I have an old sensor that requires 200mA at 5v DC, but it does not have any overcurrent protections and will blow a capacitor if the current is too high. Is there some kind of current limiter circuit I can use to restrict the current flow into the sensor without reducing the supplied voltage? Electrical engineering is not my primary field, so I apologize if I’m missing something obvious.
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\$\begingroup\$ I don't know anything about your sensor (need details) but while it may be appropriate to use a current limit circuit (they just reduce the voltage so that the current limit is met) you may also want to study up on current-foldback circuits, as well. Either may be appropriate or inappropriate depending on details you haven't shared. So I'll leave you to think about both, as well as other suggestions (such as fast fuses, etc.) \$\endgroup\$– jonkNov 2, 2022 at 21:32
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1\$\begingroup\$ Your statement that "too much current" will "blow a capacitor" doesn't make sense. The sensor draws whatever current it draws, and capacitors don't just "blow" because of over-current (well, they can, but without context, it's a specious claim). Please explain in greater detail these fears of yours, preferably with a schematic. What exactly are you trying to protect, and why do you think current might get out of control? \$\endgroup\$– Simon FitchNov 3, 2022 at 2:22
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3 Answers
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The sensor should draw only the current it needs from the supply when it is connected. There is no need to add external current limiting. See: Choosing power supply, how to get the voltage and current ratings?
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If you must protect this sensor, then use a fuse rated at slightly higher than 0.2A (200mA), such as 0.3A. These are certainly made, and will prevent any more current than that from reaching the sensor.
Of course, it does this by burning out, which creates an open-circuit and thus reduces the supplied voltage to zero. But the sensor is not damaged (further, if it failing caused the fuse to pop in the first place.)
There also exist "poly resettable" fuses, which look nothing like a fuse but will open when current is exceeded. These work by heating up slightly, which makes them an open circuit. After awhile, they cool off, then close, sort-of like a slow switch. So in that sense, they can protect the sensor while being self-resetting.
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Is there some kind of current limiter circuit I can use to restrict the current flow into the sensor without reducing the supplied voltage?
No, for a simple sensor/device you can only reduce current by reducing voltage as per ohm's law.
However, if your sensor was so designed that it consumed a fixed amount of power then, you could increase the supplied voltage in order to reduce the current. However, it's unlikely that a sensor will do that but, not as impossible as reducing the current without changing the sensor voltage.
