Home » 12V DC to 220 AC Power Converters » How to Make a Simple 200 VA, Homemade Power Inverter Circuit – Square Wave Concept
How to Make a Simple 200 VA, Homemade Power Inverter Circuit – Square Wave Concept

How to Make a Simple 200 VA, Homemade Power Inverter Circuit – Square Wave Concept

An efficiency of around 85 % and a power output of more than 200 watts is what you will get from the present design of a power inverter (home built). Complete circuit schematic and building procedure explained herein.


You might have come across many articles regarding power inverters, however you might be still confused about making a power inverter? The present content provides a complete building tutorial of a home built power inverter.

If you are planning to make your own low cost and simple home built power inverter then probably you won’t find a better circuit than the present one.

This heavy duty, easy to build design includes very few numbers of components which can be found readily available in any electronic retailer shop.

The output of the inverter will be obviously a square wave and also load dependent. But these drawbacks won’t matter much as long as sophisticated electronic equipment are not operated with it and the output is not over loaded.

The big benefit of the present design is its simplicity, very low cost, high power output, 12 volt operation and low maintenance. Besides, once it is built, an instant start is pretty assured.

If at all any problem is encountered, troubleshooting won’t be a headache and may be traced within minutes. The efficiency of the system is also pretty high, in the vicinity of around 85% and the output power is above 200 watts.

A simple two transistor astable multivibrator forms the main square wave generator. The signal is suitably amplified by two current amplifier medium power Darlington transistors.

This amplified square wave signal is further fed to the output stage comprising of parallel connected high power transistors. These transistors convert this signal into high current alternating pulses which is dumped into the secondary windings of the power transformer.

The induced voltage from the secondary to the primary winding, results a massive 230 or 120 volts conversion, as per transformer specifications.

Let’s study in details how the circuit functions.


Circuit Operation

The circuit diagram description of this home built power inverter may be simply understood through the following points:

Transistor T1 and T2 along with C1 and C2 and the other associated parts forms the required astable multivibrator and heart of the circuit.

The relatively weak square wave signals generated at the collector of T1 and T2 is applied to the base of the driver transistors T2 and T3 respectively. These are specified as Darlington pairs and thus very effectively amplify the signals to suitable levels so that they may be fed to the high power output transistor configuration.

On receiving the signal from T2 and T3, all parallel output transistors saturate well enough according to the varying signal and create a huge push pull effect in the secondary windings on the power transformer. This alternate switching of the entire battery voltage through the windings induce massive step up power into the primary windings of the transformer producing the desired AC output.

The resistors placed at the emitter of the 2N3055 transistors are all 1 Ohm, 5 Watts and has been introduced to avoid thermal runaway situations with any of the transistors.





R1, R4 = 470 Ω,

R2, R3 = 39 K,


R5, R6 = 100 Ω,

R7-----R14 = 15 Ω,

R15 ----R22 = 0.22 Ohms, 5 watt (can be connected directly if all the parallel transistors are mounted on a common heatsink, separate for each channel)


C1, C2 = 0.33 µF, 50 VOLTS, TANTALLUM,


D1, D2 = 1N5408,

T1, T2 = BC547B,

T3, T4 = TIP 127,

T5-----T12 = 2N 3055 POWER TRANSISTORS,


TRANSFORMER = 10 to 20 AMPS, 9 – 0 – 9 VOLTS,



Inverter Building Tutorial

The below given discussion should provide you with a detailed step wise explanation regarding how to build your own power inverter:

WARNING: The present circuit involves dangerous Alternating Currents, extreme Caution is advised.

The only part of the circuit which is probably difficult to procure is the transformer, because a 10 Amp rated transformer is not easily available in the market. In that case you can get two 5 Amp rated transformers (easily available) and connect their secondary taps in parallel.

Do not connect their primary in parallel; rather divide them as two separate outputs (See Image and Click to Enlarge).

Next difficult stage in the building procedure is the making of the heat sinks. I won’t recommend you to fabricate them by yourself as the task can be quite a tedious one and time consuming too. It would be rather a better idea to get them ready made. You will find variety of them, in different sizes in the market.

2N3055 Pinout Diagram

Select the suitable ones; make sure that the holes are appropriately drilled for the TO-3 package as shown in the figure. TO-3 is the code to recognize typically the dimensions of power transistors which are categorized in the type used in the present circuit i.e. for 2N3055.

Fix T5----T8 firmly over the heat sinks using 1/8 *1/2 screws, nuts and spring washers. You may use two separate heat sinks for the two sets of transistors or one single large heat sink. Do not forget to isolate the transistors from the heat sink with the help of mica isolation kit.

TIP127 Pinout Diagram

Constructing the PCB is just a matter of putting all the components in place and interconnecting their leads as per the given circuit schematic. It can be done simply over a piece of general PCB.

Transistors T3 and T4 also need heat sinks; a “C” channel type aluminum heat sink will do the job perfectly. This is can also be procured ready made as per the given size.

Now we can connect the relevant points from the assembled board to the power transistors fitted over the heat sinks. Take care of its base, emitter and the collector, a wrong connection would mean an instant damage of the particular device.

Once all the wires are connected appropriately to the required points, lift the whole assembly gently and place it on the base of a strong and sturdy metallic box. The size of the box should such that the assembly does not get crammed.

It goes without saying that the outputs and the inputs of circuit should be terminated into proper socket type of outlets, to make the external connections easy. The external fittings should also include a fuse holder, LEDs and a toggle switch.

How to Test

  • Testing this home built inverter is very simple. It may be done in the following ways:
  • Insert the specified fuse into the fuse holder.
  • Connect a 120/230 volt 100 Watt incandescent lamp in the output socket,
  • Now take a fully charged 12V/100Ah lead acid battery and connect its poles to the inverter supply terminals.
  • If everything is connected as per the given schematic, the inverter should instantly start functioning illuminating the bulb very brightly.
  • For your satisfaction you may check the current consumption of the unit through following the simple steps:
  • Take a digital multimeter (DMM), select 20A current range in it.
  • Remove the inverter fuse from its fuse holder,
  • Clip the DMM’s prods into the fuse terminals such that the DMM’s positive prod links with the battery positive.
  • Switch on the inverter, the consumed current will be instantly displayed over the DMM. If you multiply this current with the battery voltage i.e. by 12, the result will give you the consumed input power.
  • Similarly, you may find the output consumed power through the above procedure (DMM set in the AC range). Here you will have to multiply the output current with the output voltage (120 or 230)
  • By dividing output power by the input power and multiplying the result by 100, will immediately give you the efficiency of the inverter.
  • If you have any questions regarding how to build your own power inverter, feel free to comment (comments need moderation, may take time to appear).

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!

64 thoughts on “How to Make a Simple 200 VA, Homemade Power Inverter Circuit – Square Wave Concept”

  1. Howdy, Friend! Interested to Learn Circuit Designing? Let's Start Discussing below!
    • Vinod, you may connect the emitters directly with the ground if you use a common heatsink for the transistors on each channel. Meaning mount all the transistors from left channel on one common heatsink, and similarly mount all the right side transistors on a single common heatsink. Don’t use mica isolator for the transistors because since all their collectors need to be joined together so can be shorted through the heatsink

  2. how are u doing, sir pls is about the 200va square wave inverter my question is about the component u listed
    1. resistors R1,R4,R3,R2 . U said is half watt, CEF
    2.CAN U xplain what u mean by 10watt wire wound resistors and CEF as well
    3. the trans4mer 5 amps what is the rating like u rated 10amps as 9-0-9volt
    4. the xternal fittings should include a fuse holder, leds and atoggle switch, should this be connected at the output of the inverter ac pls xplain

    • 1) Those are CFR type meaning carbon film resistors.
      2) 10 watt is the power handling capacity of the resistor, wire wound means that these are not CFR based rather made by winding steel wires inside.
      3) the 5 amps will be also 9-0-9V rated
      4) the external fittings are optional, include them as per your preference…

  3. #sir which devices are work in this inverter?
    #If fan will work how much hour?
    #If I can use computer ups transformer?
    #If I can increase wattage by adding transistor more?
    #Any problem with square wave?
    Thank you sir

    • All equipment will work with this inverter, but it is not recommended for sensitive electronic equipment because it is a square wave inverter.
      computer transformer cab be tried.
      you can increase wattage by adding more transistors

  4. Be patience with sir, i meant i want to modify or convert the same square wave circuit to sine wave by adding sg3525 to the circuit

  5. Hello Sir, Pls I Have Some Question To Ask. 1. What Is The Maximum Power/wattage Of The Inverter, 2. Can I Reduce The Number Of Power Transistor And Use Low Capacity Battery? 3. Can I Change It To Sine Wave, If So, What Is The Suitable Component To Use Instead. Thanks

  6. Do you mean that if my inverter battery is 12v i should replace it with 18v solar panel,?? and also if my inverter is 200 watt, the solar panel also must be 200 watt??

    • replace the battery with a solar panel having voltage at least 6V higher than the inverter battery spec, and a couple of watts higher than the inverter transformer wattage.

  7. Dear Swagatam Majumdar, I am Krishnaa – From Chennai.
    If I use Two 10000MFD capacitors across 12-0-12 side of transformer What will happen?
    Can we get smooth 230VAC waveform at output?
    Please clarify, My Email ID is "krishnaa_m@hotmail.com"

    • Dear Krishnan, that won't help, instead you can connect both the the capacitors together right across the battery terminals, this will help to reduce harmonics and ripples within the circuit and ensure a much cleaner 220V output…however all these remedies will not keep the 230V constant because the 230V is directly dependent on the battery voltage which will keep dropping with time.

    • Hi Divya, you can try for any other similar 3 amp/1000V or 3 amp 300V diode….but according to me 1N5408 is the most standard and widely used part.

  8. Sir ,
    I read all blogs ,I have 12-0-12 transformer ,shall i used in your circuit ,it is 4 ams .how much load can be handel?

    • you will have to get a made-to-order transformer, or use any standard 9-0-9V/220V/15amp step down transformer…making it at home can be difficult

  9. Hey,
    i have an 150ah lead aside battery and,one ups 600va e184736 transformer,can you please tell me what type of inverter circuit should i do?

  10. a few questions, how are you connecting the power transistors to each other? then to each end of the transformer (1 wire to one set of 4 other wire to other set of 4) couldn't you just use the heat-sink aren't these npn power transistors? according to your symbol they are so all of their bodies are connected together. what do i search to get the correct transformer? i cant seem to find 12-0-12 10 amp to 220v ac unless this is a step down transformer in reverse? my only electrical shops are ebay or jaycar.com.au It's my first time using transformers. Lastly you said about the 1 ohm 5 watt at the emitters of the power transistors, are they 10 watts or 5 you said 5 at the intro but commented to someone 10 watts or does it no matter for this circuit?

    great circuit otherwise just needed more info in its' description

    • The transistors are connected as they are shown in the diagram, click the diagram to enlarge for getting a better view. one common heatsink is used for all the transistors on each channel, meaning two separate for the two channels, if a single common is used it would create a short circuit.

      The emitter resistors make sure that the transistors conduct uniformly so that all dissipate evenly.

      The wattage of the resistors will depend on the battery AH and transformer amp rating, if its above 40AH and 5amps respectively, the 2N3055 base/emitter resistors will need to be upgraded to 10 watts, for lower wattage a 5 watt would suffice.

      Ideally a 9-0-9V/10amp transformer is required, and it'll be a step down type used in reverse for the inverter application

    • Great! thanks for the extra info. So the heatsink can actually connect the 4 power transistors collector (body) to each other for the 2 sets and would this shock you if you touched the heat sink? that's probably why I can't find the right transformer. and to use a transformer in reverse; E.G. 240ac input 12V DC output would be connect battery to the 240ac input side and the 12V dc output side now becomes 220v ac? please let me know how to use it in reverse.

      otherwise Great circuits, keep up the good work.

    • That's correct, all transistor collectors of the respective channels join together through the heatsink and connect with the relevant transformer outer taps.

      As for the transformer, the winding rated 12V connects with the battery side that is with the 2N3055 collectors….while the 220V side becomes the output for operating the appliances.

    • Thanks heaps! I've bought all the stuff now including heat sinks and case, all I need now is the transformer, it's proven difficult that they don't sell many 10 amp transformers in Australia and when I do find them they are $30+ :/

  11. I’m very happy to see you projects thank for this wonderful site
    I’ve got a doubt I’ve seen some 8 pin transformers in inverter circuits whatis that how do i test it and know its ratings.

    • Thank you!

      The pins could be the terminals corresponding to particular winding of the transformer. These winding could be connected with a particular inverter circuit for the intended specific safety functions and other similar things.

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