What is Surge
Classification of surge protectors
According to working principle
⒈Switch type: Its working principle is that it presents high impedance when there is no instantaneous overvoltage, but once it responds to the lightning instantaneous overvoltage, its impedance suddenly changes to a low value, allowing lightning current to pass. When used as such devices, the devices include: discharge gap, gas discharge tube, thyristor, etc.
⒉Voltage-limiting type: Its working principle is high resistance when there is no instantaneous overvoltage, but its impedance will continue to decrease with the increase of surge current and voltage, and its current and voltage characteristics are strongly nonlinear. The devices used for such devices are: zinc oxide, varistors, suppression diodes, avalanche diodes, etc.
⒊Shunt type or choke type
Shunt type: It is connected in parallel with the equipment to be protected, which presents a low impedance to the lightning pulse and high impedance to the normal operating frequency.
Choke type: It is connected in series with the equipment to be protected, which presents high impedance to lightning pulses, and presents low impedance to normal operating frequencies.
The devices used for such devices are: choke coils, high-pass filters, low-pass filters, 1/4 wavelength short-circuit devices, etc.
By purpose
⑴Power protector: AC power protector, DC power protector, switching power protector, etc.
The AC power lightning protection module is suitable for the power protection of power distribution rooms, power distribution cabinets, switch cabinets, AC and DC power distribution panels, etc.; the building has outdoor input power distribution boxes and building floor power distribution boxes; power wave Surge protectors are used for low-voltage (220/380VAC) industrial power grids and civil power grids; in power systems, they are mainly used for three-phase power input or output in the power supply panel of the main control room of the automation room and substation. It is suitable for various DC power supply systems, such as: DC power distribution panel; DC power supply equipment; DC distribution box; electronic information system cabinet; output terminal of secondary power supply equipment.
⑵Signal protector: low-frequency signal protector, high-frequency signal protector, antenna feeder protector, etc.
The scope of application of the network signal lightning protection device is used for 10/100Mbps SWITCH, HUB, ROUTER and other network equipment lightning strikes and lightning electromagnetic pulse induced overvoltage protection; ·Network room network switch protection; ·Network room server protection; ·Network room other Protection of equipment with network interface; ·24-port integrated lightning protection box is mainly used in integrated network cabinets and sub-switch cabinets for centralized protection of multiple signal channels. Signal surge protectors. Video signal lightning protection devices are mainly used for point-to-point video signal equipment. The synergy protection can protect various video transmission equipment from the harm caused by the induced lightning strike and surge voltage from the signal transmission line, and it is also applicable to RF transmission under the same working voltage. The integrated multi-port video lightning protection box is mainly used for centralized protection of control equipment such as hard disk video recorders and video cutters in the integrated control cabinet.
LED street light anti-surge design scheme
LED street lights are installed outdoors and are easily damaged by lightning or surge voltage, so lightning protection units need to be designed. The lightning protection of street lights is divided into two levels. The first level is protection against direct lightning strikes, which are dealt with by using metal lamp poles to ground. The second level is to protect against conducted lightning strikes and induced lightning strikes, grid voltage fluctuations, etc. The surge absorber Varistor is used as the main component to design the lightning protection unit.
At present, there is a very popular thermal protection surge absorber on the market, which can simplify the lightning protection design of LED street lights. This new type of integrated thermal fuse and Varistor can be safely isolated before Varistor fails and catches fire. It meets the requirements of UL1449 third edition electrical safety certification.
Traditional LED drive power supplies use current fuse as overcurrent protection, and the latest generation of thermal protection winding fuse resistors have better price and performance than current fuse, and better safety performance than ordinary winding resistors.
Design a thermal protection surge absorber Thermo-fuse Varistor at the front end of the power supply to prevent surges or lightning strikes.
When ordinary wire-wound resistors are used as overcurrent protection, a fault current above 4 times the rated current is required to quickly disconnect. At 2 times the rated current, the disconnection time is long, and high temperature of 300℃~500℃ will be generated, which is a safety hazard. The latest thermal protection winding fuse resistors can be quickly disconnected at 1.5 to 2 times the rated current, which is safe and reliable.
The Defect of LED Light-Surge Voltage
All LED lamps and lanterns have this fatal defect, and so far, no one has put forward a good solution. All those engaged in LED power supply or finished LED lamps and lanterns have avoided this problem and pretended not to know it. However, in actual mass production, this problem is endless. Of course, there are more people who don’t know how to understand it.
Phenomenon description: the most common problem is that hundreds of lamps in a project are often damaged for no reason. The common one is like the LED street lamp installed on a street. It doesn’t light up from time to time, and it often breaks down. It’s repaired and broken, and then it’s repaired. There are also led fluorescent lamps, many of which use non isolated power sources. It’s often found that they are damaged during mass production. The root cause is all here. It’s all caused by surge voltage, There are many reasons for surge voltage, such as outdoor lightning strike, or large load on, off, voltage clutter and so on. According to the written method, it is a very high voltage, often up to kilovolts, which is instantly applied to the input power terminal, and then transferred from the input power terminal to the output terminal.
As we all know, the PWM adjustment of switching power supply needs several clock cycles. If the input voltage changes instantaneously (up to kilovolts) and the time is very short (tens or hundreds of MS), the switching power supply has no time to adjust at all. At this time, the performance is that the instantaneous high voltage is transmitted to the output end, especially the step-down circuit for LED fluorescent lamps, Because the load is in series in the 300V high voltage circuit, the 300V high voltage increases instantly, and the high voltage is added to the output immediately. The isolated power supply will be better, but many of them are doomed.
Some people say that TVs, choke and X-Capacitor are not very useful in fact. Because LEDs working at normal current are very sensitive to voltage changes. We know that when LEDs work at stable current, such as straw hat lamp, working at 20mA, the stable voltage is about 3.1V. When the voltage at both ends increases by 0.1V, the current at both ends may increase by tens of percent or 0.5V instead of a few percent, Although the above components can play a role, the voltage filtered by TVS is still more than 400V.
This voltage will still make the output current increase sharply. At this time, the output is equivalent to a short circuit. The performance of non isolated power supply is to instantly burst the constant current ring, or even the switch tube, which directly leads to the annihilation of LED, The phenomenon of isolating the power supply is to blow up the switch tube, resulting in the light not on. This is the root cause. This is determined by the LED characteristics.
Many constant voltage power supplies, such as 12V ordinary constant voltage power supply, often find that the damage rate is very low when they are loaded with some other loads. However, when the same power supply is used to connect three LEDs in a series, several LEDs in a series and then connect them together, many of them are damaged. This is the reason. Because of the load characteristics of LEDs, it is easier to damage itself and the power supply.
LED lamps surge test standard
Immunity test
Elecromagnetic compatibility (EMC) part 4: Testing and Measurement Techniques, Section 5:Surge Immunity Test Elecromagnetic compatibility and Ratio spectrum Matters (ERM), Telecommunication metwork equipment, EMC requirements.
Surge test conditions
1 environmental condition
1.1 electromagnetic environment:
The electromagnetic environment of the laboratory should not affect the test results.
1.2 natural environment:
Temperature: 15 ℃ ~ 35 ℃; relative humidity: 10% ~ 75%. Atmospheric pressure: 86kpa ～ 106kpa
- When the vertical equipment is placed on the grounding reference plane, it should be separated from it by insulating support. Table equipment shall be placed on the insulation test bench.
- requirements for auxiliary test equipment
In order to accurately reflect the interference of the tested equipment, CDN is used to isolate EUT and AE when possible.
Power supply requirements
1 all power supplies provided to EUT shall meet the requirements of EUT.
2 when AC power supply is used, EUT and test instrument shall be powered by different phases respectively.
Equipment requirements
1 experimental requirements
The equipment can generate voltage waveform meeting the requirements of iec61000-4-5 standard.
2 test equipment
The following equipment is part of the experimental configuration: EUT, AE, cable (specified type and length), coupling device, signal generator, decoupling network / protection device.
How to solve the surge problem in LED drive power
With the development of LED lighting technology, LED lights are used in more occasions. In urban construction, people are more and more willing to choose this energy-saving and beautiful lighting method. LED landscape lighting has electrical fault protection requirements. When electrical faults occur in the lighting circuit and LED drive power supply, short circuit protection, overload protection and grounding protection should be provided to prevent personal electric shock, electrical circuit damage and electrical fire.
Lightning strikes are a common natural phenomenon. According to statistics, the damage and losses caused by lightning strikes are calculated in hundreds of billions of dollars every year worldwide. LED landscape lighting is also afraid of this threat. This article mainly talks about how to solve the surge protection problem in LED landscape lighting drive power from the perspective of circuit protection component selection.
SMD varistor is a common over-voltage protection device, which can act quickly when a surge occurs, clamping the circuit voltage to a fixed value, so that the subsequent circuit is protected. With the increasingly mature development of LED lighting technology and for aesthetic considerations, the volume of LED lights has become smaller and smaller. The chip varistor must meet the size requirements of the package and meet the power requirements for stable radiant lighting of the LED lights. Ordinary chip varistors can no longer meet the needs of LED circuit protection.
The high-energy miniature chip varistor has the characteristics of small size and high power. In addition, it also has the following characteristics:
★ Comply with RoHS standard.
★ SMD type, product sizes are 0806, 1206, 1210.
★ Comply with IEC61000-4-5 standard.
★ Bidirectional and symmetrical V/I characteristics.
★ Large withstand voltage surge current capability: 200A (@8/20μS).
★ Operating temperature range: -40℃~+85℃.
★ Multi-layer structure can provide higher power consumption.
When the LED circuit is overloaded or overvoltage, it can immediately start the protection, so that the power supply path of the LED is disconnected, so that the LED and the power supply can be protected. At the same time, the high-energy miniature chip varistor for Shuoke LED is an economical and affordable device. Its use will not make the cost of mass-produced civilian products such as LED lamps too high.
