Measurement And Analysis Of RMS Number Of LED Driving Power Supply

- Dec 17, 2018-

It is well known that the quality of LED lighting depends on two aspects: one is LED chip light source; the other is LED driver power supply. At present, a few famous international companies such as PHILIP, OSRAM and CREEE can provide qualified LED chips with high quality. Generally speaking, there are few major quality problems in LED chips. At present, a large part of the poor quality LED lighting products in the market are on the driving power supply. In view of the importance of LED driving power supply, this paper mainly discusses some common technical instructions in the measurement and measurement of LED driving power supply.


For the measurement of LED driving power supply, there are several necessary test items, such as peak 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 there are great differences between the test data they get from the test equipment and the data they get from the power meter or multimeter. The controversy is reflected in the effective value of voltage/current, apparent power, power factor, RMS effective value and average value, etc. Many customers feedback that their own voltage/power supply (RMS value) measured by electric parameter meter or multimeter is less than or greater than the parameters obtained by driving power test equipment. It is important to note that all data displayed by driving test instrument are RMS real valid values. Usually the average current we are talking about is RMS average value. The average current is only when starting test. The RMS average current in the start-up process is only available, and the data in the software are consistent with the data in the instrument. At the same time, according to international standards, the test of driving power supply is to test RMS real RMS; the test average is meaningless. The voltage, current and power on the drive tester are displayed, but the voltage multiplied by current is not power; the value obtained directly by voltage multiplied by current is apparent power, and the active power is measured by the drive tester. If only the average value of the test is measured, then the test equipment is meaningless, and the value can be measured with a simple multimeter. According to IEC standard, the true effective values of voltage (Urms), current (Irms), active power (P), power factor (PF) are calculated according to the following formulas:


In the above formula, N is the number of points sampled in a period (the period depends on the frequency of the signal being measured) and the value at a certain sampling time. This instrument provides two methods for calculating total harmonic distortion (THD), i. e. IEC and CSA.


In the above two formulas:


THD: Relative value representing total harmonic distortion of voltage or current

C: Represents the effective value of the Kth harmonic of a voltage or current

K: Harmonic Number

N: Maximum harmonic number (50)

C: The effective value of the fundamental wave (i.e. the first harmonic) of a voltage or current.


In the actual test process, there are two different voices in the market when judging whether the output current of LED constant current drive is measured by RMS real value or average value. Some are judged by RMS value, but others are evaluated by average value. This is mainly because the ripple of output current of LED constant current drive is large, and the characteristics of each driving power supply are different. At this time, there are two different voices in the market: one is judged by RMS value, the other is evaluated by average value. The RMS value and the average value of the output current will be quite different, but judging from the actual situation and the requirements of the test standard, the only criterion to judge the quality of the driving power supply is the real RMS value. If judging from the RMS mean only seems a little rash and does not represent the actual situation, we can refer to the average value, but can never be used as a measure of indicators.


Source: Lishan Electronic Technology (Shanghai) Co., Ltd.