Introduction

In the world of DIY electronics, a reliable and efficient power supply is the backbone of almost every project. Whether you're building an embedded system, a sensor interface, or a more complex device, having the right power regulation is crucial for the stability and performance of your circuits. Power supply design is an essential skill for any electronics enthusiast, and in this article, we will guide you through the design and implementation of a high-efficiency power supply using the TEA1521T, a versatile and reliable integrated circuit (IC) from NXP Semiconductors.

The TEA1521T is a low-power, off-line switch-mode power supply (SMPS) controller designed for applications such as AC-DC converters and standby power supplies. It offers excellent energy efficiency, low standby consumption, and is ideal for use in applications requiring 5V to 15V regulated output. The TEA1521T is perfect for powering microcontrollers, sensors, and other low-power devices, making it ideal for a variety of DIY electronics projects.

In this article, we will design and build a switch-mode power supply (SMPS) using the TEA1521T to convert AC voltage (110V or 220V) into a regulated DC output. We will explore the components, circuit design, and step-by-step implementation of the project.

Overview of the TEA1521T

The TEA1521T is a high-efficiency power supply controller used primarily in offline power conversion applications. It features a pulse-width modulation (PWM) control mechanism, which allows it to efficiently convert high-voltage AC into stable, regulated DC voltages. Here are some key specifications of the TEA1521T:

● Input Voltage Range: 85V to 265V AC (universal input range), which makes it compatible with both 110V and 220V AC mains.

● Output Voltage: The IC is designed for low-voltage regulated outputs, such as 5V, 9V, or 12V.

● Low Standby Power Consumption: Ideal for energy-efficient designs.

● Internal Voltage Regulation: Provides tight regulation with an external feedback loop.

● Overvoltage, Overcurrent, and Thermal Protection: Built-in protections for enhanced reliability and safety.

● PWM Control: Used for efficient energy conversion and regulation.

● Integrated High-Voltage Start-up Circuit: Allows the IC to operate directly from high-voltage AC mains.

The TEA1521T is often used in standby power supplies for consumer electronics, chargers, LED drivers, and other low-power applications. It is compact, energy-efficient, and offers a variety of protection features, which makes it a great choice for DIY power supply designs.

Components Needed

To build a switch-mode power supply (SMPS) using the TEA1521T, you will need the following components:

Key Components:

1. TEA1521T – The main IC for controlling the power supply.

2. Transformer – A step-down transformer to convert AC voltage (110V or 220V) to a lower AC voltage suitable for rectification and regulation.

3. Rectifier Diodes (e.g., 1N5408) – To convert AC to DC.

4. Capacitors – Used for filtering and stabilizing the DC output voltage.

● Electrolytic capacitors (e.g., 470µF, 25V) for bulk filtering.

● Ceramic capacitors (e.g., 0.1µF) for high-frequency filtering and decoupling.

5. Inductor – For smoothing and reducing ripple in the output voltage.

6. Resistors – For current limiting, feedback control, and voltage setting.

7. Diode Bridge – For rectifying AC to DC before regulation.

8. Heatsinks – For dissipating heat from the power components, especially the transformer and power transistors.

9. Microcontroller (Optional) – For monitoring and controlling the power supply, such as switching between voltage rails or logging data.

Additional Tools and Accessories:

1. Soldering iron and solder.

2. Breadboard or PCB for assembling the components.

3. Multimeter for measuring voltage, current, and resistance.

4. Oscilloscope for monitoring the output waveform and ripple.

5. AC Mains Power Cord and a fuse for safety.

Step 1: Understanding the TEA1521T Pinout and Basic Operation

The TEA1521T is housed in a DIP-8 package, which makes it easy to handle and integrate into your DIY power supply circuit. Let's take a look at the pinout and the basic functionality of each pin:

1. Pin 1 (VDD): Power supply pin for the controller. Connect this to a suitable voltage source (typically around 12V to 15V DC).

2. Pin 2 (Feedback): This pin receives feedback from the output to regulate the output voltage. It is connected to a voltage divider network and provides feedback to the controller to maintain constant output voltage.

3. Pin 3 (Ground): The ground connection for the IC.

4. Pin 4 (Drain): The drain pin of the internal MOSFET. This pin is connected to the transformer primary winding and the rectifier circuit.

5. Pin 5 (Source): The source pin of the internal MOSFET. This pin is connected to the rectified DC output of the transformer.

6. Pin 6 (Gate): Controls the internal MOSFET switching. It is connected to the PWM control circuitry and determines the switching frequency of the transformer.

7. Pin 7 (FB/OC): This pin is used for overcurrent protection (OCP) and feedback. It connects to the feedback network for voltage regulation and to a current sensing resistor for OCP.

8. Pin 8 (HV): High-voltage start-up pin, which connects to the AC mains power. This pin is responsible for starting the controller directly from the AC voltage.

The TEA1521T is an integrated solution that handles the core functions of voltage regulation, switching, and protection. The chip uses a PWM-controlled internal MOSFET to drive the transformer, making it very efficient compared to linear regulators or traditional designs.

Step 2: Transformer and Rectification

The first step in converting AC power to DC is to step down the high-voltage AC signal to a lower voltage suitable for your desired output (e.g., 12V DC, 5V DC). To do this, you'll use a step-down transformer.

1. Step-down Transformer: Select a transformer with an appropriate secondary voltage rating. For example, if you want a 12V output, choose a transformer that outputs around 9V RMS on the secondary side. Remember that the output voltage of the transformer will be higher than the rated RMS value by a factor of 2\sqrt{2}2​ due to the rectification process.

2. Bridge Rectifier: Use a bridge rectifier (e.g., 1N5408 diodes) to convert the AC voltage from the transformer to DC. The rectifier will produce a pulsating DC voltage, which still contains some ripple.

3. Smoothing Capacitors: After rectification, use filter capacitors (e.g., 470µF, 25V electrolytic capacitors) to smooth the DC voltage and reduce ripple. Place these capacitors across the rectified output to provide a steady DC voltage that can be fed into the TEA1521T for regulation.

Step 3: Connecting the TEA1521T

Now that you have the rectified DC voltage, it's time to connect the TEA1521T IC.

1. VDD Pin: Connect Pin 1 to the 12V DC output from the filter capacitors.

2. Ground Pin: Connect Pin 3 to ground.

3. Feedback Pin: Connect Pin 2 to the voltage divider network. This network is used to sense the output voltage and provide feedback to the controller. The feedback voltage will control the switching duty cycle to maintain a stable output voltage.

4. Transformer Pins: Connect the Drain Pin (Pin 4) and the Source Pin (Pin 5) to the transformer and rectifier as described above.

5. Gate Pin: The Gate Pin (Pin 6) will be controlled by the internal PWM circuitry of the TEA1521T to switch the internal MOSFET.

6. Protection Pins: The FB/OC Pin (Pin 7) connects to the feedback circuit and the overcurrent protection network.

Step 4: Setting Up Feedback and Voltage Regulation

The output voltage of the power supply is determined by the feedback provided to the TEA1521T. The feedback loop uses a voltage divider to monitor the output and send a proportionate signal to the Feedback Pin (Pin 2).

For example, if you want a 12V output, you would use a voltage divider made up of two resistors to set the reference voltage at the feedback pin. This voltage is compared to an internal reference in the TEA1521T, and the controller adjusts the switching duty cycle to maintain the output at 12V.

Step 5: Testing and Troubleshooting

Once you have assembled the power supply circuit, it's time to test it. Here's how to approach the testing process:

1. Check the Connections: Verify that all connections are correct and there are no shorts.

2. Power On: Apply power to the circuit. Measure the output voltage with a multimeter.

3. Oscilloscope Testing: Use an oscilloscope to observe the output waveform. Ensure that the output voltage is stable and that there is minimal ripple.

4. Overcurrent Protection: Test the overcurrent protection by drawing more current than the design limits. The power supply should shut down or limit current.

Conclusion

In this project, we’ve demonstrated how to build a high-efficiency power supply using the TEA1521T switch-mode power supply controller. This power supply is suitable for a variety of low-power applications, including powering microcontrollers, sensors, and other electronic circuits. By following the steps outlined in this article, you can create a robust, efficient, and reliable power supply for your DIY electronics projects.

Understanding the key concepts behind switch-mode power supplies and the features of the TEA1521T will help you design more advanced power solutions in the future. With this knowledge, you can confidently build custom power supplies for a wide range of applications, from low-voltage devices to more complex systems requiring precise voltage regulation.