Figure 1.  Schematic Diagram for an Inverting Clipper Circuit

This is a circuit whose output is an inverted copy of its input waveform, with all portions exceeding preset lower and upper limits 'clipped', hence the name 'clipper'.  The lower and upper voltage limits are set by the zener breakdown voltages of zener diodes DZ1 and DZ2. For instance, if the zener diodes used have a zener voltage of 5 V, then any part of the input waveform that exceeds -5V/+5V is clipped at -5V/+5V.

The circuit uses a 741 operational amplifier IC configured as an inverting amplifier, except that a pair of back-to-back zener diodes is connected across the feedback resistor R2. This pair of zener diodes prevents the voltage across R2 from going beyond the zener voltages of the diodes in either direction.

During the positive cycle of the input waveform, the output varies as its 'negative' copy, with DZ1 always conducting and DZ2 'off' as long as the output does not exceed DZ2's zener breakdown voltage. If the output's negative value exceeds DZ2's zener breakdown voltage, DZ2 starts conducting, thereby 'clipping' the output waveform at this breakdown voltage level.  The output starts varying as a negative copy of the input waveform again its negative value goes below this limit. 

The same phenomenon happens during the input's negative cycle, except that the output is now varying as a 'positive' copy of the input with the roles of DZ1 and DZ2 reversed, i.e., DZ2 is always conducting while DZ1 'clips' the output waveform every time its level exceeds DZ1's zener breakdown voltage.  

See Also:  Non-inverting Clipper Circuit

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