Simple Inverter Circuit

Here is a simple Inverter circuit which can be made using common step down transformer. Use Transformer  1 to 5 Amp 12V or 9V according to the input and output power required.  According to the power formula, max power will be 12V X 5A=60W and not 100W or 200W Inverter as it says in many website.

Simple Inverter Circuit using 3055 Transistor

Our inverter circuit uses  one pair of 2N3055 Transistor. This NPN Transistor is commonly available in market. It is used in inverters and high watt audio amplifier devices.

Parts required:


a) Transformer, 12-0-12, 1-5A

b) Transistor 2N3055 with Heat Shrink

c) Resistance 68 Ohms, 5 Watt


This circuit is great for education purpose and easy to make. As a safety device you can include a 6A Fuse at 12V connection.



For convertig AC into DC, both Transistors and two resistors are set in an astable multivibrator mode. Current alternately flows in each half of primary coil winding. Secondary coil turns is 10 or 20 times higher than primary turns, depends on country 110 or 220V outlets. According to transformer formula  the turns ratio determines the ratio of the voltages in the two coils.


As the volts per turn is proportional to the flux in the machine, is the same for the whole winding,

V1 : V2 = T1 : T2


V1 / T1 = V2 / T2

This inverted V2 is connected with the load.



a) Easy to make without PCB.

b) Only three component used. 



a) In this circuit voltage is not accurate. Small load changes output voltage.

b) Output AC Frequency is not accurate. It also depends on inductance of transformer and output load.

c) Low power efficiency.


In daily life you will not find this circuit in any inverter or emergency light. Today complicated circuit is used for maintaining constant smart charging of battery, fast switching from mains to battery mode without fluctuation, pure sine wave, good efficiency, smaller in size.