Traditional power supplies often rely on transformers to step-up or step-down voltage levels. However, in low current applications, transformers can be bulky and inefficient. Using Transformerless power supplies solves this issue by using capacitors and resistors to achieve the desired voltage regulation without the need for a transformer. In this article we will learn how to build a Transformerless Power Supply for Low Current Applications. So let's get started.
Overview of Our Project
In this project, we will be designing a Transformerless Power Supply for low current applications. A transformerless power supply functions as a voltage divider network that takes 220V AC as input and reduces it to the desired lower DC voltage. The AC voltage is rectified through diodes and regulated to a maximum voltage.
Transformerless Power Supply systems are particularly cost-effective alternatives to traditional transformer-based products. By eliminating the need for a transformer, these systems offer a more affordable solution. Transformers are known for being bulky and expensive, making them less practical for certain applications. Many everyday electrical devices, such as LED lights, lamps, laptop and phone chargers, operate at lower DC voltages like 5V, 9V, 12V. Therefore, it is essential to reduce the 220V AC to a lower DC voltage without compromising circuit size or PCB dimensions.
Transformerless Power Supply systems are especially well-suited for powering low current logic circuits and microprocessor circuits. Their compact design and efficient operation make them an ideal solution for a variety of applications.
Lets get onto building our Transformerless Power Supply by getting the required components.
There are usually Capacitive and Resistive types of transformerless power supply. The Capacitive type is more efficient due to its low heat dissipation and minimal power loss. This makes it an ideal solution for circuits which requires very low current, typically in the range of a few milliamperes.
Considering some factors is essential before designing a power supply:
Placing a non-polarized capacitor and a resistor in series with the AC power line, a constant current can be maintained through the resistor. In this scenario, the reactance of the capacitor must exceed the resistance of the resistor used.
The current flowing through resistor R is dependent on the value of capacitor C. The higher the capacitance, the greater the current supplied to the circuit. The current passing through the X-Rated capacitor is determined by the following formula: IRMS = VIN / X
The selection of the voltage dropping capacitor is critical and is based on the Reactance of the capacitor and the required current withdrawal.
The Reactance of the capacitor can be calculated using the formula provided X = 1 / (2 * π * f * C)
For example, using a 0.47uF capacitor and a mains frequency of 50 Hz, the Reactance X is calculated as follows X = 1 / (2 * 3.14 * 50 * 0.47 * 10^-6) = 6.77 K ohm
With this information, the current (I) in the circuit can be determined by I = V / X = 230 / 6775 = 34mA
Understanding the principles behind transformerless power supplies and carefully selecting the components involved are crucial steps in designing an efficient and reliable power supply system.
Transformerless Power Supply Circuit
The above circuit shows the implementation of the Transformerless Power Supply
Circuit Explanation
A 0.47uF voltage-dropping capacitor is connected in series with the phase line of an AC power source. This capacitor is non-polarized, meaning it can be connected from either side. In parallel with the capacitor, a 470k ohm resistor is connected to discharge any stored current in the capacitor when the circuit is switched off. This serves to prevent electric shock. This resistor is commonly referred to as a bleeder resistor.
220V AC main is given as the input voltage for our circuit. For safety purposes, it is advisable to connect a fuse. The 220V AC is then rectified through a pair of diodes, specifically 1N4007, functioning as a half-bridge rectifier. The DC voltage dividers are constructed using a combination of resistors to regulate the current flow within the circuit.
To limit the voltage output to 9V, we used a 9V Zener Diode 1N4739A. If a different output voltage such as 5V or 12V is desired, a Zener diode with the appropriate voltage rating must be selected.
The circuit simulation is shown below in Proteus software. Here you can see we are getting a 9V DC output from 220V AC, without using.
Thus we have successfully built and implemented Transformerless Power Supply for Low Current Applications.
Advantages
Let's discuss some Advantages of this Power supply:
1. Compactness: Eliminating the transformer reduces the size and weight of the power supply.
2. Cost-Effectiveness: Transformerless power supply requires fewer components, which reduces the manufacturing cost.
3. Efficiency: Transformerless power supplies can achieve high efficiency levels in low power applications.
Applications
Transformerless power supplies are suitable for powering various low-power devices such as:
LED lighting circuits
Small sensors and IOT device
Battery charging circuits
Low-power audio applications.
Some Safety Measures To Take While Building This Power Supply
Please proceed with caution when working with AC mains as it can be extremely dangerous without the proper experience and precautions. Take extreme care when constructing this circuit.
Ensure that you only use a resistor and Zener diode with a rating of 1 Watt or above (5W). For added safety, consider using a 1 ampere fuse before the X-Rated capacitor, in series with the phase line.
Do not substitute an X-Rated capacitor with a normal capacitor, as it may result in bursting. If you require more output voltage and current, use a different value of X-Rated capacitor as indicated in the table.
If needed, an IC voltage regulator can be used instead of a Zener diode for voltage regulation.
Install a fuse in series with the circuit to protect against overcurrent situations.
Enclose the circuit in a non-conductive housing to prevent accidental contact with live components.
Conclusion
Finally we have designed and learned how to build a Transformerless Power Supply for our current needs and applications, while building you must follow the safety measures discussed in the article. This Power supply can be used in all low current requirement applications. If you are looking for components like Resistor, Capacitor, Diode to build this Power Supply then Campus Component is the one stop solution for electronic components online, also you can checkout different Power Supply Module and IC from top brands like Mornsun and Abilton at Campus Component.
