![<?echo $_SERVER['SERVER_NAME'];?>](/template/twentyseventeen/skin/images/header.jpg)
Long life and high efficiency of LEDs are premised, that is, suitable working conditions. The main factor affecting the life and luminous efficiency is the working junction temperature of the LED. The test data provided by mainstream LED manufacturers shows that the luminous efficiency of LED is almost inversely proportional to the junction temperature, and the lifetime decreases almost exponentially with the increase of junction temperature. Therefore, controlling the junction temperature within a certain range is the key to ensuring LED lifetime and luminous efficiency. In addition to the heat dissipation measures, it is necessary to incorporate the junction temperature into the control parameters of the driving power supply.
1LED junction temperature detection
The junction temperature of the LED refers to the temperature of the PN junction. It is difficult to actually measure the junction temperature of the LED, but it can be measured indirectly according to the temperature characteristics of the LED.
The volt-ampere characteristics of LEDs are similar to those of ordinary diodes. Typical volt-ampere characteristics of blue LEDs used for white illumination are shown in Figure 1.
Figure 1 volt-ampere characteristics of LED
The volt-ampere characteristics of LEDs have the same negative temperature coefficient as other diodes, that is, the I/V curve appears to shift left when the junction temperature rises, as shown in the following figure.
Figure 2 Temperature characteristics of volt-ampere characteristics
For every 1 °C increase in junction temperature of the LED, the I/V curve will shift to the left by 1.5~4mV. If the applied voltage is constant, then the current will increase, and the current will only increase its junction temperature. High, even leading to a vicious circle. Therefore, the current LED driving power supply is generally designed to be a constant current power supply.
According to the rule that the I/V curve increases with the junction temperature and the left shift, in the case of constant current supply, the LED junction temperature can be estimated by measuring the forward voltage of the LED.
Bark Stop Collar,Best Bark Control,Remote Pet Training Collar,No Shock Bark Collar
Elite-tek Electronics Ltd , https://www.aetertek.ca