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A Simple Current Limiter
There are many applications where some form of current limiting is needed. There are a variety of
ways to do this with circuitry. For example, here are two common methods.
http://www.radio-electronics.com/info/circuits/transistor_current_limiter/transistor_current_limiter.php
http://www.vidisonic.com/2008/07/10/current-limiting-circuit/
These are nice techniques, but if what you want is a simple, effective way to limit current without having
to design a particular circuit implementation, here is a good way to do it.
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This macro uses an NTIOFV (Nonlinear Table I of V source) to limit the current to IMAX when the
voltage across the device exceeds VMAX.
The default values are set to a common set for power systems.
The 1E15 ohm resistance serves as a convergence aide and can be eliminated if its fA of current leakage
is a problem in your application. A high-valued resistance across a current source will often help
convergence.
Here is a test circuit to be run in DC analysis to demonstrate the transfer function of the device.
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Here is the DC analysis showing the current limiting transfer function. As you can see, the device clips
currents in both positive and negative directions to +-IMAX.
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Here is a circuit to demonstrate the use of the current limiter.
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X1 is the current limiter macro and the area encircled in green is the circuitry whose input current is
being limited. The bottom waveform in the transient analysis of this circuit shows the current through
V3 and thus through the X1 limiter.
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