In the world of electronics, a reliable power supply is the backbone of any circuit or device. Whether you are building a simple microcontroller-based project or a complex audio amplifier, having a stable and efficient power source is crucial. The TNY254GN, a highly integrated, energy-efficient switch mode power supply (SMPS) IC from Power Integrations, offers a compact solution for designing low-power, high-efficiency power supplies.

In this article, we will guide you through the process of building a low-power AC-to-DC power supply using the TNY254GN. This project will help you understand the principles behind SMPS, teach you how to use the TNY254GN, and provide you with the necessary steps to design and assemble a functional power supply.

Introduction to the TNY254GN

The TNY254GN is part of the TinySwitch family of ICs designed for use in off-line switch-mode power supplies (SMPS). These ICs are intended for low-power applications, such as powering small consumer electronics, LED drivers, or communication devices.

Key features of the TNY254GN include:

1. Integrated MOSFET: The TNY254GN comes with an integrated power MOSFET, simplifying the design and reducing the need for external components like discrete transistors.

2. High Efficiency: Thanks to its internal features such as peak current-mode control and low standby power consumption, the IC can achieve high efficiency even in low-load conditions.

3. Low Standby Power: The IC is designed to operate with minimal standby power, making it ideal for energy-conscious designs.

4. Overvoltage and Overcurrent Protection: It comes with built-in protections to ensure the power supply remains safe during overloads or faulty conditions.

5. Wide Input Voltage Range: The IC can operate with a wide AC input voltage range, from 85V to 265V AC, making it versatile for global applications.

The TNY254GN is typically used in applications where a compact, efficient power supply is needed for low-power loads. With its integrated features and small form factor, it is perfect for a DIY project where space and efficiency are key considerations.

Key Components Needed

To build the power supply circuit using the TNY254GN, you will need the following components:

1. TNY254GN IC – The heart of the power supply.

2. Transformer – To step down the AC voltage from the mains to a lower AC voltage suitable for the IC.

3. Bridge Rectifier – To convert the AC voltage to DC.

4. Capacitors – To filter the rectified DC signal and provide a stable output voltage.

5. Resistors – To set the feedback loop for voltage regulation.

6. Inductor – To further filter the output and reduce ripple.

7. Diodes – For protection and rectification.

8. Heat Sink – To dissipate heat from the IC if necessary.

9. Miscellaneous Components – For connecting the circuit, such as fuses, connectors, and switches.

Step 1: Understanding the TNY254GN Pinout

The TNY254GN has a simple but effective pin configuration that makes it easy to integrate into your design. Understanding the pinout is essential before starting the circuit design. Here’s a breakdown of the pins:

1. Pin 1 (Drain): The drain of the integrated MOSFET. This pin is connected to the primary side of the transformer and also to the rectified DC output.

2. Pin 2 (Source): The source of the integrated MOSFET. This pin connects to the ground of the power supply circuit.

3. Pin 3 (Feedback): This pin is used to provide feedback to the IC, helping it regulate the output voltage. A feedback network with resistors is typically connected here.

4. Pin 4 (VDD): This is the power supply pin for the internal circuitry of the IC. It is usually powered by the rectified DC voltage and filtered to provide a stable input for the IC's control functions.

5. Pin 5 (Enable): This pin allows the IC to be enabled or disabled. It can be used in the circuit design to control when the power supply is active.

6. Pin 6 (Ground): The ground connection for the IC. This pin should be connected to the common ground of the power supply circuit.

Step 2: Designing the AC Input Stage

The first step in designing a power supply is stepping down the AC voltage from the mains (120V or 230V) to a lower voltage that the TNY254GN can use. Typically, the TNY254GN is designed for input voltages between 85V and 265V AC, making it suitable for global applications.

Transformer Selection: The AC input from the mains needs to be stepped down to a lower AC voltage, usually in the range of 5V to 20V AC, depending on the desired output. For example, if you want a 12V DC output, you would select a transformer with a secondary winding that provides around 9V AC.

Bridge Rectifier: The output from the transformer is still AC and needs to be converted to DC. A bridge rectifier is used to rectify the AC signal. The rectifier consists of four diodes arranged in a specific configuration to convert the alternating current to direct current. After rectification, the output will be a pulsating DC voltage that needs to be filtered.

Step 3: Filtering the Rectified DC Output

After rectification, the DC voltage still has ripples that need to be smoothed to provide a stable output.

Filtering Capacitors: Use electrolytic capacitors to filter the rectified DC voltage. Typically, capacitors in the range of 470µF to 1000µF are used for smoothing. These capacitors smooth out the ripple in the DC voltage, providing a stable supply to the IC.

Inductor: An inductor can be placed in series with the output to further smooth the DC signal. It helps reduce high-frequency noise and improves the quality of the output voltage.

Step 4: Setting Up the Feedback Loop

The TNY254GN regulates the output voltage using a feedback mechanism. By monitoring the output voltage, the IC adjusts the switching operation to maintain a stable voltage at the output.

Feedback Network: A resistive voltage divider is typically used to sense the output voltage and provide feedback to the IC’s feedback pin (Pin 3). The resistors in the feedback network scale the output voltage to the desired level and send a signal to the IC that adjusts the switching behavior accordingly.

Output Voltage Adjustment: The feedback resistors are carefully chosen to set the correct output voltage. For example, if you need a 12V output, the resistors will be selected based on the feedback reference voltage. In the case of the TNY254GN, this voltage reference is typically 2.5V, so the resistors are chosen to scale the output to the desired value.

Step 5: Protecting the Circuit

To ensure the longevity and reliability of your power supply, certain protection mechanisms need to be implemented.

Overcurrent Protection: The TNY254GN has built-in overcurrent protection, which will reduce the output if an overcurrent condition is detected. However, adding an external current sensing resistor can further enhance this protection, ensuring that the power supply will shut down if the current exceeds a certain limit.

Overvoltage Protection: The IC also has built-in overvoltage protection to prevent damage to the components in case of a voltage surge.

Thermal Protection: If the IC overheats, the TNY254GN will automatically reduce the output power to prevent damage. Adding a small heat sink to the IC can help dissipate heat during high loads.

Step 6: Building the Power Supply Circuit

With all the components selected, it’s time to assemble the circuit.

Mounting the Transformer: Secure the transformer in your project enclosure. Connect the primary winding to the AC input lines, and the secondary winding to the bridge rectifier.

Bridge Rectifier and Capacitors: Connect the rectifier’s DC output to the filtering capacitors. Ensure proper polarity when connecting the capacitors to avoid reverse polarity issues.

Connecting the TNY254GN: Mount the TNY254GN and connect the feedback network to Pin 3. Ensure that the source is connected to the ground, and the drain is connected to the primary side of the transformer.

Final Assembly: Once all the components are connected, make sure that the power supply is correctly wired, and the feedback network is set to the correct voltage.

Step 7: Testing the Power Supply

After assembling the circuit, it’s crucial to test the power supply to ensure it works as expected.

Initial Power Up: Power up the circuit and measure the output voltage with a multimeter. Ensure that the voltage is stable and within the desired range.

Load Testing: Connect a small electronic load to the power supply and verify that the output voltage remains stable under varying load conditions.

Thermal Testing: Monitor the temperature of the TNY254GN to ensure that it does not overheat. If necessary, attach a heat sink to the IC for additional cooling.

Ripple Testing: Use an oscilloscope to observe the ripple on the output voltage. Ensure that the ripple is within acceptable limits for your application.

Conclusion

The TNY254GN is a versatile and efficient IC for building low-power, compact power supplies. In this project, we have designed a simple yet effective AC-to-DC power supply using this IC. By carefully selecting components, understanding the pinout and operation of the IC, and building a feedback network, you can create a stable power supply suitable for a wide range of applications.

This project not only helps you understand the basics of switch-mode power supply design but also equips you with the skills to build an energy-efficient power supply for your DIY electronic projects. Whether you’re powering a small microcontroller project or building a more complex circuit, this power supply will provide you with the stability and efficiency required to ensure smooth operation.