How to Design a Square Wave Inverter?

The UPS, short for Uninterruptible Power Supply, consists of the following basic blocks in its structure –

  • The Charger Circuit – This charges the entire battery system
  • Switching Mechanism – This detects power failure. It also supplies the input power from the mains of the building, and turns the UPS in running more or standby/charging mode.
  • Inverter – The DC power supply obtained from the battery should to converted in to an AC signal, the inverter is given charge of this task.

There are two basic kinds of inverters used in UPS –

  • The Square Wave inverter
  • The Sine Wave Inverter / the Modified Sine wave inverter.

Less sensitive electronics prefer the square wave inverters to convert DC to AC mains. The design of the inverter gives the characteristics of the frequency, output voltage, and the waveform. It is important to know that the inverter itself does not draw any power. It just converts the Direct Current into Alternating Current.

AC appliances are designed to run on AC power itself. The components in the circuit of the appliance will become faulty if a DC power source is used to energise the AC appliance. In India, the appliances are designed to run at a frequency of about 50 hertz, and a voltage between 220 V and 240 V.

A symmetric square wave has constant time period in both the positive half cycle and the negative half cycle – this means that the power in both cycles remains the same. Only the phase varies. The square wave inverter can be designed by many types of circuits. The Op Amp (Operational Amplifier), The IC (Integrated Circuit) 4047, or the IC 555. The IC 555 is an astable multivibrator. The circuit design can be designated into two parts –

Designing a switching mechanism to step up the voltage from 12 V to 220 V-

Design of a square wave inverter in order to produce a peak to peak voltage of 12 V with a frequency of about 50 hertz. The following components must be used to design the circuit if the square wave inverter.

  • A DC Power Source – 12 V powered Voltage Regulator is needed to build this circuit.
  • 555 Timer – This timer has a NE555 specification. Quantity needed is 1 in number.
  • Resistor R1 – With a value of 12.5 K Ohms.
  • Resistor R2 – With a value of 100 k Ohms.
  • Capacitor C1 – With a value of 1 uF with a ceramic coating.
  • Capacitor C2 – With a value of 1 uF with a polarised coating.

The 555 timer has 8 pins –

  1. Ground – Reference voltage with respect to ground
  2. Trigger – Comparator 1 negative input is connected here
  3. Output – The output waveform is present here
  4. Reset – Resets the entire circuit – the Active/Low pin
  5. Voltage Control – Controls the output signal’s characteristic (width)
  6. Threshold – Comparator 2 positive input
  7. Discharge – Timing capacitor gets discharged through this pin when output is low.
  8. VCC – Power supply to the entire circuit.

The working and the results of the circuit is a complicated procedure. This entire circuit set up is used for designing the square wave invertor in the UPS.

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