0 DC-AC Power Inverter

DC-AC power inverter is an electronic device used to produce AC voltages from a DC source. This usually used when one needs an altering current but AC main source is not available.
There are different kinds of inverters based on their outputs. These are the square wave, modified sine wave (quasi sine wave) and pure sine wave.
Inverter types based on voltage outputs
Square wave type is one of the cheapest of the inverters. It can be used primarily for lighting and other equipments that work on both AC and Dc supply. Modified sine wave is the most common type used today. Most of the common tools, equipment work on this type of output. Some motors work using this inverter type but requires higher power. Pure sine wave is the best of all types but the most expensive of all. All equipments work on this type of inverter including motors.
Basic inverter circuit
The configuration of a basic power inverter is shown in figure above. The power inverter is a push pull connection which can be operated in a pulse width modulation (PWM) or a square wave mode of waveforms. One advantage of this inverter is it can be operated even in a very low voltage DC source but with a reduction of DC-AC power conversion. The oscillator circuit turns on and off transistor 1 and 2 but not at the same time, thus producing an alternating flux in L1 and L2 inducing AC voltage to the secondary winding of transformer T1. This general phenomenon is present in all inverters where current in one of the winding is force to go to zero with every switching. This phenomenon is important in the design of inverter. Diagram below is the commercial inverter available in the market.
Commercial inverter
Engineers and hobbyist are becoming more interested in designing inverters of high efficiency but less expensive to be used to different projects such as uninterruptible power supply (UPS) and power supply for emergency lighting. Example of this DC powered fluorescent tube is shown below.
Fluorescent inverter
The circuit operates in a form of oscillation controlled by the windings and with the aid of transistor unique characteristics. At First when the transistor is in off state, the current will initially flow through the 270 ohm resistor and feedback winding W1.When the current flowing through W1 increases, the voltage in this winding also increases. As a result, the voltage in winding W2 also increases causing the transistor to turn on. As a result this voltage in winding W2 will induce voltage to winding W3 that will drive the fluorescent tube. This process will continue until such time that the maximum current is reached, at this point, the current change is very minimal thus the voltage induced in Winding W1 and W2 is minimum and this will continue until the voltage polarity starts to reverse. This reverse voltage polarity induced in windings will cause the transistor to turn off. Then the inverter is ready for the next cycle.

Part List:
Transistor  - TIP41C [NPN, 65W, 100V, 3MHz, 6A] or any equivalent.
W1 - is 5 turns #26 AWG magnetic wire
W2 -  is 8 turns #22 AWG magnetic wire
W3 -  is 350 turns #30 AWG magnetic wire
Resistor - 270 ohm 1W
DC – 12V battery


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