Characteristics and application of TVs transient suppression diode — SUNMATE

Characteristics and application of TVs transient suppression diode

1. Characteristic curve of TVs

The circuit symbol of TVs is the same as that of ordinary zener diode. Its forward characteristic is the same as that of ordinary diode; The reverse characteristic is a typical PN junction avalanche device.

Under the action of transient peak pulse current, when the current flowing through TVs rises from the original reverse leakage current ID to IR, the voltage at both poles rises from the rated reverse shutdown voltage VWM to the breakdown voltage VBR, and TVs is broken down. With the appearance of peak pulse current, the current flowing through TVs reaches the peak pulse current IPP. The voltage at its two poles is clamped below a predetermined maximum clamping voltage. Then, as the pulse current decays exponentially, the voltage at the two poles of TVs also decreases, and finally returns to the initial state. This is the whole process of TVs suppressing possible surge pulse power and protecting electronic components.

2. Characteristic parameters of TVs

① Maximum reverse leakage current ID and rated reverse shutdown voltage VWM.

VWM is the maximum continuous working DC or pulse voltage of TVs. When this reverse voltage is added between the two poles of TVs, it is in the reverse off state, and the current flowing through it shall be less than or equal to its maximum reverse leakage current ID.

② Minimum breakdown voltage VBR and breakdown current IR

VBR is the minimum avalanche voltage of TVs. At 25 ℃, TVs will not turn on before this voltage. When TVs flows through the specified 1mA current (IR), add the voltage between the two poles of TVs as its minimum breakdown voltage VBR. According to the dispersion degree between TVs VBR and standard value, TVs can be divided into ± 5% VBR and peaceful coexistence ± 10% VBR. For ± 5% VBR, VWM = 0.85vbr; for ± 10% VBR, VWM = 0.81 VBR.

③ Maximum clamping voltage VC and maximum peak pulse current IPP

When the pulse peak current IPP with a duration of 20 microseconds flows through the TVs, the maximum peak voltage between its poles is VC. It is a combination of voltage rise on series resistance and due to temperature coefficient. VC and IPP reflect the surge suppression ability of TVs devices. The ratio of VC to VBR is called clamping factor, which is generally between 1.2 and 1.4.

④ Capacitance C

The capacitance C is determined by the cross section of TVS Avalanche junction and measured at a specific frequency of 1MHz. The size of C is directly proportional to the current bearing capacity of TVs. Too large C will attenuate the signal. Therefore, C is an important parameter for selecting TVs for data interface circuit.

⑤ Maximum peak pulse power consumption PM

PM is the maximum peak pulse dissipation power that TVS can withstand. For the specified test pulse waveform and PM values of various TVs, please refer to the relevant product manual. Under the given maximum clamping voltage, the greater the power consumption PM is, the greater the withstand capacity of surge current is; Under a given power consumption PM, the lower the clamping voltage VC, the greater the withstand capacity of surge current. In addition, the peak pulse power consumption is also related to the pulse waveform, duration and ambient temperature. Moreover, the transient pulse that TVS can withstand is not repeated, and the pulse repetition frequency (the ratio of duration to intermittent time) specified by the device is 0.01%. If there are repetitive pulses in the circuit, the "accumulation" of pulse power should be considered, which may damage TVs.

⑥ Clamping time TC

TC is the time from zero to the minimum breakdown voltage VBR. For unipolar TVs less than 1 × 10-12 seconds; For bipolar TVs less than 1 × 10-11 seconds.

2、 Classification of TVs diodes

TVs devices can be divided into unipolar and bipolar devices according to polarity, and can be divided into general devices suitable for various circuits and special devices suitable for special circuits according to purpose. Such as various AC voltage protectors, 4 ~ 200mA current protectors, data line protectors, coaxial cable protectors, telephone protectors, etc. According to the package and internal structure, it can be divided into axial lead diode, dual in-line TVS Array (applicable to multi wire protection), patch type, component type and high-power module type.

3、 Selection skills of TVs

1. Determine the maximum DC or continuous operating voltage of the protected circuit, the rated standard voltage of the circuit and the "high side" tolerance.

2. The rated reverse shutdown VWM of TVs shall 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 an avalanche or the normal operation of the circuit may be affected by too large reverse leakage current. Serial connection is divided into voltage and parallel connection is divided into current.

3. The maximum clamping voltage VC of TVs shall 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 possible peak pulse power in the protected circuit. After determining the maximum clamping voltage, the peak pulse current shall be greater than the transient surge current.

5. For the protection of data interface circuit, we must also pay attention to the selection of TVs devices with appropriate capacitance C.

6. The polarity and packaging structure of TVs are selected according to the purpose. It is reasonable to select bipolar TVs for AC circuit; It is more advantageous to select TVS Array for multi line protection.

7. Temperature considerations. The transient voltage suppressor can work between - 55 ~ + 150 ℃. If TVs is required to work at a changing temperature, because its reverse leakage current ID increases with increasing; The power consumption decreases with the increase of TVs junction temperature, which decreases linearly by about 50% from + 25 ℃ to + 175 ℃, and the rain breakdown voltage VBR increases by a certain coefficient with the increase of temperature. Therefore, it is necessary to consult relevant product data and consider the influence of temperature change on its characteristics.