Micro Inverter

By Rohan B. Rebello


A simple low-power inverter circuit is described here, which converts 12V DC into 230V AC. It can be used to power very light loads like night lamps and cordless telephones, but can be modified into a powerful inverter by adding more MOSFETs.

Battery charger circuit

This circuit has a two stage-battery charger with cut-off and battery level indicator and an inverter circuit. Charging circuit is built around IC1 (LM317) as shown below. When mains 230V AC is available, IC1 provides the gate voltage to SCR1 (TYN616) through diode D3 (1N4007). SCR1 starts charging the battery. For output voltage setting preset VR1 may be used.

Battery charger with cut-off circuit

The battery level indicator & inverter circuit is shown below. The battery level checking system is built around transistors T1 and T2 (both BC547) along with some discrete components. When the battery is charged (say, to more than 10.50V), LED1 glows and piezo-buzzer PZ1 does not sound. On the other hand, when battery voltage goes down (say, below 10.50V), LED1 stops glowing and piezo-buzzer sounds, indicating that the battery has been discharged and needs recharging for further use.

Inverter circuit

Battery level indicator & inverter circuit

The inverter is built around IC2 (CD4047), which is wired as an astable multivibrator operating at a frequency of around 50 Hz. The Q and Q outputs of IC2 directly drive power MOSFETs (T3 and T4). The two MOSFETs (IRFZ44) are used in the push-pull configuration. The inverter output is filtered by capacitor C1.

Construction & testing

Assemble the circuit on a general-purpose PCB and enclose it in a suitable metal box.

Pin configurations of TYN616, IRFZ44 and LM317

Refer the pin configurations before mounting the components on the PCB. Mount the transformer on the chassis and the battery in the box using supporting clamps. Use suitable heat-sinks for MOSFETs. The circuit can be used for other applications as well by delivering higher power with the help of a higher current rating transformer and additional MOSFETs.

The article was first published in January 2010 and has recently been updated.


  1. asslm… hi bro,.. i am from indonesia,.. i need permission about your schematic diagram, i’ll use it for my project,..with some little modification,.. i use 20x irfz44 will build for my customer,.. please,.. thanks for sharing..

  2. does the voltage between cathode of SCR and ground is same as the voltage between gate of SCR and ground?

    I mean by changing preset VR1, voltage at gate also changes, so will the voltage also change in cathode also or it will remain the same

  3. Hi sir,
    I want to build 5.5kva power inverter that can carry refrigerator and blender.
    Kindly assist me sir with such circuit diagram.
    My name is paul Emmanuel
    And here is my email: pentane009@gmail.com

  4. How much current can be drawn by this circuit? And I would like to know why we used a step-down transformer instead of a step-up transformer.

  5. Does LM 317 works properly without any dc filter capacitor ? Because only pulsating dc was used in the circuit. Waiting for reply. Thank you,sir.

  6. It is recommended to use input filter capacitor (say 1000uF) to improve input transients in practical circuits.
    An optional capacitor (say 1uF to 10uF) can be used at the output.

  7. Your project is quite interesting. I am rather new to electronics. I wish to enhance
    the output to about 1,00W. Is it possible for me to use the same components up to
    the IC CD 4047 and use several IRFZ 44 FETs in parallel plus a Transformer of high
    capacity? Please let me know the values. Look forward to your advice.
    Best regards.

  8. Please help me to design pure sine wave inverter of capacity 2A. I also want to learn SMPS design. Do you provide training classes?

  9. Please, could you provide charging and charging complete LED indicators for the “Battery charger with cut-off circuit” ?. Thank you for your immense support.

  10. Is there any base papers and any successful prototype of this project,as we are trying to do this project in our college for our pass percentage,plz kindly msg me on this number if any were there


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