Homemade AC LED energy-saving time-delay lamp

Plug a time-delay switch lamp into the socket beside the bed in the bedroom. Press the switch before going to bed and the light will turn on. When you are ready to go to bed, the light will automatically turn off. It is also convenient to relieve yourself at night. If you use white high-brightness LED as the light source, it is energy-saving and unique.

The author made an AC LED energy-saving delayed switch lamp using a TV antenna amplifier power box with a socket, an H-shaped energy-saving lamp circuit board, six components and 16 Φ3mm white high-brightness light-emitting diodes welded together. The circuit is shown in Figure 1.

1. Working Principle

Press the button S, and the AC220V mains electricity quickly charges the capacitor C1 through the primary coil of the small transformer B, the bridge rectifier diodes VD1~VD4, and the isolation diode VD5. At the same time, the trigger current is input to the unidirectional thyristor VS through the current limiting resistor R, so that Vs is turned on. At this time, the secondary output of transformer B is 12v AC, which lights up the LED. When the switch s is disconnected, the capacitor C1 is discharged, and the thyristor Vs continues to be turned on. After the delay period, when the voltage drops to a level that cannot maintain the VS conduction, VS is turned off when the AC passes zero, the power supply of the transformer B is cut off, and the LED light-emitting diode is extinguished. At this time, the circuit itself no longer consumes power. The lighting time of the light-emitting diode is mainly determined by the parameters of the capacitor C1 and the resistor R.

LED light-emitting diodes work completely in AC circuits. Because AC has a positive half cycle and a negative half cycle, 16 light-emitting diodes are divided into four groups, each with 4 diodes connected in series. The four groups are connected in parallel in the circuit, two groups are connected positively, and two groups are connected reversely. In the positive half cycle, A and B are turned on, and in the negative half cycle, C and D are turned on. LED AC drive, which turns on in turn, is conducive to heat dissipation and increases life. Since the light-emitting diode has a few ms afterglow, the flash of light cannot be seen. In order to avoid the impact of a large current on the light-emitting diode when the light is turned on, the two electrolytic capacitors C2 and C3 are reversed to form non-polar capacitors and connected in parallel in the light-emitting diode circuit. The voltage resistance of the capacitor is required to be higher than 12V.

2. Components and production

1. Leave the small transformer in the power box of the TV antenna amplifier with a socket, and remove all other components. Leave the rectifier part of the circuit board of the H-type energy-saving lamp, and remove all the rest. The model and parameters of the newly added seat parts are marked in Figure 1. Then solder them as required. Note-a large tin point should be soldered at the appropriate place of the circuit board as the fixed point of the switch, and a phosphor copper sheet should be inserted in the gap of the power supply as the moving point of the switch (see Figure 2).

2. Insert the circuit board into the inner side of the power box and connect the wires. Stick a layer of white tin foil on the appropriate position of the power box cover for reflection. Punch 16 holes in the tin foil to just fit 16 Φ3mm LEDs.

3. Make a hole slightly larger than Φ5mm on the back of the box cover, and insert a Φ5mm waste LED with the head facing outwards as a button. Note that this button must be aligned with the phosphor copper sheet as the moving point, which is the switch of the LED energy-saving delay lamp.

The circuit is simple and easy to make. If the welding is correct, it can be used normally without debugging. According to the parameters of capacitor C and resistor R in Figure 1, the delay can be more than 4 minutes. If the 100uF capacitor is replaced with 4700uF, the delay can be more than one hour.