Making a 200 watt Compact PWM Inverter Circuit – Using Tiny Ferrite Transformer

This circuit was requested by a few of the dedicated followers of this blog, namely Mr. Rashid, Mr, Sandeep and also by a few more readers. 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.

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.

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.