An inverter provides power backup for mains-based appliances in the event of a power failure. Most of the inverters available in the market have complicated circuit design and are not very economical. Some of them produce a square-wave output, which is undesirable for inductive loads. The project is a simple sine wave inverter circuit that produces 50Hz quasi sine wave output using a single IC CD4047 and some discrete components, which makes it a very cost-effective solution.

Sine wave inverter circuit description

Fig. 1 shows the sine wave inverter circuit of the MOSFET-based 50Hz inverter. It comprises a CD4047 multivibrator (IC1), IRF250 MOSFETs (T1 through T8), transistors and a few discrete components.

IC CD4047 has built-in facilities for astable and bistable multivibrators. The inverter application requires two outputs that are 180 degrees out of phase. Therefore IC1 is wired to produce two square-wave output signals at pins 10 and 11 with 50Hz frequency, 50 per cent duty cycle and 180-degree phase-shift. The oscillating frequency is decided by external preset VR1 and capacitor C1.

Fig. 1: Circuit of the sinewave inverter
Fig. 1: Circuit of the sine wave inverter circuit

463_partsThese two signals drive the two MOSFET banks (bank-1 and bank-2) alternatively. When pin 10 of IC1 is high and pin 11 low, MOSFETs of bank-1 (T1 through T4) conduct, while MOSFETs of bank-2 (T5 through T8) remain in non-conducting state. Therefore a large swing of current flows through the first half of the primary winding of inverter transformer X1 and 230V AC develops across the secondary winding.

During the next half cycle, the voltage at pin 10 of IC1 goes low, while the voltage at pin 11 is high. Thus MOSFETs of bank-2 conduct, while the MOSFETs of bank-1 remain non-conducting. Therefore current flows through the other half of the primary winding and 230V AC develops across the secondary winding.

This way an alternating output voltage is obtained across the secondary winding.

The sine wave output is obtained by forming a tank circuit with the secondary winding of the inverter transformer in parallel with capacitors C5 through C7. Two 2.2µF capacitors are connected to the gates of the MOSFETs in both the banks with respect to the ground if proper sinewave is not produced. Natural frequency of the tank circuit is adjusted to 50 Hz. Current consumption with no load is only 500 mA due to 50 per cent duty cycle of the square-wave signal. As load is increased, current consumption increases.

Supply voltage to IC1 is limited to 5.1 volts by using zener ZD1 and resistor R4 with the external battery as shown in Fig. 1.

Low-battery indicator

The low-battery indication circuit consists of transistor T9, preset VR2, zener diode ZD2, resistors R5, R6 and R7, LED2 and capacitor C2. The 12V supply voltage from BATT.1 is applied to the low-battery indicator circuit with full load (not more than 1000 watts) connected to the inverter output. The voltage across the load is 230V AC. At this instant, adjust preset VR2 such that zener diode ZD2 and transistor T9 conduct to drop the collector voltage to 0.7 volt keeping LED2 ‘off.’

If supply voltage goes below 10.5 volts, the voltage across the load decreases from 230V AC to 210V AC. At this instant, zener diode ZD2 and transistor T9 do not conduct and hence the collector voltage increases to about 10.5 volts and LED2 glows to indicate low voltage of the battery. At the same time, piezobuzzer PZ1 produces an audio tone indicating low battery.

Low-battery cut-off

If the battery is discharged to zero volt repeatedly, the battery life will decrease. The low-battery cut-off circuit consists of transistor T10, preset VR3, zener diode ZD4, resistors R8 and R9, capacitor C3 and diode D1.

Adjust preset VR3 such that when the voltage across the load is above 200 volts, zener diode ZD4 and transistor T10 conduct. The collector voltage of T10 is about 0.7 volt in this case and hence the SCR (SCR1) will not conduct.

Fig. 2: An actual-size, single-side PCB for the sinewave inverter
Fig. 2: An actual-size, single-side PCB for the sine wave inverter circuit
Fig. 3: Component layout for the PCB
Fig. 3: Component layout for the PCB

Download PCB and Component Layout PDFs: click here

But if the voltage across the load goes below 200 volts, zener diode ZD4 and transistor T10 will not conduct and the collector voltage of T10 will increase, causing the SCR to conduct.

Once the SCR conducts, the supply voltage to IC1 (CD4047) will be 0.7 volt, due to which IC1 will be unable to produce the voltage pulses at output pins 10 and 11 and the inverter will turn off automatically. During this state, the SCR remains conducting.

Low cut-off of the inverter can be set at the load voltage of 170 volts for tubelight, fan, etc. So the tubelight and fan will not be switched off until the voltage goes below 170 volts.

No-load cut-off

If there is no load connected at the output of the inverter, the output voltage is 270 to 290 volts. This voltage is sensed by the 0-12V tap at the secondary winding of inverter transformer X1, which is connected to the no-load cut-off circuit comprising zener diode ZD5, transistor T11, preset VR4, resistors R12 and R11, and capacitor C4.


  1. hi, nice post. pls i want to know how i can increase the capacity of the inverter and also how i can calculate the load that is run on the inverter. thanks

    • Here is the reply from Dr. R. V. Dhekale to nmaemeka.
      Power of the inverter can be increased by increasing battery voltage by connecting batteries in in series accordingly inverter transformer design should be changed. Because power of the inverter is given by P= I x V, where I be the primary current and V be the primary voltage of the inverter transformer. Power can be increased by increasing the current flowing through the primary of the transformer keeping the voltage constant. For that primary current and voltage of the transformer should be changed accordingly. If current increased accordingly no. of MOSFETs in two channels should be increased otherwise MOSFETs may be damaged.

  2. Sir,
    If I change 18-0-18volt 40 Ams Transformer to 12-0-12 volt 30 ams Transformer on this circuits can it work on 12volt battery or can made any changes for 12 volt battery please advice.


  3. is the PCB layout which is given is correct because I find that more components given in the component list are missing

    • The given PCB layout is correct. Yes, some components including transformers, Mosfets, etc will not be seen, because they are not to be mounted on the PCB.

  4. “When proper load is connected, the inverter will automatically turn on.”please explain how .also it is hard to believe that the output will remain sinusoidal in varying load and high o/p current condition.I guess you are from shivaji uni M.Sc.1981 batch.if yes then you would remember me.

    • Here’s the reply from author Dr. R. V. Dhekale. “Thank you Sutar Sir for showing interest in my article. I got sir, I am your student in 1981. Explaination: When load is not connected, Outpu AC voltage is high as 270 volts for the fraction of second. This voltage is steped down and rectified and given to the one of the transistor which will drive the SCR at perticular position of thr preset so SCR will be in latched state so voltage to the IC is decreased to 0.7 volt. Hence no pulses are produced threrefore inverter becomes in off state. I have used resistive load so sinewave is produced for varing load. By the use of inductive load shape of waveform can be changed.”

  5. Hello, could You please give us detailed info regarding wire size inside primary and especially secondary coils.
    I presume that “main” secondary coil is 230V and that wire in that part of wnding is not the same width like the rest of that coil up to 600V or maybe it is all the same wire ? It is not usually found 600V in any transformer and that is jus for what ? to suppres higher harmonics in order to obtain sinusiodal output ?
    Can i place those capacitances at the 230V coil ?
    Also, in order to easily construct this inverter from existing parts, is it possible to replace secondary winding with 12V with another transformer 230V/12 (Connected to the secondary (output) 230V.) which is laying around ?

  6. Can you provide me the component and PCB for the project Electronics Projects: 1kW Sine Wave Invert on Payment basis

    Tanking you
    Arvind thulasidas

  7. Dear sir i need to do this project for my home .So kindly give me Gerber format file of this PCB and kindly share the size of the board to print.or else to guide ,where i can buy this kits with all items .Plz kindly help mail


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