (LM339, for instance, 4 comparators in one IC) to watch that voltage. If it gets too high, indicating too much current, it could trigger and shut off your circuit. I might control a relay or a transistor acting as a switch. You would need it to latch, so it stays off until reset.

A downside of an active circuit like this is that it requires power. If you have DC power on board already, that may not be a problem.

What sort of current are you looking at? Maybe a low amp circuit breaker is appropriate?

#### Alec_t

Joined Sep 17, 2013
13,784
The answer may be as simple as using a resistor or two in series with whatever is supplying the stimulus to the arm. A fuse would be far too slow to operate. Have you researched what the maximum current should be, for safety reasons? It's surprisingly low.

#### mcasale

Joined Jul 18, 2011
210
As indicated, you need to provide us with maximum current (the trigger point), typical current, and what power supply voltage you are using.

Since this is hooked up to a person, you want it as simple as possible (hence reliable), and not have it rely on an MPU and software.

#### hp1729

Joined Nov 23, 2015
2,304
I am a student of Electrical Engineering and I am currently working on a biomedical device which stimulates a human arm through functional electrical stimulation technique. Now for instance, if something gets damaged in the circuit due to which a large amount of current starts flowing then, the human arm can get damaged. So, I want to make something like a breaker myself which will break the circuit right then.
I considered using a fuse but the problem with a fuse is that it will allow the current flow through to arm atleast once before cutting off the connection.
I want to make a limiting circuit that has a low foot print so that the device doesn't look too large. Could you please give me some suggestions?
Any help will be appreciated.
Thank you!
See attached schematic for a voltage source with current limiting. No voltage comparator, but that is a good idea. The current monitoring circuit sets a latch directly. Inserting a voltage comparator here gives you better control.

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#### #12

Joined Nov 30, 2010
18,224
It could be this simple:

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#### MrSoftware

Joined Oct 29, 2013
2,126
This guy explains how to make your own power supply, including how to make your own current limiting circuitry: