Stable brightness dimmer circuit 2

(2) The second circuit of the dimming lamp circuit with stable brightness is shown in Figure 2-74. It uses light feedback to stabilize brightness.     In order to stabilize the brightness, the photoelectric element VT3 is used. When the grid voltage increases, the light brightness increases, the current of VT3 also increases, the charging current of capacitor C decreases, the voltage across C rises slowly, the conduction angle of thyristor V decreases, the output voltage decreases, and the light brightness decreases; vice versa. , the light brightness increases. This ensures constant light brightness.     In order to prevent the VT3 from being saturated due to excessive light entering the photoelectric transistor VT3 and preventing normal adjustment, the installation position of the VT3 should be adjusted or a filter should be installed to weaken the detection light amount.