How to comprehend LED dimming technology? How to know it well and master it? In order to answer these questions, we need first understand the voltage-current characteristic of LEDs.
What is the voltage-current characteristic of LEDs? It is known by all that when voltage worked on PN junctions (typical construction of semiconductors), internal current will be varied with the vibration of input voltage. The characteristic curve can be cleared display on oscilloscope. A complete voltage-current curve includes the forward characteristic curve and the reverse characteristic curve. Typically, the reverse characteristic curve will be much steeper than the forward one. When input voltage surpassed a certain threshold value, the corresponding internal current will increase exponentially, and consequently, breakdown the entire LED PN junction. While the forward internal voltage is also determined by its forward internal current.
According to the voltage-current characteristic, we could conclude that LED dimming technology definitely cannot be realized through simply reducing input current or input voltage. In addition, LEDs’ sinusoidal waveform is different from the waveform of incandescent lamps, thus it is also impossible to vary the lighting effects (dimming effects) by changing their conduction angles.
For example, a LED lamp with an input voltage of 24VDC, with 8 pieces high-powered LED chips (1W/each) in series. Given that the forward current is about 350mA and the forward internal voltage for each LED chips supposed to be 3.3V, thus the total input voltage for the entire lighting sources (8 pieces LEDs connected in series) should be 26.4V. It is cleared that the load voltage (26.4V) is much higher than the input voltage (24V), thus here constant-current power suppliers should be applied. In order to realize the dimming effect, engineers have to reduce the internal current from 350mA to 100mA, causing the forward voltage in each LED chip reduced to only 2.8V. Then the total input voltage of the entire system is 22.4V (now the load voltage is smaller than the input voltage). So the constant-current is incompetent. That is the reason why many terminal users or buyers saw flickers of their LED lights. Theoretically, according to the working principles of LEDs, LED lighting applications will be free from flickers in ideal conditions.