For outdoor LED lighting fixtures, the coupling path of lightning surge voltage in the LED driver and its damage mode are analyzed, and corresponding protective measures are proposed. The related protection circuit greatly improves the anti-lightning surge performance of the LED driver and improves the performance. Quality and reliability of indoor LED driver.
Indoor Led Driver
In recent years, LED street lights have become more and more widely used. LED drivers for outdoor applications have higher requirements for product reliability, especially high lightning surge protection levels. The surge voltage in the power grid is mainly of the following types: ①Direct lightning strike refers to the lightning strike that occurs directly between a charged thunder cloud and the discharged object. Direct lightning strikes contain great energy. The peak voltage can reach 5 000 kV. Large destructive force; ② Conducted lightning refers to the transient high voltage caused by lightning hitting the grid line or electromagnetic induction, which is transmitted to the LED street light by the grid line or other communication lines; ③ Switching over-voltage, inductive load in the grid and When the capacitive load is switched on or off, transient pulse high voltage or pulse high current is generally generated on the line, and the instantaneous peak value can reach several times the rated voltage of the power grid, which will seriously damage the street light equipment, and the type of damage is similar to the lightning strike. The anti-surge design of LED driver is mainly for the protection of conducted lightning and switch over-voltage. The outdoor LED driver supplier introduced a typical LED street lightening circuit design scheme.
1.Surge immunity test requirements
IEC and ANSI have established corresponding specifications for lightning surge test equipment, test conditions and test methods. IEC 61000-4-5 is a safety specification specifically for surge immunity test equipment and test methods. The surge voltage waveform of the surge immunity test is 1. 2 / 50μs-8 / 20μs combined wave pulse, see Figure 1 for details. For LED driving power supplies for outdoor applications, the voltage level of the surge immunity test requires at least 6 kV in differential mode, 6 kV in common mode, or even higher. ANSI C82. The minimum surge protection level of outdoor lamps is specified in 77, combined wave differential mode common mode 6 kV / 3 kA, 2 Ω internal resistance.
2.Lightning protection design scheme of LED street light system
This solution consists of two levels of protection: an external SPD surge protector and a surge protection circuit built into the LED driver. SPD surge protectors are particularly important as the first stage, clamping the 10 kV to 30 kV power grid surge voltage to 4 to 8 kV. A second-level protection circuit built into the LED driver further clamps the surge voltage of 4 to 8 kV to within a few hundred V to protect other circuits in the LED driver.
Surge protection is generally divided into two types according to the coupling mode: differential mode surge and common mode surge. Differential mode surge refers to the surge voltage coupled between live line L and neutral N; common mode surge refers to the coupling of live line L and ground PE, or neutral line N and ground PE, or zero live line And ground voltage. Generally speaking, differential mode surge is more destructive to the product, and the protection circuit design is more complicated.
Surge protection is generally divided into two types according to the coupling mode: differential mode surge and common mode surge. Differential mode surge refers to the surge voltage coupled between live line L and neutral N; common mode surge refers to the coupling of live line L and ground PE, or neutral line N and ground PE, or zero live line And ground voltage. Generally speaking, differential mode surge is more destructive to the product, and the protection circuit design is more complicated.
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