DIY Electronic Project: Building a Power Supply with STRL352 for Efficient Voltage Regulation
Introduction
Power supply units (PSUs) are essential components in a wide variety of electronic projects, providing the necessary voltage and current to power devices and circuits. Whether you're working on an audio amplifier, microcontroller-based system, or any other electronics project, having a reliable power supply is critical to ensure smooth operation.
One excellent component for building a high-efficiency power supply is the STRL352, a voltage regulator from Sanken Electric Co., Ltd. The STRL352 is a high-performance, switch-mode power supply controller, particularly useful in applications requiring efficient, stable voltage conversion and regulation. It integrates a variety of features that simplify the design process, including protections against overvoltage, overcurrent, and thermal issues.
In this article, we will guide you through designing and building a switching-mode power supply (SMPS) using the STRL352 voltage regulator. This project will provide hands-on experience in designing power supplies for various electronic applications, while learning how to incorporate modern power management techniques.
Overview of the STRL352
The STRL352 is a highly integrated power supply controller that can be used for converting high input voltages to a lower, regulated output voltage. It is commonly used in flyback converters, which are ideal for applications requiring isolation and high voltage step-down capabilities, such as AC-DC power supplies for appliances, home electronics, and industrial control systems.
Key features of the STRL352 include:
● High Efficiency: The STRL352 is designed for high-efficiency power conversion, making it ideal for compact and energy-efficient designs.
● Integrated MOSFET: The controller includes an integrated MOSFET, reducing the need for external components.
● Overcurrent and Overvoltage Protection: The STRL352 provides built-in protection mechanisms to prevent circuit failure during fault conditions.
● Soft Start and Soft Shut-down: These features improve the safety of the power supply by gradually ramping up the output voltage during power-on and gently shutting down during power-off.
● Wide Input Voltage Range: The STRL352 supports a broad input voltage range (typically 90V-264V AC), which makes it suitable for various power supply applications worldwide.
● Low Standby Power Consumption: The controller is optimized to reduce standby power loss, making it an energy-efficient choice for standby-mode applications.
Components Required
Before we dive into the circuit design, let's take a look at the components needed for this project. Aside from the STRL352, the following components will be used in the construction of the power supply:
STRL352 Power Supply Controller IC
This is the core component for controlling the switching mechanism of the power supply.Power MOSFET (optional)
If not using an integrated MOSFET version, you will need an external power MOSFET to switch the high-voltage current.Diodes (e.g., Schottky Diode)
A diode will be required for rectification on the secondary side of the transformer.Transformer (Flyback Transformer)
A flyback transformer is used to step down the high AC voltage to a lower AC voltage, which is then rectified and filtered to DC.Inductors and Capacitors
Inductors (used for filtering) and capacitors (for smoothing and stability) are key components in building a reliable power supply.Resistors (for feedback loop)
A feedback loop is necessary for voltage regulation, which will require resistors for setting the output voltage.Heat Sink
To dissipate heat from the STRL352 and other power components.Protection Components
Includes fuses, transient voltage suppressors (TVS diodes), or MOVs (metal oxide varistors) for surge protection and overcurrent protection.PCB (Printed Circuit Board) or Breadboard
For prototyping your circuit. A PCB is recommended for a more permanent and professional solution.Microcontroller (Optional)
A microcontroller may be used for monitoring the power supply’s status or providing communication for advanced features like digital voltage monitoring.
Understanding the Power Supply Design
The STRL352 controller is typically used in a flyback topology for AC-DC power conversion. A flyback converter is especially useful when electrical isolation between the input and output is needed. It works by storing energy in a transformer’s magnetic field and then releasing it to the load during each switching cycle.
Here’s a high-level view of the power supply design:
AC Input Stage: The AC mains voltage (typically 110V to 240V AC) is first rectified into DC by a bridge rectifier or diode bridge. This converts the AC input into a raw DC voltage with significant ripple.
Power Converter (Flyback Transformer): The raw DC voltage is then fed into the flyback transformer. The STRL352 will drive the transformer’s primary side by controlling the switching MOSFET. The transformer steps down the voltage to a much lower, safer level.
Rectification and Filtering: The secondary side of the transformer outputs AC, which is then rectified using a Schottky diode to produce DC. The DC output is filtered by capacitors to smooth out any ripple.
Feedback Mechanism: The output voltage is sensed by the STRL352 through a feedback resistor network. The feedback loop helps regulate the output voltage, ensuring it remains stable under varying load conditions.
Protection Features: The STRL352 integrates overcurrent protection, thermal shutdown, and soft-start features to ensure safe operation and prevent damage to the power supply components.
Step-by-Step Circuit Design
Let’s now dive deeper into the circuit design and build process, focusing on a simple AC-DC power supply.
Step 1: Transformer Selection
Choose a flyback transformer suitable for the input and output voltage requirements. For instance, if you want to step down from 230V AC to 12V DC, you need a transformer with a primary winding rated for the AC input voltage (230V AC) and a secondary winding that will provide the desired output voltage after rectification.
The transformer should be rated for the power output you require, keeping in mind the load's current demands.
Step 2: Rectification Stage
On the secondary side of the flyback transformer, use a Schottky diode for rectification. Schottky diodes are preferred for their low forward voltage drop and fast switching characteristics, which are crucial for efficient power conversion.
The rectified output from the transformer’s secondary will be a pulsating DC signal. To smooth out the ripple, place an electrolytic capacitor across the rectified DC output.
Step 3: Filtering and Voltage Regulation
The output from the rectifier is still unregulated and might have significant ripple. Use a filter capacitor (typically an electrolytic capacitor) to smooth the voltage.
The STRL352 will be responsible for regulating the output voltage. This is done through a feedback mechanism that monitors the output and adjusts the duty cycle of the switching MOSFET accordingly. To set the output voltage, you will need to design the feedback loop by selecting appropriate resistors.
The feedback pin of the STRL352 will be connected to a resistor divider network, which helps maintain the desired output voltage. For example, to set a 12V output, you would calculate the resistor values based on the STRL352’s reference voltage and feedback specifications.
Step 4: MOSFET Driver Circuit
The STRL352 includes an integrated MOSFET driver, but if your specific design calls for external components, you will need to select an appropriate MOSFET that matches the current and voltage requirements of the power supply.
The MOSFET should be chosen for its low R_DS(on) (on resistance), which minimizes conduction losses and increases efficiency. Connect the MOSFET in series with the primary side of the transformer, ensuring it switches correctly based on the control signals from the STRL352.
Step 5: Protection Circuitry
The STRL352 includes built-in protections like overcurrent and thermal shutdown, but you can enhance these protections with external components.
● Fuses: A fuse in the AC input stage can protect the circuit against short circuits or overcurrent situations.
● MOVs or TVS Diodes: These components can protect against voltage spikes, which might occur during power surges or lightning strikes.
Step 6: Assembling the Power Supply
Once you’ve completed the schematic and selected the components, it's time to assemble your power supply.
● Breadboard: For prototyping, start by assembling the components on a breadboard. This allows you to easily modify the circuit if needed.
● PCB: Once you're satisfied with the breadboard prototype, design a printed circuit board (PCB) for the power supply. The PCB should provide adequate spacing between high-voltage and low-voltage areas to prevent accidental shorts or arcs.
Step 7: Testing and Debugging
Before connecting the power supply to any sensitive electronics, thoroughly test it to ensure it’s functioning correctly.
Power On: Initially, power the supply on without any load connected and measure the output voltage to confirm that it is within the expected range.
Load Testing: Gradually apply a load (e.g., a resistive load) and observe the output voltage. The regulator should maintain a stable voltage even as the load increases.
Check for Overheating: Ensure that the MOSFET and the STRL352 do not overheat during operation. If they do, consider adding a heat sink or improving ventilation.
Conclusion
In this project, we’ve demonstrated how to design and build an efficient power supply using the STRL352 controller. This power supply is ideal for providing stable DC voltages to a wide range of electronic circuits, from microcontroller projects to home appliances.
By incorporating features such as overcurrent protection, soft start, and voltage regulation, the STRL352 allows for a compact and reliable power supply design. Whether you’re creating a new power supply for an existing device or building a custom power system from scratch, this project provides a great foundation for understanding switch-mode power conversion and voltage regulation.
Always remember to follow safety guidelines when working with high-voltage circuits and ensure that your power supply meets the voltage and current requirements of your intended application.