Constant Current Regulator using LM317 | CCR | LM317 as a current regulator

Summary

In this video from Foolish Engineer, we explore the design of a constant current regulator. Unlike voltage regulators, these devices maintain a consistent current regardless of load or input changes. Using the LM317 variable voltage regulator, we can achieve this with a simple circuit and minimal components. The tutorial demonstrates the calculation for a 50mA constant current output and discusses the advantages and disadvantages of this method. Practical examples and simulations illustrate the concept, ensuring viewers understand the process. Stay tuned for the next video, where we'll design a current regulator using discrete components like transistors and zener diodes.

Takeaways

• 🔌 The script introduces the concept of a constant current regulator, which is a device that provides a constant current regardless of changes in output load or input voltage.
• 🔧 Ohm's Law is explained as the basis for understanding how a constant current is achieved, where the current is the voltage divided by the resistance.
• 🛠️ The LM317, a variable voltage regulator, is used in the example to create a constant current regulator by adjusting the resistance in series with its output and adjustable pins.
• 📏 The value of the resistor needed for a specific current can be calculated using the formula R = (1.25V / desired current in mA).
• 💡 The example given requires a 50mA constant current for an LED, and the resistor value is calculated to be 25 ohms based on the given input voltage and LED characteristics.
• ⚡ The power dissipation of components in the circuit is calculated by multiplying the voltage drop across the component by the current flowing through it.
• 🔍 The script includes a simulation of the circuit, demonstrating that the output current remains constant even when the input voltage or load is changed.
• 📉 Advantages of using the LM317 for a constant current regulator include the simplicity of the circuit, built-in overtemperature protection, and a wide input voltage range.
• 📈 Disadvantages mentioned include the potential for the regulator to be bulky for small current applications and power losses due to the quiescent current of the regulator.
• 🔬 The script suggests that in a future video, an alternative method of designing a current regulator using discrete components like transistors and zener diodes will be discussed.
• 👍 The video encourages viewers to ask questions in the comments if they have doubts, and to like, subscribe, and support the channel.

Q & A

What is a constant current regulator?

A constant current regulator is a device that provides a constant current output irrespective of changes in the output load or input voltage.

How does a constant current regulator maintain a constant current?

A constant current regulator maintains a constant current by adjusting its own resistance, which results in a change in the output voltage to maintain the desired current flow.

What is the basic principle behind Ohm's law in the context of a voltage source and a resistor?

Ohm's law states that the current flowing through a resistor is directly proportional to the voltage applied across it and inversely proportional to its resistance, expressed as I = V/R.

How can a voltage regulator like the LM317 be used as a current regulator?

The LM317 can be used as a current regulator by adding a resistor in series between its output and adjustable pin. The regulator maintains a 1.25V drop across this resistor, sourcing a constant current to the output branch.

What is the purpose of the 1.25V drop in the LM317 circuit when used as a current regulator?

The 1.25V drop across the resistor in the LM317 circuit is maintained by the regulator to ensure a constant current output, regardless of changes in input voltage or load.

How is the value of the resistor calculated in the LM317 current regulator circuit?

The value of the resistor is calculated using the formula R = 1.25 / I_desired, where I_desired is the desired current in amperes.

What is the power dissipation in the resistor used in the LM317 current regulator circuit?

The power dissipation in the resistor is calculated as P_r = V_drop * I_load, where V_drop is 1.25V and I_load is the load current.

How does the LM317 circuit maintain a constant current output when the input voltage changes?

When the input voltage changes, the LM317 adjusts its output voltage to maintain the 1.25V drop across the resistor, thus ensuring a constant current output.

What are some advantages of using a voltage regulator like the LM317 for a constant current regulator?

Advantages include the need for very few components, overtemperature protection, and a wide input voltage range, making it versatile and easy to use.

What are some disadvantages of using a voltage regulator like the LM317 for a constant current regulator?

Disadvantages include the potential for bulky designs for small current requirements and power losses due to the quiescent current from the regulator.