Rail Limit Clips Output - Electronic Circuits V & VI: Front-End Conditioning and Op-Amp Feedback Step by Step

A rail limit clips any ideal gain result that would exceed the declared output range, so the output is the smaller of the requested voltage and the rail. The examples map 6 V through gain 1/2 to 3 V and clip an 8 V request to a 5 V rail exactly for the ideal limiter model; real stages add rail headroom, saturation recovery, slew rate, loading, noise, supply variation, temperature drift, and voltage measurement uncertainty.

A rail-limited ideal gain output is clipped by the declared high rail. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.

highlighted = computed this step

Exact fractional gain is allowed

A gain of one half maps 6 volts to 3 volts.

V_{\text{out}} = \tfrac{1}{2}\cdot 6\ \text{V} = 3\ \text{V}

The declared rail limits the output

The unclipped result would be 8 volts, but the declared high rail is 5 volts.

\min(8\ \text{V}, 5\ \text{V}) = 5\ \text{V}