Automatic air freshener circuit

Automatic air freshener This automatic air freshener can automatically generate negative oxygen ions to keep the air fresh when indoor air is dirty or harmful gases reach a certain concentration. The working principle 　  　　 circuit is shown in Figure 1. The circuit is divided into two parts. The circuit with QM-N5 as the central component forms an air detection switch circuit, which can detect flammable gases. When the harmful gas in the room reaches a certain concentration, VT1 becomes saturated and conducts due to the increase in the potential of point B, which plays the role of a detection switch. Rt is a negative temperature coefficient thermistor, used to compensate for the deviation of QM-N5 caused by temperature changes. A circuit with TWH8751 as the central device forms a negative oxygen ion generator. Its oscillation frequency is about 1KHz, and a high voltage of about 5kV can be obtained at the T2 secondary. The discharge end adopts an open type, which greatly increases the concentration of negative oxygen ions, reduces the concentration of ozone, and increases the number of negative oxygen ions reaching the outside. When the ② pin of TWH8751, the non-inverting input terminal, is at high potential, the oscillator stops vibrating. Under normal indoor environment, the resistance between A and B is very large, the potential of point B is very low, VT1 is cut off, the ② pin of TWH8751 is at high potential, the oscillator does not work, and no negative ions are generated; when the indoor harmful gas concentration exceeds the RP setting At a certain critical value, VT1 is saturated and turned on, the ② pin of TWH8751 is at low potential, and the oscillator starts to vibrate, generating negative oxygen ions. To a certain extent, negative ions can eliminate indoor smoke and achieve the purpose of fresh air that is beneficial to your health. The component selection and production component list is shown in the table below. No. Name Model Quantity R1, R3 Resistor 470Ω 1/8W 2 R2 Resistor 47K 1/8W 1 R4 Resistor 100K 1/8W 1 R5 Resistor 4.7M 1W 1 RP Adjustable resistor 2.2K 1 Rt Thermistor 430Ω Negative temperature coefficient 1 C1 Electrolytic capacitor 220V/16V 1 C2, C3 electrolytic capacitor 100u/16V 2 C4 polyester capacitor 0.01u 1 VD1-VD6 rectifier diode IN4001 6 VD7 silicon stack 18kV 1 LED1, LED2 light-emitting diode green, red 2 IC1 three-terminal voltage stabilizing IC LM7812 1 IC2 three-terminal voltage regulator IC 78L05 1 IC3 power switch IC TWH8751 1 QM gas sensor QM－N5 1 S switch toggle switch 1 FU fuse 1A 1 T1 power transformer 12V 15W 1 T2 homemade high frequency transformer 1 T2 for 14 inches The output transformer was restructured, its high-voltage package was immovable, all low-voltage winding coils were removed, and 45 turns were re-wound with Φ=0.6mm enameled wire. There are no special requirements for other components. The discharge terminal is made of a pin, and three rows of holes are drilled on a copper-clad plate with a length of 170mm and a width of 40mm, with 16 holes in each row, all with Φ=1mm. Insert the pins into the holes one by one and weld them firmly. Make sure the solder joints are smooth and without burrs. When choosing pins, pay attention to the same length, and the sharper the point, the better. The whole machine is packed into a 180×110×80 (mm3) ABS engineering plastic box. When in use, the RP knob can be adjusted to make the whole machine have appropriate sensitivity. Place this device in places where smoking is common, such as coffee tables and desks. For families with indoor fires in winter, you can place it by the bedside at night to keep the air fresh during sleep.