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Home > Mall Dynamic > Analysis Of The Working Principle, Circuit And Function Of Clamp Diode (TVS)
As we all know, a diode is a semiconductor made of a PN junction. When the positive voltage is connected to the anode and the negative cathode, the diode is said to be forward biased. As long as the applied voltage is greater than the junction voltage, usually 0.7V, current will flow through the diode.But what if the voltage is applied in the opposite direction? Under negative bias, as long as the voltage at both ends does not exceed the breakdown voltage, the diode will be in a non-conducting state. In this state the diode acts as an open circuit because the reverse-biased PN junction prevents electrons from flowing through. The clamp diode is where these two characteristics are applied in the circuit to manipulate the input voltage, so the clamp diode can be used as a level converter and can also be used to protect the component from transient voltages.
A clamp represents a limiting voltage in a circuit, and a clamp diode is a diode used to limit the potential at a point in the circuit.
Under normal circumstances, the potential connected to one end of the clamp diode must be constant voltage, that is, assuming that the potential of the end is unchanged, as a reference potential end. The other end is the clamp end, and its potential occurs
Fetishization is the end that needs to be limited.
The clamping action of the diode forces the potential of the clamping end to the reference end, which is called clamping.
The difference between clamping and voltage regulation is that clamping is to limit the potential at a certain point so that it is not greater than or less than the value of the reference end, the potential at the point is variable, and it is the positive use of the diode
Conduction characteristics for clamping. Voltage regulation is to stabilize the potential at a certain point at a constant value, the potential is unchanged, is to use the reverse breakdown characteristics of the diode to stabilize the voltage.
In the circuit, clamping refers to the voltage control within a fixed voltage range, and the diode is characterized by a single pilot. When it is turned on forward, it has a fixed voltage drop. Zener diodes are characterized by reverse breakdown, positive pilot diodes and reverse breakdown Zener diodes can be used in the design of clamping circuits, diodes for dislocation circuits called clamping diodes, different clamping applications use different diodes.
In the overvoltage protection circuit, a clamping circuit with a Zener diode can be designed.
In the 12V overvoltage protection circuit shown below, a 12V voltage regulator diode is used for clamping. When the input voltage is less than or equal to 12V, the PNP transistor Q2 shuts off the PMOS(Q3) tube, and the VCC obtains normal power supply. When the input voltage rises to 12.5V or above, due to the clamp of the 12V voltage regulator diode, the base of the PNP transistor will control the voltage at 12V, and Q2 will start to switch on, causing the PMOS(Q3) to turn off and the VCC power to stop.
The addition of clamping diodes can protect the input and output ports of the single chip microcomputer. As shown in the figure below, two Schottky diodes are added as clamping diodes, which can effectively prevent the GPIO from being broken down by electrostatic. When the electric music is large VDD, D1 is connected, and static electricity is released to VDD through D1: When the electric music is small, D2 is connected, and the electricity is placed to the GND through D2. Due to the need for rapid static electricity release, generally choose a Schottky diode or a fast switching diode as the clamping diode.
The clamp diode is actually a TVS tube, which is short for transient suppression diode. It is developed on the basis of voltage regulator diode, voltage regulator diode is a new type of high performance protection device in the form of diode, that is, voltage limiting overvoltage protection device.
TVS usually uses diode type axial lead package structure, also has SMD, the core unit of TVS is the chip, the chip has a unipolar and bipolar two structures, unipolar TVS has a PN junction, bipolar TVS has two PN junction. The unipolar type provides protection against wave voltage shocks in only one direction
Transient diode can prevent the opposite polarity of the surge voltage impact, equivalent to two reverse series of voltage regulators, its outstanding characteristics are low breakdown voltage, response time tens of ps, small leakage current, large transient power, no noise, etc., so in the signal system has been widely used and recognized.
Let's take a look at how the following two diodes work in reverse series. As shown in Figure d1 and d2, the two diodes are in series in reverse, which belongs to the clamp protection circuit, and the clamp is used to take the zero signal. In the clamp circuit, the negative electrode of the diode is grounded, and the positive circuit is clamped below the zero potential. When working, only one diode can be switched on, and the other is in the cut-off state, then its forward and reverse voltage drop will be clipped to the diode on-voltage drop of 0.5-0.7(plus the on-voltage drop is this), so as to protect the circuit.
The following figure shows the voltage-current characteristics of TVS tubes. Under the action of surge voltage, when the voltage between the poles of TVS tube rises from the rated reverse turn-off voltage VWM to the breakdown voltage VBR, the [VS tube electrode repulsion is broken down, and the breakdown current occurs, so the current flowing through the IVS tube will reach the peak pulse current! PP, the voltage at both ends is also mislocated below the predetermined maximum aluminum potential voltage VC. Then, with the exponential attenuation of pulse current, TVS tube electrode, voltage continues to decline, and finally return to the initial state, which is the TVS tube to suppress the surge current pulse power, protect electronic devices principle.
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