How to design a power supply for Raspberry Pi

In this do-it-yourself circuit, we’ll design a Raspberry Pi (RPi) power supply. First, we’ll create a list to follow as a blueprint for the circuit, ensuring we design it correctly. Let’s start with a list of our goals for the circuit.

Goals

1. A steady power supply: Ensure RPi receives a consistent and stable 5V power supply that we can check at different points.

2. Data protection: Prevent power issues from causing problems with the RPi’s memory card, which stores important data.

3. A safe start and stop: Build a system that can turn on, off, and restart without issues or damage.

4. Backup power: Ensure the power supply works reliably for at least one hour, even if there’s a temporary power problem.

5. A simple design: Keep the design easy to understand and build, even for people who aren’t engineers.

6. A versatile design: Design a circuit for small embedded systems and regular desktop computers.

7. A step-by-step guide: Create a complete set of instructions for a classroom project, explaining how to do it from start to finish.

Designing a power supply for a Raspberry Pi means ensuring a stable and reliable source of 5V dc power that’s safe and efficient.

Here’s a general guide on how to design RPi’s power supply:

Basic design

Principles of operation
The following devices are needed to build a safe and effective circuit.

Ac to dc adapter: Start with a suitable ac-to-dc adapter or power source. Ensure it provides a stable 5V output with sufficient current (at least 2.5A for most Raspberry Pi models).
Voltage regulator: A voltage regulator is important to ensure a stable power output. The LM7805 or similar regulators are commonly used for this purpose. They take the higher voltage from an adapter and provide a steady 5V output.
Filter capacitors: Include filter capacitors (e.g., electrolytic and ceramic capacitors) to smooth out voltage ripples and provide stable power.
Input protection: Consider adding protection components like fuses and transient voltage suppressors (TVS diodes) to safeguard against voltage spikes or over-current situations.
Power indicator LED: Optionally, you can add an LED to indicate when power is applied.

Figure 2. Ensuring safe circuit protection.

How the circuit works

Note: Always double-check the power requirements of your specific Raspberry Pi model, as they may vary slightly. Additionally, safety is crucial when working with power supplies and electronics. If you’re inexperienced, consider seeking help or advice from someone with more expertise, especially when designing power supplies for critical applications.

Voltage regulation: Connect the ac-to-dc adapter to the voltage regulator’s input. Ensure the regulator’s output is adjusted to provide a steady 5V dc.
Filtering: Place the filter capacitors (typically one electrolytic and one ceramic capacitor) at the regulator’s input and output to reduce noise and stabilize the voltage.
Protection: Include any necessary protection components, such as a fuse or TVS diode, to safeguard against power surges or reverse polarity.
Output connector: Connect the 5V output of the regulator to a suitable connector (usually a micro USB or USB-C connector) that can plug into the Raspberry Pi’s power input.
Indicator LED: If desired, add an LED and a current-limiting resistor in parallel with the output to indicate when the power supply is active.
Testing: Before connecting RPi, test the power supply separately to ensure it provides a stable 5V output.
Connecting to RPi: Plug the power supply connector into the RPi’s power input, and the circuit should be ready.

The experiment

Goal: To demonstrate how we can design a power supply for Raspberry Pi.
Setup: Here’s a basic testing setup for a secured power supply for an RPi.

Components:

1. Raspberry Pi (any model)
2. Power source (such as a USB wall adapter)
3. Voltage regulator (e.g., L7805)
4. Capacitors (for filtering)
5. Diodes or transient voltage suppressors (TVS)
6. Breadboard
7. Jumper wires
8. Multi-meter
9. Optional: Oscilloscope for more detailed measurements

Testing steps
The circuit setup is as follows:

Connect the power source to the input of your voltage regulator.
Connect the voltage regulator’s output to the RPi’s input.
Include the filtering capacitors across the input and output of the voltage regulator.
Implement protection components like diodes or TVS to safeguard against voltage spikes.

Figure 3. The testing setup.

Connection checks
Ensure all of the connections are secure and correct. Also, double-check the polarities and wiring.

Initial voltage and current measurement:

Use a multi-meter to measure the voltage output from the power supply. Ensure it matches the required voltage for the RPi (e.g., 5V for most models).
Measure the current output capability of the power supply to ensure it meets the RPi’s requirements.

Figure 4. Live testing setup.

Voltage regulation testing:

Apply different loads to the power supply by connecting various components to RPi (e.g., USB peripherals, GPIO devices).
Measure the voltage output from the power supply under different load conditions using the multi-meter.
Ensure the voltage remains stable within an acceptable range.

Current limiting testing:

Apply varying loads to the RPi to simulate different usage scenarios.
Monitor the current drawn by the RPi using the multi-meter.
Ensure that the current stays within safe limits and that the current-limiting components, if any, function as intended.

Transient protection testing:

Introduce voltage spikes or transients into the circuit (e.g., by disconnecting and reconnecting the power source).
Monitor the voltage output using the oscilloscope or multimeter to ensure the protection components effectively suppress transient events.

Long-term stability testing:

Leave the circuit powered on for an extended period, monitoring voltage and current periodically to ensure stability over time.
Check for any signs of overheating or component failure.

Optional remote shutdown/control testing:

If your power supply setup includes remote shutdown or control mechanisms, test their functionality to ensure they work as intended.

Documentation:

Document all test results, including the voltage and current measurements under different conditions, any observed issues, and their resolutions.

Final evaluation:

Evaluate the overall performance of the secured power supply setup against your requirements and make any necessary adjustments.

By following these testing steps, you can ensure a secure power supply for Raspberry Pi that meets the necessary criteria for reliability, stability, and safety.