Disadvantages and problems of SCR dimming
However, there are a series of problems with SCR dimming.
1. Thyristor destroys the waveform of the sine wave, thereby reducing the power factor value, usually PF is less than 0.5, and the smaller the conduction angle, the worse the power factor (only 0.25 at 1/4 brightness).
2. Similarly, the non-sinusoidal waveform increases the harmonic coefficient.
3. Non-sinusoidal waveforms can cause severe interference signals (EMI) on the line
4. It is easy to be unstable at low load, for which a bleeder resistor must be added. This drain resistor must consume at least 1-2 watts of power.
5. Unexpected problems will also occur when the ordinary thyristor dimming circuit outputs to the driving power of the LED, that is, the LC filter at the input will cause the thyristor to oscillate, which does not matter for the incandescent lamp, Because the thermal inertia of the incandescent lamp makes the human eye can not see this oscillation. But for the LED driving power, audio noise and flicker are generated.