As we all know, the quality of LED lighting products depends on two aspects: one is the LED chip light source; the other is the LED drive power supply. At present, only a few international well-known companies such as PHILIP, OSRAM and CREE can provide high-quality qualified LED chips. Generally speaking, LED chips rarely have major quality problems. Now there are many low-quality LED lighting products on the market. Part of it is on the drive power. In view of the importance of LED driver power, this article mainly discusses some technical specifications commonly used in LED driver power measurement and measurement.
For LED drive power measurement, there are several necessary test items such as crest factor, effective power, reactive power, apparent power, power factor, voltage/current (RMS effective value, average value) and THD harmonic parameters. In the actual measurement process, many people find that the test data they get on the test equipment is quite different from the data they get with the power meter or multimeter. Power, power factor, RMS and average values, etc. Many customers have reported that the voltage/power (RMS value) obtained by their own power meter or multimeter test is less than or greater than the parameters obtained on the drive power test equipment. It is necessary to explain that all data displayed on the drive tester are It is the real effective value of RMS. Usually, the average current we talk about is also the average value of RMS. The average current is only available during the startup test and is the RMS average current during the startup process. The data on the software is consistent with the instrument data. At the same time, testing the drive power according to international standards is to test the RMS true effective value; it is meaningless to test the average value. The voltage, current and power displayed on the drive tester, but the voltage multiplied by the current is not the power; the value obtained by directly multiplying the voltage by the current is the apparent power, and the drive tester measures the active power. There is no point in testing equipment if you just test the average value, you can test the value with a simple multimeter. According to the IEC standard, the voltage RMS (Urms), the current RMS (Irms), the active power (P), and the power factor (PF) are calculated as follows:
In the above formula, N is the number of points sampled in the cycle (the cycle depends on the frequency of the measured signal) and the value at a certain sampling time. This instrument provides 2 methods for calculating Total Harmonic Distortion (THD), namely IEC and CSA, which are:
In the above two formulas:
THD: Relative value representing total harmonic distortion of voltage or current
C: Indicates the rms value of the Kth harmonic of the voltage or current
K: harmonic order
N: Maximum harmonic order (50 for this instrument)
C: The effective value of the fundamental wave (ie, the 1st harmonic) of the voltage or current.
In the actual test process, when judging whether the output current of the LED constant current drive is to use the RMS real value or the average value to measure the quality of the driving power supply, there are two different voices in the market: some use the RMS value to judge, but some Using the average value to evaluate, this is mainly because the LED constant current drive output current ripple is large, and the characteristics of each drive power supply are different, then the RMS value of the output current and the average value will be quite different, but from the actual situation If it is judged according to the requirements of the test standard, judging the quality of the drive power still depends on the true effective value of RMS, which is the only standard. It seems a bit sloppy to judge only from the RMS mean and does not represent the actual situation. We can refer to the mean but never as a measure.