Monday, 7 August 2017

Do voltage-limiting resistors exist?


I see sometimes that resistors are specified as current-limiting resistors, so I decided to see if voltage-limiting ones exist. When I do a search though, I don't see anything mentioning voltage-limiting resistors.



Answer



A voltage source is theoretically capable of supplying an infinite current into a short circuit hence if a series resistor is used then that short circuit current becomes amps or milliamps rather than infinite amps.


A current source, on the other hand, will not be affected by a series resistor at all - it will continue to produce whatever voltage is needed into an "open circuit" resorting to making a sustained electrical arc to create a conductive path if necessary. In these circumstances a parallel resistor will restrict the open circuit voltage because it will conduct the current back to the other terminal of the current source.


So, in short, a resistor can be a voltage limiting AND a current limiting device.



I see sometimes that resistors are specified as current-limiting resistors




They are not specified as such i.e. a resistor isn't to be regarded as a current limiting resistor rather, it is the function it plays in the target circuit that may be described as "current limiting".


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