1 is equivalent to an open circuit before breakdown (conducting), the resistance is large, there is no leakage current or leakage current is very small;
2 After the breakdown (conduction) is equivalent to a short circuit, can pass a large current, the pressure drop is very small;
3 has bidirectional symmetry.
4 The response speed is fast, ns level.
5 Breakdown voltage consistency is good.
Disadvantages:1 The traffic is small, only a few hundred A.
2 breakdown voltage only a few specific values.
3 Larger capacitance, tens to hundreds of pF
TVS tube has one-way and two-wayThe TVS tube has one-way and two-way division (the letter behind the one-way model number is "A" and the bidirectional one is "CA"), and the characteristics of the one-way TVS tube and the voltage stabilizing diode TVS tube are generally connected in parallel. On the circuit. In order to limit the current flowing through the TVS tube not to exceed the peak current IPP allowed by the tube, the current limiting element should be connected in series on the line, such as resistance, self-healing fuse, and inductance. Similarly, the characteristics of a bidirectional TVS tube are equivalent to two zener diodes in reverse series.
The device is connected in parallel with the circuit. When the circuit works normally, it is in the cut-off state (high impedance state) and does not affect the normal operation of the line. When the circuit experiences abnormal overvoltage and reaches its breakdown voltage, it quickly changes from high impedance to The low-impedance state provides a low-impedance conduction path for the transient current while clamping the abnormal high voltage within a safe level to protect the protected IC or circuit. When the abnormal overvoltage disappears, it returns to a high-impedance state and the circuit works normally.
The forward surge current allowed by TVS can reach 50-200A under the conditions of TA=250C and T=10ms. The bidirectional TVS can absorb instantaneous large pulse power in both positive and negative directions and clamp the voltage to a predetermined level. The bidirectional TVS is suitable for AC circuits and the unidirectional TVS is generally used for DC circuits. It can be used for lightning protection, overvoltage protection, anti-jamming, and surge power absorption. It is an ideal protection device. The tolerance is expressed in Watts (W).
TVS diodes can be easily integrated with other devices on a single chip. There are many devices that integrate EMI filtering and RFI protection functions with TVS tubes. This not only reduces the number of devices used in the design, lowers the cost, but also avoids PCBs. On-board wiring is easy to induce associated self-inductance.
This ensures that the following circuit components are protected from transient high-energy shocks. The response speed of TVS is definitely much faster than that of the RC loop. The one-way TVS that suppresses the reverse is used, and the two-way TVS is used for the exchange.
TVS tube power calculation
The figure above is the schematic diagram of the common automotive power supply parts, which are the reverse connection module and LDO module. Our customers require ISO7637-2 pulse 5 is 40V/400ms, internal resistance is 2 ohms, I started with SMBJ20CA, the result TVS The tube was burned and later changed to SMBJ36CA. Now it is possible to pass ISO7637-2 pulse 5.
problem:
1) The input voltage of TLE42644G is 40V at the maximum, Vbrmin of SMBJ36CA=40V, Vrsm=58.1V. In the above module, I think that SMBJ36CA does not play any role. According to the TVS tube selection criteria, at this moment I should choose to meet Vrsm<40V and TVS tube with Vbrmin>18V (supply voltage), but I do not know how to calculate the TVS tube power of 400ms required by the customer?
2) If the customer has no special requirements, do I need to select an LDO that can withstand high input voltage according to ISO7637-2 Pulse 5 standard? In this way, the high voltage TVS tube can be selected and the power consumption on the TVS tube can be reduced.
Reply:
The energy of this pulse is the largest, and TVS plays a role in stabilizing the voltage within a certain range.
My calculation method in the book is to use TVS as a variable resistor and calculate the maximum power applied to it during the entire process.
In essence, I may be superficial in the book. Here, the static power is accounted for for the us level pulse, because this failure mechanism is an instantaneous thermal failure; for this 40 ms to 400 ms, the two final ones can be calculated first. impedance:
For SMBJ20CA:
In the first stage, the resistance of the TVS is infinite and the voltage quickly rises to 22.2 to 24.5V. The TVS tube begins to breakdown.
In the second phase, the voltage of the TVS rises and its impedance begins to drop. During the entire process, the voltage rises to 32.4V. At this time, the equivalent resistance is 1.74Ohm and the current is 10.7A. This is the highest current.
In the third stage, the voltage of the TVS tube begins to drop, the impedance becomes larger, and the voltage is in a stable range. This steady state value can be calculated by an iterative method. The linear method in the book is actually an assumption. For computational convenience, we assume that the stable voltage here is 24.5V+2V, and the resistance at this time is 4Ohm, and the power is 175W. There is no suspense, and this is sure to be burned.
Therefore, most vehicles are trying to add a central suppressor to the generator block to directly absorb the pulse energy directly. And most of the top components need to be able to withstand 40V.
SMBJ36CA, the energy is very limited, so it will not be burned, but the entire rear-end system is subject to a large voltage.
So here is the best way to confirm the simulation method, as shown below:
Pulse generation mechanism: While the battery is disconnected, the alternator is generating a charge current to charge the battery, and transients generated when the generator circuit is still loaded with other loads. Pulse 5 is a simulaTIon of a load dump transient occurring in the event Of a discharged battery being disconnected while the alternator is generaTIng charging current with other values ​​remaining on the alternator circuit at this moment.
1, RS232/RS422/RS485 interface card
2, XDSL and ISDN, HDSL transmission equipment
3, the user's front-end equipment, such as: telephone, modem, etc.
4, Centralofficelinecards
5, T1/E1
6, PBX and other exchange equipment
We are supplier of Disposable Vapes 3000 puffs also distributor a lot of brand. We offer full range of 3000+ Puffs Disposable Vapes, You'll find all Disposable Vape on tsvaping.com.
Disposable Vape 3000 Puffs FOLI BAR Factory Wholesale ;
We offer full range of 3000+ Puffs Disposable Vapes.tsvaping has served thousands of vape wholesalers from worldwide since 2018. Is your e-cigarette wholesale good partner.
The FOLI BAR 3000 Puffs Disposable Vape Wholesale Pen Device is a great way to enjoy your favorite nicotin salt e-liquids.
Wholesale vape 3000 puffs rechargeable disposable vape pen . Short Description: Model Number, air glow fun. Brand Name, FOLI. Origin from China.
Vape 3000 Puffs,Hqd Vape Flavors,Hyde Vape Puffs,Flash Vape Pen
TSVAPE Wholesale/OEM/ODM , https://www.tsecigarette.com