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Effects of Diode Voltage and Thermal Resistance on the Performance of Multichip LED Modules

This paper investigated the thermal characteristics of multichip LED modules under varying chip distances, driving currents, and number of chips in both parallel and series connections. The experimental results showed that, under the same input power, the thermal resistance and junction temperature were higher in series than in parallel due to the different diode resistances of individual chips. The deviations increase with increasing input power. Diode resistance variations significantly affected the current distributions in LED modules due to the restricted constant forward voltage in parallel connections. Nonlinear incremental increases in thermal resistance also enhanced the temperature nonuniformity in the LED module with increasing driving current. The theoretical approach substantially underestimates the junction temperature for two-chip and four-chip modules in both parallel and series connections, especially when the input power is high. The results are helpful for designing high-performance and long-term reliability multichip LED lighting modules.