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What does Transient Suppression Diode TVS Transient Suppression Diode TVS mean

Time:2023-10-02 Views:648
What does Transient Suppression Diode (TVS)/Transient Suppression Diode (TVS) mean?
    Transient Suppression Diode (TVS), also known as Clamping Diode, is a high-efficiency circuit protection device commonly used internationally. Its appearance is the same as ordinary diodes, but it can absorb up to several kilowatts of surge power. Its main feature is that under reverse application conditions, when subjected to a high-energy large pulse, its working impedance immediately drops to an extremely low conduction value, allowing large currents to pass through, Simultaneously clamping the voltage at a predetermined level with a response time of only 10-12 milliseconds can effectively protect precision components in electronic circuits.
    The allowable forward surge current of TVS can reach 50-200A under the conditions of TA=250C and T=10ms. Bidirectional TVS can absorb instantaneous large pulse power in both positive and negative directions, and clamp the voltage to a predetermined level. Bidirectional TVS is suitable for AC circuits, while unidirectional TVS is generally used for DC circuits. It can be used to prevent lightning strikes, overvoltage, interference, and absorb surge power, making it an ideal protective device. The tolerance is expressed in watts (W).
Electrical characteristics of TVS devices
    (1) V-I characteristics of unidirectional TVS
    As shown in Figure 1, the forward characteristics of unidirectional TVS are the same as those of ordinary voltage regulator diodes, and the reverse breakdown inflection point is approximately "right angle" for hard breakdown, which is a typical PN junction avalanche device. The curve segment corresponding to the breakdown point to the VC value indicates that when there is an instantaneous overvoltage pulse, the current of the device suddenly increases, while the reverse voltage rises to the clamping voltage value and remains at this level.
    (2) V-I characteristics of bidirectional TVS
    As shown in Figure 2, the V-I characteristic curve of bidirectional TVS is like a "back to back" combination of two unidirectional TVS, with the same avalanche breakdown characteristics and clamping characteristics in both forward and reverse directions. The symmetry relationship of the breakdown voltage on both sides is 0.9 ≤ V (BR) (positive)/V (BR) (negative) ≤ 1.1. Once the interference voltage applied at both ends exceeds the clamping voltage VC, it will be immediately suppressed, making bidirectional TVS very convenient for application in AC circuits.
Main electrical parameters of TVS devices
    (1) Breakdown voltage V (BR)
    The voltage at both ends of the device measured at the specified test current I (BR) in the area where breakdown occurs is called breakdown voltage. In this area, the diode becomes a low impedance path.
    (2) Maximum reverse pulse peak current IPP
    The maximum pulse peak current that the device is allowed to pass under specified pulse conditions during reverse operation. The product of IPP and the maximum clamping voltage VC (MAX) is the maximum value of transient pulse power.
    When using, TVS should be selected correctly to ensure that the rated transient pulse power PPR is greater than the maximum transient surge power that may occur in the protected device or line.
    Figure 3 shows that when the instantaneous peak pulse current occurs, TVS is broken down and the breakdown voltage increases to the maximum clamping voltage. As the pulse current exponentially decreases, the clamping voltage also decreases and returns to its original state. Therefore, TVS can suppress the potential impact of pulse power, thereby effectively protecting electronic circuits.
      E=∫i(t)‧V(t)dt
     In the formula, i (t) represents the pulse current waveform, and V (t) represents the clamping voltage waveform.
    This rated energy value cannot be repeatedly applied to TVS in an extremely short period of time. However, in practical applications, surges usually occur repeatedly. In this case, even if the individual pulse energy is much smaller than the pulse energy that TVS devices can withstand, if applied repeatedly, these individual pulse energy accumulates and in some cases, it will exceed the pulse energy that TVS devices can withstand. Therefore, circuit design must carefully consider and select TVS devices at this point, so that the accumulation of repeatedly applied pulse energy within the specified interval time does not exceed the pulse energy rating of TVS devices.
    (6) Capacitor CPP
    The capacitance of TVS is determined by the area of the silicon wafer and the bias voltage. Under zero bias conditions, the capacitance value decreases with the increase of the bias voltage. The size of the capacitance will affect the response time of TVS devices.
    (7) Leakage current IR
    When the maximum reverse working voltage is applied to the TVS, the TVS transistor has a leakage current IR, which is an important parameter when TVS is used in high impedance circuits.
    The test waveform of TVS peak current adopts standard waveform (exponential waveform), which is determined by TR/TP.
    Peak current rise time TR: The time when the current reaches 0.9IPP from 0.1IPP.
    Half peak current time TP: The time when the current passes through the maximum peak from zero and then drops to a value of 0.5IPP. The waveform is shown in Figure 4.
    (3) Maximum reverse working voltage VRWM (or deflection voltage)
    When the device operates in reverse, the voltage value at both ends of the device under the specified IR is called the maximum reverse operating voltage VRWM. Usually VRWM=(0.8~0.9) V (BR). At this voltage, the power consumption of the device is very small. When using, VRWM should not be lower than the normal working voltage of the protected device or circuit.
    (4) Maximum clamping voltage VC (max)
   The maximum voltage value at both ends of the device under the action of pulse peak current Ipp is called the maximum clamping voltage. When using, VC (max) should not be higher than the maximum allowable safe voltage of the protected device. The ratio of the maximum clamping voltage to the breakdown voltage is called the clamping coefficient. Namely:
    Clamping coefficient=VC (max)/V (BR)
    The general clamping coefficient is around 1.3.
    (5) Reverse pulse peak power PPR
    The PPR of TVS depends on the peak pulse current IPP and the maximum clamping voltage VC (max). In addition, it is also related to the pulse waveform, pulse time, and ambient temperature. When the pulse time Tp is constant, PPR=K1 ············· K2 ·VC (max) ·Ip
    In the formula, K1 is the power coefficient, and K2 is the temperature coefficient of the power.
    The typical pulse duration tp is 1MS. When the pulse time tp applied to the transient voltage suppression diode is shorter than the standard pulse time, its peak pulse power will increase with the shortening of tp.
    Figure 5 shows the relationship curve between PPR and tp. The reverse pulse peak power PPR of TVS is related to the pulse waveform subjected to surges, represented by the power coefficient K1. The K1 values of various surge waveforms are shown in Table 1.
Classification of TVS diodes
    TVS devices can be divided into two types based on polarity: unipolar and bipolar. They can be divided into general-purpose devices suitable for various circuits and specialized devices suitable for special circuits according to their purpose. For example, various AC voltage protectors, 4-20mA current protectors, data line protectors, coaxial cable protectors, telephone protectors, etc. According to packaging and internal structure, it can be divided into: axial lead diode, dual inline TVS array (suitable for multi line protection), patch type, component type, and high-power module type.
The Application of TVS Diodes
    At present, it has been widely used in computer systems, communication equipment, AC/DC power supplies, automobiles, electronic ballasts, household appliances, instruments and meters (kWh meters), RS232/422/423/485, I/O, LAN, ISDN, ADSL, USB, MP3, PDAS, GPS, CDMA, GSM, digital camera protection, common mode/differential mode protection, RF coupling/IC drive reception protection, motor electromagnetic wave interference suppression, audio/video input, sensors/transmissions, industrial control circuits Various fields such as noise suppression of relays and contactors.
Characteristics of TVS diodes
    (1) Adding TVS diodes to the signal and power lines can prevent the failure of microprocessors or microcontrollers due to transient surges, such as electrostatic discharge effects, AC power surges, and switching power supply noise.
    (2) The electrostatic discharge effect can release pulses exceeding 10000V and 60A, and can last for 10ms; However, general TTL devices may be damaged when encountering 10V pulses exceeding 30ms. The use of TVS diodes can effectively absorb pulses that can cause device damage and eliminate interference caused by switches between buses (Crosstalk).
    (3) Placing the TVS diode between the signal line and ground can prevent unnecessary noise from affecting the data and control bus.
Selection Techniques for TVS
    (1) Determine the maximum DC or continuous operating voltage of the protected circuit, the rated standard voltage of the circuit, and the "high end" tolerance.
    (2) The TVS rated reverse turn off VWM should be greater than or equal to the maximum operating voltage of the protected circuit. If the selected VWM is too low, the device may enter avalanche or the normal operation of the circuit may be affected by excessive reverse leakage current. Serial connection for voltage sharing and parallel connection for current sharing.
    (3) The maximum clamping voltage VC of TVS should be less than the damage voltage of the protected circuit.
    (4) Within the specified pulse duration, the maximum peak pulse power consumption PM of TVS must be greater than the peak pulse power that may occur in the protected circuit. After determining the maximum clamping voltage, the peak pulse current should be greater than the transient surge current.
    (5) For the protection of data interface circuits, attention must also be paid to selecting TVS devices with appropriate capacitance C.
    (6) Choose the polarity and packaging structure of TVS according to its purpose. The selection of bipolar TVS for AC circuits is more reasonable; Choosing TVS array for multi line protection is more advantageous.
    (7) Temperature considerations. The transient voltage suppressor can operate between -55 ℃ and+150 ℃. If TVS needs to operate at a changing temperature, its reverse leakage current ID increases with increasing; The power consumption decreases with the increase of TVS junction temperature, from+25 ℃ to+175 ℃, approximately linearly decreasing by 50%. The rain breakdown voltage VBR increases with a certain coefficient as the temperature increases. Therefore, it is necessary to consult relevant product information and consider the impact of temperature changes on its characteristics.




 












   
      
      
   
   


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