## Simple circuit diagram of DC to AC converter (1)

The inverter uses power field effect transistor as inverter device. It’s powered by a car battery. Therefore, the input voltage is 12 V DC. The output voltage is 100 V AC. However, the input and output voltages are not limited to this. You can use any voltage. They rely on transformers. The waveform output is square wave. According to experience, the power of this circuit is about 100W. The circuit must be fused because the oscillator stops when too much input current flows.

## Simple circuit diagram of DC to AC converter (2)

The circuit is actually a digital quasi sinusoidal DC / AC inverter with the following characteristics:

(1) Using PWM switching power supply circuit, the conversion efficiency is more than 90%, and its power consumption is low;

(2) The output AC voltage is 220 V, and has the function of voltage stabilization;

(3) The output power is 30qw, which can be expanded to more than 1000W;

(4) It adopts 2KHz quasi sinusoidal waveform, no power frequency transformer, small volume and light weight.

Vehicle power converter circuit consists of pulse width modulator, switch circuit, boost circuit, sampling circuit and so on. The IC is a pulse width modulation (PWM) switching power supply integrated circuit cw3525a, which integrates a reference power supply, an oscillator, an error amplifier, a pulse width comparator, a trigger, a latch, etc. the output stage circuit is in the form of totem pole with a driving capacity of 200mA. Fig. 2 shows the functions of each pin of cw3525a (the same as cw2525a and cwl525a). The working frequency of IC internal oscillator is determined by the external timing resistor and timing capacitor of 5 and 6 pins. In Fig. 1, the oscillation frequency is about 4kHz. After being distributed by internal trigger and gate circuit, the driving pulse is output from 11 pin and 14 pin in turn to control the wheel current conduction of power field effect transistor VT1 and vt2. When VT1 is on (at this time, vt2 is cut off), the + 12V power supply is connected to the ground through VT1 through the upper part of transformer T primary (2-terminal → 1-end). When vt2 is on (at this time, VTL is cut off), the + 12V power supply is connected to the ground through vt2 through the lower part of transformer T primary (2-terminal → 3-terminal). Through the synthesis and boost of transformer T, the AC voltage of 220 V can be obtained in the secondary of T, and the frequency is about 2KHz. Due to the obstruction of transformer coil to high frequency component, the secondary waveform is not square wave, which can be called quasi sine wave. The use of high frequency quasi sinusoidal waveform can improve the efficiency and eliminate the power frequency transformer, and also make most electrical appliances work normally.

The resistance between the 5-pin and 7-pin of the IC is used to adjust the dead time. In Fig. 1, the dead time is about 2 μ s. Setting the dead time can ensure that VT1 and vt2 will not conduct at the same time, which improves the security and reliability of the circuit.

The rectifier full bridge ur and C4, r1-r3 constitute the sampling feedback circuit. After being rectified by ur, filtered by C4, and divided by R1, R2 and R3, the 220 V AC voltage at the output end is sent to the IC internal error amplifier and comparator for processing from pin 1, and then the output pulse width (i.e. pulse width modulation) of 11 pin and 14 pin is automatically controlled to achieve the purpose of stabilizing the output voltage.

The integrated switching power supply pulse width modulator cw3525a (or SG3525A, x3525) is selected as the IC, and the working environment temperature is 0 ℃ ~ 70 ℃, which can meet the requirements. Cw2525a (- 25 ℃ ~ 85 ℃) or cw1525a (- 55 ℃ ~ 125 ℃) can be used in cold areas. For VT1 and vt2, n-channel power field effect transistor 2sk851 or other n-channel power field-effect transistor with voltage above 30V and current above 30A shall be selected, and heat sink shall be installed during fabrication. Both VT1 and vt2 work in the switch state, so the power consumption of the tube itself is not very large. Transformer T needs to be wound by itself. High frequency magnetic core with cross-section of about 4cm2 is selected. For primary winding, 1.5mm diameter enameled wire is used for double wire and 20 turns. The tail of line a is connected with that of line B as central tap 2. The head of line a is used as lead pin 1, and the tail of line B as lead 3. The secondary is wound 500 times with 0.8mm diameter enameled wire.

The 12V DC power input terminal adopts the automobile cigarette lighter interface, which is very convenient to use. A commercially available cigarette lighter interface can be selected, with the metal core connected to the positive connection and the outer metal to the negative connection. The electric wire in the cigarette lighter can also be removed and connected with the wire according to the above method. According to the size of the cigarette lighter, take a cylindrical plastic or plexiglass, fix a small copper column in the middle and connect the positive lead, and fix the elastic copper plate on the outer ring and connect the negative lead.

The 220 V output end adopts the city power socket, so as to facilitate the use. The whole machine should be installed in an insulating shell, which can be reformed by using the commercial multi-purpose power wiring board: remove the contact parts of some sockets, so as to put them into the machine center, and retain the contacts of some sockets as the 220 V power output socket. There should be cooling holes on the casing.

During debugging, use AC voltmeter to monitor the AC voltage at the output end, adjust R1 resistance value to make the output voltage is 220V, and fix R1. When in use, the input plug of the power converter is inserted into the socket of the automobile cigarette lighter, and the electrical appliance is inserted into the power conversion output socket.

If you want to output more power, you can choose the power FET with higher current. For example, the output power can be increased to 600W by selecting the power field effect transistor with current up to 60A. The output power can also be increased by using two parallel tubes. As shown in the figure, a 600W power converter can be made by using four 2sk851 in parallel. If the VT1 ~ vt4 in Fig. 6 all use power field effect transistor with current up to 60A, the output power can reach more than 1000W. It should be noted that the cross section of the magnetic core and the diameter of the enameled wire must be increased correspondingly when the output power is increased. In addition, the input current increases with the increase of output power. The allowable load of the connecting wire between the cigarette lighter and the battery should be considered. The thick wire can be replaced or the input terminal wire of the power converter can be directly connected to the 12V battery.