Does the engineer understand the volt-ampere characteristic curve, parameters, and selection of TVS?

Transient interference of voltage and current is the main cause of damage to Electronic circuits and equipment, and often brings incalculable losses to people. These interferences usually come from the start-stop operation of power equipment, the instability of the AC power grid, lightning interference and electrostatic discharge, etc. Transient interference is almost everywhere and all the time, making people feel unpredictable. Fortunately, the emergence of a high-efficiency circuit protection device TVS has effectively suppressed transient interference.

Transient interference of voltage and current is the main cause of damage to electronic circuits and equipment, and often brings incalculable losses to people. These interferences usually come from the start-stop operation of power equipment, the instability of the AC power grid, lightning interference and electrostatic discharge, etc. Transient interference is almost everywhere and all the time, making people feel unpredictable. Fortunately, the emergence of a high-efficiency 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 Zener tube technology. Its circuit symbol is the same as that of ordinary Zener diode, and its shape is the same as that of ordinary diode. When TVS tube When both ends are subjected to an instantaneous high-energy impact, it can suddenly reduce its impedance at a very high speed (up to 1*10-12 seconds), and at the same time absorb a large current, and clamp the voltage between its two ends to one Predetermined value, so as to ensure that the following circuit components are not damaged by transient high-energy impacts.

The characteristics and parameters of TVS

Does the engineer understand the volt-ampere characteristic curve, parameters, and selection of TVS?

Figure 1 TVS characteristic curve

Features of TVS

If you observe the characteristics of the TVS with a graphic instrument, you can get the waveform shown on the left in Figure 1. If you look at this curve alone, there is no difference between the breakdown characteristics of the TVS tube and the ordinary voltage regulator tube, and it is a typical PN junction avalanche device.

But this curve only reflects a part of the TVS characteristics, and the characteristic curve shown on the right must be supplemented to reflect all the characteristics of the TVS. This is the current and voltage waveform when the TVS tube is subjected to a large current impact observed on a dual trace oscilloscope.

Curve 1 in the figure is the current waveform in the TVS tube. It indicates that the current flowing through the TVS tube suddenly rises from 1 mA to the peak value, and then decreases exponentially. The cause of this current impact may be lightning strikes, overvoltages, etc. Curve 2 is the waveform of the voltage across the TVS tube. It indicates that when the current in the TVS suddenly rises, the voltage across the TVS also rises, but it only rises to the VC value, which is slightly larger than the breakdown voltage VBR. The following circuit components play a protective role.

TVS parameters

Does the engineer understand the volt-ampere characteristic curve, parameters, and selection of TVS?

Figure 2 TVS characteristics and parameters

A. Breakdown voltage (VBR): The impedance of the TVS drops suddenly at this time, and it is in an avalanche breakdown state.

B. Test current (IT): The breakdown voltage VBR of TVS is measured at this current. Under normal circumstances, IT takes 1MA.

C. Reverse displacement voltage (VRWM): The maximum rated DC working voltage of the TVS. When the voltage at both ends of the TVS continues to rise, the TVS will be in a high-impedance state.

D. Maximum reverse leakage current (IR): The maximum current flowing through the TVS measured under the working voltage.

E. Maximum peak pulse current (IPP): The maximum surge current allowed by the TVS, which reflects the surge suppression capability of the TVS.

F. Maximum clamping voltage (VC): When the TVS tube is subjected to a transient high-energy impact, a large current flows in the tube, the peak value is IPP, and the terminal voltage rises from the VRWM value to the VC value and no longer rises, thus realizing protection effect. After the surge, IPP decays exponentially over time. When it decays to a certain value, the voltage at both ends of the TVS starts to drop from VC and returns to its original state. The ratio of the maximum clamping voltage VC to the breakdown voltage VBR is called the clamping factor Cf, expressed as Cf = VC /VBR, and the general clamping factor is only 1.2 to 1.4.

G. Peak pulse power (PP): PP is divided into four types according to different TVS of peak pulse power, including 500W, 600W, 1500W and 5000W. Maximum peak pulse power: The maximum peak pulse power is: PN=VC·IPP. Obviously, the greater the maximum peak pulse power, the greater the peak pulse current IPP that the TVS can withstand; on the other hand, after the rated peak pulse power PP is determined, the peak pulse current IPP that the TVS can withstand increases with the maximum clamping voltage VC The decrease and increase. The maximum allowable pulse power of TVS is not only related to peak pulse current and clamping voltage, but also related to pulse shape, pulse duration and ambient temperature.

The instantaneous pulse peak value that TVS can withstand can reach hundreds of amperes, and its clamp response time is only 1*10-12 seconds; the forward surge current allowed by TVS is at 25°C, 1/120 second, It can also reach 50-200 amperes. Generally speaking, the instantaneous pulse that TVS can withstand is a non-repetitive pulse. In practical applications, repetitive pulses may appear in the circuit.

TVS devices stipulate that the pulse repetition rate ratio (the ratio of pulse duration to intermittent time) is 0.01%. If this condition is not met, the accumulation of pulse power may burn the TVS. Circuit designers should pay attention to this. The work of TVS is reliable. Even if it is subjected to high-energy impacts of non-repetitive large pulses for a long time, there will be no “aging” problems. Tests have proved that after TVS works safely after 10,000 pulses, its maximum allowable pulse power is still more than 80% of the original value.

TVS is mainly used for rapid overvoltage protection of circuit components. It can “absorb” surge signals with power up to several kilowatts. TVS has many advantages such as small size, high power, fast response, no noise, low price, etc. It has a wide range of applications, such as: household appliances; electronic instruments; meters; precision equipment; computer systems; communication equipment; RS232, 485 and CAN Communication ports; ISDN protection; I/O ports; IC circuit protection; audio and video input; AC and DC power supplies; noise suppression of motors and relays, etc. It can effectively protect against over-voltage surges caused by human operation errors such as lightning, load switches, etc. The following are a few typical examples of TVS in circuit applications.

How to choose TVS

1. Determine the DC voltage or continuous working voltage of the circuit to be protected. If it is alternating current, the maximum value should be calculated, that is, the effective value *1.414 should be used.

2. The reverse displacement voltage of the TVS is the working voltage (VRWM)-select the TVS whose VRWM is equal to or greater than the operating voltage specified in step 1 above. This ensures that the current absorbed by the TVS is negligible under normal operating conditions. If the voltage specified in step 1 is higher than the VRWM of the TVS, the TVS will absorb a large amount of leakage current and be in an avalanche breakdown state, thereby affecting the operation of the circuit.

3. Maximum peak pulse power: Determine the interference pulse condition of the circuit, and determine the TVS peak pulse power that can effectively suppress the interference according to the waveform and pulse duration of the interference pulse.

4. The maximum clamping voltage (VC) of the selected TVS should be lower than the maximum withstand voltage allowed by the protected circuit.

5. Unipolar or bipolar-there is often a misunderstanding that bidirectional TVS is used to suppress reverse surge pulses, which is not the case. Two-way TVS is used for alternating current or occasions from positive and negative bidirectional pulses. TVS is sometimes used to reduce capacitance. If the circuit only has a positive level signal, then a one-way TVS is sufficient. The TVS operation mode is as follows: during a forward surge, the TVS is in a reverse avalanche breakdown state; during a reverse surge, the TVS conducts and absorbs the surge energy like a forward-biased diode. This is not the case in low-capacitance circuits. Two-way TVS should be selected to protect the low-capacitance components in the circuit from reverse surge damage.

6. If you know the more accurate inrush current IPP, you can use VC to determine its power. If you cannot determine the approximate range of the power, generally speaking, it is better to choose a larger power.

Transient interference of voltage and current is the main cause of damage to Electronic circuits and equipment, and often brings incalculable losses to people. These interferences usually come from the start-stop operation of power equipment, the instability of the AC power grid, lightning interference and electrostatic discharge, etc. Transient interference is almost everywhere and all the time, making people feel unpredictable. Fortunately, the emergence of a high-efficiency circuit protection device TVS has effectively suppressed transient interference.

Transient interference of voltage and current is the main cause of damage to electronic circuits and equipment, and often brings incalculable losses to people. These interferences usually come from the start-stop operation of power equipment, the instability of the AC power grid, lightning interference and electrostatic discharge, etc. Transient interference is almost everywhere and all the time, making people feel unpredictable. Fortunately, the emergence of a high-efficiency 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 Zener tube technology. Its circuit symbol is the same as that of ordinary Zener diode, and its shape is the same as that of ordinary diode. When TVS tube When both ends are subjected to an instantaneous high-energy impact, it can suddenly reduce its impedance at a very high speed (up to 1*10-12 seconds), and at the same time absorb a large current, and clamp the voltage between its two ends to one Predetermined value, so as to ensure that the following circuit components are not damaged by transient high-energy impacts.

The characteristics and parameters of TVS

Does the engineer understand the volt-ampere characteristic curve, parameters, and selection of TVS?

Figure 1 TVS characteristic curve

Features of TVS

If you observe the characteristics of the TVS with a graphic instrument, you can get the waveform shown on the left in Figure 1. If you look at this curve alone, there is no difference between the breakdown characteristics of the TVS tube and the ordinary voltage regulator tube, and it is a typical PN junction avalanche device.

But this curve only reflects a part of the TVS characteristics, and the characteristic curve shown on the right must be supplemented to reflect all the characteristics of the TVS. This is the current and voltage waveform when the TVS tube is subjected to a large current impact observed on a dual trace oscilloscope.

Curve 1 in the figure is the current waveform in the TVS tube. It indicates that the current flowing through the TVS tube suddenly rises from 1 mA to the peak value, and then decreases exponentially. The cause of this current impact may be lightning strikes, overvoltages, etc. Curve 2 is the waveform of the voltage across the TVS tube. It indicates that when the current in the TVS suddenly rises, the voltage across the TVS also rises, but it only rises to the VC value, which is slightly larger than the breakdown voltage VBR. The following circuit components play a protective role.

TVS parameters

Does the engineer understand the volt-ampere characteristic curve, parameters, and selection of TVS?

Figure 2 TVS characteristics and parameters

A. Breakdown voltage (VBR): The impedance of the TVS drops suddenly at this time, and it is in an avalanche breakdown state.

B. Test current (IT): The breakdown voltage VBR of TVS is measured at this current. Under normal circumstances, IT takes 1MA.

C. Reverse displacement voltage (VRWM): The maximum rated DC working voltage of the TVS. When the voltage at both ends of the TVS continues to rise, the TVS will be in a high-impedance state.

D. Maximum reverse leakage current (IR): The maximum current flowing through the TVS measured under the working voltage.

E. Maximum peak pulse current (IPP): The maximum surge current allowed by the TVS, which reflects the surge suppression capability of the TVS.

F. Maximum clamping voltage (VC): When the TVS tube is subjected to a transient high-energy impact, a large current flows in the tube, the peak value is IPP, and the terminal voltage rises from the VRWM value to the VC value and no longer rises, thus realizing protection effect. After the surge, IPP decays exponentially over time. When it decays to a certain value, the voltage at both ends of the TVS starts to drop from VC and returns to its original state. The ratio of the maximum clamping voltage VC to the breakdown voltage VBR is called the clamping factor Cf, expressed as Cf = VC /VBR, and the general clamping factor is only 1.2 to 1.4.

G. Peak pulse power (PP): PP is divided into four types according to different TVS of peak pulse power, including 500W, 600W, 1500W and 5000W. Maximum peak pulse power: The maximum peak pulse power is: PN=VC·IPP. Obviously, the greater the maximum peak pulse power, the greater the peak pulse current IPP that the TVS can withstand; on the other hand, after the rated peak pulse power PP is determined, the peak pulse current IPP that the TVS can withstand increases with the maximum clamping voltage VC The decrease and increase. The maximum allowable pulse power of TVS is not only related to peak pulse current and clamping voltage, but also related to pulse shape, pulse duration and ambient temperature.

The instantaneous pulse peak value that TVS can withstand can reach hundreds of amperes, and its clamp response time is only 1*10-12 seconds; the forward surge current allowed by TVS is at 25°C, 1/120 second, It can also reach 50-200 amperes. Generally speaking, the instantaneous pulse that TVS can withstand is a non-repetitive pulse. In practical applications, repetitive pulses may appear in the circuit.

TVS devices stipulate that the pulse repetition rate ratio (the ratio of pulse duration to intermittent time) is 0.01%. If this condition is not met, the accumulation of pulse power may burn the TVS. Circuit designers should pay attention to this. The work of TVS is reliable. Even if it is subjected to high-energy impacts of non-repetitive large pulses for a long time, there will be no “aging” problems. Tests have proved that after TVS works safely after 10,000 pulses, its maximum allowable pulse power is still more than 80% of the original value.

TVS is mainly used for rapid overvoltage protection of circuit components. It can “absorb” surge signals with power up to several kilowatts. TVS has many advantages such as small size, high power, fast response, no noise, low price, etc. It has a wide range of applications, such as: household appliances; electronic instruments; meters; precision equipment; computer systems; communication equipment; RS232, 485 and CAN Communication ports; ISDN protection; I/O ports; IC circuit protection; audio and video input; AC and DC power supplies; noise suppression of motors and relays, etc. It can effectively protect against over-voltage surges caused by human operation errors such as lightning, load switches, etc. The following are a few typical examples of TVS in circuit applications.

How to choose TVS

1. Determine the DC voltage or continuous working voltage of the circuit to be protected. If it is alternating current, the maximum value should be calculated, that is, the effective value *1.414 should be used.

2. The reverse displacement voltage of the TVS is the working voltage (VRWM)-select the TVS whose VRWM is equal to or greater than the operating voltage specified in step 1 above. This ensures that the current absorbed by the TVS is negligible under normal operating conditions. If the voltage specified in step 1 is higher than the VRWM of the TVS, the TVS will absorb a large amount of leakage current and be in an avalanche breakdown state, thereby affecting the operation of the circuit.

3. Maximum peak pulse power: Determine the interference pulse condition of the circuit, and determine the TVS peak pulse power that can effectively suppress the interference according to the waveform and pulse duration of the interference pulse.

4. The maximum clamping voltage (VC) of the selected TVS should be lower than the maximum withstand voltage allowed by the protected circuit.

5. Unipolar or bipolar-there is often a misunderstanding that bidirectional TVS is used to suppress reverse surge pulses, which is not the case. Two-way TVS is used for alternating current or occasions from positive and negative bidirectional pulses. TVS is sometimes used to reduce capacitance. If the circuit only has a positive level signal, then a one-way TVS is sufficient. The TVS operation mode is as follows: during a forward surge, the TVS is in a reverse avalanche breakdown state; during a reverse surge, the TVS conducts and absorbs the surge energy like a forward-biased diode. This is not the case in low-capacitance circuits. Two-way TVS should be selected to protect the low-capacitance components in the circuit from reverse surge damage.

6. If you know the more accurate inrush current IPP, you can use VC to determine its power. If you cannot determine the approximate range of the power, generally speaking, it is better to choose a larger power.

The Links:   NLB150XG01L-01 NL6448AC63-01

Author: Yoyokuo