Application of Multivibrator in Car Air Freshener

Central topics:

• Application of Multivibrator in Car Air Freshener

Solution:

• Component Selection
• Select two time base circuits CB555

• Choose a dual time base circuit CB556

The 555 time base circuit IC2 and R4, R5, C5 form a multivibrator. After the power is turned on, because the voltage on C5 is very low, the output end of IC2 (pin 3) is high level, and the 12V voltage is charged to C5 through R4 and R5, and the voltage on C5 gradually increases. When the voltage on C5 rises to 2/3VCC, the internal trigger of IC2 flips, and the 3rd pin outputs a low level. At the same time, the internal discharge tube is turned on, and the voltage on C5 begins to discharge through R5 through the 7th pin. When the voltage on C5 drops to 1/3Vcc, the internal trigger of IC2 flips again, and the 3rd pin outputs a high level. At the same time, the internal discharge tube is turned off, and the 12V voltage is charged to C5 through R4 and R5. This cycle forms an oscillation, and the oscillation frequency.f=1.44/[(R4+2R5)C5], and its 3rd pin outputs a high-frequency pulse voltage of about 48k Hz.

When the output terminal (pin 3) of IC2 is at a high level, the switch tube VT is turned on, and the 12V power supply flows through the primary winding of the transformer T through the diode VD. When the output terminal (pin 3) of IC2 is at a low level, the switch tube VT is turned off, and the energy stored in the transformer T is released through its secondary. Since the primary-secondary transformation ratio of T is 1:300, the secondary pulse voltage will be as high as 3000V. Above, the air is ionized by the tip discharge of the discharger to produce negative ions. The function of the fan M is to make the negative ions diffuse into the surrounding air faster and better.

The 555 time base circuit IC1 and R1, R2, C2 ultra-low frequency oscillator have an oscillation period of about 6 minutes, and its output terminal (pin 3) outputs a square wave with a pulse width of 180 seconds and an interval of 180 seconds. The reset terminal (pin 4) of the high-frequency oscillator IC2 is controlled by the output terminal (pin 3) of IC1: when the output terminal of IC1 is at a high level, IC2 oscillates; when the output terminal of IC1 is at a low level, IC2 stops oscillating, and the output terminal of IC2 is at a low level. The result of the joint action of IC1 and IC2 is that the circuit works for 3 minutes and pauses for 3 minutes, generating negative ions intermittently. The fan motor M is also controlled by the output of IC1 and works synchronously with IC2. The light-emitting diode VD1 is the working indicator of the negative ion generating circuit. It forms another multivibrator, which is an ultra-low frequency oscillator with an oscillation period of about 6 minutes. Its output end (pin 3) outputs a square wave with a pulse width of 180 seconds and an interval of 180 seconds. The reset end (pin 4) of the high-frequency oscillator IC2 is controlled by the output end (pin 3) of IC1: when the output end of IC1 is at a high level, IC2 oscillates; when the output end of IC1 is at a low level, IC2 stops oscillating and the output end of IC2 is at a low level. The result of the joint action of IC1 and IC2 is that the circuit works for 3 minutes and pauses for 3 minutes, generating negative ions intermittently. The fan motor M is also controlled by the output of IC1 and works synchronously with IC2. The light-emitting diode VD1 is the working indicator of the negative ion generating circuit.

Component selection

IC1 and IC2 use two time base circuits CB555, or one dual time base circuit CB556. Note that CMOS time base circuits CB7555 or CB7556 are not suitable for this machine due to their low drive current. Switch tube VT uses medium power tubes such as 2SC2073. Diode VD2 uses fast recovery rectifiers such as FR104. Fan M can use a cooling fan for computer CPUs with a power of about 12V and 150mA. It is small in size, thin in thickness, and has very low noise, which is more suitable for this production. It can also be replaced by a 12V toy motor with homemade fan blades.

Transformer T needs to be wound by yourself. Use N27 type E-shaped ferrite core. The coil is wound on its insulating frame. The primary is wound with 11 turns of 0.4mm diameter enameled wire, and the secondary is wound with 3300 turns of 0.1mm diameter enameled wire. There should be an insulating layer between the primary and secondary. After the coil is wound, it needs to be wrapped with insulating tape.

The method of making the discharger is shown in the figure on the right. Make a circuit board, install the transformer T and other components on the left side, hollow out the middle of the right side, and connect a copper foil on the upper and lower sides to the secondary of T. The discharge electrode is 4 bare copper wires with a diameter of 0.6mm and a length of 10mm, and the top is sharpened. The 4 discharge electrodes are welded to the upper copper foil strip, with a spacing of about 15mm. The common electrode is a bare copper wire with a diameter of about 1mm, which is bent into a "┍┐┑┎┑" shape as shown in Figure 3 and welded to the copper foil strip below. The tip of each discharge electrode is 2mm away from the common electrode.

The fan M is fixed under the circuit board, and the center of the fan is facing the discharger, about 15mm away. The air outlet direction of the fan should be upward so that the negative ions generated by the discharger can be blown upward into the air. The whole machine should be installed in an insulating shell, and some holes should be opened on the top of the shell facing the discharger as air outlets, and holes should be opened on both sides of the shell near the fan as air inlets. The 12V power cord is connected to the car cigarette lighter plug.