Ordinary incandescent and halogen lamps commonly used SCR to dimmer. Led high bay lights and RGB dimmable LED down lights is a pure resistance device, it does not require the input voltage sine wave, because the current waveform is always the same voltage waveform, so regardless of how the voltage waveform deviate from the sine wave, as long as the change of the valid values of the input voltage, can be dimming. SCR of the AC sine wave to be cut to achieve change its valid values for the purpose. Load and thyristor switch in series.
Change the variable resistor divider ratio can change the conduction angle, in order to achieve the purpose of change of RGB dimmable LED down lights valid values. Usually the potentiometer with a switch connected to the input of n for the light switch. In addition to the SCR, there are transistors along the dimming technology, because their basic problem is the same, not in this introduces.
SCR dimming the shortcomings and problems
However, SCR dimming range of issues.
1) SCR destruction of the sinusoidal waveforms, thereby reducing the power factor value, usually the PF is less than 0.5, and the conduction angle is smaller the worse the power factor (1/4 brightness only 0.25).
2) Similarly, the non-sinusoidal waveforms to increase the harmonic coefficients.
3) non-sinusoidal waveform line to cause serious interference signal (EMI)
Also produce unexpected problems, in the ordinary thyristor dimmer circuit output to the LED drive power for RGB dimmable LED down lights is input LC filter causes SCR oscillation, this oscillation is insignificant for the incandescent because the thermal inertia of the incandescent lamp makes the human eye do not see this oscillation.