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You are here: Home / Inverter Circuits / 250 Watt Pure Sine Wave Inverter Circuit

250 Watt Pure Sine Wave Inverter Circuit

Last Updated on March 16, 2022 by Matrix 19 Comments

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The cost and quantity of parts necessary to develop the proposed 250 watt sine wave power inverter circuit is actually much less compared to a noisy square wave switching-type inverter circuit.

Only an extra three or four tiny transistors, a some resistors and capacitors, a couple of pots and a small driver transformer are all the additional parts which are required.

A glance at the block diagram will be enough to indicate that the fundamental concept of this sine wave power inverter is extremely basic.

The block diagram matches one of the simple 80 meter CW transmitter circuit. Essentially, it is only the frequency that is different ; 60 Hz instead of 3.5 MHz. And producing 250 watts of sine wave ac actually becomes drastically easier with the 500,000 meters (60 Hz) as opposed to the 80 meters (3.5 MHz).

A complete circuit diagram of the 250 watt sine wave inverter is shown below. The requirements are a sine wave oscillator, a buffer amplifier, and a power amplifier.

The Oscillator

The oscillator could be in fact of any variety, however your best option for sensible reasons can be one particular implementing RC combinations.

Actually an oscillator involving inductor-capacitor combination as for example in the Hartley or Colpitts oscillator circuits could be incorporated at 60 Hz.

However the difficulty of adjusting the frequency to be able to adapt it to 60 Hz happens to be greatly simplified by utilizing an oscillator which has its frequency implemented using an RC network. The frequency now could be altered by simply adjusting a potentiometer.

Referring to the circuit diagram, here the 10K potentiometer in the oscillator stage permits us to adjust the frequency. Do not forget that the oscillator stage will create a sine wave.

Several RC oscillator circuits are usually built to generate square waves while some others generate a sawtooth output.

We don 't want to employ these types, simply because we may end up with an inverter which is may be a low quality modified inverter. The 3.9K potentiometer in the oscillator section is positioned to regulate the level of gain in the feed back loop. Very high gain setting using this pot might lead to extreme distortion of the sine wave.

Setting the Frequency

How could you set the oscillator frequency to 60 Hz? You can use just about any common methods for computing, just like an audio frequency is measured . You could possibly evaluate your oscillator's frequency with the mains utility line voltage frequency either by seeing Lissajous statistics with an oscilloscope or by listening to and setting the beat frequency to zero.

Or perhaps for those who have a digital frequency counter, that' the best option you can have, so use it to measure and set the frequency to 60 Hz.

Output Voltage

Besides getting the frequency correct , you should have the output voltage fairly close to the preferred range of 115 - 120 volts (or to 220V depending on the transformer). As indicated in the circuit diagram the output voltage is dependent on the adjustment of t he 4 K potentiometer which can be seen situated between the oscillator and the buffer amplifier stages.

A simple way to measure and confirm the output volts is by using a standard DMM set to the AC 500 V range and then measure the output voltage while simultaneously adjusting the 4 K pot.

Transformers

In this stage the both the transformers are ordinary 60 Hz step down transformers. The driver transformer, for instance is actually a tiny power transformer having about three filament windings. One winding may be employed for the primary , and the remaining two in series might be used for creating the center tapped secondary.

A very common type center-tapped filament transformer could be very much appropriate for the output power transformer. With a 12 volt battery supply, you might anticipate the power amplifier transistors to generate an ac voltage of around 7-9 volts peak value or 5 to 6.5 volts rms.

It means that a 12 volt center-tapped filament transformer rated at 115 volt secondary winding output must be pretty sufficient.

The dimensions or current rating of the filament transformer depends upon the total power output you would want to generate. A 25 ampere, 12V transformer is going to be pretty enough for generating power outputs up to 200 to 250 watts. Picking out the transistor type in the power amplifier stage also will be dependent mainly by simply how much output power you want to generate.

Waveforms

The true waveform that can be acquired from this 250 watt sine wave inverter is slightly different from a true sine wave. As indicated in the above figure, each power transistor of this power inverter amplifier comes with an operating angle marginally lower than 180λ , that is certainly, near to a Class C type working.

A little deviation in the biasing of the transistors might pull the amplifier back to genuine Class B, however because no noises can be seen developing, this further hard work to improve the bias doesn't appear to be useful.

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About Matrix

I am a contributing editor to homemade-circuits.com. Although I am mechanical engineer by profession, my great passion for practical electronics has helped me to learn a lot over the years. I also love answering to forum questions, and am always happy to help in this amazing field of electronics.

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  1. Chris says

    May 16, 2022 at 5:07 pm

    Sir thanks for your support on all your posts I’m grateful. Pls sir can you help me with an advanced pure sine wave inverter circuit design? I will be very glad if given this circuit. Sir I need this for my house and I think 1500w is ok

    Reply
    • Swagatam says

      May 16, 2022 at 5:33 pm

      Thanks Chris, you can probably try the following easy to build concept:

      https://www.homemade-circuits.com/1500-watt-pwm-sinewave-inverter-circuit/

      For the mosfets you can use 4 nos of IRFP2907 in parallel

      Reply
  2. Poloko says

    April 2, 2022 at 11:13 pm

    Hello Mr swagatam says how about replacing 2N278 with 2sc5200 for high power output? Thanks in advance looking forward hearing from you.

    Reply
    • Swagatam says

      April 3, 2022 at 9:16 am

      Hi Poloko, yes you can definitely do that, you can replace the output transistor with other powerful versions to get a more powerful output.

      Reply
  3. chris says

    March 16, 2022 at 5:30 pm

    Hi sir I have constructed the circuit and it worked but having challenge with its upgrading. Most of the components are not available here so I used other transistors(2n5401 and 2n5551) at the driver stage but output drops when load is applied to the circuit. pls can you help me with a sinewave circuit that uses mosfets ?

    Reply
    • Swagatam says

      March 16, 2022 at 6:05 pm

      Hi Chris, thanks for updating the results. You can upgrade the power output by replacing the output transistors (2N278) with high power transistors such as TIP36. Along with this you will also have to upgrade the output transformer and the battery appropriately.

      Reply
  4. Chris says

    February 13, 2022 at 9:57 pm

    Hello sir what is the precise driver transformer 12v or 6v center tap because the voltage switching the output transistor should be around 4.5 to 6v. Pls assist me.

    Reply
    • Swagatam says

      February 14, 2022 at 8:57 am

      Hello Chris, if the output is switching at 6V RMS, then you can use a 6-0-6 center tap output transformer.

      Reply
  5. Anthony says

    December 18, 2021 at 7:12 pm

    Pls sir can we use a normal transformer In this inverter and also how can we increase the wattage output. Thanks and look forward to hearing from you.

    Reply
    • Swagatam says

      December 19, 2021 at 9:48 am

      Anthony, you can use any ordinary step down transformer in the above circuit….to increase wattage, increase current rating transformer and battery, and the output transistors.

      Reply
  6. SAJI TR says

    October 5, 2021 at 7:42 pm

    I like this circuit but have a boubt about driver transformer can we use ordinary transformer step down

    Reply
    • Swagatam says

      October 5, 2021 at 7:56 pm

      yes, driver transformer can be any small step down transformer!

      Reply
      • Chris says

        December 8, 2021 at 3:39 pm

        Pls the capacitor 1uf hooking 100k resistors. Pls is polarized or non polarized.

        Reply
        • Swagatam says

          December 8, 2021 at 4:12 pm

          I would recommend a non-polar capacitor

          Reply
          • Chris says

            December 9, 2021 at 2:09 am

            Thanks Swagatam. Pls is the circuit a pure sine wave? and can I use MOSFET at output stage?

            Reply
            • Swagatam says

              December 9, 2021 at 8:57 am

              You are welcome Chris, it is a pure sine wave, but mosfets might not work perfectly at the output stage….

              Reply
  7. john c bristol says

    May 13, 2021 at 8:59 pm

    Any pics of the final layout pcb,pics of transformers to use?

    Reply
    • Swagatam says

      May 14, 2021 at 11:20 am

      It was take from an old electronic magazine, which did not include the practical images.

      Reply
      • Atta Ur Rehman says

        January 6, 2022 at 11:48 pm

        I am required pure sine wave ups circuit diagram

        Reply

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