Constructing a dual ±12V power supply from a 24V SMPS is a common requirement in many electronic circuits. This configuration is particularly useful for powering operational amplifiers, audio amplifiers, and other circuits that necessitate both positive and negative voltage rails. This article will delve into the different methods for achieving this conversion, exploring the pros and cons of each approach. We will discuss the underlying principles, essential components, and practical considerations involved in building a reliable and efficient dual ±12V supply from a 24V SMPS.
Understanding the Requirements
Before embarking on the construction of a dual ±12V supply, it's vital to grasp the fundamental principles and requirements involved:
- Input Voltage: The starting point is a 24V SMPS (Switched Mode Power Supply). These supplies are known for their efficiency and ability to deliver a stable output voltage.
- Output Voltages: The goal is to generate both +12V and -12V rails with respect to a common ground.
- Current Capacity: Determine the current requirements for each output rail. The capacity of your chosen components must meet or exceed these demands.
- Voltage Regulation: Achieving a stable and precise output voltage is crucial for proper circuit operation. Regulation methods will be discussed later.
Common Approaches for Creating Dual ±12V Supplies
There are several widely used techniques for converting a 24V SMPS output to a dual ±12V supply. Each approach has its strengths and weaknesses, influencing its suitability for specific applications:
1. Voltage Divider with Center Tap
This method utilizes a voltage divider circuit comprising two resistors connected across the 24V input. The center tap of this divider acts as the common ground, resulting in a +12V output at one end and a -12V output at the other.
Advantages:
- Simplicity: The circuit is straightforward to implement, requiring only a few passive components.
- Low Cost: Resistors are inexpensive, making this a cost-effective solution.
Disadvantages:
- Poor Regulation: Voltage divider circuits are inherently susceptible to variations in the input voltage and load conditions.
- Limited Current Capacity: The current capacity of the divider is limited by the resistor values, often resulting in low output currents.
2. Linear Regulator with Ground Reference
This approach employs a linear voltage regulator, such as the LM317 or LM338, to regulate the +12V output. The -12V rail is then derived by inverting the positive voltage using a dedicated negative voltage generator circuit.
Advantages:
- Good Regulation: Linear regulators offer excellent voltage stability, minimizing output fluctuations.
- Low Noise: The output of linear regulators is generally low noise, which is desirable for sensitive circuits.
Disadvantages:
- Power Dissipation: Linear regulators dissipate heat proportional to the voltage drop across them, leading to efficiency losses.
- Increased Complexity: The circuit requires an additional negative voltage generator, adding complexity and cost.
3. Switched-Mode DC-DC Converter
This method utilizes a dedicated switched-mode DC-DC converter, often in the form of a buck-boost converter, to generate both the +12V and -12V outputs directly from the 24V input.
Advantages:
- High Efficiency: Switched-mode converters are highly efficient, minimizing power dissipation and heat generation.
- Precise Regulation: These converters offer excellent voltage regulation and can handle varying load conditions.
- Compact Size: Modern DC-DC converters are available in compact packages, reducing the overall footprint.
Disadvantages:
- Higher Cost: Switched-mode converters are generally more expensive than linear regulators and passive voltage dividers.
- Increased Complexity: These converters require specialized ICs and supporting components, adding complexity to the design.
Practical Considerations for Building a Dual ±12V Supply
1. Component Selection:
- SMPS: Select a 24V SMPS with sufficient current capacity to meet your application's requirements.
- Regulators: If using linear regulators, choose devices with appropriate current ratings and voltage drop characteristics.
- DC-DC Converters: Select buck-boost converters with adjustable output voltages and current ratings suitable for your application.
2. Heat Dissipation:
- Linear regulators and DC-DC converters generate heat. Ensure adequate heat sinking is provided to prevent overheating and component failure.
3. Filtering:
- Include capacitors on both the input and output of the supply to filter out noise and improve voltage stability.
4. Ground Connections:
- Establish a solid ground connection for the entire circuit to minimize noise and ensure proper operation.
5. Safety Precautions:
- Handle high voltages with caution and use appropriate safety equipment.
- Double-check the polarity of all components before powering the circuit.
Conclusion
Creating a dual ±12V supply from a 24V SMPS is a valuable skill for electronics hobbyists and professionals alike. The choice of method depends on factors such as the required current capacity, regulation accuracy, efficiency, and cost. Whether opting for a voltage divider, linear regulator, or switched-mode converter, understanding the design considerations and component selection criteria is essential for constructing a reliable and efficient dual ±12V power supply. By following these guidelines and adhering to safety precautions, you can successfully implement this conversion for various electronic projects.