In the world of DIY electronics, one of the most useful projects you can build is a regulated power supply. Power supplies are crucial components in almost every electronic circuit, and having one that provides stable, regulated output is essential for powering sensitive devices. Today, we’ll explore how to create a 5V regulated power supply using the LM117H adjustable voltage regulator. This is a versatile, reliable, and simple circuit to construct, which can provide a stable 5V output from a higher voltage input source.
Project Overview
This project involves designing and building a power supply circuit using the LM117H voltage regulator, which can take an input voltage higher than 5V (typically in the range of 8V to 12V) and provide a stable 5V output. The LM117H is an adjustable voltage regulator, which allows you to set the output voltage to a desired level with the use of external resistors.
The LM117H is popular for DIY power supply projects due to its ease of use, reliability, and ability to handle higher input voltages. Additionally, it features an internal current limiting and thermal shutdown feature, making it a safe and reliable choice for building a power supply that can be used for various projects like Arduino boards, sensors, and even small motors.
Components Needed
● LM117H Adjustable Voltage Regulator – This is the heart of the circuit. It will regulate the output voltage to 5V.
● Capacitors (0.1µF, 10µF) – Capacitors will be used for filtering input and output voltages to ensure stability and minimize noise.
● Resistors (220Ω, 240Ω) – These resistors will be used to set the output voltage of the LM117H.
● Diode (1N4007) – This diode will protect the circuit from voltage spikes and reverse current.
● Heat Sink – The LM117H may generate some heat under load, so a heat sink is recommended to keep it cool.
● Transformers (optional) – If you're starting with an AC input, you'll need a transformer to convert the AC voltage to a DC voltage.
● Input Capacitor (100µF) – To help smooth out any ripple in the DC input voltage.
● Breadboard or PCB – A breadboard for prototyping or a PCB for the final version of the power supply.
● Jumper wires – For connecting the components.
● Multimeter – For testing and calibration.
Step 1: Understanding the LM117H Voltage Regulator
The LM117H is a three-terminal adjustable voltage regulator that can output voltages from 1.25V to 37V, depending on the input voltage and external resistors. It is capable of providing up to 1.5A of current with proper heat dissipation. The output voltage is set using two resistors, connected between the output and adjustment pins of the LM117H.
The LM117H has several important features that make it suitable for this project:
● Adjustable Output Voltage: By varying the resistance between the adjustment pin and the output pin, you can select the output voltage.
● Thermal Protection: The regulator will shut down if it overheats, preventing damage to the circuit.
● Overcurrent Protection: If the current exceeds the maximum limit, the LM117H will limit the output current to protect the circuit.
Step 2: Setting the Output Voltage to 5V
To set the output voltage to 5V, you need to select two resistors: one between the output pin and the adjustment pin (R1) and another between the adjustment pin and ground (R2). While the LM117H is capable of outputting a wide range of voltages, the combination of these two resistors determines the final output voltage.
For a 5V output, you can use a 220Ω resistor for R1 and a 240Ω resistor for R2. These resistors will set the output voltage at approximately 5V, which is ideal for powering devices like microcontrollers and small sensors.
Step 3: Constructing the Circuit
Now that we have an understanding of the components and how to set the output voltage, let’s walk through the steps of building the circuit.
3.1 Preparing the Components
Gather all the components required for the circuit. The LM117H comes in a TO-220 package, so you will need a heat sink to attach to the regulator to keep it cool. If you're using a breadboard, insert the LM117H in the appropriate spots.
3.2 Connecting the Input
The input voltage is applied to the Input Pin of the LM117H. Typically, this would be a DC voltage in the range of 8V to 12V. If you are using an AC source, use a bridge rectifier and a smoothing capacitor to convert the AC to DC before applying it to the LM117H.
Insert a 100µF capacitor between the input pin and ground to filter any high-frequency noise or ripple from the DC input. This will help ensure that the LM117H receives a stable voltage.
3.3 Setting the Output Voltage
Next, place the 220Ω resistor (R1) between the output pin and the adjustment pin of the LM117H. Then, place the 240Ω resistor (R2) between the adjustment pin and ground. These resistors will set the output voltage to approximately 5V.
3.4 Filtering the Output
To ensure that the output voltage is stable and clean, insert a 10µF capacitor between the output pin and ground. This will help smooth out any ripples or fluctuations in the output voltage, which could affect the performance of the devices powered by the supply.
3.5 Adding Protection
To protect the LM117H and your circuit from potential reverse voltage spikes, place a 1N4007 diode across the input. The cathode (marked end) should be connected to the input, and the anode should be connected to ground. This will protect the circuit from any reverse current that may be generated.
3.6 Heat Sink Installation
The LM117H is capable of dissipating significant heat under load, especially when there’s a high input-to-output voltage difference. To prevent overheating, attach a heat sink to the back of the LM117H regulator. This will improve its performance and extend its lifespan.
Step 4: Testing and Calibration
Once your circuit is assembled, it’s time to test it.
4.1 Powering the Circuit
First, connect the input voltage to the circuit. Use a regulated DC power supply or battery pack in the range of 8V to 12V. Check the connections and make sure everything is properly placed on the breadboard or PCB.
4.2 Measuring the Output Voltage
Using a multimeter, measure the output voltage across the output terminal and ground. If everything is set up correctly, you should get a stable 5V output. If the voltage is too high or too low, double-check your resistor values and connections.
4.3 Testing Under Load
Once you have confirmed that the power supply is providing a stable 5V output, test the circuit by connecting a load. This could be a small LED circuit, an Arduino board, or any other low-power device that operates at 5V. Ensure that the power supply can handle the load without dropping voltage or overheating.
Step 5: Finalizing the Project
Once the circuit is working correctly, you can proceed with finalizing the design. If you used a breadboard for prototyping, you may want to solder the components onto a PCB for a more permanent solution. Make sure to use a proper enclosure to protect the circuit from environmental factors, and provide ventilation if necessary, especially if the regulator is operating under heavy load.
Conclusion
Building a 5V regulated power supply using the LM117H voltage regulator is a straightforward and rewarding DIY project. By following the steps above, you can create a reliable power source for a wide variety of electronic projects. Whether you're powering microcontrollers, sensors, or small motors, this power supply will provide the stability and reliability needed to ensure the proper operation of your devices.
With the LM117H, you can easily adjust the output voltage by changing the resistor values, making this power supply versatile enough to be used in a range of applications. This project serves as a great introduction to voltage regulation, and the skills you learn can be applied to more advanced power supply designs in the future.