Instrument test requirements for LED constant current source

The quality of LED power supply directly restricts the reliability of LED products . Therefore, as the LED industry chain is gradually improving, LED driver power supply plays an important role in LED products as a guarantee of high performance.

1. Test the electronic load of LED constant current source:

At present, the traditional electronic loads on the market cannot fully meet the testing requirements of LED constant current sources, and the voltage and current will be unstable. This is determined by the characteristics of the LED constant current source itself. The current waveform output by the LED constant current source usually has a large current ripple. In view of such characteristics, only electronic loads that professionally test LED constant current sources can make the test results more accurate and ensure the quality of the product.

With the widespread application of LEDs, some manufacturers have gradually launched electronic loads for professional LED testing. The most noteworthy of these is the IT8800 programmable high-precision electronic load series from ITECH, which has the CR-LED function for professional LED constant current source testing. Its unique LED mode can be used for LED power supply testing and is applied to simulated LED current. It is known as an LED testing expert. The following article will carefully analyze the characteristics of LED constant current sources and introduce the working principle of CR-LED in detail.

2. Characteristics of LED constant current source:

The output waveform of the LED constant current source we usually call usually has a large current ripple. It is precisely because of the existence of the ripple that the CR mode of the traditional electronic load cannot truly simulate the characteristics of the LED driver load, and the test voltage or current will continue to fluctuate.

The following is the LED driver load circuit diagram:

As shown in the figure above: if the CV mode is used for testing, the load voltage will be constant, which is inconsistent with the actual voltage output waveform of the constant current source. Therefore, the CR mode is often selected when testing the constant current source, but it will be found in the work that the traditional CR mode will have the phenomenon that the test waveform does not conform to the actual situation, and even the voltage and current values ​​​​keep jumping. The following is my analysis of the problems and reasons of the traditional CR mode test.

3. Problems and reasons of traditional CR mode testing:

LED can only conduct (power on) in one direction, which is called forward bias (forward bias). When current flows through it, electrons and holes overlap inside it and emit monochromatic light, which is called electroluminescence effect.

Assuming that the current value I0 output by the LED driver is 100mA, R=10Ω, and the diode conduction voltage Vd=30V, then when the actual LED lamp is loaded, the output voltage U0 of the LED driver is 100mA*10Ω+30V=31V, and the output is 31V/100mA. Assuming that the output current ripple of the constant current source is 10mA, the output voltage ripple of the LED driver is actually 10mA*10Ω=0.1V.

Using the traditional CR mode test, the simulated CR value is 31V/100mA=310Ω. Similarly, the output current ripple of the constant current source is 10mA, and the output voltage ripple of the constant current source becomes 10mA*310Ω=3.1V. The voltage fluctuation is very high and cannot work normally.

4. Professionally test the function of the electronic load of LED constant current source - CR-LED:

In the traditional CR mode, the electronic load of IT8800 series of ITECH adds the setting of diode conduction voltage, so that the electronic load works only when the voltage applied to both ends of the electronic load is greater than the conduction voltage of the diode, which completely simulates the working principle of the diode. The operation is also simple and convenient. You only need to set the conduction voltage value of the diode inside the instrument and set the CR value of the load at the same time, so as to completely simulate the real characteristics of the LED lamp.

The figure below is the waveform of the ITECH IT8800 simulating LED lamp to test the LED constant current source:

in conclusion

Only by professionally testing the electronic load of LED constant current source can the test results be more accurate and the quality of the product be guaranteed. ITECH fully integrates the characteristics of LED constant current source into the design concept, and the developed CR-LED function can truly simulate the characteristics of LED lamps. It meets the testing needs of many LED constant current source manufacturers, ensures the quality of LED products, and adds powerful chips for enterprises in the increasingly fierce market competition.