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10 Problems that Can Cause Led Driver Failure (Part 1)

Mar. 10, 2020


The main function of CE LED driver is to convert the input ac voltage source into the output voltage source which can change with LED Vf (positive wizard on voltage drop). As a key component of LED lighting, the quality of LED driver directly affects the reliability and stability of the whole lamp. CE LED driver manufacturer, starting from LED driver and other related technologies and customer application experience, sorted out and analyzed many failures in lamp design and application:

1. The change range of LED bead Vf is not considered, resulting in low lamp efficiency and even unstable work

The load end of LED lamps is generally composed of a number of LED strings and its working voltage Vo=Vf*Ns, where Ns refers to the number of LED series.LED Vf changes with the temperature, in general, at a constant current, Vf becomes low at high temperature, Vf becomes high at low temperature.Therefore, the load working voltage of LED lamp corresponds to VoL at high temperature, and the load working voltage of LED lamp corresponds to VoH at low temperature. When selecting LED driver, it is necessary to consider that the output voltage range of the driver is greater than VoL~VoH.

If the maximum output voltage of the selected LED driver is lower than VoH, the maximum power of the lamp may not reach the actual required power at low temperature; if the minimum voltage of the selected LED driver is higher than VoL, the output of the driver may be out of the working range at high temperature, the work is unstable, and the lamp will flicker.

However, considering the comprehensive cost and efficiency, we cannot blindly pursue the ultra-wide output voltage range of dimmable LED driver: because the driver voltage is only in a certain range, the driver efficiency is the highest.Beyond the range of efficiency, power factor (PF) will become worse, and the driver output voltage range design is too wide, resulting in higher costs, efficiency can not be optimized.

12v 15w Mini Led Driver

12v 15w Mini Led Driver

2. Power margin and reduction requirements are not considered

In general, the nominal power of LED driver refers to the data measured under the rated environment and rated voltage. Considering that different customers will have different applications, most LED drive suppliers will provide power downsizing curves (common ones are load vs ambient temperature downsizing curves and load vs input voltage downsizing curves) in their product specifications.

The red curve represents the power reduction curve of the LED driver's load with the change of ambient temperature under the input of 120Vac. When the ambient temperature is below 50℃, the driver is allowed to be 100% full load. When the ambient temperature is up to 70℃, the driver can only reduce the load to 60%. When the ambient temperature is between 50℃ and 70℃, the driver load decreases linearly with the temperature.

The blue curve shows the power reduction curve of LED driver under the input of 230Vac or 277Vac with the load changing with the ambient temperature. The principle is the same.

LED driver at the ambient temperature of 55℃, its output power with the change of input voltage curve.When the input voltage is 140Vac, the load of the driver is allowed to be 100% full load.If the output power is unchanged, the input current will rise, resulting in increased loss at the input end, reduced efficiency, rising device temperature, some temperature points may exceed the standard, or even cause device failure.

When the input voltage is less than 140Vac, the output load of the driver is required to decrease linearly with the input voltage. After understanding the above derating curve and the corresponding requirements, when choosing LED driver should be based on the actual use of the ambient temperature and input voltage, comprehensive consideration and selection, and set aside the derating margin.