LED harmonic test application

LED lamps are closely related to our lives. They have the advantages of low power consumption and long life, but there are also some problems that need to be paid attention to, such as the impact of power supply harmonics on LEDs. Today, let's take a look at the working principle of LEDs and harmonic testing.

LED lamps composition and working principle

LED lights can be seen everywhere in life, and everyone must be familiar with them, such as stage lights, car lights, street lights, miner's lamps, table lamps, etc. The composition of LED lamps can generally be divided into: LED lamp beads, LED lens, lamp board, power driver, lamp body (shell), some high-power applications, when multiple sets of LED lamp combination are required, there will be a sub-controller. Among these components, LED lamp beads and LED power driver are essential core components. Without LED lamp beads, it is impossible to bring light source, so why is the LED power driver essential?

Why do LED lights have to be equipped with power drivers? LED stands for light-emitting diode. Since it is a diode, LED has the same volt-ampere characteristics as a diode. Let us look at a typical diode volt-ampere characteristic graph.

As shown in the figure, we can see that when the LED is powered in the forward direction, once the voltage exceeds the turn-on voltage, the current will increase rapidly as the voltage increases, which also shows that the LED forward resistance is very small. So if we use voltage power supply, we must ensure that the power supply voltage is very stable, otherwise a small change in the voltage may cause a sudden change in the current and burn the LED. Therefore, the driving of the LED requires a dedicated power driver, and the current most used method is constant current driving, of course, there are also some constant voltage driving methods.

The schematic diagram of the LED power driver is shown in the figure below. The input signals generally include AC, low-voltage DC, high-voltage DC, etc. The front-end rectification and filter circuits of different signals will be different; the switching device is controlled by the PWM signal to control the isolation transformer to generate the secondary side Signal; the back end realizes stable DC output through the rectifier and feedback loop. The DC output adjusts the rectifier and filter circuit according to the constant voltage and constant current.

The necessity of LED harmonic test

From the above analysis, we know that LED lights are generally driven by constant current, and the production of constant current sources requires switching devices. In the actual research and development process, in order to reduce the loss of low-voltage DC current in various transmission links, high-power LED products are often driven by It is composed of multiple low-power units and works in a distributed manner. And we know that the switching circuit is often the source of harmonics, and the harmonic content of the switching signal is very high, and its waveform is an intermittent spike. If we use LED lamps with low power or small number of applications, such as home use, we often ignore the impact of harmonics. However, if a large number of LED lamps are working at the same time, the harmonics generated by them will not be ignored. If they are not treated, they may cause pollution to the power supply network and cause unpredictable harm to other equipment in the same power grid.

LED harmonic test program

Since LED lights produce harmonics when they are in use, testing for harmonics is essential. There are many instruments on the market that can test harmonics, such as power meters, power analyzers, power quality analyzers, and even oscilloscopes. So how should we choose?

Through the comparison of the above table, it can be seen that the PA series power analyzer not only has the highest accuracy of 0.01%, but also has 5MHz bandwidth, 2MS/s sampling rate, and can analyze up to 500 harmonics. It has FFT function and is very suitable for Accurate analysis of high frequency harmonics such as LED.

LED harmonic simulation program

In the research and development process of LED lights and LED power drivers, not only the harmonics must be tested, but there will also be a demand for simulating the impact of harmonics on the power driver and the normal operation of the LED lamps.

ZLG Zhiyuan Electronics PWR/PSA power supply can not only output DC, AC, DC+AC signals, but also freely edit signal waveforms, and the frequency conversion range supports 0.1Hz～10KHz, and can perform analog output on the equipment according to IEC standards. Users can also edit up to 50 Sub-harmonics, customize the amplitude of each harmonic, and generate specific harmonic waveforms.