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　　Working principle and circuit sharing of DC to AC inverter

　　Working principle and circuit sharing of DC to AC inverter - This article first introduces the working principle of DC to AC inverter, then introduces a simple DC to AC inverter circuit, and finally introduces the inverter 12V DC to AC inverter circuit. into 220V AC schematic diagram. Working principle of DC to AC inverter

　　Using the principle of the oscillator, the direct current is first converted into pulse alternating current whose size changes with time. The DC component is removed through the DC isolation system and the alternating component is retained. It is then transformed, shaped and stabilized by the conversion system (boost or buck). We get AC that meets our needs. An oscillation circuit is used to generate a pulsating DC current of a certain frequency, and a transformer is used to convert this current into the required AC voltage. The three-phase inverter simultaneously generates three-phase AC voltages with a phase angle of 120 degrees from each other.

　　The inverter consists of many parts, the most core part of which is the oscillator. The earliest oscillators were electromagnetic, and later developed into electronics. From discrete components to application-specific integrated circuits, and then to microcomputer control, they became more and more perfect. The functions of inverters became stronger and stronger, and they were used in various fields. has a wide range of applications.

　　Simple DC to AC inverter circuit

　　This inverter uses power field effect transistors as the inverter device. Powered by car battery. Therefore, the input voltage is 12 Vdc. The output voltage is 100V AC. However, the input and output voltages are not limited to this. You can use any voltage. They rely on transformers for use. The waveform output is a square wave. As a rule of thumb, this circuit has about 100W power.

　　The circuit must be fused as the oscillator stops when excessive input current flows.

　　Inverter principle circuit: convert 12V DC into 220V AC

　　Converting 220V AC to 24V, 36V, and 48V is relatively simple and only requires the use of the principle of a transformer. Through electromagnetic mutual inductance, different voltages can be obtained.

　　Assume that the closed circuit is an n-turn coil, and the change rate of the magnetic flux passing through each turn of the coil is the same. This is equivalent to n single-turn coils connected in series, so the induced electromotive force becomes

　　According to the formula, E is the electromotive force, which is the voltage. Because it remains unchanged, as long as the number n of coils at both ends of the iron block is different, the voltage transformation effect can be achieved.

　　To convert alternating current into direct current, you only need to add a diode to achieve the desired effect. A diode is a device with two electrodes that only allows current to flow in one direction. Many uses apply its rectifying function. Then using the transformer principle, the 220V AC power can be converted into 12V DC power, and the 5V DC output voltage of our mobile phone charger.

　　So how to convert 12V DC into 220V AC? First, let’s understand the inverter. What is an inverter?

　　The inverter converts DC power (battery, storage battery) into AC power (generally 220V, 50Hz sine wave). It consists of inverter bridge, control logic and filter circuit. It is a DC to AC transformer. It is actually a voltage inversion process with the converter. The converter converts the AC voltage of the power grid into a stable 12V DC output, while the inverter converts the 12V DC voltage output by the Adapter into high-frequency, high-voltage AC power.

　　Then let’s take a look at the circuit diagram of the whole process: 12V DC → high frequency boost → 220V DC → full bridge rectifier → 220V DC → inverter bridge inverter → 220V AC

　　High frequency boost inverter control circuit:

　　(1) The non-inverting input terminal of the first group of amplifiers detects the output current and divides the voltage with three 0.33R resistors. When the current is too large, the voltage on the dividing resistor exceeds the reference voltage of (2) pin, and (3) pin The amplifier output terminal outputs high level, and when pin (3) is high level, the circuit enters the protection state. (2) Pin is the inverting input terminal of the comparator. It is connected to pin (14) as the reference voltage of the comparator. The control signal from the external input terminal can be input to the cut-off time control terminal (also called dead time) of pin (4). control), and the input end of the error amplifier with pins (1), (2), (15), (16), the offset voltage at its input endpoint is 120mV, which can limit the output cut-off time to the minimum value, which is approximately the initial sawtooth wave 4% of cycle time. When the output mode control terminal of pin 13 is connected to ground, 96% of the maximum working cycle can be obtained, and when pin (13) is connected to the reference voltage, 48% of the maximum working cycle can be obtained. If we set a fixed voltage at the cut-off time control input of pin 4, ranging from 0V to 3.3V, the additional cut-off time must appear on the output. Pins (5) and (6) are a fixed-frequency pulse width modulation circuit with a built-in linear sawtooth wave oscillator. The oscillation frequency can be adjusted through an external resistor and a capacitor. The oscillation frequency is as follows:

　　The width of the output pulse is achieved by comparing the positive sawtooth wave voltage on the capacitor CT with the other two control signals. Power output tubes Q1 and Q2 are controlled by NOR gates. The bistable flip-flop will be gated when the clock signal is low, that is, it will be gated only during the period when the sawtooth wave voltage is greater than the control signal. As the control signal increases, the width of the output pulse will decrease. (7) Pin is grounded. Pins (8) and (11) are the collectors of the internal switching tubes of Q1 and Q2. They are connected to the power supply in this circuit. Pins (9) and (10) are the emitters of Q1 and Q2. The switch tube drives the output terminal and is connected to the external amplifier circuit Q1 and Q2 in the figure below. To drive the rear pole push-pull circuit. (12) Pin power terminal, (13) pin is the output control terminal, when connected to (14) pin reference voltage, the two output pulses are 180 degrees apart, each output is about 200MA driving push-pull or half-bridge circuit. (15), the inverting input terminal of the second group amplifier, is connected to the reference voltage, and (16), the non-inverting input terminal, detects the power supply voltage. When the voltage is too high and exceeds the reference voltage of pin (15), pin (3) outputs high level and the circuit enters the protection state.

　　High frequency boost inverter circuit and rectifier:

　　This is a push-pull topology inverter circuit. When E1 is driven by a pulse, Q1 is turned on, turning on VT3 and VT6, and turning off VT7 and VT8. At this time, the circuit amplifies the positive half-cycle waveform and the transformer boosts the voltage to the secondary. Through high-frequency rectifier rectification, when E2 pulse drive, Q2 is turned on, driving VT7 and VT8 to turn on. VT3 and VT6 are cut off, and the negative half-cycle waveform is amplified. After being boosted by a step-up transformer, it is rectified at high frequency.

　　(This VT3 8 exists in the circuit in push-pull mode, each responsible for the waveform amplification task of the positive and negative half cycles. When the circuit is working, only one pair of two symmetrical power switch tubes are turned on at a time, so the conduction loss is small and the efficiency is low. High. The push-pull output can sink current into the load).

　　Inverter bridge inverter:

　　Finally, the pulse width frequency is determined by the 5-pin external point capacitance C3 and the 6-pin external resistor R15 of the TL494CN chip as F=1.1÷(0.1×220) KHZ=50HZ to control Q10, Q11, Q13, and Q14 to work at a frequency of 50HZ. 220V DC power is inverted into 220V/50HZ AC power. The above picture will complete this part of the function. When TL494 is in the forward direction, IC2 controls Q3 to be in a saturated conduction state and Q4 to be in a cut-off state. Since Q3 is in a saturated conduction state, Q10 is in a saturated conduction state. Since Q4 is in the off state, Q11 is in the off state because the gate has no positive bias, and Q14 is in the off state because the gate has no positive bias, and Q13 is in the saturated conduction state. At this time, 220V DC passes through VT6 along the XAC socket to the load and then through VT10 to ground, forming a positive half-cycle current; in the reverse direction, IC2 controls Q3 to be in a cut-off state, and Q4 is in a saturated conduction state. Since Q3 is in a cut-off state, Q10 and Q13 Because the gate has no positive bias, it is in a cut-off state. Since Q4 is in a saturated conduction state, Q11 is in a saturated conduction state. At the same time, Q14 is in a saturated conduction state. Q11 is in a cut-off state because the gate has no positive bias. At this time, the 220V DC power passes through VT9 along the XAC socket to the load and then is grounded through VT7, forming a negative half-cycle current; in this way, the 220V DC power is successfully converted into a 220V/50HZ AC power output for the load.

　　Protection circuit in the circuit:

　　The dual operational amplifier comparison amplifier LM358 is used in the circuit to control the output overcurrent protection and low output voltage protection circuit. TL431 sets the 2.5V reference voltage here to serve as the reference voltage for the non-inverting input terminal of the comparator. The non-inverting terminal of the first group of operational amplifiers The input terminal is connected to the output current detection, and the inverting input terminal is connected to the reference voltage. When the current is too large, the comparator input voltage rises. When it exceeds 2.5V, the output terminal outputs a high level, which is sent to pin 3 of IC1, and the IC turns off the output. . The non-inverting input terminal of the second group of operational amplifiers is connected to the reference voltage, and the inverting input terminal is connected to the output voltage. When the voltage is too low and the voltage after detection is lower than 2.5V after dividing the voltage, the output terminal outputs a high level, Q1 is turned on, and the buzzer Call the police.

　　Technical area briefly explains the role of pwm converter, working principle and circuit sharing of DC to AC inverter, why to realize the diversity of solar inverter, introduction to inverter circuit diagram (TL494/555 inverter/pure sine wave inverter (Inverter circuit) Detailed explanation of the working principle of high-frequency inverter_Introduction to the difference between high-frequency inverter and low-frequency inverter

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