How to Limit a 12V Supply to 2V at a Maximum Current of 70mA

When working with electronic circuits, it often becomes necessary to limit a 12V input to a 2V output, while strictly maintaining a limit on the maximum current to 70mA. This article outlines three methods to achieve this: Voltage Regulator, Resistor Voltage Divider, and Buck Converter. Each method comes with its own set of advantages and disadvantages, making the choice dependent on the specific requirements of your project.

Method 1: Voltage Regulator

Using a linear voltage regulator is one of the simplest methods to achieve this voltage regulation. A low-dropout LDO (Low Dropout) voltage regulator is highly suitable for this purpose. One popular choice is the LM317, which can be configured to output 2V with appropriate resistor values.

Step 1: Choose a Voltage Regulator

For a detailed setup, you need a low-dropout LDO voltage regulator that can output 2V, such as the LM317. This regulator is known for its low-voltage drop and ability to deliver stable output even with very low input voltage.

Step 2: Calculate Resistor Values

The formula to set the output voltage of the LM317 is given by:

Vout 1.25 * (R2 / R1)

For a 2V output, you can set R1 240 Ω and then calculate the appropriate value for R2.

Step 3: Connect the Circuit

Connect the input of the regulator to the 12V supply. The output will now provide a consistent 2V. Ensure that the regulator can handle the power dissipation, which is given by:

P (Vin - Vout) * I (12V - 2V) * 0.07A 0.7W

Use a heatsink if necessary to avoid overheating.

Method 2: Resistor Voltage Divider (Not Recommended for Variable Loads)

While a resistor voltage divider is another option, it is not ideal for supplying current as it depends heavily on the load. This method can only be used for a fixed load and may not provide a stable voltage under varying conditions.

Step 1: Calculate Resistor Values

The formula for a voltage divider is:

Vout Vin * (R2 / (R1 R2))

To achieve 2V from 12V, you can choose R1 220 Ω and R2 40 Ω.

Step 2: Limit Current

Ensure that the combined resistance allows for a maximum of 70mA. The total resistance needed is calculated as:

Rtotal Vout / I 2V / 0.07A approx; 28.57 Ω

As this method is not recommended for applications where the load is variable, it is a less ideal choice for most practical purposes.

Method 3: Buck Converter

A buck converter is a more efficient way to step down voltage and is particularly suitable for applications where power efficiency is a priority. Buck converters are available in many adjustable forms, making them a versatile choice.

Step 1: Choose a Buck Converter Module

Select a buck converter that can handle the input and output voltage, ensuring it meets the 12V input and 2V output requirements. Many adjustable buck converter modules are available, which can be configured to meet specific needs.

Step 2: Set the Output Voltage

Adjust the onboard potentiometer to set the output voltage to 2V.

Step 3: Connect the Circuit

Connect the 12V supply to the input, and take the 2V output from the converter. This method offers higher efficiency and is a better choice for power-sensitive applications.

Conclusion

For most applications, using a voltage regulator (Method 1) or a buck converter (Method 3) is recommended for stable and efficient voltage regulation. A resistor divider (Method 2) is generally not suitable for providing a stable voltage under varying loads as it is highly dependent on the load.