Different from the traditional dimming technology, SCR dimming adopts the phase control method to adjust the voltage and light. This technology has risen in recent years. At present, most dimming systems use silicon controlled rectifier, so it is very necessary to understand the advantages and disadvantages of this dimming method. This article will introduce the disadvantages and problems of thyristor dimming.
In the process of dimming, the following problems are usually encountered:
1. During the dimming process, with the change of the internal conduction angle, the sine wave of the input voltage is destroyed by the thyristor, thus reducing the power factor value (PF), which is usually lower than 0.5. In addition, when the conduction angle is smaller and smaller, the power factor value is lower and lower (only 0.25 at 1/4 brightness).
2. As mentioned above, the sine wave of the input voltage is destroyed, and the non sinusoidal waveform increases the harmonic coefficient.
3. The input non sinusoidal voltage waveform in the LED driving circuit will produce serious interference signal (EMI) on the line.
4. During the dimming process, it is easy to be unstable due to insufficient maintaining current at low load. The solution is to add a discharge resistance. Usually, this discharge resistor consumes at least 1-2 watts of power, which reduces the efficiency of the constant current source circuit.
5. When using the thyristor dimming circuit to dimming the incandescent lamp, when the LC filter at the input end vibrates with the thyristor, the human eye cannot see this oscillation at all due to the thermal inertia of the incandescent lamp. However, when the thyristor dimming circuit is used together with the LED driving circuit, it will produce audio noise and flicker, which is often unacceptable.
The above 5 points are the problems that are easily exposed in the process of SCR dimming. It can be seen that although SCR can achieve good dimming effect, it still faces many problems, especially in terms of voltage and load. Therefore, the design must be familiar with these shortcomings when using thyristor dimming, so as to check the errors in the circuit.