Diode Limiter

Limit both polarities of a signal with antiparallel diodes and a series resistor.

V1 applies a ±5 V, 1 kHz sine wave through R1 = 1 kΩ. D1 and D2 are antiparallel from the output to the return. Each diode conducts on a different polarity. RL = 100 kΩ is a light load.

$$|V_{\mathrm{out}}|\approx V_F\approx0.7\,\mathrm{V}$$ $$I_{R1}=\frac{V_{\mathrm{in}}-V_{\mathrm{out}}}{1\,\mathrm{k\Omega}}$$

The output flattens around ±0.7 V at large input amplitudes. At small amplitudes the diodes are nearly off and the output follows the input. A diode threshold is gradual and depends on current; it is not an exact hard switch.

Read the results. Vin is green, Vout red and the input-resistor current Iin blue. The current plot shows where the source supplies clipping current.

Model limits. Ideal bias and signal sources have unlimited current capability. R1 is essential for limiting current. Junction capacitance, reverse recovery, heating and source impedance are omitted.

Try it. Set V1 peak voltage to 0.2 V; the small signal passes with little limiting. Restore the original values after comparing the results.