200W Modified Square Wave Inverter With Crystal Control
Introduction: 200W Modified Square Wave Inverter With Crystal Control
Hello everyone! Thank you for stopping by this tutorial on how to build a modified square wave inverter that is capable of delivering 200Watts of power.
This inverter delivers a modified square wave AC signal of exactly 50 Hz. This is possible by using a crystal oscillator which helps us to get super accurate frequencies. Other features of this inverter include:
* Waveform shape control and dead time adjustment
* Low Voltage cutoff
* Precise frequency operation without using microcontroller.
The best thing about this design is that it is free from microcontrollers and complex programming and uses traditionally available PWM control chips, counters, frequency dividers and some smart combination of these classic ICs.
So without further adieu let's get started!
** WARNING : This project includes working with high voltage and can give you a lethal shock if you are not careful. Please proceed with these kind of projects only if you have proper electrical knowledge and experience of working with high voltages. Consider yourself warned **
Step 1: Modules/Components Needed
Since this inverter is different from most DIY classical designs available over the internet so I have made the entire project in parts and have eventually combined all of them to make the final product.
Basically the inverter consists of 3 parts:
1. DC to DC converter module. It converter the low 12V DC to high voltage till about 300volts. The link to this module, build process details and theory can be found here:
https://www.instructables.com/200Watts-12V-to-220V...
2. DC to AC converter module. It is basically a High voltage H bridge circuit that is capable of converting DC voltage to AC voltage. The link to this module, build process details and theory can be found here:
https://www.instructables.com/220V-DC-to-220V-AC-D..
3. 552
The Modified square wave control module. This is a crystal oscillator controlled TL494 based module that generates the control signals for the MOSFETS of the H bridge. The deadtime and this the waveform can be easily varied using a potentiometer based on requirement. The link to this module, build process details and theory can be found here:
https://www.instructables.com/TL494-Working-With-a...
All these 3 modules come together in this project and make the final intended inverter.
Step 2: The H Bridge
The H bridge essentially converts the DC signal to AC signal, utilizing 4 MOSFETS as switches which turn ON and OFF based on the control signals and generate an alternating signal as output. This topology is very common with controlling motors and their direction.
Here you can see that I have used a small 12V battery to just demonstrate the process and we have a signal which is purely an AC square wave and not the modified square we wish to have. This is because of the SG3525 chip which cannot generate any such signals for a modified output. The SG3525 however features a soft start function which is not there with this TL494 card
Step 3: Making the H-Bridge Module Compatible for Modified Square Wave
As you can see that the H bridge module was controlled by the very popular PWM control IC SG3525 which was producing square wave of 50Hz which was set by the RC timing components. Now to make this module compatible with the TL494 module (which is in the form of a module/card with header pins), I needed some adapter/breakout board that would be a link to connect both the modules ( H bridge and TL494 card).
Now the square wave output on SG3525 came from pins 11 and 14 which went to the MOSFET driver IC. Luckily I has used an IC socket to make the project instead of directly soldering the IC which made it very very east to completely remove the IC.
So the idea was to just connect the outputs of the TL494 card to the connections where pins 11 and 14 of the SG3525 would initially connect. The power to the TL494 comes from the H bridge module (which is 12Volts).
I gathered a small dot veroboard/ perf board and a couple of male and female headers to make this breakout module. The exact parts include:
* A small piece of perf board
* 1 * 8 male header pins - 2 sets
* 1 * 6 female header pins - 1 set
* 100 ohm current limiting resistors -2
Step 4: Completing the Breakout Board
After about 15 minutes of soldering the breakout board was ready.
One part of the board would fit into the IC socket while the TL494 card would fit on to the female header pin with the connections as described in the previous step. 552