Diode Clipping Circuits

Also known as diode crushing circuits, the diode limiteris a waveforming circuit that takes two halves by cutting the lower or upper part of the input waveform.

Trimming the input signal produces an output waveform that resembles a flattened version of the input.For example, the half-wave rectifier is a cutting circuit, as all voltages below zero are eliminated.

However, diode clipping circuits can be used in a variety of applications to provide extreme voltage protection using zener diodes to change an input waveform using signal and Schottky diodes, or to ensure that the output voltage never exceeds a certain level.Then, if necessary, diode clipping circuits can be used in voltage limiting applications.

In the training of Signal Diodes, we found that when a diode is forward polarized, it compresses the voltage, allowing the current to pass through itself.When the diode is inverted, the current does not pass through it and the voltage in its terminals is not affected, and this is the basic process of the diode clipping circuit.

Although the input voltage to the diode clipping circuits can have any waveform, here we will assume that the input voltage is sinusoidal.

Positive Diode Clipping Circuits

diode clipping circuits

In this diode clipping circuit, the diode is polarized forward during the positive half cycle of the sinusoidal input waveform (the anode is more positive than the cathode).In order for the diode to be advanced polarization, the input voltage size must be greater than +0.7 volts (0.3 volts for a germanium diode).

When this happens, the diodes begin to transmit and keep the voltage on itself constant at 0.7V until the sinusoidal waveform falls below this value.Thus, the output voltage received through the diode can never exceed 0.7 volts during a positive half cycle.

During the negative half cycle, the diode is inverted (the cathode is more positive than the anode) and prevents the current from passing through itself, and as a result, it has no effect on the negative half of the sinusoidal voltage that passes unchanged to the load.Thus, the diode limits the positive half of the input waveform and is known as a positive cutting circuit.

Negative Diode Clipping Circuits

diode clipping circuits

The positive diode is the exact opposite of the clipping circuit.The diode is inclined forward during the negative semi-cycle of the sinusoidal waveform and limits or trims it to –0.7 volts while allowing the positive semi-cycle to pass unchanged at reverse polarization.Since the diode limits the negative half-cycle of the input voltage, this is called a negative interrupt circuit.

Trimming Both Half Cycles

diode clipping circuits

If we connect the two diodes in reverse parallel, as shown, then both positive and negative half-cycles are trimmed because diode D2 cuts the negative half-cycle of the diode D1 sinusoidal input waveform.Diode clipping circuits can then be used to cut positive half cycle, negative half cycle or both.

For ideal diodes, the above output waveform will be zero.However, due to the forward voltage drop along the diodes, the actual trimming point occurs at +0.7 volts and –0.7 volts, respectively.However, we can raise this ±0.7V threshold to any value we want up to the maximum value of the sinusoidal waveform (VPEAK), or we can create 0.7 volt multiples by connecting more diodes together in series.

Pole/Polar Diode Clipping Circuits

To produce diode clipping circuits for different levels of voltage waveforms, a pre-voltage, VBIAS is added in series with diode to produce a combination clipr as shown.Before the diode becomes advanced polarized enough to transmit, the voltage in the series combination should be greater than VBIAS + 0.7V.For example, if the VBIAS level is set to 4.0 volts, the diode must be greater than 4.0 + 0.7 = 4.7 volts for the sinusoidal voltage in the anode terminal to be polarized forward.Any level of anod voltage above this polar point is trimmed.

Positive Polar Diode Clipping

diode clipping circuits

Similarly, by reversing the diode and battery pre-charge voltage, a diode is maintained at –V BIAS – 0.7V, as shown when it executes the negative half-cycle of the output waveform.

Negative Polar Diode Clipping

diode clipping circuits

Your diodesa variable diode clipping or diode limitation level can be obtained by changing the polarity voltage.If both positive and negative half loops are to be trimmed, a two-sided crop diode is used.However, for both positive and negative diode trimmingthe polarity voltage does not have to be the same.The positive polar stress can be at one level, for example, 4 volts and negative polaration voltage, for example, 6 volts, as shown.

Diode Clipping at Different Polar levels

diode clipping circuits

When the voltage of the positive half loop reaches +4.7 V, the D1 diode transmits and limits the waveform at +4.7 V. Diode D2 does not transmit until the voltage reaches -6.7 V. Therefore, all positive voltages above +4.7 V and negative voltages below –6.7 V are automatically interrupted.

The advantage of polar diode clipping circuits is that the output signal prevents the input waveform, which can be an input from a noisy sensor or a power supply's positive and negative supply rails, from exceeding preset voltage limits for both half cycles.

If the diode clipping levels are set too low or the input waveform is too large, then eliminating both waveform vertices can result in a square waveform waveform.

Zener Diode Clipping Circuits

The use of polar voltage means that the amount of the cropped voltage waveform can be accurately controlled.But one of the main drawbacks of using voltage-based diode clipping circuits is that they need an additional EMF power supply, which may or may not be a problem.

An easy way to create side-sided diode clipping circuits without the need for an additional emf source is to use zener diodes.

As we know, zener diode is another type of diode specially manufactured to work in the reverse pole fault zone and therefore can be used for voltage regulation or zener diode trimming applications.In the forward zone, zener acts like an ordinary silicon diode with an advanced voltage drop of 0.7V (700mV) during transmission.

However, in the reverse polarity zone, the voltage is blocked until the refractive voltage of the zener diodes is reached.At this point, the reverse current passing through the zener increases sharply, but the zener voltage, VZ , zener current throughout the device, remains constant even if IZ changes.

Then, using them to trim a waveform as shown, we can turn this zener action into a good effect.

Zener Diode Clipping Circuit

diode clipping circuits

The Zener diode acts as a polarizer diode clipping circuit whose polarity voltage equals the zener fault voltage.In this circuit, during the positive half of the waveform, the zener diode is inverted, so that the waveform zener voltage is trimmed in VZD1.During a negative half-cycle, zener behaves like a normal diode with a normal connection value of 0.7V.

We can further develop this idea by using reverse voltage characteristics of zener diodes to trim both halves of a waveform using series-linked zener diodes, as shown.

Full Wave Zener Diode Clipping Circuit

diode clipping circuits

The output waveform of full wave zener diode clipping circuits is similar to that of the previous voltage polarity diode clipping circuit.The output waveform will be trimmed at a 0.7V forward voltage drop of zener voltage plus other diode.Therefore, for example, the positive half-loop will be trimmed in the sum of the zener diode, ZD1 plus ZD2to 0.7V, and for the negative half loop it will be the opposite.

Zener diodes are produced in a wide voltage range and can be used to give different voltage references in each half cycle as above.Zener diodes are available with VZ, typically 1 or 5 zener failure voltages ranging from 2.4 to 33 volts.

Summarize

In addition to being used as a rectifier, diodes can also be used to crop the top or bottom of a waveform at a certain DC level or both and transmit it to the output without distortion.In the examples above, we assumed that the waveform was sinusoidal, but in theory any shaped input waveform can be used.

Diode Clipping Circuits are used to produce new waveforms from an existing signal, such as eliminating amplitude noise or voltage spikes, taking the square of the vertices of a sinusoidal waveform to achieve voltage regulation or a rectangular waveform as seen above.

The most common application of diode clipping circuits is a flywheel or free-rotating diode that connects in parallel along an inductive load to protect the switching transistor from reverse voltage transitions.