Summary :
In the field of electrical circuit engineering, the goal is to achieve the capabilities of the product that is being developed. Engineers take proper care of any side effects caused by the elements, like heat issues. This is accomplished through effective heat dissipation control, high-frequency radiation, such as EMI or RFI, and the possibility of harmonic distortions being minimized. However, external effects could significantly impact the life span of an electrical circuit, for instance, overload or overvoltage on the electric lines. The majority of electric boards must contain specific components, which under normal conditions are ‘invisible” and in a position to safeguard the circuit in the event of sudden events such as the high-voltage transient. These transients are usually caused by sudden changes in the load of connected courses, as well as power source fluctuations and electronic disturbances in coupled cables or switching events, lightning, or ESD. This abstract will discuss the possibilities of circuit protections to stop transient overvoltage using cost-effective solutions.
Two kinds of transient overvoltage suppression devices use action when spikes occur. Their task is to limit the voltage to the level the circuit behind could tolerate.
The clamping” devices start conducting when the surge voltage is the voltage known as breakdown, which is the limit the machines are built for. They also maintain the same clamping voltage. The devices are restored to their non-conducting status when the voltage falls below this threshold. The high voltage spikes are cut off and maintained to a reasonable level through clamping. Clamping suppressors include TVS diodes (Transient Voltage Suppressor Diodes) and varistors ( MOV, MLV, etc.).
The “crowbar” devices start to operate when they exceed the threshold voltage and cause the voltage to fall to a low level. The protected circuit is mainly connected to the ground by an extremely low impedance. The transient energy generated by the brief event must be absorbed by the line or source impedance. The circuit won’t function when the device’s TVS has been turned “ON.” Crowbars can be switched to a non-conductive mode after the voltage of the driver returns after the transient has passed. The most common crowbars include GDTs (Gas Discharge Tubes) and Thyristors.
Device Advantages
- Clamping devices Limiting voltage to clamp voltage
- Quick reaction time (<0.1 ns)
- Limited power rating
- Capacitance rises with increasing power rating.
Device Disadvantages
- Crowbar devices have a High power rating
- Shunting surge currents back to the ground
- It is not able to absorb the energy
- It can be not easy to turn off
Suppressor structures
Metal oxide varistors (MOV)
MOVs are resistors that depend on voltage by forming a matrix from zinc oxide grains separated by bismuth and other metal oxide boundaries. These possess the same properties as making a semi-conductive PN junction with breakdown voltages of 2 and 3 Volts. The hundreds of parallel and serial grain boundaries work like diodes that are in series and parallel. As junction conduct increases, current flows across them when a surge occurs. By altering the grain size, the thickness and size, and the MOV parameters, such as the voltage and current limits, can be determined from the size of the chip to multi-kV units. MOVs are bi-directional and symmetrical. Since they are inexpensive devices, they are frequently used in surge protection. However, a negative aspect is known as “ageing,” in which MOVs can only handle large surge currents in a minimal time. The greater the voltage of the surge is, the smaller the number of waves that MOV will be able to handle during its life. In the event of overload, MOVS initially fails short, and the following current results in a burning out and an open circuit. The heat is then released from the MOV. A lot of heat is generated, which could lead to the carbonization of the PCB.
Consequently, in the open state, leakage currents will flow. It is also crucial to shield the circuit by fusing it with a device. (Good illustration is the 2Pro Devices of TE Circuit Protection described in Elektronet 2011/05. MOV is thermally connected to the PolySwitch device, which offers overcurrent and overheat protection.)
Multilayer varistors (MLV)
MLVs are designed to ward off electrical discharges or surges (ESD) and are constructed with various fine-grain semi-conductive ceramic layers within a particular installation. The second layer is attached to identical electrodes. This arrangement provides a significantly greater cross-sectional space for the active conduction of transients. This allows for greater power output and higher resistances at lower voltages, with quicker response times than MOVs. The device’s Sharp, symmetrical breakdown properties offer excellent protection against harmful voltage fluctuations.
Polymer devices
Polymer devices are typically utilized to provide ESD protection due to their TVS-specific behavior and extremely low capacitance. They make ideal choices for high-speed data lines. The polycrystalline material has electrical properties comparable to the thyristor’s current curve. The voltage that triggers the polymer could be within the kV range, while the clamping voltage can typically be 20 to 50 V. The properties are usually assured for a small amount (few thousand) of batteries.
Transient Voltage Suppressor Diodes (TVSD)
Silicon TVS devices feature a P-N junction similar to the Zener diode but with a more extensive cross-section and a proportional increase in the power rating of its surges. They can be stacked in series and parallel to increase the power and voltage capabilities. TVS Diodes could be bi-directional or unidirectional, and they have a rapid response in the sub-nanosecond area of response time and also have a low clamping factor (1,33, which is the proportion between the breakdown and clamping voltage). The cause of failure in TVSD TVSD is a short circuit.
Gas Discharge Tubes (GDT)
GDTs are like carbon and air gaps, except that electrodes in parallel are sealed hermetically and placed in a ceramic or glass cavity containing low-pressure inert gas. When the surge voltage exceeds the limit, the gas can ionize, and the GDT “fires” and begins to conduct the voltage to the ground. These devices are” voltage rated. The dimensions and spacing of electrodes determine the current and voltage ratings. They can handle highly high surge currents while they have a prolonged response. In the OFF state, their impedance is exceptionally high. The failure mechanisms for GDT are generally open.
Thyristors
Thyristors are multi-layered silicon devices and can be bi-directional or unidirectional. They are tiny when compared to their powerful capacity for surge. The response is a quick and precise turn-on and smooth within the power limit. The capacitance is extremely low, and so is the leakage voltage. There is no issue with lifetime; however, the switch-off is something to consider during the design phase. The most common cause of failure is an electrical short.
DeviceAdvantagesDisadvantagesProperties
- MOVLow cost
- Transient energy dissipates as heat
- Ability to handle high surge currents
- Aging effect
- Currents of high leakage and high clamping voltage
- Very nonlinear V-I relation
- Clamping factor 4
- Capacity increase
- Medium response time
- Thermal runaway
- Inherently bi-directional
- Power rating is increasing along in proportion to the size
- MLVsLow cost
- Small size, outstanding energy/volume ratio
- Capacity reduction
- Aging
- Currents with high leakage
- Faster response time than MOVs
- Low operating voltage
- Polymer devices have very low capacitance
- Small size
- Cost-effective
- Rapid response
- Lifetime limit
- A limited temperature range ( typically 85degC)
- High trigger voltage
- TVSDNo effect of aging
- Rapid response time
- The clamping force is low, ~1.33 (standard part)
- Low clamping voltages
- Low capacitance
- Very low leakage in the current
- Costs higher
- A bit less current for surge rating
- The dissipation of energy is minimal due to the low volume of material in the junction.
- In arrays and other unique combinations
- GDTHigh-voltage current
- High-OFF-state impedance There is no leakage current
- Response time is slow
- Very expensive
- High breakdown voltage
- Sometimes it is necessary to utilize another device
- Inherently bi-directional
- The smallest Shunt resistance
- Capacity low 1 to 5 pF
- ThyristorsHigh potential for surge current
- Low leakage current, high off-state impedance. leakage current
- Low On-State Voltage
- No issue for the rest of your life.
- It isn’t easy to turn off the computer.
- They have quicker responses than varistors but are slower than TVSD.
SFI Super High Peak Current Suppressor Series – cost-optimized general solutions
SFI has developed new overvoltage protection devices, including the SMD SUPER Series, that utilize unique ceramic and technical formulas using multilayer varistor technologies that result in Chip Surge Protection Devices (CSPD). The unique technology SFI developed has broken through traditional systems’ technology bottlenecks. In comparison to the existing products such as MLV / MOV/TVS and GDT, CSPD offers several advantages that focus on cost optimization and the concept of downsizing into account, an excellent option for surge suppressors, transients, and other overvoltage protection components. In the engineering field, disk-type varistors are generally extensively used if a protection device with a large capacity of up to 6500A is needed.
The new professional suppression device is multilayer SHC Series (Super High Peak Current). SFI can offer more current products in the size of a compact. In comparison to other market MLV range products. The latest SHC Series upgrades the present capabilities with less wear and tear and an increased temperature characteristic. In many cases, the components could even replace TVS and Zener diodes.
Features :
- ultra-high current capability for handling up to 6500A
- the ability to generate high voltage surges and current capability
- Ultra-high ESD handling capacity ( ESD Test > 30kV)
- It can withstand further storm events
- breakdown voltage concentration ratio greater than 99.5 percent
- Exponents with high nonlinearity high nonlinear exponent of up to 50
- ultra-low leakage current at 5uA
- high temperatures of up to high temperatures up to
- RoHS fully compliant and lead-free SMD types
- compatible with IR Reflow and Wave SMT process that is compatible with IR reflow and wave
Compared to the existing devices operating under the same power and current conditions, this CSP is smaller and reflow-solderable, which means that the additional technological steps required to make through-hole disk varistors are removed. In some instances, even costly MOV and GDT combos can be replaced by a single SHC CSPD, giving more area on the PCB and reducing the cost of spare components.
Samples of engineering and datasheets and consultation are available at the Budapest Office of Endrich Bauelemente Vertriebs GmbH.