Simple Inverter Circuit using Two 2N3055 Transistors

Using only a two 2N3055 transistors we will discuss in this post how to construct a simple cross coupled inverter circuit.

With a 12V battery this simple inverter can produce 100 watts of 220V AC power which can be used to run low household equipment.

Circuit Working:

Parts List:

The inverter operates as a saturable core oscillator.

It uses a filament transformer and two general purpose germanium power transistors.

Cross coupled connections in the manner of a multivibrator generate the necessary feedback for oscillation.

The inverter is designed to power from an automobile battery.

In the circuit the filament transformer is important.

For the inverter to operate the transformer helps in stepping up or stepping down the voltage to the necessary level.

The germanium power transistors function as switches in the circuit

These transistors generate an AC output by continuously turning on and off during oscillation.

At full load the efficiency of the inverter is approximately 75%.

The output voltage is around 220V.

To suppress the spike in the output waveform a mild pi section filter is used.

This filter causes a trapezoid wave rather than the usual square wave to be available at the output.

The filtered waveform is more suitable for powering radios, recorders and other electronic equipment.

The efficiency, frequency, output voltage and starting ability are interdependent.

Experimentation with biasing resistances especially R1 is necessary to improve performance.

To prevent waveform mismatch and defects the biasing networks for the two transistors must be balanced.

Once the circuit is put together turn it on and observe how well it works.

The output voltage is measured with a multimeter to make sure it meets design requirements.

If necessary adjust the circuit parameters to get the desired results.

A thorough circuit schematic with component values and connections is necessary for an actual implementation so one should keep that in mind.

One should understand the inverters operation during constructing and by following the description which offers a theory of how it operates.

Formulas:

The cross coupled transistor based inverter functions primarily as a flip flop or bistable multivibrator circuit and does not require a capacitors but instead it uses resistors simply for timing.

The frequency in this type of circuit is set by transistor features and resistor timing rather than capacitive charging and discharging.

For example the time constants developed by the resistors and the basic features of the transistors (such as switching speed and delay in transmission) are often used to measure the frequency at which the flip flop circuit oscillates.

The frequency formula for this kind of circuit is calculated by:

f = 1 / 2 * R * C_eff​

where,

• f is the oscillation frequency in hertz Hz
• R represents the timing resistors resistance in ohms Ω
• The effective capacitance is represented by Ceff due to the parasitic and junction capacitances of the transistors.

The particular transistors ues and the circuit design might affect C_effs precise value.

It is crucial to remember that in contrast to conventional oscillator circuits using capacitors the properties of the transistor and the cross coupled arrangement also have a role in calculating the frequency in a resistor based on flip flop circuit.

Therefore simulation or actual measurement are required for exact frequency calculation for practical uses.

How to Build:

For Building a Simple 50 Hz Inverter circuit follow the below steps:

• Gather all of the above mentioned components.
• As mentioned in the circuit design make sure your resistor, capacitor and inductor values are accurate.
• Examine the following circuit schematic paying particular attention to the connections, positioning of the transistors and general design.
• Recognize the function of each circuit component.
• The components should be soldered onto the PCB or placed on the breadboard as per with the circuit diagram.
• Make sure there are no loose connections or short circuits by staying careful with your connections.
• Connect the vehicles battery to the inverter.
• Verify that the battery has enough charge and that the polarity is correct.
• Try adjusting the biasing resistances especially R1 to improve the inverters performance.
• In order avoid waveform inequalities and other problems it can be required to balance the biasing networks for both transistors.
• Switch the inverter on and check how it works.
• Measure the output voltage with a multimeter to make sure it is about 220V.
• Check that the desired load is handled by the inverter without it overheating or breaking down.
• If you want to get the needed efficiency, frequency and starting ability than adjust the circuits settings as necessary.
• This might require further modifications for biasing resistances or other elements.

Caution:

• When handling power supplies and electronic parts one should maintain precaution.
• To prevent electrical risks observe safety regulations and follow the required safety measures.
• By carefully applying the circuit design and following the necessary instructions one can construct a working 50 Hz inverter that can power a number of electrical devices.

Conclusion:

With just two 2N3055 transistors and the construction instructions in this post beginners as well as professionals may build a basic cross coupled inverter circuit operating at 50 Hz that is both effective and efficient.

Using tried and true designs and gaining knowledge from makers, actual design troubleshooting will surely result in successful construction and circuit improvements.

References:

Cross- Coupled Inverter Circuit

Data sheet 2N3055