Every electrical or electronic application requires circuit protection whose purpose is not only to protect the application but to advance the safety of people. Circuit protection devices protect sensitive electronic applications against imminent damages as a result of overvoltage, overcurrent, power surges, electrostatic discharge (ESD) and other catastrophic events that could be caused by the irregular flow of electric power. The protective devices serve as weak links that have been intentionally placed to promote controlled electric flow. A TVS Diode serves just that function.
A Transient Voltage Suppression diode (TVS diode) is a circuit protection device whose main function is to suppress overvoltage spikes that could potentially cause damage to the electric circuit of an electronic application. The transient suppressor protects the circuit by interrupting any instance of an overcurrent activity and diverts the overvoltage transients. These processes help to improve the overall safety of the end application and protect the application from harsh electrical conditions.
Therefore, the choice of the most appropriate TVS diode requires careful thought and consideration. When determining the most suitable choice of the transient suppressor component, it is important to strike a balance between the interplay of the factors that enhance the circuitry protection of the electronic application. These include the potential threat level posed by transient overvoltage, the operating requirements of the transient suppressor component and the protection requirements of the electronic application. Essentially, it is important to ensure that the electrical characteristics of the transient suppressor device conform to the form factor of the specific type of electrical application that will use the suppressor.
Before choosing the ideal transient attenuator for your application, you need to understand the cause and origin of transients. Transients are temporary surges in electrical current or voltage. Transients occur as a result of a sudden release of previously stored electrical energy in an electric circuit. They usually affect the circuit of electronic applications in varying degrees that range from minor glitches to catastrophic malfunctions. The transients could either be sporadic like in the case of ESD activities or could be repetitive as is the case of signal processing. In addition, the transients could either be generated from external electric abnormalities or from internal circuit connections.
Use a TVS Diode to Protect Against Transients From Internal Circuit Connections
Internal circuit connections that potential cause transients include:
- Electrical arcing- This is an instance whereby there is an electrical breakdown on the flow of the electric current as a result of an air gap occurring between the conductors thus causing a disruption in the electric field. The main cause of arcing include poor electrical wiring and grounding, poor insulation and use of faulty connectors or switches just to mention a few.
- Integrated Circuit (IC) logic switching- IC logic switching may result in the release of electric energy stored in the transistor of a circuit. The sudden release of the electric energy also causes the occurrence of transients.
- Inductive load switching – These are instances whereby the inductive reactance resists any changes in electric current thereby causing the circuit current to lag the voltage. When switching inductive loads such as transformers, generators, relays, and motors, there is a likelihood of a release of high voltages that cause transients.
Use a TVS Diode to Protect Against Transients From External Circuit Connections
Externally generated transients that could enter into an electric circuit include:
- Interruptions of electric power lines by lightning strikes or inductive switching as a result of turning on other electric applications sharing the same power sources
- Interruptions of data or signal input/ output lines such as Ethernet connection cables or serial communications lines that share the same power connection with electronic applications.
- Electrostatic discharge (ESD) – This is electric energy that could result due to an imbalance between the positive and negative charges of external objects. The electric energy is characterized by extremely high peak voltages that occur rapidly.
Understanding How Transient Voltage Suppressors Work
A TVS diode makes a popular transient attenuator because of the fact that they have the ability to clamp transient overvoltage and limit their amplitudes to safe levels that cannot cause any damages to the electronic application. The diodes instantaneously launch their clamping functionality by initiating a conducting process as soon as they detect an abnormal voltage that surpasses the preset threshold. This helps to clip the electric spikes resulting from the overvoltage to safe levels. When the overvoltage drops to normal or below the preset voltage threshold level, the diodes reverts to a non-conducting mode.
Therefore, for the devices to work, they must be placed across the supply of the electric current and be in parallel with the electric load of a circuit in order to be able to protect the load in the event that voltage transients occur.
Importance of Selecting a Suitable Circuit Protection Device
The advent of sophisticated circuitry designs has enhanced the importance and functionality of voltage suppression devices. In essence, voltage suppression devices are not only meant to protect the circuit from overvoltage transients but play a significant role in enhancing the safety of the users and in reducing the maintenance costs of the electronic applications.
Typically, the ideal selection of the appropriate circuit protection device will increase the reliability and sustainability of an electrical application. Making the right choice helps to improve the overall application uptime by minimizing the potential risks of operating malfunction; the risks of electrical shocks or fire induced by electrical shocks; the costs of repairs and replacements of critical electronic parts; and the potential liabilities as a result of low warranty return options.
Therefore, it is important to select the appropriate transient attenuator that suits a given electric application. There is the need for a user or the electrical engineer to carefully understand the distinct functions that a particular type of transient voltage device provides. A careful choice of the device helps to enhance the functionality of the protective device.
Considerations in Choosing the Ideal TVS Diode
- Circuit Operating Requirements
One of the core consideration when determining the most suitable circuit protective device is the circuit operating requirements of the electronic application. It is critical to understand the nature of the circuit that the diode powers and helps to protect.
In essence, the operating requirements of the application’s circuit will include the maximum steady-state voltage that has been defined, the optimal ambient temperature recommended and the electric current values and capacities of the electric load of a circuit.
- Clamping Voltage (VC)
Voltage clamping plays a significant role in limiting the amplitude of an electric transient across a circuit to a given threshold. Therefore the circuit protective device will begin conducting when the maximum threshold voltage that has been preset is exceeded. The device will cease conducting and return back to a non-conducting mode when the overvoltage scenario drops below the maximum preset threshold. This process ensures that the overvoltage surges have been successfully clipped off to safe levels.
- Breakdown Voltage Level (VBR)
Sometimes referred to as peak reverse standoff voltage, this is the fault current level whereby the transient suppressor component can safely divert incidences of overvoltage without necessarily interrupting the flow of the electric current. One advantage of TVS diodes is their ability to continue conducting electric current even after the voltage flowing across the diodes significantly drops below the preset breakdown voltage level.
Generally, any circuit protective device will have a preset breakdown voltage level. This is the control level of voltages in electrical circuits. When determining the suitable breakdown voltage it is imperative to ensure that the maximum breakdown voltage is higher than the maximum rated standoff level. On the other hand, care should be taken to ensure that the maximum breakdown voltage does not exceed the absolute maximum rating for the output capacitors.
The breakdown voltage is usually measured as a test current (IT) of 1mA or 10mA. When selecting the appropriate transient suppressor component, it is important to consider this parameter in relation to the electronic application which will use the diode.
- Rated standoff voltage (VWM)
Also commonly referred to as rated or maximum working peak voltage, this is the normal operating voltage specified for a device. When the electric voltage rises to this point the device will begin acting as an impedance so that it could protect the circuit from a high electric current that could cause damage. In normal circumstances, it is usually 10% below the maximum breakdown voltage hence it helps to minimize incidences of standby leakage current.
- Peak impulse current (lPP)
This is the maximum capacity of electric energy spike that a protective device can withstand without getting damaged. When selecting a suitable transient suppressor, it is critical to specify the peak impulse capability for a given transient waveform. In most diodes, the peak pulse capability will be rated either 8/20µs or 10/1000µs impulse waveform.
- Peak Pulse Power Dissipation (PPP)
The actual power dissipation of the transient suppressor component is a key determinant that should be considered when selecting the most suitable circuit protective device for your electronic application. It is calculated by multiplying the peak impulse current by the clamping voltage.
Summary: The Process of Selecting a Suitable Transient Suppressor Device
Foremost, it is imperative to determine the maximum peak operating voltage that might result at the point where you intend to protect the circuit. The maximum peak operating voltage that you determine should include the continuous DC or any repetitive AC peak voltages that are intended for normal operation. The maximum operating voltage that you have determined will then be used in establishing the suitable rated standoff voltage selection when choosing the TVS diode.
Next, you will need to choose the TVS component by establishing the breakdown voltage of the device. This voltage should be at least 10-15% higher than the rated standoff voltage.
Lastly, you will need to choose the TVS component by establishing the maximum clamping voltage of the devices when subjected to high-voltage pulse impulse conditions. In normal circumstances, the most suitable clamping voltage should be about 35-30% higher than the maximum breakdown voltage or at least 60% higher than the rated standoff voltage. Ideally, this will be your maximum clamping voltage that will trigger the conducting mode of the diode when a specified peak impulse current is reached, hence, prevent the overvoltage from damaging the electric circuit.