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Jul 30 2019

What is a TVS Diode? Difference between Zener Diode and TVS Diode

Article coreTVS Diode,Zener diode
1. Principle of TVS diode
2. Device characteristics of TVS diodes
3. Main parameters of TVS diode 
4. TVS diode selection process
5. Function of TVS diode
6. Four major applications of TVS tubes:
7. Introduction to Zener diode
8. The difference between Zener diode and TVS diode

1. Principle of TVS diode

 

TVS (Transient Voltage Suppressor) diode, also known as transient suppression diode, is a new type of high-efficiency circuit protection device, which has extremely fast response time (sub-nanosecond order) and relatively high surge absorption capability. When its two ends are subjected to an instantaneous high-energy impact, the TVS can change the impedance between the two ends from high impedance to low impedance at a very high speed and can also absorb a large instantaneous current and clamp the voltage across it. A predetermined value protects the subsequent circuit components from transient high voltage spikes.

 

TVS diodes work similarly to conventional Zener diodes. If the breakdown voltage is higher than the standard, the TVS diode turns on. Compared to the Zener diode, the TVS diode has higher current conduction capability. When the two poles of the TVS diode are subjected to a reverse transient high-energy shock, the high impedance between the two poles is changed to a low impedance at a speed of 10^-12S, and the surge power of up to several kilowatts is absorbed. The voltage between the two poles is clamped to a safe value to effectively protect the precision components in the electronic circuit from surge pulses.

 

 

2. Device characteristics of TVS diodes

 

Under the specified reverse application conditions, the TVS diode is in a high impedance state to the protected line. When the instantaneous voltage exceeds its breakdown voltage, the TVS diode provides a low-impedance path and shunts the instantaneous current flowing to the protected component to the TVS diode through a large current, while limiting the voltage across the protected component at the clamping voltage in the TVS. When the overvoltage condition disappears, the TVS diode returns to a high impedance state. Compared with ceramic capacitors, TVS diodes can withstand a voltage of 15 kV, but ceramic capacitors have a weaker bearing capacity. A 5 kV shock will cause approximately 10% of the ceramic capacitor to fail, and at 10 kV, the damage rate will be as high as 60%.

 

 

3. Main parameters of TVS diode  

 

(1) Minimum breakdown voltage VBR

 

When a specified current flows through the TVS, the voltage across the TVS is called the minimum breakdown voltage, in which the TVS diode is a low impedance path. At 25°C, the TVS diode will not avalanche breakdown below this voltage.

 

(2) rated reverse shutdown voltage VWM

 

VWM is the voltage that the TVS diode can withstand under normal conditions. This voltage should be greater than or equal to the normal operating voltage of the circuit being protected. However, it needs to be as close as possible to the normal operating voltage of the circuit being protected, so that the entire circuit is not exposed to an overvoltage threat before the TVS diode operates. According to the dispersion of VBR and standard value of TVS diode, VBR can be divided into 5% and 10%. For 5% VBR, VWM=0.85VBR; for 10% VBR, VWM= 0.81VBR.

 

(3) Maximum peak pulse current IPP

 

IPP is the maximum pulse peak current that the device is allowed to pass under specified pulse conditions when the TVS diode is operating in the reverse state.

 

(4) Clamping voltage Vc

 

When the pulse peak current Ipp flows through the TVS diode, the maximum voltage value appearing across it is called the clamp voltage Vc. Vc and Ipp reflect the surge suppression capability of TVS diodes. The ratio of Vc to VBR is usually called the clamp factor (coefficient), and its value is generally between 1.2 and 1.4. In actual use, Vc should be made no larger than the maximum allowable safety voltage of the protected circuit, otherwise the protected device will be damaged.

 

(5) Maximum peak pulse power consumption PM

 

The PM is usually the product of the maximum peak pulse current Ipp and the clamp voltage Vc, that is, the maximum peak pulse power consumption. It is the maximum peak pulse power consumption that a TVS diode can withstand. At a given maximum clamping voltage, the greater the power consumption PM, the greater the surge current capability. In addition, peak pulse power consumption is also related to pulse waveform, pulse duration, and ambient temperature. Moreover, the transient pulses that the TVS diode can withstand are not reproducible.

 

(6) Capacity C

 

The capacitance of a TVS diode is determined by the cross-sectional area and bias voltage of its silicon, which is measured at a specific frequency of 1 MHz. The size of C is proportional to the current carrying capacity of the TVS diode, and C is too large to attenuate the signal. Therefore, the capacitance C is an important parameter for selecting a TVS diode for the data interface circuit.

 

(7) Leakage current IR

 

IR is the leakage current of the TVS tube when the maximum reverse operating voltage is applied to the TVS diode. This leakage current IR is an important parameter when TVS diodes are used in high impedance circuits.

 

 

4. TVS diode selection process

 

(1). Determine the DC voltage or continuous operating voltage of the circuit to be maintained. If it is AC, calculate the maximum value, that is, use the useful value *1.414.

 

(2). The reverse displacement voltage of the TVS tube, that is, the operating voltage (VRWM)--the VRWM of the selected TVS is equal to or greater than the operating voltage prescribed by the above process 1. This ensures that the current absorbed by the TVS tube under normal operating conditions is negligible. If the regular voltage of Process 1 is higher than the VRWM of the TVS tube, the TVS tube will absorb a lot of leakage current and be in an avalanche breakdown condition, thus affecting the operating of the circuit.

 

(3). Maximum peak pulse power: Determine the disturbance pulse condition of the circuit. According to the waveform of the disturbance pulse and the pulse duration, determine the peak pulse power of the TVS tube that can be used to disturb the disturbance.

 

(4). The maximum clamp voltage (VC) of the selected TVS tube should be lower than the maximum accepted voltage allowed by the circuit under maintenance.

 

(5). Unipolarity is still bipolar - often the misunderstanding is that the bidirectional TVS tube is used to press the reverse surge pulse, which is not the case. The bidirectional TVS tube is used for alternating current or from positive and negative bidirectional pulses. TVS tubes are also sometimes used to reduce capacitance. If the circuit has only a positive level signal, then a one-way TVS tube is sufficient. The TVS tube operation method is as follows: in the case of a forward surge, the TVS tube is in a reverse avalanche breakdown condition; in the case of a reverse surge, the TVS tube is similarly turned on and forwardly absorbs the surge energy. This is not the case in low-capacitance circuits. Bidirectional TVS tubes should be used to maintain low capacitor materials in the circuit from reverse surges.

 

(6). For example, if you know the exact inrush current IPP, you can use VC to determine its power. If you can't determine the power scale, for TVS selection, the selection power is better.

 

 

5. Function of TVS diode

 

TVS diode is a high-performance circuit protection device commonly used in the world. Its appearance is the same as that of ordinary diodes. It is divided into two types: shaft and patch. Its main function: it can absorb surges of up to several kilowatts power. Its main feature is that under reverse application conditions, when subjected to a large pulse of high energy, its working impedance immediately drops to a lower conduction value, allowing large currents to pass while clamping the voltage at a predetermined level. Its response time is only 10-12 milliseconds. Therefore, the precision components in the electronic circuit can be effectively protected.

 

Then the bidirectional TVS can absorb the instantaneous large pulse power in both the positive and negative directions and clamp the voltage to a predetermined level. The bidirectional TVS is suitable for the AC circuit, and the unidirectional TVS is generally used for the DC circuit. It can be used for lightning protection, over voltage protection, anti-interference, and absorption of surge power. It is an ideal protection device. Tolerance is expressed in watts (W)

 

6. Four major applications of TVS tubes:

 

(1). Application of TVS tube in TN power system

 

Overvoltages caused by human error such as lightning overvoltage waves, load switches, etc., easily invade the inside of electrical and electronic equipment through the power supply line, causing failure or malfunction of the electrical and electronic equipment, and even causing permanent damage to the equipment. Two-stage protection is implemented by installing surge absorbers MOV and TVS on the power line, and common mode and differential mode protection are applied to the L and N lines. The specific method is to install MOV as the first-stage SPD protection at the front end of the line to weaken most of the lightning current. And install a high-power TVS tube at the end of the line (the front end of the device) as the second-stage SPD protection, further weakening the overvoltage amplitude to reduce the grid voltage within the E/I safe withstand voltage range. It should be noted that MOV and TVS should achieve voltage and energy coordination and coordination. The line length between AB should not be less than 5 m. Otherwise, the line length should be increased or decoupling devices should be installed.

 

(2). Application of TVS tube in network signal line

 

The TVS tube can be used not only for surge protection of power supply systems, but also for surge protection of signal lines. The gas discharge tube GDT and TVS tubes are combined into a signal surge protector, which is characterized by fast response and small leakage. Almost no loss to the signal, it provides safe and reliable protection for high-speed network lines.

 

(3). Application of TVS tube in DC power system

 

The mains AC 220 V is stepped down to AC 20 V through the transformer, and then modulated and rectified circuit, output DC 10 V DC power supply, and connected to the load. By installing a bidirectional transient voltage suppressor TVS1 at the output of the transformer, the instantaneous impulse current of the L and N lines is absorbed, and the circuit voltage is clamped at a safe voltage level. The TVS1 can protect the transformer back-end rectifier and other circuit components. A unidirectional transient voltage suppressor TVS2 is installed at the DC power output of the rectifier to protect the DC load from overvoltage current surges.

 

(4). Application of TVS tube in transistor circuit

 

As a current-controlled device, the transistor is an important part of electronic integrated circuits. It can be divided into NPN tube and PNP tube, which are used in switching circuits, amplifier circuits and voltage regulator circuits. In order to protect the transistor circuit from surge voltages such as ESD/EFT (electrostatic discharge/electric fast transient pulse group), TVS1 and TVS2 are added to the input and output terminals of the circuit for protection.

 

 

7. Introduction to Zener diode

 

By using the reverse breakdown state of the pn junction, the current can be varied over a wide range and the voltage is substantially constant, and the diode that acts as a voltage regulator is fabricated. This diode is a semiconductor device that has a very high resistance until the critical reverse voltage breaks down . At this critical breakdown point, the reverse resistance is reduced to a small value. In this low resistance region, the current increases and the voltage remains constant. The Zener diode is binned according to the breakdown voltage because of this characteristic. It is mainly used as a voltage regulator or voltage reference component. Zener diodes can be connected in series for use at higher voltages, resulting in higher regulated voltages in series.


The forward characteristics of the volt-ampere characteristic curve of the Zener diode are similar to those of a conventional diode. The reverse characteristic is that when the reverse voltage is lower than the reverse breakdown voltage, the reverse resistance is large and the reverse leakage current is extremely small. However, when the reverse voltage approaches the critical value of the reverse voltage, the reverse current suddenly increases, called breakdown, at which the reverse resistance suddenly drops to a small value. Although the current varies over a wide range, the voltage across the diode is substantially stabilized near the breakdown voltage, thereby achieving a diode regulation function.

 

(1) Principle of Zener diode :

 

The forward characteristics of the volt-ampere characteristic curve of the Zener diode are similar to those of a conventional diode. The reverse characteristic is that when the reverse voltage is lower than the reverse breakdown voltage, the reverse resistance is large and the reverse leakage current is extremely small. However, when the reverse voltage approaches the critical value of the reverse voltage, the reverse current suddenly increases, called breakdown, at which the reverse resistance suddenly drops to a small value. Although the current varies over a wide range, the voltage across the diode is substantially stabilized near the breakdown voltage, thereby achieving a diode regulation function.

 

(2) Application of Zener diode :

 

1, a typical series regulator circuit

In this circuit, the base of the transistor T is stabilized at 13V by the Zener diode D, then its emitter outputs a constant voltage of 13-0.7=12.3V, within a certain range, regardless of the input voltage rises or falls, regardless of The load resistor changes in size and the output voltage remains the same. This circuit is used in many situations. The 7805 is a series-type integrated voltage regulator circuit that can output 5V. The 7805-7824 can output 5-24V. There are applications on many electrical appliances.

 

2, overvoltage protection circuit in the TV

115V is the main power supply voltage of the TV. When the output voltage of the power supply is too high, D is turned on, and the transistor T is turned on. The collector potential will change from the original high level (5V) to the low level, and the voltage through the standby control line. Put the TV into standby protection.

 

3, arc suppression circuit

When a suitable Zener diode is connected in parallel on the inductor coil (or the same principle as a normal diode), when the coil is turned off, the high voltage generated by the release of electromagnetic energy is used by the diode. Absorbed, so when the switch is turned off, the arc of the switch is eliminated. This application circuit is used more in the industry, such as some higher power electromagnetic control circuits.

 

 

8.  The difference between Zener diode and TVS diode

 

Transient interference of voltage and current is the main cause of damage to electronic circuits and equipment, often causing incalculable losses. These disturbances usually come from the start-stop operation of power equipment, the instability of the AC grid, lightning strikes and electrostatic discharges. Fortunately, the emergence of a high-performance circuit protection device TVS has effectively suppressed transient interference. TVS (TRANSIENT VOLTAGE SUPPRESSOR) or transient voltage suppression diode is a new product developed on the basis of the Zener process. Its circuit symbol is the same as that of a normal Zener diode. Its shape is similar to that of a normal diode. When the TVS tube is subjected to an instantaneous high-energy shock, it can be made at a very high speed (up to 1*10-12 seconds). The impedance is suddenly reduced while absorbing a large current, clamping the voltage across it to a predetermined value, thereby ensuring that subsequent circuit components are protected from transient high energy shocks.

 

Both TVS and Zener regulators can be used as voltage regulators, but the TVS tube Zener breakdown current is smaller. The voltage regulation greater than 10V is only 1mA. Relatively, the Zener diode breakdown current is much larger, but Zener Diode voltage regulation accuracy can be done relatively high.

 

It generally works in a reverse-off state in the circuit, at which point it does not affect any function of the circuit. Under the specified reverse application conditions, TVS has a large transient transient voltage or pulse current due to lightning and various electrical interferences in the circuit (which can reach up to 1×10-12 seconds in a very short time) quickly turn into the reverse conduction state and clamp the voltage of the circuit to the required safety value, thus effectively protecting the precision components in the electronic circuit from damage. After the interference pulse has passed, the TVS turns to the reverse cut-off state. Since the clamp voltage is lower than the maximum withstand voltage of other devices in the circuit during reverse conduction, it protects other components. The TVS can withstand transient pulse power up to kilowatts and has a clamping time of only 1 ps. TVS can be divided into one-way and two-way TVS according to polarity. Unidirectional TVS is generally applicable to DC circuits, and bidirectional TVS is generally applicable to AC circuits. Because TVS has a fast action, long life and easy to use, it has a wide range of applications in the field of transient voltage protection.

 


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