Master the Basics: Protect Against Large Singnals

Some electronic circuits are highly sensitive and can be damaged by signals that exceed a certain voltage range. Just like loud noises can hurt your ears, a large voltage spike can harm delicate components. That’s where clipper circuits come in.

What Is a Clipper Circuit?

A clipper is a protective circuit that limits the amplitude of a signal. It “clips off” parts of a signal that go beyond a predefined voltage threshold—either above, below, or both—keeping the output within a safe voltage range.

Clipper circuits are used in applications like audio systems, where an amplifier’s output could become too strong and damage an analog-to-digital converter (ADC). By inserting a clipper between them, you can protect the ADC from being overloaded.

Clipping Negative Voltages

A basic negative clipper uses a diode and resistor in series:

• When the input voltage is positive, the diode stays off and the signal passes through.

• When the input swings negative past the diode’s forward voltage (typically ~0.6V), the diode conducts and limits the output.

This keeps the output from dropping below –0.6V.

Clipping Positive Voltages

To clip positive voltages instead:

• Reverse the direction of the diode.

• This limits the output to no more than +0.6V, while allowing the negative portion of the signal to pass freely.

Dual-Direction Clipping

To protect against both high and low voltages, use two diodes facing opposite directions:

• When the input exceeds ±0.6V, one of the diodes conducts and limits the voltage.

• This keeps the output range safely between +0.6V and –0.6V.

Demonstration

On an oscilloscope:

• The input signal (yellow) is a 10V peak-to-peak sine wave.

• The clipped output (blue) stays within ±0.6V, as expected.

Smaller signals pass through unchanged, while larger signals get clipped.

Extending the Clipping Range

You’re not limited to the diode’s built-in voltage drop:

• By adding bias voltages, you can set custom clip limits.

• Example: A 1.4V source in series with a diode gives a +2V clipping threshold.

• A –2.4V source with an upward diode gives a –3V clipping threshold.

In real-world designs, these reference voltages are often generated using voltage regulator circuits or precision references, rather than separate power supplies.

Key Takeways

Clipper circuits are simple, powerful tools for protecting sensitive electronics from large or damaging signals. Whether you're working with audio, analog sensors, or ADCs, a properly designed clipper can ensure your components stay safe. By using diodes, resistors, and bias voltages, you can tailor the clipping behavior to your project’s exact needs.