# Simple 12V to 230VAC Inverter Circuit – MOSFET

In this post we are going to construct a simplest 12VDC to 230VAC inverter using transistor and MOSFETs.

**We will learn:**

**Different Stages in an Inverter Circuit.****Circuit Diagram of the Inverter.****Analysis of this Inverter’s Waveform.****Understanding Astable Multivibrator.****Maximum Power Output of an Inverter.****Advantages and Disadvantages of this Inverter.**

Power Inverters need no introduction; we use them when there is a power cut or in an emergency situation or simply you are on a camp.

Power inverters can deliver power anywhere between 10 watts to 10000 watts depending on your needs and inverters can also be single phase or three phase depending on your application.

Inverters can be with any specifications, but a standard inverter has these important stages:

**Stages of an Inverter:**

**Power source i.e. battery****Oscillator****Driving Stage****Transformer**

Let’s explore one by one:

**Battery / DC Power source:**

The DC power source can be a deep cycle battery or a DC generator or a solar panel. They all gives stable DC power to the inverter.

The voltage to an inverter can be 6V or 12V or 24V or 48V or even 84V, it depends on the inverter’s input specification.

**Oscillator:**

The oscillator is the stage where the constant DC from the battery is converted to AC; we can say this stage as the heart of the Inverter because this generates frequency or pulses like human heart.

Initially the LOW voltage DC is converted LOW voltage AC by means of a multivibrator or any oscillator circuit. The oscillation produced by the oscillator may be a square wave or sine wave or modified sine wave with a fixed frequency and fixed duty cycle mostly 50/60 Hz at 50% duty cycle.

The LOW voltage AC is fed to the next stage which is the driving stage consists of MOSFETs or Transistors.

**Driving Stage:**

The oscillating stage just gives oscillating AC weak signal which cannot be fed to a transformer to boost the voltage.

The driving stage increases the strength of the oscillating AC signal.

The driving stage consists of MOSFETs or Transistors. Most commercial Inverters are packed with MOSFETs for driving stage because it is very efficient in switching, less resistance path between source and drain terminal which translates to less heat.

Driving a MOSFET is easy as it can be directly controlled by a microcontroller or ICs

Power transistor needs intermediate driving stage to bias the power transistor to optimum level, which takes more space on PCB and increase components cost as well.

In this project we are using MOSFETs.

**Transformer:**

The transformer is the component which converts Low voltage AC to high voltage AC.

The amplified AC signal from the driving stage is strong and ready to feed the transformer. The transformer can be with centre tap or without centre tap.

Let’s explore the example of center taped transformer.

The center tap terminal is generally connected to +Ve of the battery, because the MOSFETs used for inverters are N-Channel (N-channel MOSFETs are more efficient).

The MOSFETs are placed at X and Y terminal and one of the two MOSFETs are turned ON at an instant and in alternating manner.

Say MOSFET at ‘X’ is turned on, now the current flows from centre tap to ‘X’, energizing that particular winding. Due to mutual induction the other side of the coil with higher number of turns get energized and the output shoots volt high due to higher number of turns.

After 10ms (For 50Hz), the MOSFET at ‘Y’ gets turn ON and at ‘X’ turns OFF, the current flows from centre tap to ‘Y’ and energizing that particular winding.

Now the coil with higher number of turns gets energized with opposite polarity and shoots the output voltage high.

This cycle continues and gives out 230VAC / 50Hz which can be utilized by our everyday gadgets.

Now you know how a basic inverter works.

**Circuit Diagram of Inverter:**

Download a better high resolution circuit diagram here

**Component List:**

**BC548 / Any NPN Transistor x 2****27K ohm x 2****1K ohm x 2****47 uF x 2 – Electrolytic or ceramic****MOSFET IRF540N or any N-channel MOSFET x2****Transformer 9V-0-9V / 10A (At-least 5A)****Fuse 5A (For short circuit protection of battery)****12V 7Ah Battery**

**Circuit Description:**

The circuit is very easy, even a beginner can accomplish with ease.

The circuit consists of Astable multivibrator which uses two transistors and tuned to generate 50 Hz to 60 Hz at 50% duty cycle. The frequency can be from 50 to 60 Hz; this is due to the tolerance of the capacitors and resistors which creates inaccuracy.

This Astable multivibrator acts as oscillator for this inverter. The driving stage has 2 MOSFETs IRF540N and the 230V / 9V-0-9V / 10A transformer boosts the output voltage.

**Analyzing the waveform:**

The oscilloscope is probed at gate terminal of the both MOSFETs and we get the above waveform which is square wave at around 50Hz and 50% duty cycle.

**Understanding Astable Multivibrator:**

If you take a close look at the circuit diagram you can find a circuit similar to below one:

This is called Astable multivibrator. Astable means the output is not stable, but the output switches ON and OFF with a fixed frequency and duty cycle.

The output frequency is determined by capacitors C1, C2 and R2, R3 from the above circuit diagram.

To get 50% duty cycle C1 and C2 should have same value and R2 and R3 should also have same value at the same time the two transistors should have similar gain.

**The Frequency of transistor based Astable multivibrator is given by:**

**F = 1 / 1.38 x R x C**

- F is frequency in Hertz.
- R is resistance in ohm.
- C is capacitance in Farad.

**Let’s try calculating the frequency of this inverter:**

**F = 1 / 1.38 x 27 x 10 ^{3} x 0.47 x 10^{-6}**

**F = 57.10 Hz**

NOTE: Due to the tolerance of the components we will get around 50Hz to 60Hz stable. Most gadgets will work happily on this frequency.

**How much power output do I get?**

**For this Inverter you may get around 75 watts or less output from 9V/10A transformer which is driven by IRF540N MOSFET with 12V 7Ah battery.**

**The output power of any Inverter depends on these three things:**

**DC Source****Current Delivering Capacity of MOSFETs/Driving Stage****Transformer**

**DC Source:**

The power output of your Inverter depends on the battery’s or solar panel’s maximum power rating.

A battery has certain limit to deliver current if you force above its limit there will be degradation of battery life. You should not expect a 12V 7Ah battery to deliver 500 Watts of power.

If you want to power some higher wattage appliances you should upgrade your battery / solar panel.

**MOSFET / Driving Stage:**

The driving stage has limitation to conduct current from battery to the transformer. The IRF540N can deliver 33A as per its data sheet. So 12V (battery) x 33A = 396 Watts maximum if your battery and transformer can handle.

If you want even more power output you can chose more powerful MOSFET or connect two or more IRF540N in parallel.

**Transformer:**

The transformer is the most expensive part in an inverter circuit.

The transformer’s limit can be calculated by multiplying voltage and current of secondary side of the step-down transformer (we are using in reverse, so the inverter sees as step-up transformer).

For example: With 9V/10A transformer 9V x 10A = 90 Watts Maximum. You will get around 75 watts after losses.

Now you know the limiting factors with your inverter.

**Advantages of this Inverter:**

**Simple design can be built by beginners.****Decent efficiency around 75 to 80%.****Stable frequency around 50 to 60 Hz.****Well tested circuit.**

**Disadvantage of this Inverter:**

**Output voltage varies as the load increases.****Square wave is not suitable for sensitive electronic gadgets such as medical equipments.**

**If you have any further questions regarding this project, please comment below, you will get a guaranteed reply.**

Super

Thanks,

Glad you like it.

Regards

Hi, you stated that a transformer without a centre tap could be used, could you show the circuit for a transformer without a centre tap, i have a few without but none with centre tap.

Thank you.

Hi John,

Take a look at this: https://electronics-project-hub.com/ic-555-inverter-circuit/

Scroll down and you can find a circuit using H-bridge and a center-tap-less transformer.

Regards

Where can you get the transformer from. Please answer asap, thanks for your time.

Hi,

You can get a step down transformer rated at more than 10A from your nearest electronics shop or try searching online.

Regards

do you know what stores carry these, either physical or online. I’m having a hard time finding one at at least 5 amps. Thanks for your help.

Also if we wanted to instead get a voltage like 120 ac, would we need as large of a transformer

To get same power output at 120V you need to get douple the specified amper rating for transformer.

Hi,

I purchased it from local store, but i am sure you can get it from ebay or bangood etc. If not the same, closer value one.

Regards

Where can you get the transformer from. Please answer asap, thanks for your time.

If you see this a second time I’m sorry I wasn’t sure if it posted.

No worries!

Sorry to be bugging you so much. i was wondering how you did the calculations and got 230 vac and the wattage, thanks for all your help.

No worries,

The transformer is rated for 9V on secondary and 230V as primary, if we apply 9V AC at secondary we will get approx 230V at output.

The wattage can be calculated by using P = VI formula . V is the 9V and I is the specified amper rating on transformer.

Regards

can i use a 200AH, 12v battery and 150va or above, 230/9v transformer on this circuit? thanks

Yes, You can.

I’m using a step down transformer 240v to 6.3v – 6.3v.

Of course, I reversed it. So primary becomes secondary.

So in this case only the secondary has a center tap, but I’m using the secondary as the primary – so now it’s step up.

I’m assuming I can’t use the center tap on the high impedance (primary) side using this circuit, I would need a step up with a center tap on the secondary side?

If I can, how would it be wired please?

Hi,

So, you have a normal 240V (primary) to secondary 6.3 – 6.3V. Ahhh so you have 0-12.6V at secondary (as step-down) and you don’t have a center tap as mentioned in the circuit (only two wires available). If so, you need to drive the transformer using 4 MOSFETs in H-bridge configuration.

Regards

Pls I built a small inverter with Ic 4047, 500watt ups transformer. It supplies AC , but it draw current too fast. I used irf150 (2). Tested with 12 7Ah battery.

Pls I need ur advice on what to do.

Can you elaborate us exactly what suggestion do you want?

Please, i need an inverter circuit which gives out sine waves

Sorry, prince currently we don’t have one, but we will consider in future.

Regards

What wattage resistors did you use. Thank you in advance for your answer.

You can use low wattage resistors, I used 1/4 watt resistors.

Another question in the schematic it is not very clear do you hook the capacitor to the resistors if you could please give some written instructions I would very much appreciate it as I am planning on building it thank you

Hi,

I have updated a link with colored wirings below the main circuit diagram. I hope now you can identify the wires.

Regards

Thank you so much it really clarified things. I got 1/2 watt resistors for the 27 k resistors will they work. From my research it should but just thought I would ask you

Yes, they will work, even SMD resistor will work which is 1/8 watt.

Here the resistor wattage is not critical because we are not consuming huge amount of current from it.

Regards