These 7 inverter circuits may look simple with their designs, but are able to produce a reasonably high power output and an efficiency of around 75%. Learn how to build this cheap mini inverter and power small 220V or 120V appliances such drill machines, LED lamps, CFL lamps, hair dryer, mobile chargers, etc through a 12V 7 Ah battery.
Let's begin with the most simplest in the list which utilizes a couple of 2N3055 transistors and some resistors.
1) Simple Inverter Circuit using Cross Coupled Transistors
The article deals with the construction details of a mini inverter. Read to know regrading the construction procedure of a basic inverter which can provide reasonably good power output and yet is very affordable and sleek.
There may be a huge number of inverter circuits available over the internet and electronic magazines. But these circuits are often very complicated and hi-end type of inverters.
Thus we are left with no choice but just to wonder how to build power inverters that can be not only easy to build but also low cost and highly efficient in its working.
Well your search for such a circuit ends here. The circuit of an inverter described here is perhaps the smallest as far its component count goes yet is powerful enough to fulfill most of your requirements.
To begin with, first make sure to have proper heatsinks for the two 2N3055 transistors. It can be fabricated in the following manner:
- Cut two sheets of aluminum of 6/4 inches each.
- Bend one end of the sheet as shown in the diagram. Drill appropriate sized holes on to the bends so that it can be clamped firmly to the metal cabinet.
- If you find it difficult to make this heatsink you can simply purchase from your local electronic shop shown below:
- Also drill holes for fitting of the power transistors. The holes are 3mm in diameter, TO-3 type of package size.
- Fix the transistors tightly on to the heatsinks with the help of nuts and bolts.
- Connect the resistors in a cross-coupled manner directly to the leads of the transistors as per the circuit diagram.
- Now join the heatsink, transistor, resistor assembly to the secondary winding of the transformer.
- Fix the whole circuit assembly along with the transformer inside a sturdy, well ventilated metal enclosure.
- Fit the output and input sockets, fuse holder etc. externally to the cabinet and connect them appropriately to the circuit assembly.
Once the above heatsink installation is over, you simply need to interconnect a few high watt resistors and the 2N3055 (on heatsink) with the selected transformer as given in the following diagram.
Complete Wiring Layout
After the above wiring is completed, it's time to hook it up with a 12V 7Ah battery, with a 60 watt lamp attached at the transformer secondary. When switched ON the result would be an instant illumination of the load with an astonishing brightness.
Here the key element is the transformer, make sure the transformer is genuinely rated at 5 amp, otherwise you may find the output power a lot lesser than the expectation.
I can tell this from my experience, I built this unit twice, once when I was in college, and the second time recently in the year 2015. Although I was more experienced during the recent venture I could not get the awesome power that I had acquired from my previous unit. The reason was simple, the previous transformer was a robust custom built 9-0-9V 5 amp transformer, compared to the new one in which I had used probably a falsely rated 5 amp, which was actually only 3 amp with its output.
You will require just the following few components for the construction:
R1, R2= 100 OHMS./ 10 WATTS WIRE WOUND
R3, R4= 15 OHMS/ 10 WATTS WIRE WOUND
T1, T2 = 2N3055 POWER TRANSISTORS (MOTOROLA).
TRANSFORMER= 9- 0- 9 VOLTS / 8 AMPS or 5 amps.
AUTOMOBILE BATTERY= 12 VOLTS/ 10Ah
ALUMINUM HEATSINK= CUT AS PER THE REQUIRED SIZE.
VENTILATED METAL CABINET= AS PER THE SIZE OF THE WHOLE ASSEMBLY
Video Test Proof
How to Test it?
- The testing of this mini inverter is done in the following method:
- For testing purpose connect a 60 watt incandescent bulb to the output socket of the inverter.
- Next, connect a fully charged 12 V automobile battery to its supply terminals.
- The 60 watt bulb should immediately light up brightly, indicating that the inverter is functioning properly.
- This concludes the construction and the testing of the inverter circuit.
- I hope from the above discussions you must have clearly understood how to build an inverter which is not only simple to construct but also very affordable to each of you.
- It can be used to power small electrical appliances like soldering iron, CFL lights, small portable fans etc. The output power will lie in the vicinity of 70 watts and is load dependent.
- The efficiency of this inverter is around 75%. The unit may be connected to your vehicles battery itself when outdoors so that the trouble of carrying an extra battery is eliminated.
The functioning of this mini inverter circuit is rather unique and different from the normal inverters which involve discrete oscillator stage for powering the transistors.
However here the two sections or the two arms of the circuit operate in a regenerative manner. Its very simple and may be understood through the following points:
The two halves of the circuit no matter how much they are matched will always consist a slight imbalance in the parameters surrounding them, like the resistors, Hfe, transformer winding turns etc.
Due to this, both the halves are not able to conduct together at one instant.
Assume that the upper half transistors conduct first, obviously they will be getting their biasing voltage through the lower half winding of the transformer via R2.
However the moment they saturate and conduct fully, the entire battery voltage is pulled through their collectors to the ground.
This sucks-out dry any voltage through R2 to their base and they immediately stop conducting.
This gives an opportunity for the lower transistors to conduct and the cycle repeats.
The whole circuit thus starts to oscillate.
The base Emitter resistors are used to fix a particular threshold for their conduction to break, they help to fix a base biasing reference level.
The above circuit was inspired from the following design by Motorola:
UPDATE: You may also want to try this: 50 watt Mini Inverter Circuit
Output Waveform better than square wave (Reasonably suitable for all electronic appliances))
PCB Design for the above explained simple 2N3055 Inverter Circuit (Track Side Layout)
2) Using IC 4047
As shown above a simple yet useful little inverter can be built using just a single IC 4047. The IC 4047 is a versatile single IC oscillator, which will produce precise ON/OFF periods across its output pin#10 and pin#11. The frequency here could be determined by accurately calculating the resistor R1 and capacitor C1. These components determine the oscillation frequency at the output of the IC which in turn sets the output 220V AC frequency of this inverter circuit. It may set at 50Hz or 60Hz as per individual preference.
The battery, mosfet and the transformer can be modified or upgraded as per the required output power specification of the inverter.
For calculating the RC values, and the output frequency please refer to the datasheet of the IC
3) Using IC 4049
In this simple inverter circuit we use a single IC 4049 which includes 6 NOT gates or 6 inverters inside. In the diagram above N1----N6 signify the 6 gates which are configured as oscillator and buffer stages. The NOT gates N1 and N2 are basically used for the oscillator stage, the C and R can be selected and fixed for determining the 50Hz or 60 Hz frequency as per country specs
The remaining gates N3 to N6 are adjusted and configured as buffers and inverters so that the ultimate output results in producing alternating switching pulses for the power transistors. The configuration also ensures that no gates are left unused and idle, which may otherwise require their inputs to be terminated separately across a supply line.
The transformer and battery may be selected as per the power requirement or the load wattage specifications.
The output will be purely a square wave output.
Formula for calculating frequency is given as:
f = 1 /1.2RC,
where R will be in Ohms and F in Farads
4) Using IC 4093
Quite similar to the previous NOT gate inveter, the NAND gate based simple inverter shown above can be built using a single 4093 IC. The gates N1 to N4 signify the 4 gates inside the IC 4093.
N1, is wired as an oscillator circuit, for generating the required 50 or 60Hz pulses. These are appropriately inverted and buffered using the remaining gates N2, N3, N4 in order to finally deliver the alternately switching frequency across the bases of the power BJTs, which in turn switch the power transformer at the supplied rate for generating the required 220V or 120V AC at the output.
Although any NAND gate IC would work here, using the IC 4093 is recommended since it features Schmidt trigger facility, which ensures a slight lag in switching and helps creating a kind of dead-time across the switching outputs, making sure that the power devices are never switched ON together even for a fraction of a second.
5) Another Simple NAND gate Inverter using MOSFETs
Another simple yet powerful inverter circuit design is explained in the following paragraphs which can be built by any electronic enthusiast and used for powering most of the household electrical appliances (resistive and SMPS loads).
The use of a couple of mosfets influences a powerful response from the circuit involving very few components, however the square wave configuration does limit the unit from quite a few useful applications.
Calculating MOSFET parameters may seem to involve a few difficult steps, however by following the standard design enforcing these wonderful devices into action is definitely easy.
When we talk about inverter circuits involving power outputs, MOSFETs imperatively become a part of the design and also the main component of the configuration, especially at the driving output ends of the circuit.
Inverter circuits being the favorites with these devices, we would be discussing one such design incorporating MOSFETs for powering the output stage of the circuit.
Referring to the diagram, we see a very basic inverter design involving a square wave oscillator stage, a buffer stage and the power output stage.
The use of a single IC for generating the required square waves and for buffering the pulses particularly makes the design easy to make, especially for the new electronic enthusiast.
Using IC 4093 NAND Gates for the Oscillator Circuit
The IC 4093 is a quad NAND gate Schmidt Trigger IC, a single NAND is wired up as an astable multivibrator for generating the base square pulses. The value of the resistor or the capacitor may be adjusted for acquiring either a 50 Hz or 60 Hz pulses. For 220 V applications 50 Hz option needs to be selected and a 60 Hz for the 120 V versions.
The output from the above oscillator stage is tied with a couple of more NAND gates used as buffers, whose outputs are ultimately terminated with the gate of the respective MOSFETs.
The two NAND gates are connected in series such that the two mosfets receive opposite logic levels alternately from the oscillator stage and switch the MOSFETs alternately for making the desired inductions in the input winding of the transformer.
The above switching of the MOSFETs stuffs the entire battery current inside the relevant windings of the transformer, inducing an instant stepping up of the power at the opposite winding of the transformer where the output to the load is ultimately derived.
The MOSFETs are capable of handling more than 25 Amps of current and the range is pretty huge and therefore becomes suitable driving transformers of different power specs.
It’s just a matter of modifying the transformer and the battery for making inverters of different ranges with different power outputs.
Parts List for the above explained 150 watt inverter circuit diagram:
R1 = 220K pot, needs to be set for acquiring the desired frequency output.
R2, R3, R4, R5 = 1K,
T1, T2 = IRF540
N1—N4 = IC 4093
C1 = 0.01uF,
C3 = 0.1uF
TR1 = 0-12V input winding, current = 15 Amp, output voltage as per the required specs
Formula for calculating frequency will be identical to the one described above for IC 4049.
f = 1 /1.2RC. where R = R1 set value, and C = C1
6) Using IC 4060
If you have a single 4060 IC in your electronic junk box, along with a transformer and a few power transistors, you are probably all set to create your simple power inverter circuit using these components. The basic design of the proposed IC 4060 based inverter circuit can be visualized in the above diagram. The concept is basically the same, we use the IC 4060 as an oscillator, and set its output to create alternately switching ON OFF pulses through an inverter BC547 transistors stage.
Just like IC 4047, the IC 4060 requires an external RC components for setting up its output frequency, however, the output from the IC 4060 are terminated into 10 individual pinouts in a specific order wherein the output generate frequency at a rate twice that of its preceding pinout.
Although you may find 10 separate outputs with a rate of 2X frequency rate across the IC output pinouts, we have selected the pin#7 since it delivers the fastest frequency rate among the rest and therefore may fulfil this using standard components for the RC network, which may be easily available to you no matter in which part of the globe you are situated in.
For calculating the RC values for R2 +P1 and C1 and the frequency you can use the formula as described below:
Or another way is through the following formula:
f(osc) = 1 / 2.3 x Rt x Ct
Rt is in Ohms, Ct in Farads
More info can be obtained from this article
Here's yet another cool DIY inverter idea which is extremely reliable and uses ordinary parts for accomplishing a high power inverter design, and can be upgraded to any desired power level.
Let's learn more about this simple design
7) Simplest 100 Watt Inverter for the Newcomers
The circuit of a simple 100 watt inverter discussed in this article can be considered as the most efficient, reliable, easy to build and powerful inverter design. It will convert any 12V to 220V effectively using minimum components
The idea was published many years back in one of the elecktor electronics magazines, I present it here so that you all can make and use this circuit for your personal applications. Let's learn more.
The proposed simple 100 watt inverter circuit disign was published quite a long time ago in one of the elektor electronics magazines and according to me this circuit is one of the best inverter designs you can get.
I consider it to be the best because the design is well balanced, well calculated, utilizes ordinary parts and if done everything correctly would start working instantly.
The efficiency of this design is in the vicinity of 85% that's good considering the simple format and low costs involved.
Using an Transistor Astable as the 50Hz Oscillator
Basically the whole design is built around an astable multivibrator stage, consisting of two low power general purpose transistors BC547 along with the associated parts consisting of two electrolytic capacitors and some resistors.
This stage is responsible for generating the basic 50 Hz pulses required for initiating the inverter operations.
The above signals are at low current levels and therefore requires to be lifted to some higher orders. This is done by the driver transistors BD680, which are Darlington by nature.
These transistors receive the low power 50 Hz signals from the BC547 transistor stages and lift them at higher current levels so that it can be fed to the output transistors.
The output transistors are a pair of 2N3055 which receive an amplified current drive at their bases from the above driver stage.
2N3055 Transistors as the Power Stage
The 2N3055 transistors thus are also driven at high saturation and high current levels which gets pumped into the relevant transformer windings alternately, and converted into the required 220V AC volts at the secondary of the transformer.
Parts List for the above explained simple 100 watt inverter circuit
R1,R2 = 27K, 1/4 watt 5%
R3,R4,R5,R6 = 330 OHMS, 1/4 watt 5%
R7,R8 = 22 OHMS, 5 WATT WIRE WOUND TYPE
C1,C2 = 470nF
T1,T2 = BC547,
T3,T4 = BD680, OR TIP127
T5,T6 = 2N3055,
D1,D2 = 1N5402
TRANSFORMER = 9-0-9V, 5 AMP
BATTERY = 12V,26AH,
Heatsink for the T3/T4, and T5/T6
- Power Output: 100 watts if single 2n3055 transistors are used on each channels.
- Frequency: 50 Hz, Square Wave,
- Input Voltage: 12V @ 5 Amps for 100 Watts,
- Output Volts: 220V or 120V(with some adjustments)
From the above discussion you might be feeling thoroughly enlightened regarding how to build these 7 simple inverter circuits, by configuring a given basic oscillator circuit with a BJT stage and a transformer, and by incorporating very ordinary parts which may be already existing with you or accessible by salvaging an old assembled PC board.
How to Calculate the Resistors and Capacitors for 50 Hz or 60 Hz Frequencies
In this transistor based inverter circuit, the oscillator design is built using a transistorized astable circuit.
Basically the resistors and capacitors associated with the bases of the transistors determine the frequency of the output. Although these are correctly calculated to produce approximately 50 Hz frequency, if you are further interested to tweak the output frequency as per own preference you can easily do so by calculating them through this Transistor Astable Multivibrator Calculator.
For the Advanced Users
The above explained were a few straightforward inverter circuit designs, however if you think these are pretty ordinary for you, you can always explore more advanced designs which are included in this website. Here are a few more links for your reference:
More Inverter Projects for You with Full online Help!