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

Discussion in 'General Electronics Chat' started by Hooriya, Mar 13, 2016.

1. ### Hooriya Thread Starter New Member

Oct 4, 2015
5
0
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!

2. ### wayneh Expert

Sep 9, 2010
12,403
3,250
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?

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3. ### Alec_t AAC Fanatic!

Sep 17, 2013
5,980
1,138
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.

4. ### mcasale Member

Jul 18, 2011
210
12
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.

5. ### hp1729 Well-Known Member

Nov 23, 2015
2,105
235
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.

• ###### Design 679 13.8 V battery charger, test circuit.pdf
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6. ### #12 Expert

Nov 30, 2010
16,705
7,358
It could be this simple:

• ###### voltage limiter.png
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7. ### MrSoftware Active Member

Oct 29, 2013
545
133
This guy explains how to make your own power supply, including how to make your own current limiting circuitry:

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