Summary： The article is about positive clipper circuits as used in power electronic boards and circuits.
In power electronics, engineers sometime would like to reject part of the specified wave while allowing part of it to pass. This action requires the design of a special circuit known as a clipper circuit. A Clipper circuit is a circuit that rejects a section of a specified input signal while allowing a remaining portion to pass through. The part of the wave below or above the cut-off output voltage is known as cut-off or clipped-off. Standard clipping circuits consist of both linear and non-linear components such as diodes and resistors with the absence of energy-storing elements such as resistors. Clipping circuits are very significant in the area of power electronics in that they help in:
There exist several types of clippers and one of them is the diode clipper. There exist positive diode clippers and negative diode clippers. In this clipper circuit part 1, we are going to focus on the positive clipper circuit, and in part 2, we shall dwell on the negative clippers. Let us dive deeper into the actual content!
The intention of designing this type of clipper circuit is to attenuate the positive part of the power system input signal. There exist several types of positive clippers as listed and discussed below:
This type of clipper has a diode connected in series with the input voltage signal to attenuate all the positive waveform portions.
The Circuit Diagram of the Positive Series Clipper
Figure 1:Positive Series Clipper
Positive Input Cycle
On inputting a positive signal, the circuit’s point A becomes positive concerning the circuit’s point B. The action reverse-biases the diode, which behaves similarly to an open electric switch. This effect makes the voltage across the connected load zero because zero current flows through. Therefore, the output voltage VO is zero.
Negative Input Cycle
On the other hand, when the input signal is negative, point A goes negative concerning point B. The action makes the diode forward-biased and hence starts conducting just like what happens with an open switch. The action makes the voltage across the connected load resistor equal to the voltage supplied at the input. Therefore, Vo is equal to Vi.
The Waveforms of the Positive Series Clipper
Figure 2: Positive Series Clipper Waveforms
From the discussion of Figure One, we can deduce that only the positive side of the input signal was clipped. This can be explained further using the waveforms above. Unlike what happens in the ideal waveform, practically, some positive waveforms are observed due to 0.7V which represents the conduction voltage of the diode. This is what creates the difference observed in the ideal and practical waveforms of the output signals.
This is a clipper circuit where a diode is connected in series with a supply signal and biased using a positive reference voltage and it performs attenuation of the waveform’s positive portion.
Circuit Diagram
Figure 3:Positive Series Clipper with Positive Vr
The input’s positive cycle reverse-biases the diode and the reference voltage Vr is detected at the circuit output. In the process of the negative signal cycle, the diode becomes forward-biased and it starts conducting hence giving out a waveform shown below.
Figure 4:Input and Output Waveforms of Positive Series Clipper with Positive Vr
This is an electrical clipper circuit that has a diode that is connected in series with the input signal where the biasing is achieved using a negative reference voltage and it serves the purpose of attenuating the waveform’s positive portion. See the Figure 5 below:
Figure 5:Positive Series Clipper with Negative Vr
During the input positive cycle, the diode operates in reverse mode making the reference voltage appear at the output. This reference voltage is negative and the exact voltage with its constant amplitude appears at the work. On applying negative input the diode becomes forward-biased and it conducts just like a closed switch does. Hence, on positive information, an input signal which is more than the reference voltage signal is observed at the circuit output.
Below are the waveforms of the input and output for a practical system.
Figure 6:Waveforms for Positive Series Clipper with Negative Reference Voltage, Vr
This is a clipper circuit in which the diode connection is in shunt with the input electric signal and it still attenuates the waveform positive portion.
Circuit Diagram
Figure 7:Circuit Diagram of the Positive Shunt Clipper
Positive Input Cycle
Applying an input to the circuit makes point A marked on the circuit above positive when compared to point B. The effect is that the diode is forward-biased hence conducting like a close switch. The voltage that goes across the load goes to zero since we have no current flowing through it. In other words, VO is zero.
Negative Input Cycle
During the negative cycle at the input, point A becomes negative as compared to point B. The diode becomes reverse-biased and it operates like an open switch thus the voltage that goes across the load is equal to the voltage at the input. That is to say that Vi is equal to VO.
The Waveforms
Figure 8:Positive Shunt Clipper Waveforms
Unlike what is observed on the ideal waveform, practically, a bit of positive cycle portions are present and this is caused by the 0.7V which is the conduction voltage of the diode.
Here the diode is connected in shunt with the input signal and the biasing is done using a positive reference voltage.
The circuit is connected as shown below.
Figure 9: Circuit Diagram of Positive Shunt Clipper with Positive Reference Voltage, Vr
Here the diode is connected in shunt with the input signal and the biasing is done using a negative reference voltage.
The circuit connection is done as shown below.
Figure 10: Circuit Diagram of Positive Shunt Clipper with Negative Reference Voltage, Vr
· In part 2 of the clipper, circuits we shall look at the negative clipper circuits.
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