When waterproof panel light is used in complex environments such as industry and outdoors, it needs to withstand surge impacts caused by lightning strikes and grid switching.
The flyback topology is often used in low-power waterproof panel light due to its simple structure and low cost, but its surge resistance is weak. By increasing the matching design of transformer leakage inductance and output capacitance, the impact of surge current on the switch tube can be alleviated. The LLC resonant topology, with its zero voltage switching (ZVS) characteristics, can quickly reduce switching losses when a surge occurs, making it suitable for medium and high power scenarios. For example, the use of integrated PFC+ half-bridge resonant control chips such as ICL5102 can achieve efficient constant current output under wide voltage input while enhancing surge suppression capabilities.
At the AC input end, the varistor (MOV) can absorb surge energy, but its failure mode may cause a short circuit. By connecting a gas discharge tube (GDT) in parallel, secondary protection can be provided when the MOV fails, discharging the surge current to the ground. For example, when using a combination of MOV+GDT, it is necessary to ensure that the DC reference voltage of the MOV is more than 1.4 times the rated voltage of the line, and the breakdown voltage of the GDT is 20%-30% higher than that of the MOV to avoid false triggering.
Surge voltage can easily impact the subsequent circuit through the rectifier bridge. The use of a π-type filter (common-mode inductor + X capacitor + Y capacitor) can effectively suppress differential-mode and common-mode interference. For example, the common-mode inductor must meet the impedance ≥100Ω at 100kHz and the X capacitor capacity ≤0.47μF to balance surge suppression and EMI performance.
At the back end of the DC/DC conversion, a series constant current diode (CRD) can limit LED current fluctuations to avoid overcurrent damage caused by surges. At the same time, the integrated NTC thermistor and temperature sensor automatically reduce the output power when the temperature exceeds 85℃ to prevent thermal runaway.
Traditional optocouplers are easily damaged by overvoltage during surges. The use of magnetic isolation chips such as ADM2682E can withstand ±15kV ESD shocks and achieve dual isolation of signals and power supplies. By optimizing the feedback loop compensation network, the power supply can restore constant current output within 10ms after the surge to ensure stable LED brightness.
Surge current can easily cause oscillation through high-frequency parasitic parameters, so a 4-layer PCB design is required to separate the power ground from the signal ground. For example, the distance between the primary and secondary sides of the transformer is ≥8mm to reduce the coupling of the primary surge to the secondary side; the input capacitor is close to the rectifier bridge to reduce the wiring inductance (≤10nH) and reduce the surge spike.
The surge generator simulates an 8/20μs waveform to test the power supply's immunity under differential mode 1kV and common mode 2kV. For example, connecting a 1000μF electrolytic capacitor and a 0.1μF ceramic capacitor in parallel at the output end can absorb surge energy and ensure that the LED does not flicker or go out after the surge.
The constant current drive power supply of the waterproof panel light needs to be optimized in multiple dimensions such as topology, protection, filtering, feedback, and layout. For example, an industrial lighting project uses a combination of LLC resonant topology + MOV + GDT + π-type filtering, passes the IEC 61000-4-5 test, achieves output recovery within 0.5 seconds after a surge, and extends the LED life by 30%.
