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3 Best Transformerless Inverter Circuits

3 Best Transformerless Inverter Circuits

The post helps us to understand 3 inverter circuits designed to work without a transformer, and using a full bridge IC network and a SPWM generator circuit.



The first idea as given below was requested by Mr. Ralph Wiechert

Main Specifications

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!

The 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.

transformerless 3kva sinewave inverters full bridge 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.

A More Comprehensive Transformerless Inverter Design#2

The second circuit diagram of a compact transformeress inverter without incorporating bulky iron transformer is discussed below. Instead of an heavy iron transformer it uses a ferrite core inductor as shown in the following article. The schematic is not designed by me, it was provided to me by one of the avid readers of this blog Mr. Ritesh.

The design is a full fledged configuration with includes most of the features such as ferrite transformer winding details, low voltage indicator stage, output voltage regulation facility etc.

transformerless ferrite core inverter circuit

The explanation for the above design hasn't been updated yet, I will try to update it soon, in the meantime you can refer the diagram and get your doubts clarified through comment, if any.

200 watt Compact Transformerless Inverter Design#3

A third design below shows a 200 watt inverter circuit without a transformer (transformerless) using a 310V DC input. It  is a sine wave compatible design.

Introduction

Inverters as we know are devices which convert or rather invert a low voltage DC source to a high voltage AC output.

The produced high voltage AC output is generally in the order of the local mains voltage levels. However the conversion process from a low voltage to high voltage invariably necessitates the inclusion of hefty and bulky transformers. Do we have an option to avoid these and make a transformerless inverter circuit?

Yes there is a rather very simple way of implementing a transformerless inverter design.

Basically inverter utilizing low DC voltage battery require to boost them to the intended higher AC voltage which in turn makes the inclusion of a transformer imperative.

That means if we could just replace the input low voltage DC with a DC level equal to the intended output AC level, the need of a transformer could be simply eliminated.

The circuit diagram incorporates a high voltage DC input for operating a simple mosfet inverter circuit and we can clearly see that there's no transformer involved.

Circuit Operation

The high voltage DC equal to the required output AC derived by arranging 18 small, 12 volt batteries in series.

The gate N1 is from the IC 4093, N1 has been configured as the oscillator here.

Since the IC requires a strict operating voltage between 5 and 15 volts,the required input is taken from one of the 12 volt batteries and applied to the relevant IC pin outs.

The entire configuration thus becomes very simple and efficient and completely eliminates the need of a bulky and heavy transformer.

The batteries are all 12 volt, 4 AH rated which are quite small and even when connected together does not seem to cover too much of space.They may stacked tightly to form a compact unit.

The output will be 110 V AC at 200 watts.

transformerless PWM inverter circuit

Parts List

Q1, Q2 = MPSA92
Q3 = MJE350
Q4, Q5 = MJE340
Q6, Q7 = K1058,
Q8, Q9 = J162
NAND IC = 4093,
D1 = 1N4148
Battery = 12V/4AH, 18 nos.

Upgrading into a Sinewave Version

The above discussed simple 220V transformerless inverter circuit could be upgraded into a pure or true sinewave inverter simply by replacing the input oscillator with a sine wave generator circuit as shown below:

200 watt transformerless sinewave inverter circuit

Parts List for the sinewave oscillator can be found in this post

Transformerless Solar Inverter Circuit

Sun is a major and an unlimited source of raw power which is available on our planet absolutely free. This power is fundamentally in the form of heat, however humans have discovered methods of exploiting the light  also from this huge source for manufacturing electrical power.

Overview

Today electricity has become the life line of all cities and even the rural areas. With depleting fossil fuel, sun light promises to be one of the major renewable source of energy that can be accessed directly from anywhere and under all circumstances on this planet, free of cost. Let's learn one of the methods of converting solar energy into electricity for our personal benefits.

In one of my previous posts I have discussed a solar inverter circuit which rather had a simple approach and incorporated an ordinary inverter topology using a transformer.

Transformers as we all know are bulky, heavy and may become quite inconvenient for some applications.
In the present design I have tried to eliminate the use of a transformer by incorporating  high voltage mosfets and by stepping up the voltage through series connection of solar panels. Let's study the whole configuration the with the help of the following points:

How it Works

Looking at the below shown solar based transformerless inverter circuit diagram, we can see that it basically consists of three main stages, viz. the oscillator stage made up of the versatile IC 555, the output stage consisting of a couple of high voltage power mosfets and the power delivering stage which employs the solar panel bank, which is fed at B1 and B2.

Circuit Diagram

solar transformerless inverter circuit

Since the IC cannot operate with at voltages more than 15V, it is well guarded through a dropping resistor and a zener diode. The zener diode limits the high voltage from the solar panel at the connected 15V zener voltage.

However the mosfets are allowed to be operated with the full solar output voltage, which may lie anywhere between 200 to 260 volts. On overcast conditions the voltage might drop to well below 170V, So probably a voltage stabilizer may be used at the output for regulating the output voltage under such situations.

The mosfets are N and P types which form a pair for implementing the push pull actions and for generating the required AC.

The mosfets arenot specified in the diagram, ideally they must be rated at 450V and 5 amps, you will come across many variants, if you google a bit over the net.

The used solar panels should strictly have an open circuit voltage of around 24V at full sunlight and around 17V during bright dusk periods.

How to Connect the Solar Panels

solar panels in series for transformerless inverter application

Parts List

R1 = 6K8
R2 = 140K
C1 = 0.1uF
Diodes = are 1N4148
R3 = 10K, 10 watts,
R4, R5 = 100 Ohms, 1/4 watt
B1 and B2 = from solar panel
Z1 = 5.1V 1 watt

Use these formulas for calculating R1, R2, C1....

Update:

The above 555 IC design may not be so reliable and efficient, a much reliable design can be seen below in the form of a full H-bridge inverter circuit. This design can be expected  of providing much better results than the above 555 IC circuit

Another advantage of using the above circuit is that you won't require a dual solar panel arrangement, rather a single series connected solar supply would be enough to operate the above circuit for achieving a 220V transformerless inverter output.

SHARING IS CARING!


About the Author

I am an electronic engineer (dipIETE ), hobbyist, inventor, schematic/PCB designer, manufacturer. I am also the founder of the website: https://www.homemade-circuits.com/, where I love sharing my innovative circuit ideas and tutorials. If you have any circuit related query, you may interact through comments, I'll be most happy to help!



54 thoughts on “3 Best Transformerless Inverter Circuits”


  1. Howdy, Friend! Interested to Learn Circuit Designing? Let's Start Discussing below!
  2. sir I complete transformer less circuit but 1 problem here 2SK 4124 MOSFET is not in my local area
    can i used any igbt for this circuit

  3. Hello!dear swag sir I complete 3 kva transformer less circuit but facing two problems 1st,ic 2354d over heating 12 &15 volt both tried 2ndly there is 150 volt out put how to phase split for getting 220 volt out put input is 230 v DC Rt is 470 ohm CT is 100 nf 104 please guide me
    Thanks

      • Hello, yes I completed as per schematic of 5 kva ,but supply 220 v dc through solar panels , in result of giving 240 v DC from s.panels I got 160 v ac and secondly ic 2353 d getting hot .

        • what is the voltage across the Vcc and ground? make sure it is not more than 15V or 12V preferably, also connect a 1000uF capacitor across these pins.

          • Hello dear swag sir,I checked completely before questioning to you ,all as per scheematic but still I’m facing there’s two problems first ic become hot mybe this happens and secondly out but is 150 v ac while I m giving 240 vdc directly from s,panels ,because I’m trying to make ac220 directly from s,panels through ur circuit ,please guide me how I can get result of 220 v ac
            Thanks

            • Hello Gulab,
              Could you tell me how did you convert the panel voltage to 15V for the IC?

              For getting 220V from SPWM based circuit you must provide a 310V DC input to the mosfet bridge. A 220V input will only result in producing around 150V

            • sir, I used 10 k 10 watt resistance and 15 v 2watt zener for ic now I got ur answer for 220 v ac I must give 310 v in input as u answered Thank to u I later try then tell u

  4. Hi,
    I built the 3KVA transformerless inverter. initially I had problem that the IRS2453D would not oscillate, Once i grounded the pin no.5 it started oscillating. Now My problem is I am getting a square wave output and not sine wave as needed. What suggestion can you give. For the supply to Ic’s I have used a small 12 V 1 amp SMPS whose primary I connected to 160V D.C. input as its a universal input it works fine. your comment on this?

    • Yes, pin#5 which is the shut down pin needs to be grounded, I’ll correct the diagram soon.
      For getting sinewave PWM you must implement everything that has been shown in the diagram, right from the opamp, IC 555 stages to the low side BJT connections….you will have do it stage wise by checking and verifying each of the stages separately.

  5. sir my inverter ic is sg3525 can i join the pin6 (RT) of the sg3525 to pin3 of ic741,and join the output of lm555 with pin2 of ic741 while the output of ic741 goes to the bjt/fets to turn it to pure sinewave inverter

    • abioye, you will have to show a schematic to enable me to quickly understand it….if possible draw a schematic and send it my email address…

    • the specifications solely depend on the mosfet rating, and the input supply rating, and these can be tweaked as per user preference.

      The IC basically works with 12V DC

  6. Just as the original requester mentioned, Prius’s are still being manufactured but the 200 VDC 120VAC inverter isn’t. I’m a computer geek and photographer, with no experience or expertise in building these types of devices. Is there anyone out there who would be willing to build this for $100 to $300+/- and I’m probably not the only one who would be willing to pay to get this. 🙂 Thanks for any help.

  7. Hi interesting article , Is any one out there interested in developing a 4 kw single phase with high dc voltage input .. 800 vdc . must be off grid My company requires 6000 next year as well as 1000 3 phase units same input

    over the next 4-5 yrs we will need some 200,000 units

    please contact me directly on my email neil@uk-esc.com

  8. Sir,
    Actually, I am designing 3 kva transformerless inverter as per your circuit and there are 160v DC input and 230v output. Now there are 15v DC supply is required to operate 555, 741 and IRS2453 ics. Now my question is that how can I providing 15v DC to that ics from 160v DC input.

    • Prashant, you will have to do it as suggested in my previous “48V inverter” link…use MJE13005 for the BC546, for the resistor use 10K 5watt, and 12V zener for the zener, and instead of 48V you will supply it with 160V and obtain 12V across the emitter side….measure it with a load connected

      • There are some questions related 3 kva inverter.
        1. At full load, only 4 mosfet enough or required more!
        2. 741 op amp required negative voltage, so how can generate it?
        3. DC voltage is 160v and 555 & 741 required 15v. So how can generate it?
        4. What is the values of 10k preset pot set?
        5. In circuit diagram, mje13005 indicated. So what is the use of it in this circuit?

        • 1) The total current of the mosfet on each channel must be higher than the output max current, this you will have to verify from the datasheet, by the way I have already provided the mosfet details in the article.
          2) IC 741 will not require a dual supply, just make sure that the leakage or the offset voltage from pin#6 is appropriately blocked, the attached 3V zener should be hopefully able to do it.

          3) 12V for the ICs can be achieved using an emitter follower design, as depicted in the following 48V inverter circuit:
          https://homemade-circuits.com/48-v-inverter-circuit/

          for 160V replace the 10k with 100K, and replace the BC546 with a TIP122, the zener can be a 12V zener
          4) 10K presets are normal presets, use good quality ones, multiturn type.
          5) MJE13005 is a mistakenly shown, please ignore it.

  9. 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.

  10. 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.

  11. 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.

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