Transformerless Power Supply – 220V AC to 9V DC:
The Transformerless Power Supply is used to low current applications. Basically a transformerless power supply is just a voltage divider network that takes the 220V AC as input and divides it down to Lower DC voltage that we want. The AC voltage need is rectified through a few diodes and regulated to a maximum voltage. Earlier we learnt about DC – DC Converter circuit. But now we will convert the AC to DC.
Transformerless Power Supply is especially inexpensive products where the cost of a transformer is removed. Transformers are bulky and expensive. Most of the electrical appliances used in our daily life like LED light, Lamp, Laptop & Phone Battery Chargers, Hair Drier, Toys, etc work at lower DC voltage like 5V, 9V, 12V, or 15V. So we need to lower down the 220V or 110V AC to lower DC without making the circuit bulky and keeping the PCB size small.
To power low current demanding logic circuits and microprocessor circuits, the transformerless power supply is an ideal solution.
|2||470 K Ω||Resistor||1|
|3||0.47 µF, 450V||Electrolytic Capacitor||1|
There are two types of transformerless power supplies that are Capacitive & Resistive. Capacitive type is more efficient compared to Resistive Type because of the low heat dissipation and very low power loss. If a circuit requires a very low current of a few milliamperes, such power supply is an ideal solution.
Before designing a power supply, we need to go through some design considerations. If a non-polarised capacitor and a resistor are kept in series with the AC power line, a constant current can be maintained through the resistor. In this case, the reactance of the capacitor should be greater than the resistance of the resistor used.
The current flowing through resistor R depends on the value of capacitor C. The more the Capacitance, the more the current to the circuit. Current flow through dropping capacitor C depends on its reactance (X). The value of the current passing through the X-Rated capacitor is defined as:
IRMS = VIN /X
he selection of the voltage dropping capacitor is very crucial. it is based on Reactance of Capacitor and the amount of current to be withdrawn. The Reactance of the capacitor is given by below formula:
We have used 0.47uF capacitor and frequency of mains is 50 Hz so the Reactance X is:
X = 1 / 23.14500.4710-6 = 6.77 Kohm
Now we can calculate the current (I) in the circuit:
I = V/X = 230/6775 = 34mA
We used 220V AC main as the input voltage. You may connect fuse for safety reasons. The 220V AC is then rectified through a few diodes. In this circuit, we used 2 diodes 1N4007 as a half-bridge rectifier. Normally, DC voltage dividers are made with a pair of resistors. Combined, they define the current flowing through the path.
Here 9V Zener Diode 1N4739A to limit the voltage to 9V. If you want 5V or 12V or any other output voltage, you need the specific Zener diode according to voltage rating. You can use our DIY Voltmeter to measure the output voltage.
Simulation with Proteus Software.