pure sinewave inverter

What is an Inverter?

An inverter converts the DC voltage to an AC voltage. In most cases, the input DC voltage is usually lower while the output AC is equal to the grid supply voltage of either 120 volts, or 240 Volts depending on the country.



The inverter may be built as standalone equipment for applications such as solar power, or to work as a backup power supply from batteries which are charged separately.



The other configuration is when it is a part of a bigger circuit such as a power supply unit, or a UPS. In this case, the inverter input DC is from the rectified mains AC in the PSU, while from either the rectified AC in the in the UPS when there is power, and from the batteries whenever there is a power failure.



There are different types of inverters based on the shape of the switching waveform. These have varying circuit configurations, efficiencies, advantages and disadvantages



An inverter provides an ac voltage from dc power sources and is useful in powering electronics and electrical equipment rated at the ac mains voltage. In addition they are widely used in the switched mode power supplies inverting stages. The circuits are classified according the switching technology and switch type, the waveform, the frequency and output waveform.

Basic inverter operation

The basic circuits include an oscillator, control circuit, drive circuit for the power devices, switching devices, and a transformer.



The conversion of dc to alternating voltage is achieved by converting energy stored in the dc source such as the battery, or from a rectifier output, into an alternating voltage. This is done using switching devices which are continuously turned on and off, and then stepping up using the transformer. Although there are some configurations which do not use a transformer, these are not widely used.



The DC input voltage is switched on and off by the power devices such as MOSFETs or power transistors and the pulses fed to the primary side of the transformer. The varying voltage in the primary induces an alternating voltage at secondary winding. The transformer also works as an amplifier where it increases the output voltage at a ratio determined by the turn’s ratio. In most cases the output voltage is raised from the standard 12 volts supplied by the batteries to either 120 Volts or 240 volts AC.



The three commonly used Inverter output stages are, a push-pull with centre tap transformer, push-pull half-bridge, or push-pull full bridge. The push pull with centre tap is most popular due to its simplicity and, guaranteed results; however, it uses a heavier transformer and has a lower efficiency.

Modified sine wave inverter using pic microcontroller

Modified sine wave inverter is designed to using pic microcontroller and push pull topology. MOSFET used as a switches in Push pull operated through control circuit in such a way that iron core transformer produced step up battery voltage having modified sine wave form. PIC16F877A microcontroller is used to generated control signal to derive. Control circuit is also discussed at the end of this article. MOSFET driver tlp250 is used as a MOSFET driver to drive both low side mosfet. If you don’t have idea about MOSFET driver tlp250, I recommend you to go through following article to know how to use MOSFET driver tlp250 as a low /high side MOSFET driver.

Control Circuit :

Control circuit is used to generate signals for MOSFET driver which turn on and turn off MOSFET of push pull high voltage transformer is such a way that Modified sine wave is produced at the output of high voltage step up transformer. PIC16F877A microcontroller is used to generate control signal.

Push pull circuit and transformer selection:

Push pull topology and iron core transformer is used to in this project to generate modified sine wave. Circuit diagram of push pull transformer is shown below. MOSFET driver tlp250 is used for both high/low side MOSFET drivers. Because to operate MOSFETS fully we need to give gate signal of 10 volt and voltage level of control signals from control circuit is about 5 about which is not enough to drive MOSFETS fully. That’s why MOSFET driver is used to driver low side MOSFETS. Remember I have used only one MOSFET with legs of push pull transformer. You should connect MOSFETS in parallel according to power rating of your inverter and also use proper heat sinks for MOSFET.



NOTE: Use separate heat sinks for MOSFETS connect to upper and lower leg of push pull transformer.Otherwise drains of both sides will become short and short circuit will occur.

Output wave from of  modified sine wave inverter :

CODING :

Code is written in Mplab and 16Mhz crystal is used. I have also explained the code with comments, but if you still have any issue, you can ask me by commenting on this post. Share this article with your friends.