A simple and practical design of triode inverter power supply circuit

Capacitors C1 and C2 use polyester capacitors, transistors BG1- BG5 can use 9013: 40V 0.1A 0.5W; BG6-BG7 can use field effect tube IRF150: 100V 40A 150W 0.055 ohm. Do not connect the power tube first, measure the voltage of point A and point B to the ground, adjust R1 or R2 to make the voltage of points A and B the same, so that the output square wave is symmetrical and the static current is the least. Pay attention to the following matters during installation: BG6 and BG7 must be welded with a well-grounded electric soldering iron or the power supply must be cut off before welding. Large currents should be connected with thick wires with a diameter of more than 2.5MM, and the connection should be as short as possible. The battery voltage is 12V and the capacity is more than 12AH. The power tube should be equipped with an appropriate heat sink, such as a 100*100*3MM aluminum plate for heat dissipation. If you want to increase the power, add power tubes of the same model in parallel and increase the power of the transformer accordingly.

Design and calculation method of inverter

Transistor selection: Considering safety factors, it must have a certain safety factor. Experience data is as follows:

DC power supply voltage: Transistor collector-emitter withstand voltage BVCEO

6～8V ≥20～30V

12～14V ≥60～80V

24～28V ≥80～100V

Calculate transistor collector current: ICM (A) = output power P (W) ÷ input voltage V (V) × efficiency. Input voltage is the power supply voltage. Efficiency depends on the selected circuit, generally between 60% and 80%. Core cross-sectional area: S (square centimeters) = k × square root of transformer rated power, k is selected as shown in the table below

Selection of transformer core: amateur production does not have strict requirements on transformer core. However, it is best to use thin and brittle silicon steel sheets, or use ferrite cores. Use high-strength enameled wires, and use a winding machine to wind the wires tightly and flatly. When inserting silicon steel sheets, they must be strictly flat. The relationship between the voltage at both ends of the primary winding and parameters such as the core cross-sectional area and operating frequency can be expressed by the following formula: V=4.44×10-8SKFBN

Where S --- core cross-sectional area (square centimeters);

K --- Silicon steel sheet gap coefficient (0.9 ~ 0.95);

F ---  inverter operating frequency (Hz);

B --- Saturation magnetic flux density (T);

N --- the number of turns of the coil;

V --- Primary winding voltage (volts).

The value of K is related to the thickness of the silicon steel sheet and the gap between the sheets. The tighter the core is stacked, the higher the K value is. Generally, K can be 0.9. The operating frequency of the inverter is mainly determined by the selected core. When using silicon steel sheet core, the inverter operating frequency is lower than 2KHZ. When using different ferrite cores, the operating frequency is between 2KHZ and 40KHZ. If the operating frequency exceeds the natural frequency of the core, the high-frequency loss is very serious. The saturation flux density B has different values ​​for silicon steel sheets of different specifications, generally between 0.5 and 1.4T. If the silicon steel sheet is thin and brittle, the magnetism is good, and B can be larger; if the silicon steel sheet is thick and soft, the magnetism is poor, and B can be smaller. The B of the ferrite core is about 0.2 to 0.5T.

The primary winding is wound in parallel with two wires. When winding the transformer, people are accustomed to using turns per volt, which can be expressed by the following formula: Turns per volt N = 2500/SKFB, where K is the gap coefficient of the silicon steel sheet (0.9~0.95); wire diameter D (mm) = 0.715×the square root of I.