## Circuit Concept

Initially I could not figure out the concept behind these compact inverters which completely eliminated the bulky iron core transformers.

However after some thinking it seems I have succeeded in discovering the very simple principle associated with the functioning of such inverters.

Lately the Chinese compact type inverters have become pretty famous just because of their compact and sleek sizes which make them outstandingly light weight and yet hugely efficient with their power output specs.

Initially I thought the concept to be unfeasible, because according to me the use of tiny ferrite transformers for low frequency inverter application appeared highly impossible.

Inverters for domestic use requires 50/60 Hz and for implementing ferrite transformer we would require very high frequencies, so the idea looked highly complicated.

However after some thinking I was amazed and happy to discover a simple idea for implementing the design. Its all about converting the battery voltage to 220 or 120 mains voltage at very high frequency, and switching the output to 50/60 HZ using an push-pull mosfet stage.

### How it Works

Looking at the figure we can simply witness and figure out the whole idea. Here the battery voltage is first converted to high frequency PWM pulses.

These pulses are dumped into a step up ferrite transformer having the required appropriate rating. The pulses are applied using a mosfet so that the battery current can be utilized optimally.

The ferrite transformer steps up the voltage to 220V at it output. However since this voltage has a frequency of around 60 to 100kHz, cannot be directly used for operating the domestic appliances and therefore needs further processing.

In the next step this voltage is rectified, filtered and converted to 220V DC. This high voltage DC is finally switched to 50 Hz frequency so that it may be used for operating the household appliances.

Kindly note that though the circuit has been exclusively designed by me, it hasn't been tested practically, make it at your own risk and on;y if you have sufficient confidence over the given explanations.

#### Circuit Diagram

#### Parts List for 12V DC to 220V AC compact ferrite core inverter circuit.

R3---R6 = 470 Ohms

R9, R10 = 10K,

R1,R2,C1,C2 = calculate to generate 100kHz freq.

R7,R8 = 27K

C3, C4 = 0.47uF

T1----T4 = BC547,

T5 = any 30V 20Amp N-channel mosfet,

T6, T7 = any, 400V, 3 amp mosfet.

Diodes = fast recovery, high speed type.

TR1 = primary, 13V, 10amp, secondary = 250-0-250, 3amp. E-core ferrite transformer....ask an expert winder and transformer designer for help.

An improved version of the above design is shown below. The output stage here is optimized for better response and more power.

##### Improved Version

**Need Help? Please send your queries through Comments for quick replies!**

## 22 Comments

Hi Swagatam,

ReplyDeleteI am working on a design project to develop a circuit that converts 250V DC to AC voltage. The circuit has to meet the following requirements,

- Input voltage and current = 250V DC and 20A

- Output voltage and current = Pure sine wave AC (250V minus voltage drop) and 20A

- Maintain pure sine wave output like utility power over the entire load range (0 to 20A) for all types of load.

- Operate continuously

- Minimize power loss between input and output

- Minimize waste heat

- Smallest possible size

Please I need your help in drawing the circuit diagram to meet these requirements above, also please give me a list of the components required for this circuit. I will very much appreciate all your help in this matter. Thank you very much for your time and help.

Hi Koffi,

ReplyDeleteI'll try to design it soon, and let you know and it's posted.

Hi Swagatam how do i design my ferritr transformer. imean the formular or method

ReplyDeleteHi Benson, The formulas could be difficult to understand and impractical for a newcomer, that's why i have not yet included them in my blog.

ReplyDeleteHi Mr Swagatam, how can i do for obtain only 120 VAC from your circuit, i've seen that its give 220 VAC output voltage, thanks for your answers.

ReplyDeleteHi Frenando, the above circuits are not confirmed and could possess design flaws, so presently I won't recommend it.

ReplyDeletehi mr.swagatam sir,

ReplyDeleteplease give me its details for transformer winding

Hi Rakesh, presently I do not have it, I'll try to to research and get it soon.

ReplyDeleteSwagatam..... Av this circuit bin implemented buy you u or by anyone yet. I really like d topology. Great work. Thankz

ReplyDeleteThanks Toni, no it has not been tested yet but the design looks quite straightforward and could be easily implemented with a few minor tweaks.

ReplyDeletesir please it transformer a step up transformer or ferrite core transformer i mean it a chopper transformer? thank you.

ReplyDeleteit's a chopper transformer...

ReplyDeletewhat changes do I have to make to use a 24 volt instead of a 12 volt one

ReplyDeletethe transformer and the BJT, mosfet will need to be changed accordingly.

ReplyDeleteHi. I would like to build this inverter, but I don't know how to calculate R1,R2,C1,C2 to generate high frequency. Can you help me please

ReplyDeleteHi, you can fix them by some trial and error, initially use 27K for the base for the resistors, 2k2 for the collector, and 0.47uF for the capacitors, measure the frequency for this set up and then you can evaluate the other appropriate values for other desired frequencies using cross multiplication

ReplyDeletehello Swagatam , how can I increase the power (wattage ) to 500 Watt

ReplyDeleteHi Lufono,

ReplyDeleteyou can do it by upgrading the fet ratings and the trafo wattage appropriately

Would it not make the output waveform of the inverter significantly more sinusoidal if you were to place an iron core transformer with a turn ratio of 1:1 on the output. Im relatively new to this type of electronics, and was hoping to build this circuit, however i want to make the output more city power-like to run inductive loads.

ReplyDeletethe main idea of this design is to avoid the bulky iron core transformer, if the size is not a concern for you then you could perhaps go for a much easier design using a iron core trafo as discussed in the following article:

ReplyDeletehttps://homemade-circuits.com/2013/04/how-to-modify-square-wave-inverter-into.html

how to adjust the output voltage to 220v

ReplyDeleteby adjusting R7/R8

ReplyDelete