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Principle parameters of TVS diode
Publish：SHENZHEN ENXIC ELECTRONICS CO., LTD,Schottky diodes, rectifier diodes, fast recovery diodes, switching transistors, thermistors, MOS tube, TVS tube, Youze Electronics Time：2017-12-22 Views:1049
Transient voltage suppressor, also called TVS diode, is a diode type high efficiency protection device. When the two poles of the TVS diode are subjected to an inverse transient high energy shock, it can change the high impedance between the poles of the two poles to a low impedance at a rate of 10 minus 12 seconds, and absorb the surge power of up to several kilowatts. The voltage of the two poles is clamped to a predetermined value, and the precision components in the electronic circuit are effectively protected. Damaged by a variety of surge pulses.
The positive inrush current of TVS diode can reach 50 to 200A under the condition of TA=250C and T=10ms. The bidirectional TVS can absorb the instantaneous large pulse power in the positive and negative two directions, and clamp the voltage to the predetermined level. The bidirectional TVS is suitable for the AC circuit, and the unidirectional TVS is generally used in the DC circuit. It can be used for lightning protection, overvoltage protection, anti-interference, and surge power absorption. It is an ideal protection device. Tolerance is expressed by Watt (W).
The main electrical parameters of the TVS diode
(1) breakdown voltage V (BR)
In the area where the device is broken down, the voltage at both ends of the device is known as the breakdown voltage under the prescribed test current I (BR). In this area, the diode becomes a low impedance path.
(2) maximum reverse pulse peak current IPP
In reverse operation, the maximum peak current allowed by the device is under the specified pulse condition. The product of IPP and the maximum clamp voltage VC (MAX) is the maximum value of transient pulse power.
The TVS should be selected correctly when used, so that the rated transient pulse power PPR is greater than that of the maximum transient surge power that may occur on the protected device or line.
Application of TVS diode
The TVS diode is generally parallel to the protected circuit. In order to limit the current flowing through the TVS tube not more than the peak current allowed by the tube, IPP, the current limiting elements, such as resistance, self recovery fuse, inductor, etc., should be connected to the line. TVS diodes are widely used in computer systems, communication equipment, AC / DC power, automotive, electronic ballasts, household appliances, instruments (meter), common mode / differential mode protection, RF coupled /IC drive receiving protection, motor electromagnetic wave interference suppression, audio / video input, sensor / transmission, industrial control circuit, and relay. Various fields such as the suppression of the noise of the contactor and the contactor.
Characteristics of transient voltage suppression diodes
(1) the addition of the TVS diode to the signal and the power line can prevent microprocessors or singlechip from failure due to the instantaneous shock, such as the electrostatic discharge effect, the surge of AC power supply and the noise of the switching power supply.
(2) the electrostatic discharge effect can release more than 10000V and more than 60A, and can continue 10ms; and the general TTL device, when it meets the 10V pulse of 30ms, will lead to damage. The use of TVS diode can effectively absorb the pulse that will cause device damage, and eliminate the interference caused by switches between buses (Crosstalk).
(3) TVS diode can be placed between signal line and ground to avoid unnecessary noise from data and control buses.
The selection technique of TVS diode
(1) determine the maximum DC or continuous working voltage of the protected circuit, the rated standard voltage of the circuit and the "high end" tolerance.
(2) TVS rated reverse turn off VWM should be greater than or equal to the maximum working voltage of the protected circuit. If the selected VWM is too low, the device may enter the avalanche, or the reverse leakage current is too large, which will affect the normal operation of the circuit. The serial connection is divided into voltage, parallel connection and current division.
(3) the maximum clamping voltage VC of TVS should be less than that of the protected circuit.
(4) in the specified pulse duration, the maximum peak power consumption PM of TVS must be greater than that of the peak pulse power that may occur in the protected circuit. After determining the maximum clamping voltage, the peak pulse current should be larger than the transient surge current.
(5) for the protection of data interface circuit, we must also pay attention to selecting TVS devices with suitable capacitance C.
(6) choose polarity and packaging structure of TVS according to its purpose. It is more reasonable to choose bipolar TVS for AC circuit, and TVS array is more favorable for multi line protection.
(7) temperature consideration. Transient voltage suppressor can operate between -55 C to +150 C. If TVS is required to work at a changing temperature, because its reverse leakage current ID increases with the increase of the temperature, the power consumption decreases with the increase of TVS junction temperature. From +25 to +175, the linear drop of 50% rain breakdown voltage VBR increases with a certain coefficient with the increase of temperature. Therefore, we must consult the relevant product information and consider the influence of temperature change on its characteristics.
The best way of instantaneous pulse element damage is the instantaneous current away from the sensing element processing. The TVS diode is parallel to the protected line on the circuit board. When the instantaneous voltage exceeds the normal operating voltage of the circuit, the TVS diode produces an avalanche, which is provided to the instantaneous current with an ultra low resistance path. The result is that the instantaneous current through the diode is opened, avoiding the protected element, and before the voltage is restored to the normal value. The protected loop keeps the cut-off voltage. When the instantaneous pulse ends, the TVS diode automatically returns the high impedance state, and the whole circuit goes to the normal voltage. When many components are subjected to multiple shocks, their parameters and properties will degenerate, and the diodes will not be damaged or degraded as long as they are working in a limited range.
From the above process, we can see that when choosing TVS diodes, we must pay attention to the following parameters.
1. minimum breakdown voltage VBR and breakdown current I R. VBR is the minimum breakdown voltage of TVS, and it will not produce avalanche when TVS is below 25. When TVS flows through the specified 1mA current (IR), the voltage applied to the TVS poles is the smallest breakdown voltage V BR. According to the discrete degree of VBR and standard value of TVS, VBR can be divided into 5% and 10% two kinds. For 5% of VBR, V WM =0.85VBR; for 10% of VBR, V WM =0.81VBR. In order to meet IEC61000-4-2 international standards, the TVS diode must reach the ESD impact that can handle the minimum 8kV (contact) and 15kV (air), and some semiconductor manufacturers use higher anti impact standards on their products. For some portable applications with special requirements, designers can choose components as needed.
2., maximum reverse leakage current ID and rated reverse shut off voltage VWM. VWM is a voltage that the diode can bear in normal state. This voltage should be greater than or equal to the normal working voltage of the protected circuit, otherwise the diode will continue to cut off the circuit voltage; but it needs to be close to the normal working voltage of the protected circuit, so that the whole loop will not face the overvoltage threat before the TVS work. . When the rated reverse cutting voltage VWM is added to the two poles of the TVS, it is in a reverse state, and the current passing through it should be less than or equal to the maximum reverse leakage current of ID.
3., the maximum clamping voltage VC and the maximum peak current I PP. When the pulse peak current IPP of 20ms duration flows through TVS, the maximum peak voltage at both ends is VC. V C and IPP reflect the ability of TVS to suppress the sudden wave. The ratio of VC to VBR is called clamping factor, which is usually between 1.2~1.4. VC is the voltage provided by the diode in the cut-off state, that is, through the voltage of the TVS when the ESD is impacted, it can not exceed the tolerable limit voltage of the protected circuit, otherwise the element will be in danger of being damaged.
4. Pppm rated pulse power, which is based on the maximum cut-off voltage and the peak pulse current at this time. For handheld devices, TVS of 500W is generally enough. The maximum peak power consumption PM is the maximum peak power consumption TVS can withstand. Under the maximum clamping voltage, the larger the power PM is, the greater the surge current will be. Under the specific power consumption of PM, the lower the clamp voltage VC, the greater the capacity of its surge current. Besides, peak pulse power is also related to pulse waveform, duration and ambient temperature. Moreover, the transient pulse that TVS can withstand is not repeated. The pulse repetition frequency (the ratio between duration and intermittent time) is 0.01%. If repetitive pulse occurs in the circuit, the accumulation of pulse power should be considered, which may damage TVS.
5.: C capacitor. The measure of C capacitance is determined by the TVS avalanche junction section, is measured at the frequency of 1MHz under specific. The size of C is directly proportional to the current endurance of TVS. Too much C will cause signal attenuation. Therefore, C is an important parameter to select TVS for data interface circuit. The higher the frequency of the data / signal frequency of the
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