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Application and case analysis of TVS transient diode
Publish:Shenzhen Tergy Technology Co., Ltd.  Time:2016-10-18
Transient voltage suppressor (TVS transient diode) with fast response time, transient power, low leakage current, breakdown voltage of small deviation, the clamp voltage is easy to control, no damage limit, small volume etc.. Has been widely used in computer systems, communications equipment, AC / DC power supply, automotive, household appliances, instrumentation and other fields. This paper will combine the TVS transient diode application characteristics and the matters needing attention, this paper introduces several typical application circuit of TVS transient diode, and through the example TVS transient diode used in hot swap protection circuit and auto power line protection, to explore how to correctly apply the TVS transient diode and TVS transient diode the best application performance.
In the actual application circuit, instantaneous pulse device best way to damage, is the instantaneous current away from the sensitive device. In order to achieve this goal, the TVS transient diode is connected in parallel with the protected line on the circuit board. So, when the instantaneous voltage exceeds the normal working voltage circuit, TNS avalanche breakdown, thus providing instantaneous current of a low impedance path, the result is the instantaneous current through TVS transient diode is off, so as to avoid the protected device and restore the normal value before to be kept in the cut-off voltage protection circuit voltage. After that, when the instantaneous pulse is over, the TVS transient diode is automatically recovered to the high resistance state, and the whole circuit is in the normal voltage state.
1, TVS transient diode applications three characteristics
1) the TVS transient diode is added to the signal and power line, which can prevent the microprocessor or single chip microcomputer from failure due to the transient impulse, such as the electrostatic discharge effect, the surge of the AC power supply and the noise of the switching power supply.
2) electrostatic discharge effect can release more than 60A, more than 10000V of the pulse, and can continue to 10ms; while the general TTL device, encountered more than 10V 30ms pulse, it will lead to damage. Using TVS transient diode, can effectively absorb the pulse that can cause the device damage, and can eliminate the interference caused by switching between the bus (Crosstalk).
3) TVS transient diode is placed between the signal line and the ground, which can avoid the influence of the data and the control bus.
2, TVS transient diode tube should be paid attention to in the use of
The relationship between the absorption power (peak value) of transient voltage and the pulse width of transient voltage. The only specific handbook to the pulse width of the absorbed power (peak), and the pulse width of the actual line in the prior to the estimated change constantly. Wide pulse should be used to reduce the amount of.
To protect the small current load, can consciously in the line to increase the current limiting resistor current limiting resistor, as appropriate, will not affect the normal operation of the line, but the current flow resistance of interference can be greatly reduced. It is possible to select the TVS transient diode with small peak power to protect the small current load line.
For the suppression of transient voltage, it is worth noting that the steady state average power of TVS transient diode is in the safe range.
3, TVS transient diode typical application circuit
Application of 3.1 TVS transient diode in AC circuit
Figure 1 shows the application circuit of a bidirectional TVS transient diode in an AC circuit. Application of TVS transient diode can effectively restrain the overload impulse caused by the power grid, thus it can protect the rectifier bridge and all the components in the load. Figure 1 TVS transient in the maximum allowable voltage of diode clamped voltage should be not greater than the circuit.
Application circuit of bidirectional TVS transient diode in AC circuit
  Fig. 1 application circuit of bidirectional TVS transient diode in AC circuit
3.2 with TVS transient diode protection DC power supply
Figure 2 is a DC power supply, the regulated output plus TVS transient protection diode, can use the power equipment, but also can absorb the collector of the transistor circuit to the emission peak voltage between the electrodes, thereby protecting the transistor. It is suggested that the output of each voltage stabilized source can be increased by a TVS transient diode tube, which can greatly improve the reliability of the whole machine.
TVS transient diode protection DC regulated power supply
  Figure 2 TVS transient diode protection DC regulated power supply
3.3 using TVS transient diode protection transistor circuit
All kinds of transient voltage can make the transistor EB or CE junction breakdown and damage, especially with inductive transistor collector (coil, transformer and motor load), usually have a high EMF, which may damage the transistor. In practical application, the proposed TVS transient diode is used as a protective device. Figure four shows the 3 circuit examples of TVS transient diode protection transistors.
TVS transient diode protection transistor circuit  
  Figure 3 TVS transient diode protection transistor circuit
3.4 TVS transient protection diode integrated operational amplifier
The integrated operational amplifier to external electric stress is very sensitive. Therefore, in the process of using the operational amplifier, if due to improper operation or take the normal working conditions, often appear excessive voltage or current, especially the surge and electrostatic pulse, so it is easy to make operational damage or failure. Figure 4 shows the change in the differential input amplifier diode end protection circuit with TVS transient overvoltage damage.
TVS transient voltage differential input overvoltage protection circuit in the amplifier end to prevent damage  
  Figure 4 TVS transient diode differential input overvoltage protection circuit in the amplifier end to prevent damage
4, TVS transient diode application examples
4.1 TVS transient diode for hot swap circuit protection
In hot swap applications, the TVS transient diode is mainly used as the grounding shunt path of the differential mode current which needs to be interrupted. Hot swap system is often used in the distributed power system provides reliable electrical system protection and management, interface card and hot swap circuit principle diagram of a typical server system as shown in figure 5.
Card interface and hot swap circuit principle diagram of typical server system  
  Card interface and hot swap circuit principle diagram 5 typical server system
In essence, when the current conversion rate of fault and current interruption may reach 100A/ s or more, the path Q1 MOSFET in Figure 5 will be quickly shut down by the Hot Swap Controller. However, the input power path of the power supply rail bus structure is inevitable parasitic inductance (with the power bus length and the inherent loop area). The energy stored in the inductor will be transferred to the other components in the circuit, so that the overvoltage dynamic behavior. In order to prevent downstream components from being damaged, the shunt protection configuration from VIN to GND is connected to a fast response speed of one way TVS transient diode (transient voltage suppression) silicon diode, as shown in figure 5.
The selection of TVS transient diode used in hot swap circuit can be carried out according to the following steps:
1) by cutting off the voltage VR to select a unidirectional TVS transient diode, the voltage is equal to or greater than the DC or continuous peak operating bus voltage level. 14V or TVS 15V transient diode suitable for low impedance 12VDC + 10% server system input bus.
2) according to the threshold voltage of the circuit breaker of the Hot Swap Controller, the response time and the selected shunt resistor to determine the peak pulse current level IP.
3) typical applications and case analysis using the formula TVS transient diode - they look for opportunities between tea (type, VC: IP: peak voltage clamp; pulse current; VC (max): maximum clamp voltage; breakdown voltage; VBR: IPP: 10/1000 MS VC (max) maximum waveform peak pulse current conditions). The clamping voltage of the circuit is calculated by the second step and the IP level given by the related data table parameter VC. VC is it low enough? If not, the alternative is to use a larger TVS transient diode to obtain a steeper drop. Note that the voltage temperature coefficient of VC is similar to that of VBR (for example, at a working environment of 75 degrees C, 0.1%/ means the coefficient increases by 5%).
4) calculate the product of VC and IP in order to obtain the actual peak power level maintained by the TVS transient diode.
5) typical applications and case analysis using the formula TVS transient diode - they look for opportunities between tea (in the formula, L is the parasitic inductance in the circuit parasitic inductance and input) known to determine the pulse duration TD triangular pulse waveform (i.e. decay to zero time).
(6) using the fifth step pulse duration of the similar figure 6 (a) curve to reduce the amount of PPP. As mentioned above, the triangular pulse current waveform can be achieved with a pulse power of 33% higher than the double exponential reference waveform curve.
(7) using a similar figure 6 (b) curve of ambient temperature drop PPP. At the same time, the interaction of adjacent elements should be considered.
(8) does the seventh step net drop PPP achieve a sufficient design margin (at least 50%) of the actual TVS transient diode peak power calculated by the fourth step? If not, select a larger TVS transient diode and repeat the 1-8 step.
 (a) peak pulse power and pulse duration, (b) thermal drop characteristics  
  Figure 6 (a) peak pulse power and pulse duration, (b) thermal drop characteristics
4.2 TVS transient diode for automotive power line protection and secondary protection
Electronic control unit, sensor and information entertainment system and other automotive electronic devices connected to a power line, as shown in figure 7. The power of these electronic products is the battery and AC generator, the output voltage of these two kinds of power are not stable, easy to be affected by temperature, working conditions and other conditions. In addition, the use of fuel injection system, valve, motor, electric car controller and hydrolysis system solenoid load, the ESD, the spike noise and other types of transient and surge voltage into power and signal line. Therefore, it is necessary to protect the electronic equipment (such as control unit, sensor and information entertainment system) from the harmful surge voltage, transient voltage, ESD and noise of the power line. Transient voltage suppressor (TVS transient diode) is an ideal scheme for automotive electronic protection, the following describes the TVS transient diode in the automotive power line in the primary and secondary protection protection application.
Typical automobile power line  
  Fig. 7 typical automobile power supply line
4.2.1 automotive power line protection (load rejection)
The rejection load TVS transient diode for automotive electronics has two types: Epitaxial Type and non epitaxial type. In the reverse bias mode, the two groups of products with similar breakdown characteristics. The difference is that the epitaxial TVS transient diode has low forward voltage drop (VF) characteristics in the forward mode, and the non epitaxial TVS transient diode is relatively high in the same condition VF.
In the reverse power input mode, voltage power line voltage diode VF and TVS transient is the same as that of the reverse bias mode will cause the electronic circuit fault, epitaxial TVS transient diode low forward voltage drop can solve this problem well, as shown in figure 8.
TVS transient diode for automotive power line protection  
  Figure 8 TVS transient diode for automotive power line protection
Secondary protection of 4.2.2 automotive power supply line
The primary object of the protection circuit in the automotive system is the high surge voltage, but the voltage of the clamp is still very high. Therefore, it is particularly important to protect the secondary protection in the 24V power assembly, such as the power train in the truck and the truck. The main reason is that most of the regulator and DC-DC converter IC the maximum input voltage is 45V~60V. For such applications, the proposed use of the secondary protection in figure 9. Increasing the resistance R on the power supply line can reduce the transient current, which can be used as the secondary protection of the TVS transient diode with smaller power rating.
Secondary protection of automobile power supply line
    Figure 9 secondary protection
5, TVS transient diode performance optimization
How to make the TVS transient diode in the circuit application of the best performance? Wiring and circuit components of the printed circuit board is very important to choose reasonable treatment by placing the TVS transient diode position, grounding selection, parasitic inductance and loop area, and avalanche type TVS transient diode and diode array, unidirectional and bidirectional avalanche type TVS transient diode, external and internal chip protection circuit comparison of the scientific and reasonable wiring and TVS instantaneous PCB variable diode element selection, performance optimization to TVS transient diode.
6, this article summarizes
This paper introduces the typical application characteristics, TVS transient diode applications, two aspects and variable diode element from the wiring and TVS transient printed circuit board option to explore how to make the TVS transient diode performance optimization measures of protection circuit design engineer in rational and efficient application of transient TVS diode circuit protection design is very valuable.
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