Transformerless Power Supply: Understanding Voltage Output and Applications
For those interested in electronics and power supplies, understanding the typical voltage output of a transformerless power supply is crucial. This article aims to provide clear insights into what a transformerless power supply is, how it works, and the typical voltage output in different scenarios.
Introduction to Transformerless Power Supply
A transformerless power supply is a type of power supply that does not use a traditional transformer to step-down the mains voltage. Instead, it relies on other methods such as resistive dividers or semiconductor-based voltage reducing circuits to achieve the desired voltage output. Contrary to the name, many vintage radios and inquisitive users might think that radio designs with no visible transformer are truly transformerless, but they often are not. Some chargers for modern devices, especially mobile phones, also might not appear to have transformers, but they actually do have small ferrite core transformers operating in switching mode to simulate the behavior of a transformerless supply.
Types of Transformerless Power Supplies
Transformerless power supplies can be categorized into different types based on their methods of voltage reduction. Here, we explore two main types:
Resistance Divider Circuit
A simple and common method for a transformerless power supply is the use of a resistive divider circuit. This circuit divides the input voltage using two resistors connected in series. The output voltage can be calculated using the formula:
V_out V_in * (R2 / (R1 R2))
Where V_in is the mains voltage, and R1 and R2 are the values of the resistors. This method is effective for lower voltage requirements but can introduce significant voltage drop and overheating, especially for higher wattage applications.
Semiconductor Voltage Reducing Circuit
Another type of transformerless power supply uses semiconductor devices such as diodes and transistors to reduce the voltage. This method typically involves a voltage divider and a control circuit that switches the voltage on and off in a manner that averages to the required output voltage. The output voltage can be precisely controlled, making these circuits suitable for applications requiring stable output voltages.
Rectified Mains Voltage and Its Applications
Rectified mains voltage is a key component in transformerless power supplies. It is the process of converting AC (alternating current) voltage to DC (direct current) voltage. In an antique radio, for instance, the rectified mains voltage might be used directly to power the radio's circuits. This voltage could range from 120V to 240V AC, depending on the region, and after rectification, it could vary between 150V to 300V DC.
Some radios were designed with battery packs up to 90V DC, which is sufficient to operate off the rectified mains voltage. However, it’s important to note that this setup can create a "hot chassis" situation if the orientation of a non-polarized power plug is not properly managed. A hot chassis can pose electrical hazards, so it’s crucial to understand the implications and take safety measures.
Transformerless vs. Conventional Power Supply
Conventional power supplies that use a transformer offer a safer and more efficient way of reducing voltage. Transformers are designed to handle higher currents and provide isolation between the input and output circuits. However, they can be bulky and heavy, which limits their use in portable or compact devices.
In contrast, transformerless power supplies are often lighter and physically smaller, making them ideal for portable devices like mobile phone chargers and other compact applications. Despite their advantages, transformerless power supplies are not without drawbacks. They can be less efficient, introduce electrical noise, and require careful design to ensure safety and reliability.
Conclusion
Understanding the typical voltage output of a transformerless power supply is essential for designing and troubleshooting electronic devices. Whether you are working with a vintage radio, a modern phone charger, or designing a custom power supply, knowing the principles and practical applications of transformerless power supplies can help you make informed decisions. Balancing efficiency, safety, and reliability is key to developing effective and user-friendly power solutions.
For more information on transformerless power supplies and related topics, please refer to the following resources:
Designing Efficient Power Supplies Using Resistive Dividers Safety Considerations for Hot Chassis Types of Voltage Reducing Circuits