Summary :
If the voltage of the electric element or circuit rises over the max-rated amount, the aspect may be under-stressing, based on the time, which could be a temporary spike or a constant surge. Overvoltage can occur due to natural causes such as lighting or human-caused, such as electrostatic discharge, switching loads with high inductive power, or operating circuits that produce electromagnetic interference. Reliable protection against overvoltage is crucial to practical design. Avalanche Breakdown Diodes (Transient Voltage Suppressor Diodes) made by Protek Devices offer a great range of protection against circuit overvoltage that ranges starting at 2.8V up to 400 Volts with a power range of 80 watts to 30 watts.
Overvoltage events
Voltage transients can be classified into ESD, Surge, and Load dump. Electrostatic discharge (ESD) occurs when a charge exchanges between two objects of different directions, mostly between metal objects. A visible spark is typically created by dissolving the isolation layer between the two things. This is demonstrated by a 2-15 kV (level 1 to 4) voltage of discharge from the air, relatively low energy, and a short (ns) time.
A surge can be described as a distinct type of transient overvoltage and is distinguished by a longer (microsecond) duration and enormous energy. Short switches or lightning strikes cause a surge.
A load dump is a lengthy, typically millisecond-long overvoltage event that is usually triggered by shutting off the inductive source, such as a battery cut off from the charging circuit and charging. The long rise of milliseconds will be followed by a gradual decline, which results in significant energy transient.
Transient Voltage Suppressors
Silicon Avalanche Junction TVS (transient voltage suppressor) devices have P/N junctions similar to the Zener diode but with larger cross-sections proportional to the surge power handling capability of the gadget. One may choose larger sizes to handle longer-lasting transients for more excellent heat dissipation. These devices range in size from chip size to larger modules. While they are rated at lower levels of surge current than MOVs, their voltage and power capability capacity can be enhanced by using more devices in series or in parallel. TVS diodes can handle today’s high surge currents. For instance, Protek’s 2700SM78CA can take 18 kA. A 600W device with a 12V rating can take an 8/20 second surge power at 140 A. The failure mechanism for the TVS diode is due to a short circuit. They respond rapidly because of silicon technology, as the response frequency is proportional to the electron’s speed. Since the device’s protection should appear invisible under normal operating conditions, it is not visible on higher frequencies; there are times when ultra-low capacitance must be reached (pF). GBLC08CLC has a capacity of 0.4 percent. TVS devices can be utilized in unidirectional configurations to support DC lines and in bidirectional arrangements to support AC applications. Contrary to MOVs, which show an initial perfect leakage behavior but then the performance declines after each exposure to surges, TVS does not exhibit any aging effects as the leakage current feature is not affected by time. Its response time is in the sub-nanoseconds range and has a deficient clamping factor (~1.33).
Solutions for protection against lightning flashes
Lightning poses the greatest danger to outdoor electronics that typically have 20 kA peak power and produce powerful magnetic and electric fields, which can cause coupling between nearby power lines and data lines, causing damage to equipment. Typically, a two-stage security comprising a crowbar as the primary and secondary protection that clamps are a good solution. On the primary side, damping resistors (R1, R2) are employed to limit current flow and GDT devices. Thyristor Surge Suppressors in standard mode protections are utilized for shunting this to the ground.
To comply with the standards, the primary protection must withstand voltages greater than 5 kV and surge currents of up to 250 A in the case of TSS and 10-20 kA in GDT.
Near the indoor equipment, a secondary level of protection needs to be set to block the remaining light and switching transients. The TVS devices divert the current from the transient to clamp the voltage and protect the equipment. The rapid response and small clamping current of the TVS is a way to compensate for the high firing voltage of GDTs. By norms and standards, the secondary protection is required to stand up to voltages of 1500V or more and surge currents that exceed 100A (8/20 us 10, 1000 us, and 10/700 US surge waves).
The figure shows that protection is provided to both sides of an Ethernet magnet transformer. On the side connected to the line of the isolation transformer, a low-capacity TVS (Z1) offers protection against current and voltage differential modes of surges. On the chip side, two TVS devices are shifted into the ground to shield the IC from the energy of transients, which is transmitted to the transformer. Another option is to utilize steer diodes for the chip that is not as high in junction capacitance, decreasing the loss of signals inserted in high-speed data lines.
Solutions for protection against ESD
Electrostatic discharge is a one-time quick high voltage, and highly current-intensive event. Flip chips are suggested in low-speed I/O or power supply applications due to their compact size and affordable cost. For applications requiring high speeds, using low-capacitance devices is essential ( SR2.8, SVLU2.8-4, the GBLCxxC, and the SRV05-4). A TVS/Steering diode combo can reduce lines-line ESD transients.
Paralleling TVS devices for more excellent power capabilities
Protek’s TVS diodes can be found in a voltage range from 2.8V to 400V and in power ratings ranging from 20W up to 30kW. They are, however, used in higher power and voltage combination by arranging the devices in serial or parallel. Its power ratings can use the pulse waveform used in industry ( e.g., 10/1000 us) with an increased time of 10us and an exponential decay that is half of its peak at 1000 us. For applications where the transient power goes beyond the limit, it is possible to set up multiple TVs in a parallel arrangement that will give similar voltage responses to a single unit. However, the capability to handle current is increased. Each diode must be identical in the clamping voltage to share equally that transient voltage.
Even if all three TVS diodes share the same part numbers, their breakdown voltage, reverse leakage current, and clamping voltage are distinct values. Therefore, matching must be achieved by making selections.
Peak pulse power (Ppp)
Peak power ratings classify TVS devices for a specific pulse shape. Power rating can be displayed as a graph representing an estimate of power (P pp) for a specified period (t d).
The pulse duration is defined as the front time minus the fall time. In other words, the first time represents the time required to reach the peak, while fall time is defined as the time needed for the pulse to fall to 50% of the peak value.
The maximum peak power of the pulse is the sum of the maximum clamping voltage multiplied by the max peak power of each pulse. The maximum clamping voltage is constant, independent of the time, which is that of the threshold voltage at the junction that forms the diode. Thus, the power curve is the rate of current over time.