Light-controlled circuit design and analysis

The working principle of the device application circuit is shown in Figure 5. During the day, due to the strong light, the internal resistance of the photoresistor RG is very small. At this time, a large current passes through RG, which makes the transistor VT saturated and turned on. After VT is saturated, the voltage at the ④ end of the controller DM is much lower than 1.6V, so DM is cut off internally and the lighting lamp H cannot be lit.

When night falls, the light becomes dim, the luminous flux shining on RG weakens, the internal resistance of RG becomes larger and larger, and the internal circuit of the controller DM is gradually turned on, so that current flows through the lighting lamp H to make it glow. This circuit is a soft start mode, that is, the filament of the lighting lamp H gradually transitions from red to incandescent state, and it is not easy to flicker when the filament is red.