How to use a simple method to estimate the number of LED junction temperature?
When multiple LEDs are connected in series and a constant current power supply is used, the temperature effect of the volt-ampere characteristic is used to infer the degree of rise of the junction temperature
In many applications (such as fluorescent lamps and street lamps), many LEDs are often connected in series. At this time, the temperature coefficient effect of LEDs is more obvious. Because the effect of using a constant current power supply is equivalent to superimposing the volt-ampere characteristics of each LED along the voltage axis.
If the temperature rise is 60 degrees, then the volt-ampere characteristics will shift to the left by 0.12V. If 10 LEDs are connected in series, all volt-ampere characteristics will be shifted to the left, and the total deviation will reach 1.2V. This is a considerable number.
Conversely, this characteristic of LED can also be used to measure its junction temperature. For example, there is a combination of 10 series and 3 parallel LEDs. After the constant current power supply is connected, the measured forward voltage drop is reduced from 32.3V to 30.6V. The change reaches 1.7V. Then it can be inferred that the junction temperature rises to 1.7/10/.002=85 degrees
