The PWM controlled modified sine wave inverter circuit presented here uses just a single 4093 for the specified functions.
Parts you will Ned to Build this 200 Watt Inverter Circuit
All Resistors are 1/4 watt, 5 %, unless otherwise specified.
R1 = 1 M for 50 Hz and 830 K for 60 Hz
R2 = 1 K,
R3 = 1 M,
R4 = 1 K,
R5, R8, R9 = 470 Ohms,
R6, R7 = 100 Ohms, 5 Watt,
VR 1 = 100 K,
C1, C2 = 0.022 uF, Ceramic Disc,
C3 = 0.1, disc ceramic
T1, T4 = TIP 122
T3, T2 = BDY 29,
N1, N2, N3, N4 = IC 4093,
D1, D1, D4, D5 = 1N4007,
D3, D2 = 1N5408,
Transformer = 12 -0 – 12 volts, current from 2 to 20 Amps as desired, output voltage can be 120 or 230 volts as per country specifications.
Battery = 12 volts, typically a 32 AH type, as used in cars is recommended.
The proposed design of a 200 watt modified sine wave inverter obtains its modified output by discretely “cutting” the basic square wave pulses into smaller sections of rectangular pulses. The function resembles to a PWM control, commonly associated with IC 555.
However, here the duty cycles cannot be varied separately and is kept equal throughout the available variation range. The limitation does not affect the PWM function by much, since here we are only concerned in keeping the RMS value of the output close to its sine wave counter, which is executed satisfactory through the existing configuration.
Referring to the circuit diagram, we can see that the entire electronics hovers around a single active part – the IC 4093.
It consists of four individual NAND Schmitt gates, all of them have been engaged for the required functions.
N1 along with R1, R2 and C1 forms a classic CMOS Schmitt trgger type of oscillator where the gate is typically configured as an inverter or a NOT gate.
The pulses generated from this oscillator stage are square waves which forms the basic driving pulses of the circuit. N3 and N4 are wired up as buffers and are used for driving the output devices in tandem.
However these are ordinary square wave pulses and do not constitute the modified version of the system.
We can easily use the above pulses solely for driving our inverter, but the result would be an ordinary square wave inverter, not suitable for operating sophisticated electronic gadgets.
The reason behind this is that, square waves may differ greatly from the sine waveforms, especially as far as their RMS values are concerned.
Therefore, the idea is to modify the generated square waveforms so that its RMS value closely matches with a sine waveform. To do this we need to dimension the individual square waveforms through some external intervention.
The section comprising N2, along with the other associated parts C2, R4 and VR1, forms another similar oscillator like N1. However this oscillator produces higher frequencies which are tall rectangular shaped.
The rectangular output from N2 is fed to the basic input source of N3. The positive trains of pulses have no effect on the source input pulses due to the presence of D1 which blocks the positive outputs from N2.
However, the negative pulses are allowed by D1 and these effectively sink the relevant sections of the basic source frequency, creating kind of rectangular notches in them at regular intervals depending upon the frequency of the oscillator set by VR1.
These notches or rather the rectangular pulses from N2 can be optimized as desired by adjusting VR1.
The above operation cuts the basic square wave from N1 into discrete narrow sections, lowering the average RMS of the waveforms. It is advised that the setting is done with the help of a RMS meter.
The output devices switch the relevant transformer windings in response to these dimensioned pulses and produce corresponding high voltage switched waveforms at the output winding.
The result is a voltage which is quite equivalent to a sine wave quality and is safe for operating all types of household electrical equipment.
The inverter power may be increased from 200 watts to 500 watts or as desired simply by adding more numbers of T1, T2, R5, R6 and T3, T4, R7, R8 in parallel over the relevant points.
Salient Features of the Inverter
The circuit is truly efficient and moreover it is a modified sine wave version which makes it outstanding in its own respect.
The circuit utilizes very ordinary, easy to procure types of components and is also very cheap to build.
The modifying process of the square waves into sine waves can be done by varying a single potentiometer or rather a preset, which makes the operations pretty simple.
The concept is very basic yet offers high power outputs which may be optimized as per ones own needs just by adding a few more number of output devices in parallel and by replacing the battery and the transformer with the relevant sizes.