To make LED lamps and lanterns can work reliably for a long time, need to get the LED drive power MOSFET in power switch tube (including single chip LED drive power supply integrated circuit), as well as high-power LED installation radiator, right so that the chip internal heat from escaping through the timely, avoid caused by bad cooling tube core temperature more than the highest junction temperature, make the power supply cannot work normally, even damage the chip. This chapter introduces the design method of single-chip LED drive power supply, power switch tube and high-power LED radiator respectively, and gives the corresponding design examples. Finally, the methods to improve the heat dissipation performance of PCB, common faults of main heating components and solutions are introduced.
According to the original diagram provided by the manufacturer, the radiator design of a single LED driven power integrated circuit can be completed by calculating the average power consumption of the chip PD. This method is simple and practical, and has the value of popularization and application.
Single chip LED drive power supply integrated circuit power mainly by the internal power switch tube (MOSFET) generated, the power of other units in the chip circuit generally negligible, in low voltage, large current transmission time also need to consider the power output rectifier tube. The important difference between the switching power supply and the linear regulator power supply is that the power switch tube works in the high frequency switching state. Due to the constant change of power loss P in the switching cycle, it is difficult to accurately calculate the PD value.
According to the analysis, the power loss of the single LED driver mainly includes two parts: conduction loss and switching loss. Conduction loss is caused by Rs(ON) of MOSFET. Monolithic switch power supply, for example, early products TO227Y Rns (ON = 4.392 (100 ℃ when the typical values, similarly hereinafter), and the output power and the fairly new product model TOP258 RAScON 2.5 Ω; The smaller the on resistance, the lower the on resistance loss. Switching loss is refers to the MOSFET drain capacitance C nu caused by the loss. Normally, the on-state resistance loss is much larger than the switching loss, and the switching loss can be neglected. It should be pointed out that when calculating the thermal parameters of a monolithic IFD drive power supply integrated circuit, only the loss of the device itself should be considered.