3kva Transformerless Inverter Circuit

The post helps us to design a relatively simple transformerless 3kva inverter circuit using a full bridge IC network and a SPWM generator circuit. The idea was requested by Mr. Ralph Wiechert


The Circuit request

Hi Swagatam,
Greetings from Saint Louis, Missouri.
Would you be willing to collaborate on an inverter project? I would pay you for a design and/or your time, if you'd like.

I have a 2012 & 2013 Prius, and my mother has a 2007 Prius. The Prius is unique in that it has a 200 VDC (nominal) high-voltage battery pack. Prius owners in the past have tapped into this battery pack with off-the-shelf inverters to output their native voltages and run tools and appliances. (Here in the USA, 60 Hz, 120 & 240 VAC, as I'm sure you know). The problem is those inverters are no-longer made, but the Prius is still is.

Here are a couple inverters that were used in the past for this purpose:

1) PWRI2000S240VDC (See attachment) No longer manufactured!

2)Emerson Liebert Upstation S (This is actually a UPS, but you remove the battery pack, which was 192 VDC nominal.) (See attachment.) No longer manufactured!


Ideally, I'm looking to design a 3000 Watt continuous inverter, pure sine wave, output 60 Hz, 120 VAC (with 240 VAC split phase, if possible), and transformer-less. Perhaps 4000-5000 Watts peak. Input: 180-240 VDC. Quite a wish-list, I know.

I am a mechanical engineer, with some experience building circuits, as well as programming Picaxe micro-controllers. I just don't have much experience designing circuits from scratch. I'm willing to try & to fail, if needed! Anyways, let me know if you're interested.

Happy Diwali,

Ralph Wiechert

The Circuit Design


In this blog I have  already discussed more than 100 inverter designs and concepts, the above request can be easily accomplished by modifying one of my existing designs, and tried for the given application.

For any transformerless design there has to be a couple of basic things included for the implementation: 1) The inverter must be a full bridge inverter using a full bridge driver and 2) the fed input DC supply must be equal to the required output peak voltage level.

Incorporating the above two factors, a basic 3000 watt inverter design can be witnessed in the following diagram, which has a pure sinewave output waveform feature.


3kva Transformerless Inverter Circuit

The functioning details of the inverter can be understood with the help of the following points:

The basic or the standard full bridge inverter configuration is formed by the full bridge driver IC IRS2453 and the associated mosfet network.

Calculating the Inverter Frequency

The function of this stage is to oscillate the connected load between the mosfets at a given frequency rate as determined by the values of the Rt/Ct network. The values of these timing RC components can be set by the formula: f = 1/1.453 x Rt x Ct where Rt is in Ohms and Ct in Farads. It should be set for achieving 60Hz for complementing the specified 120V output, alternatively for 220V specs this could be changed to 50Hz.

This may be also achieved through some practical trial and error, by assessing the frequency range with a digital frequency meter.

For achieving a pure sinewave outcome, the low-side mosfets gates are disconnected from their respective IC feeds, and are applied the same through a BJT buffer stage, configured to operate through an SPWM input.

Generating SPWM

The SPWM which stands for sinewave pulse width modulation is configured around an opamp IC and a single IC 555 PWM geneartor.

Although the IC 555 are configured as PWM, the PWM output from its pin#3 is never used, rather the triangle waves generated across its timing capacitor is utilized for the carving of the SPWMs. Here one of the triangle wave samples is supposed to be much slower in frequency, and synchronized with the main IC's frequency, while the other needs to be faster triangle waves, whose frequency essentially determines the number of pillars the SPWM may have.

The opamp is configured like a comparator and is fed with triangle wave samples for processing out the required SPWMs. One triangle wave which is the slower one is extracted from the Ct pinout of the main IC IRS2453

The processing is done by the opamp IC by comparing the two triangle waves at its input pinouts, and the generated SPWM is applied to the bases of the BJT buffer stage.

The BJTs buffers switch according to the SPWM pulses and make sure that the low side mosfets are also switched at the same pattern.

The above switching enables the output AC also to switch with an SPWM pattern for both the cycles of the AC frequecny waveform.

Selecting the mosfets

Since a 3kva transformerless inverter is specified, the mosfets need to be rated appropriately for handling this load.

The mosfet number 2SK 4124 indicated in the diagram will actually not be able to sustain a 3kva load because these are rated to handle a maximum of 2kva.

Some research on the net allows us to find the mosfet: IRFB4137PBF-ND which looks good for operating over 3kva loads, due to its massive power rating at 300V/38amps.

Since it is a transformerless 3kave inverter, the question of selecting transformer is eliminated, however the batteries must be appropriately rated to produce a minimum of 160V while moderately charged, and around 190V when fully charged.

Automatic Voltage Correction.

An automatic correction can be achieved by hooking up a feedback network between the output terminals and the Ct pinout, but this may be actually not required because the IC 555 pots can be effectively used for fixing the RMS of the output voltage, and once set the output voltage can be expected to be absolutely fixed and constant regardless of the load conditions, but only as long as the load does not exceed the maximum power capacity of the inverter.

10 thoughts on “3kva Transformerless Inverter Circuit

  1. Have questions? Please feel free to post them through comments! Comments will be moderated and solved ASAP.
  2. Hi Swagatam,
    Thanks for the post! So I am not able to meet the circuit requirement that the fed input DC supply must be equal to the required output peak voltage level. So if I’m interested in using a transformer design instead, can you point me to one of your former projects that I can study? As another option, I’m wondering if using some Vicor V300A48C500B modules to convert the 200 VDC to 48 VDC would be easier (though perhaps more expensive) and then running the 48 VDC into an off-the-shelf 48 VDC (solar?) inverter. Thanks for the help!

    • Thanks Ralph,

      You mentioned 200VDC, you can use this DC for operating the above inverter circuit. 200V may be slightly higher than the the required 160V specs, however it can be adjusted by suitably adjusting the PWM pots associated with the IC 555. By the way could you specify the source of this 200V DC, will it be from the batteries?

      If you think a readymade option would be better, you can go ahead with it as that would save you from making this complex design and all the hard work. 200V to 48V converter would be fine but it could cause some unnecessary power dissipation, and waste precious watts in the process.

  3. Hi Swagatam,
    im wondering is there any refferences diagram to make andj V and A ps using dc input around 50v, its unknown amperage, so i wish to have it (PS) as the maximum as possible V and A from the source. i cant find transistor LM317HV or K D718 on local electronic store, i only have IRF 540 and 530, also 555.

  4. Dear Swagatam sir,
    I regularly watch , try to learn and enjoy your informative site.
    I would like to do a 50v dc in 600w inverter , using mosfet full bridge and transfo with out center tap.
    I plan to use 2 nos LM5109, half bridge gate driver and 4 Nos mosfet STP80100., and a transformer.

    Regarding LM5109, half bridge gate driver, i need to know about the input to be provided at pin 2 and 3. Request you to give me this information.

    • Thank you dear Musthafa,

      you can use any standard IC 4047 oscillator circuit and use its two outputs to feed pin#2/3 of the your half bridge driver IC…but remember the second bridge IC should be fed with an anti-phase signals from the IC 4047…this may be done by using NPN BJT stages or by using NOT gates.

    • So kind of you sir.
      I have used one of your ckt,Pure Sine Wave Inverter Circuit Using IC 4047, feeding the 4047 otputs to the LM5019 Full bridge half bridge gate drive,Q to left top, Q Not to right top, q to right low and q Not to left low.
      In this arrangement, how can I add voltage feedback control for getting a stable output?

      • Dear sir,
        Thank you very much for your kind and quick reply
        .I have emailed to homemadecircuits@gmail.com , the schematic that I plan to use, utilising your 4070 (by mistake mentioned it as 4047) oscillator circuit, with 555 ic generated pwm for sinewave, as input to the LM5109, x 2 nos gate drivers for controlling a full bridge mosfet inverter.; also output voltage regulation schematic.
        Kindly correct me the mistakes, in the attatched circuit that I have concluded.
        I will be thankfull, and appreciate, if you could post the circuit after refinement, in your website.

        • Dear Musthafa, the wiring is correct except the following:

          use 1K resistors for the low side mosfets, otherwise the voltage regulator circuit will short circuit the IC outputs directly.
          In parallel with the 1K resistors put 1n4148 diodes, cathode towards the IC and anode towards the gate

          and I hope you would be using only the 4047 stage and exclude the lower PWM stage because it is not required.

          by the way you have used a 4047 circuit and not 555/4017 circuit in your diagram, which is correct and the recommended design

          rest all looks fine.

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