What does Transient Suppression Diode TVS Transient Suppression Diode TVS mean

    (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.