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Diode Clamper Circuits Applications and Types Comparison

Author: Apogeeweb Date: 21 Jul 2021  257

diode clamping circuit types

Introduction

Clamper circuit is a circuit that fixes a certain part of the pulse signal at a specified voltage value and keeps the original waveform shape unchanged. In other words, a clamper is an electronic circuit that changes the DC level of a signal to the desired level without changing the shape of the applied signal. 

What is Clamper Circuit?

Catalog

Introduction

Ⅰ Clamper Circuit Applications

Ⅱ Diode Clamper Circuit

2.1 Why Diode Clamper Circuit?

2.2 Diode Clamper Circuits Types

Ⅲ Experiment: Clamper Circuit Problems Detection


Ⅰ Clamper Circuit Applications

What are the uses of clampers? Clamper circuits are often used in various display devices, such as test equipment, amplifiers protection, sonar, and radar systems. For example, in oscilloscopes and radars, a clamper circuit is used to restore the DC component of the scanning signal to solve the problem of image position movement on the screen caused by the different scanning speed. In the TV system, a clamp circuit is used to keep the top of the sync pulse of the full TV signal at a fixed voltage to overcome the level fluctuation caused by the loss of the DC component or interference, so as to realize the separation of the sync signal. A simple clamper circuit comprises of a capacitor, a diode, a resistor and so on. Here we will introduce diode clamper circuits types and make comparisons among them.

 

Ⅱ Diode Clamper Circuit

2.1 Why Diode Clamper Circuit?

As we all known, the diode clipper circuit cuts the amplitude of the waveform. In some applications, the original waveform cannot be damaged. It is necessary to shift up or down on the basis to set the signal peak value at the required level. In this case, you need to use a diode clamp circuit.
A simple diode clamp circuit is composed of diodes, capacitors, and load resistors. Use of the relatively stable forward voltage drop of the diode, and the small value (sometimes can be approximated to zero) characteristics to limit the potential of a certain point in the circuit and maintain the top or bottom of the periodically changing waveform at a certain DC level.
In addition, the dual-diode clamper protection circuit is composed of two diodes in reverse parallel connection. Only one diode can be conducted at a time, and the other is in the off state, then the forward and reverse voltage drop will be clamped below 0.5-0.7 in the forward direction of the diode, so as to protect the circuit.

2.2 Diode Clamper Circuits Types

Diode clamper circuits are mainly divided into two categories: positive clamper circuits, and negative clamper circuits, including simple types and biased types.
✅Diode Positive Clamper
When the input waveform is in the positive half cycle, the diode is cut off, which is equivalent to an open circuit, and the capacitor is charged to Vi. In the negative half cycle of the input waveform, the diode conducts, which is equivalent to a short circuit, and the Vo output is 0. According to Kirchhoff's voltage law, the corresponding output waveform can be calculated according to the positive and negative cycle conditions.
(1) Simple Type

Diode Positive Clamper (simple)

Figure 1.

When Vi is in half negative cycle, D→ON, C are charged to the value of V (negative left, positive right), Vo=0V.
When Vi is half positive cycle, D→OFF, Vo=VC+Vi = 2V.
(2) Biased Type

Diode Positive Clamper (biased)

Figure 2.

A simple way to judge the output waveform:
1) The reference point of the output waveform on the coordinate axis is determined by the reference voltage V1.
2) The direction of the diode D determines which direction the original waveform moves. If the direction of the diode is Diode Direction (up), the waveform must move upward; if the direction of the diode is Diode Direction (down), the waveform must move down.
3) After deciding the reference point and direction, use the reference point as the benchmark and draw the original waveform on the output coordinate axis, which is what we want.


↪️Diode positive clamper circuits comparison:

Diode Positive Clamper Circuits Comparisons

 

✅Negative Clamper Circuit
(1) Simple Type

Diode Negative Clamper (simple)

Figure 3.

When Vi is in positive half cycle, D→ON, C is charged to the value of V, where Vo=0V.
When Vi is in negative half cycle, D→OFF, Vo=-2V.
(2) Biased Type

Diode Negative Clamper (biased)

Figure 4.

When Vi is in positive half cycle, diode D→ON, and C is charged to the value of V (positive left, negative right), Vo=+V1 or -V1.
When Vi is negative half cycle, diode D→OFF, RC time constant is large enough, Vo=VC+Vi (negative half cycle)=2V.


↪️Diode negative clamper circuits comparisons:

Diode Negative Clamper Circuits Comparisons

 

✅Summery
1) The direction of the diode determines the wave movement direction.
2) The bias voltage determines the basic reference point of the waveform.
3) The product RC of the capacitance and the load capacitance should be large enough, generally greater than 5T (T is the input waveform change cycle).

 

Ⅲ Experiment: Clamper Circuit Problems Detection

In terms of the application of clamping diodes, here gives an example experiment. When working on the Qualcomm MSM8909 platform, I often encountered electrostatic breakdown of the GPIO pins, which is EOS. Why is GPIO mentioned here? Because there is a diode clamper circuit in the internal circuit structure of GPIO, as shown in the figure below.

MSM8909 IC Application Circuit

Figure 5. MSM8909 IC Application Circuit

Let's analyze it.
The reference power supply VDD of the GPIO pulled up by the cathode of the clamper diode D1, and the anode of the clamp diode D2 is connected to GND.
When the output voltage is greater than VDD, D1 is turned on, D2 is turned off, and the voltage of Pin is VDD (ignoring the turn-on voltage drop of the diode).
When the input voltage is less than GND, D1 is off, D2 is on, and the voltage of Pin is GND (ignoring the conduction voltage drop of the diode).
Therefore, the input voltage range can be controlled between [GND, VDD] to protect Pin from damage. How to determine whether the GPIO is damaged? Methods as below:
First, adjust the multimeter to the diode position, connect the red lead to the GND of the motherboard and the black lead to test the GPIO pin. At this time, it is to measure whether the diode D2 is damaged. The test value is the conducted value of the diode, in the general range 0.4-0.6V, beyond which is the diode breakdown.
Secondly, connect the red lead to the test GPIO pin, and the black lead to GND. At this time, it is to measure whether the diode D1 is damaged.

 

Frequently Asked Questions about Clamper Circuits

1. What is clamper circuit and its types?
A Clamper Circuit is a circuit that adds a DC level to an AC signal. ... As the DC level gets shifted, a clamper circuit is called as a Level Shifter. Clamper circuits consist of energy storage elements like capacitors. A simple clamper circuit comprises of a capacitor, a diode, a resistor and a dc battery if required.

 

2. How do clamper circuits work?
A clamper is an electronic circuit that changes the DC level of a signal to the desired level without changing the shape of the applied signal. In other words, the clamper circuit moves the whole signal up or down to set either the positive peak or negative peak of the signal at the desired level.

 

3. What is diode clamper circuit?
A Clamper circuit can be defined as the circuit that consists of a diode, a resistor and a capacitor that shifts the waveform to a desired DC level without changing the actual appearance of the applied signal.

 

4. How many diode is used in clamper circuit?
For a clamping circuit at least three components — a diode, a capacitor and a resistor are required. Sometimes an independent dc supply is also required to cause an additional shift.

 

5. What is a clamping diode used for?
A clamp diode is where both characteristics of being applied in a circuit to manipulate the input voltage. Clamping diodes can function as a level shifter or can be used to guard components against transient voltages.

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