At present, about 70% of the failures of LED lamps are caused by power problems. When formulating a UVC LED power supply plan, should you choose a constant voltage solution and a constant current solution?
1. Comparison of constant voltage and constant current solutions
According to statistics, about 70% of the current failures of LED lamps are power problems, about 20% are wiring and structural problems, and less than 10% are the quality problems of the LED lamp beads. Therefore, the choice of power management solutions is important for the product. Quality and reliability matter.
When formulating power solutions for UVC LEDs, one often hears about constant voltage solutions and constant current solutions. What is the difference between these two solutions?
The so-called constant current power supply means that no matter how the load changes, the output current does not change. If you connect an ammeter to a load and measure the load in parallel with a voltmeter, you will find that the greater the internal resistance of the load, the higher the output voltage, while the ammeter indication remains unchanged, which is usually used in high-power LED products. Constant voltage power supply is what we often say about regulated power supply. No matter how the load changes, the output voltage will not change. If you connect an ammeter to the load and measure the load in parallel with a voltmeter, you will find that the greater the internal resistance of the load, the smaller the output current, while the voltmeter indication remains unchanged. It is currently used in low-power LED modules and low-power LED strips. More. Of course, the above are all ideal power supplies. The actual constant current and constant voltage power supplies have power range limitations, and the power supply will automatically protect or stop output and give an alarm.
2. The choice of power supply scheme for UVC LED
Should UVC LED modules be powered by a constant voltage power supply or a constant current power supply? First of all, because the brightness of the LED lamp bead is proportional to its forward current; and the heat generation of UVC is relatively large, the size of the current directly determines the amount of heat generated by the lamp bead. Secondly, the UVC LED itself is a light-emitting diode, and its volt-ampere characteristic curve is very similar to the volt-ampere characteristic curve of a general diode. Taking a UVC chip from a well-known manufacturer as an example, its volt-ampere characteristic curve is shown in the figure below:
A well-known manufacturer's UVC chip volt-ampere characteristic curve
As can be seen in the figure, due to the non-linearity of the volt-ampere characteristic curve of the UVC chip, a small voltage change will cause a large current change. For example, if the voltage increases from 6.71V to 6.87V, the current increases by 20mA.
Due to the large electrical differences between the different chips of the current UVC chip manufacturers, in the process of use, if the constant voltage solution is adopted, the brightness difference between different lamp beads will be large, and the heat generation of the UVC chip is large and the The current is positively correlated, which will also cause a large difference in operating temperature between different lamp beads, which is not conducive to reliability management. When the constant current solution is adopted, it can ensure that the brightness of each lamp bead is the same and the calorific value is equal, which has a huge advantage compared with the constant voltage solution.
At the same time, because the resistance of semiconductor devices decreases with increasing temperature. If the constant voltage scheme is adopted, the temperature of the UVC lamp beads will rise after the lamp beads are lit for a period of time, and the chip resistance will decrease, which will cause the current to rise, forming a positive feedback to further increase the temperature of the device. High temperature affects the reliability of the device. For example, when a UVC lamp bead is first lit at a constant voltage of 7.2V, the current is 350mA. After a period of time, as the temperature rises, the chip resistance decreases, the current passed reaches 1000mA, and the load of the light source device rises to 3. About times.
Therefore, the constant current solution is often recommended when choosing a power supply solution.
