Inverter is brain of backup system and without inverter, battery is useless for AC, as it changes DC power to AC power.
We can use inverter at home, solar and for battery backup, as this project is a mini and Simple 3.7V DC to 220V AC Inverter Circuit
Also, only with a 3.7V battery, one transistor, one transformer and with one resistor, we can get AC output; therefore, this circuit is easy to try, good for students for learning.
Circuit Working:
Parts List:
| Components | Values | Quantity |
|---|---|---|
| Resistor | 120 ohms 1/4 watt | 1 |
| Semiconductors | Transistor TIP41C NPN | 1 |
| Transformer step-up ferrite core from 3.7V to 220V AC | 1 | |
| Battery Li-ion 3.7V DC | 1 |
The mini inverter works on oscillation and transformer action and battery gives DC supply.
Also, TIP41C transistor act like switch and it drives the transformer and then transformer changes low DC to high AC.
Then resistor at base limit current and control switch and current flow in primary coil and it makes changing magnetic field; hence, this field induce voltage in secondary coil and finally, secondary coil give AC output.
Transformer Specification:
Type: Step-up transformer
Input (Primary Winding): 3.7V to 6V with low voltage side and connected to battery and transistor
Output (Secondary Winding): 220V AC for small load like LED lamp or night bulb
Turns Ratio: Around 1:60 for Primary:Secondary
Example: 10 turns in primary and 600 turns in secondary
Frequency: Works at transistor switching frequency (not 50Hz pure sine) which gives square wave AC.
Current Rating: About 500mA to 1A on primary side (depends on load).
Core Type: Small ferrite core or laminated EI core transformer commonly for 1 to 2W power.
Formulas and Calculations:
Below are the formulas for Simple 3.7V DC to 220V AC Inverter Circuit.
1: Input Power formula:
Input Power P = V × I
If battery is 3.7V and 1A then power = 3.7W.
2: Transformer ratio:
Transformer turns ratio = Vout / Vin.
If we want 220V from 3.7V then ratio = 60:1.
3: Base Resistor Calculation:
Base current Ib = Ic / hFE.
If Ic = 1A, hFE = 75, Ib = 13mA.
Resistor R = (Vin – Vbe) / Ib.
= (3.7 – 0.7) / 0.013 = 230 ohm.
Although you can use a standard 220–270Ω resistor, this circuit uses a 120Ω resistor to increase the base current and improve switching performance.
How To Build:
To build a Simple 3.7V DC to 220V AC Inverter Circuit follow the below steps for connections:
- First, take all the parts as shown in circuit diagram
- Next, connect base pin of transistor Q1 to secondary pin of step-up transformer, connect collector pin of transistor Q1 primary winding of step-up transformer and then connect emitter pin of transistor Q1 to 3.7V DC input
- Also, connect one end of resistor R1 to one pin of primary winding of step-up transformer and other end of resistor connect to secondary winding of the transformer
- After that, connect 2 pin of secondary winding of transformer to output AC of the circuit
- Finally, one end of 3.7V input DC pin goes between primary winding pin of transformer and one end of resistor R1 as shown in circuit diagram.
Conclusion:
Overall, we can easily try this simple 3.7 V DC to 220 V AC inverter circuit because it is low-cost and provides a good learning experience.
Also, it is good for LED lamp or small project, easy to build at home and is good for students and beginners.