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                  TVS diode principle and characteristics
                  Number:1647   Date:2017-04-08  

                  【TVS -Transient Voltage Suppressor】

                       Is a form of diode zener diode (evolution) of highly efficient protection devices.When the poles TVS diode reverse transient high-energy impact, it can be at very fast speed, high impedance between the poles is a low impedance, power supply and signal lines on the surge of power, voltage clamp which is located in between the poles of a predetermined value.

                    Two-way TVS and one-way TVS

                  One-way TVS and in terms of features and zener is similar, can only absorb the positive surge voltage pulse, only commonly used in dc (and not the reverse and negative pulse).

                  Two-way TVS can flow in two directions to absorb surge voltage pulse, implements the muzzle of voltage, two-way TVS use wide (dc, ac are available)。

                  See below contrast more clear:

                  TVS diode characteristics:

                  Advantages: fast response time, the transient power, low leakage current, clamping voltage control more easily                   and without damage to the limit, small volume, etc.
                  Disadvantages: low breakdown voltage, the price is more expensive.
                  Compared with the MOV results:

                  TVS diode parameters:

                  1) The breakdown voltage (V (BR).
                  TVS in the event of a breakdown, within the areas under the specified test current (I) (BR), the measured voltage is called the breakdown voltage at the ends of the device.
                  2) The largest reverse pulse peak current,
                  When the breakdown of pulse conditions 】 【 device allows maximum pulse peak current.

                  We should pay attention to this parameter, because the maximum transient pulse power = IPP x maximum clamping voltage VC (MAX).To guarantee the normal work of the TVS can, need to confirm the rated transient pulse power PPR is greater than the maximum transient surge of power.
                  In fact peak current test waveforms with a standard wave waveform (index), is decided by the TR/TP.
                  Peak current rise time TR: current IPP started from 0.1 to 0.9 time of IPP.
                  TP: half peak current time passed the maximum peak current from scratch, fell to 0.5 IPP value of time.

                  3) The largest reverse voltage VRWM 】 
                  TVS in the process of the protection circuit in the regulation of reverse power flow, TVS at the ends of the voltage value is called the biggest VRWM reverse working voltage.
                  Generally VRWM = (0.8 ~ 0.9) V (BR).Under the voltage, the power consumption of the device is very small.We usually design to choose VRWM is greater than 16 v devices.
                  (4) The largest clamping voltage VC (Max).
                  Under the effect of pulse peak current Ipp maximum voltage at the ends of the device is called the biggest clamping voltage.When using, should make VC (Max) are not higher than the maximum permissible safe voltage protection device.The ratio of the maximum clamping voltage and breakdown voltage is called the clamping coefficient.
                  5, Reverse pulse peak power PPR
                  The PPR TVS depends on pulse peak current IPP and maximum clamping voltage VC (Max), in addition to this, and pulse waveform, pulse time and environmental temperature.
                  When pulse time Tp must, PPR = K1 x K2 * Ipp VC (Max), type of power coefficient K1, K2 for temperature coefficient of power.
                  Typical pulse duration Tp is 1 ms, when applied to the transient voltage suppression diode on the pulse of time Tp than standard pulse time short, the pulse peak power will increase along with the shortening of Tp.

                  TVS reverse pulse peak power of PPR related to undergo surge pulse waveform, with power coefficient K1 said: E = ∫ I (t)?In V (t) dt, type: (I) (t) as the pulse current waveform, V (t) as the clamping voltage waveform.

                  This a rated power in a very short period of time on TVS are not repeatable.However, in practical applications, the surge is usually appear repeatedly, in this case, even a single pulse energy than TVS device can support the pulse energy is much smaller, but if repeated applied, the single pulse energy accumulation, in some cases, will be more than TVS device can withstand pulse energy.Circuit design, therefore, have to seriously consider and choose TVS on this device, make its within the prescribed time interval, repeat on the accumulation of pulse energy pulse energy rating of not more than TVS device.

                  6, Capacitance CPP
                        TVS capacitance determined by the area of the silicon wafer and offset voltage, capacity under the condition of zero bias, with the increase of the bias voltage, the capacitance value is on the decline.The size of the capacitance affects the response time of TVS device.

                  7, Leakage current IR
                       When the maximum reverse voltage applied to the TVS, TVS tube, there is a leakage current Ir in automotive electronics, this parameter affects the static current.

                  【Previous】Electrostatic protection principle and design (ESD)
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