Hello everyone! Thank you for reading this tutorial to learn how to build improved square wave inverters that provide 200 watts.
This inverter provides an accurate 50 Hz correction square wave AC signal. This can be achieved by using a crystal oscillator that helps us get a super precise frequency. Other features of the inverter include:
Waveform control and dead time adjustment
Low pressure deadline
Exact frequency operations of the microcontroller are not used.
The best of this design is that it does not have microcontrollers and complex programming and uses traditional PWM control chips, counters, dividers, and some intelligent combinations of these classic ICs.
So let's get started!
** WARNING: The project includes using high voltages, if you are not careful, you may give you a fatal electric shock. Such projects can only be conducted only when you have appropriate electrical knowledge and high-pressure work experience. **
Video demo
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Step 1: Module / Components required
Since the inverter is different from most DIY classic design on the Internet, I will divide the entire project into several parts and eventually produce all of these combinations into the final product.
The inverter is basically consisting of three parts:
1. DC to the DC converter module. It converts the low 12V DC to a high voltage until approximately 300V.
2. DC to the AC converter module. It is basically a high pressure H-bridge circuit that converts the DC voltage to an alternating voltage.
3. Improve the square wave control module. This is a crystal oscillator controlled the TL494-based module that generates a control signal for the MOSFET of the H-bridge. The dead time and waveform can be easily changed using potentiometers as needed.
All three modules combine together in this project constitutes the final expected inverter.
Step 2: H Bridge
The H bridge substantially converts the DC signal into an AC signal, using four MOSFETs as the switch, open and close according to the control signal, and generate an AC signal as an output. This topology is very common in controlling the motor and its direction.
Here you can see that I use a 12V small battery to demonstrate this process, we have a pure communication square wave signal, rather than the modified squares we want. This is because the SG3525 chip cannot generate any such signals for the modified output. However, the SG3525 has a soft start function, which is not there.
Step 3: Compare the H-bridge module to correct the square wave
As you can see, the H-bridge module is controlled by a very popular PWM control IC SG3525, which generates a 50Hz square wave set by the RC timing component. Now, in order to make the module compatible with the TL494 module (using a module / card with plug pin), I need some adapter / division board as a link to connect two modules (H bridges and TL494 cards).
The square wave output on the SG3525 is now from pins 11 and 14, which enters the MOSFET drive IC. Fortunately, I used an IC socket to make this project, not directly weld IC, which makes it completely removed IC.
Therefore, our idea is to connect the output of the TL494 card to the Pin 11 and 14 of the SG3525 initial connection. The power supply of TL494 comes from the H bridge module (12 volts).
I collected a small Veroboard / PERF board and several male fi to make this breakthrough module. The exact part includes:
A small piece of perforated plate
1 * 8 male needle - 2 sets
1 * 6 female needle - 1 set
100 ohm limit resistor-2
Step 4: Complete the bracket board
After the welding is approximately 15 minutes, the division board is ready.
A portion of the board will be mounted to an IC outlet, while the TL494 card will be mounted to the bobbin pin with a connection, as described in the previous step.
You can refer to the picture with a clear understanding.
Step 5: Observe the waveform
Now after inserting the TL494 control card into the H bridge module, we can clearly see that we have a modified square as an AC output signal, not simply.
This applies to 12V and other small test voltages, now let us increase several grades!
Step 6: High voltage generator
This is a 200W DC to the DC converter that converts 12C in the battery to a higher voltage until 300 volts DC. This has an active feedback to stabilize the output voltage and low voltage turns to protect your battery from over-discharge. This will be the high voltage source we produce an AC voltage.
Step 7: Test the entire setting
I have now connected to the high voltage output of the DC-DC converter to the input of the H-bridge, and the two modules are powered by the 12 volt voltage supplied by the battery itself for their internal operation. MOSFETs are responsible for switching high voltage direct current.
I have connected the multimeter to the H-bridge AC output. If you see, I get a stable 200V AC value from this setting. This value can be changed by changing the feedback of the DC to the DC converter.
Step 8: Waveform assessment
Now because my oscilloscope cannot process an input voltage of more than 20 volts, I use a buck transformer (central tap 12-0-12 volt) to reduce AC voltage and evaluate the final AC waveform. As you can see from the image, we get the correct waveform at the output.
Step 9: Testing using actual AC load
OK! Therefore, after all tests have been completed, I am convinced that there is a confidence that ultimately uses AC and better things better than small desktop fans. As you can see, I have set up a complete system, which contains the multimeter and antihypertensive transformer systems for the measurement of AC voltage, which can help me visualize waveforms during load.
Step 10: Efficiency calculation and conclusion
Surprisingly, despite an inductive load, my inverter waveform is still a modified square wave. The fan works very well with my settings. I have run about about 10-15 minutes during the test, and MOSFETs are just slightly fever.
Talking about efficiency, as you can see in the first picture, when the fan works at full speed, it will absorb about 4.6 amps in the battery. We used batteries with a nominal voltage of 12V.
This is calculated:
Input Power: 12V * 4.6 a = 55Watts
Output power: 45 watts (fan rated power)
Efficiency: (output / input) * 100 = 83%
In general, I found that the efficiency of battery voltage and load is approximately 82% to 84%, taking into account this is a complete DIY design, this is not bad.
This is the full content of this article, I hope you can learn from middle school.
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For this setting, I used a 45-watt-type desktop fan and a 7.2 AH lead-acid battery as all power supplies.
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