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If a loud sound spikes a microphone signal beyond the voltage limits of a sensitive microcontroller, the input transistors can permanently burn out. A clipping circuit (or voltage limiter) prevents this by cleanly slicing off voltage peaks above or below a set threshold without altering the rest of the signal.
How does a simple two-terminal component decide exactly when to let a waveform pass and when to cut it off?

The Diode as a Voltage-Controlled Switch

A standard silicon p-n junction diode acts like a one-way electrical valve. When reverse-biased (anode voltage lower than cathode voltage), it conducts virtually zero current and acts like an open switch.
When forward-biased with at least 0.7 V0.7\text{ V} across its terminals, it turns ON and maintains a nearly constant forward voltage drop (VF≈0.7 VV_F \approx 0.7\text{ V}), acting like a closed switch in series with a 0.7 V0.7\text{ V} opposing source.
What happens if we place a resistor in series with an AC input and connect a diode across the output terminals to ground?

Unbiased Positive Clippers

In a positive clipper, the diode is connected in parallel with the output load with its anode pointing to the signal line and cathode connected to ground.
During the positive half-cycle, once VinV_{\text{in}} exceeds +0.7 V+0.7\text{ V}, the diode turns ON and clamps the output to +0.7 V+0.7\text{ V}, dropping all additional input voltage across the series resistor RR.
During the negative half-cycle, the diode is reverse-biased (OFF), drawing no current, so the entire negative waveform passes through untouched (Vout=VinV_{\text{out}} = V_{\text{in}}).
What if you need to protect an integrated circuit that operates safely up to +5 V+5\text{ V} instead of clipping at +0.7 V+0.7\text{ V}?