An inverter provides backup power for grid-based devices in the event of a power failure. Most of the available inverters in the market have complicated circuit design and are not very economical. Some of them produce a square wave output, which is undesirable for inductive loads.
Here a simple inverter circuit that produces a 50Hz quasi-sinusoidal wave output using a single CD4047 IC and some discrete components, making it a very cost effective solution.
Circuit description
FIG. 1 shows the MOSFET-based 50 Hz inverter circuit. It includes a CD4047 multivibrator (IC1), MOSFET IRF250 (T1 to T8), transistors and some discrete components.
IC CD4047 has integrated installations for astable and bistable multivibrators. Application of the inverter requires two outputs that are 180 degrees out of phase. Therefore, IC1 is wired to produce two square wave output signals on pins 10 and 11 with a frequency of 50 Hz, a duty cycle of 50% and a phase change of 180 degrees. The oscillation frequency is decided by the external preselection VR1 and the capacitor C1.
These two signals alternately drive the two MOSFET banks (bank-1 and bank-2). When pin 10 of IC1 is high and pin 11 is low, bank-1 MOSFETs (T1 to T4) conduct, while bank-2 MOSFETs (T5 to T8) remain in a non-conducting state. Thus, a large current oscillation flows through the first half of the primary winding of the inverting transformer X1 and 230V AC is developed through the secondary winding.
During the next half cycle, the voltage at the pin 10 of IC1 drops, while the voltage at the pin 11 is high. Hence bench-2 conduct MOSFETs, while bank-1 MOSFETs remain non-conductive. Therefore, the current flows through the other half of the primary winding and 230V AC develops through the secondary winding.