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.

Outlines

00:00

🔌 Understanding Constant Current Regulators

This paragraph introduces the concept of a constant current regulator, which is a device that maintains a constant current output regardless of changes in load or input voltage. The explanation begins with a basic review of Ohm's law, highlighting how a normal voltage source behaves when connected to a resistor. The paragraph then delves into the operation of a constant current regulator, explaining that it adjusts its own resistance to maintain a constant output current, which can result in a varying output voltage. The discussion is illustrated with a practical example of powering an LED with a constant current of 50mA, using the LM317 variable voltage regulator. The LM317 is described as being versatile, capable of being repurposed from a voltage regulator to a current regulator by adding a resistor in series between its output and adjustable pins. The paragraph concludes with a formula for calculating the necessary resistor value and a brief mention of power dissipation considerations.

05:08

🔋 Designing a Constant Current Regulator with LM317

This paragraph continues the discussion on designing a constant current regulator, focusing on the practical application of the LM317 IC. The simulation of a circuit providing a constant 50mA output is described, demonstrating that the output current remains constant even when the input voltage is changed from 8V to 10V. The paragraph also explores the effect of changing the load by adding an additional LED, emphasizing that the output current still remains consistent. Advantages of using the LM317 for this purpose are highlighted, including the minimal number of components required, overtemperature protection, and a wide input voltage range. However, disadvantages such as potential bulkiness for small current requirements and power losses due to quiescent current are also acknowledged. The paragraph concludes by suggesting that future content will cover alternative methods of designing current regulators using discrete components like transistors and zener diodes, and encourages viewers to engage with the content by watching the video again, asking questions, and interacting with the channel.

Keywords

💡Constant Current Regulator

A constant current regulator is a device that provides a steady current to a load, regardless of changes in the load's resistance or the input voltage. It's central to the video's theme as it explains how to design such a regulator using simple circuits. In the script, the concept is introduced as a device that maintains a constant output current, which is crucial for applications like powering LEDs where a consistent current is necessary to prevent damage or fluctuating brightness.

💡Ohm's Law

Ohm's Law is a fundamental principle in electrical engineering that states the relationship between voltage (V), current (I), and resistance (R) in an electrical circuit: V = I x R. It's mentioned in the script to illustrate the basic concept of how current changes with resistance and voltage, which is essential for understanding the need for a constant current regulator that can maintain a steady current despite these variations.

💡Load

In the context of the video, a load refers to the electrical component or components being powered by the current regulator, such as an LED. The load's resistance and requirements can change, and the constant current regulator must adapt to provide the necessary current to maintain stable operation. The script discusses how the regulator adjusts its resistance to accommodate changes in the load.

💡LM317

The LM317 is a type of adjustable voltage regulator integrated circuit (IC) that can be repurposed to function as a current regulator, as explained in the video. It's significant because it demonstrates how a single component can be used in different ways to achieve the desired outcome of a constant current supply. The script details how the LM317 maintains a 1.25V drop for the purpose of regulating current.

💡Voltage Divider

A voltage divider is a passive linear circuit that produces an output voltage that is a fraction of its input voltage. In the context of the LM317, a voltage divider is typically used in its voltage regulation mode. However, the script explains an innovative use of the LM317 where a simple resistor is used instead of a voltage divider to create a current regulation setup.

💡Resistor

A resistor is an electrical component that opposes the flow of current through a circuit. In the script, a resistor is used in series with the LM317 to create a constant current regulator. The value of this resistor is critical, as it determines the current that will flow through the load, which is calculated based on the desired output current and the 1.25V drop across it.

💡Power Dissipation

Power dissipation refers to the amount of power converted to heat in a component due to the resistance of the component. In the video script, power dissipation is calculated for the resistor and the LED to ensure that the components can handle the heat generated during operation. This is important for designing a safe and efficient current regulator circuit.

💡Forward Voltage Drop

The forward voltage drop is the voltage required to forward-bias a diode or LED, allowing current to flow. In the script, the forward voltage drop of the LED is 2.2V, which is a key parameter in calculating the resistor value needed for the constant current regulator design.

💡Filter Capacitors

Filter capacitors are used in power supply circuits to smooth out the output voltage, reducing voltage ripple and noise. In the context of the video, adding filter capacitors to the current regulator design can improve the stability and quality of the output current supplied to the load.

💡Quiescent Current

Quiescent current is the current drawn by a device when it is in its lowest power mode or idle state. The script mentions that for small current requirement applications, the quiescent current from the regulator might make the solution bulky and lead to unnecessary power losses, indicating a potential disadvantage of using certain regulators for low-current applications.

💡Overtemperature Protection

Overtemperature protection is a safety feature in some ICs, including voltage regulators, that prevents damage to the component by shutting it down or reducing its operation if the temperature exceeds a certain threshold. In the script, this feature is highlighted as an advantage of using ICs like the LM317 in current regulator designs, as it can protect the circuit under heavy load conditions.

Highlights

Introduction to the concept of a constant current regulator and its function to provide constant current regardless of changes in load or input voltage.

Explanation of how a constant current regulator adjusts its resistance to maintain a constant output current.

Basics of current and voltage relationship using Ohm's law in the context of a battery and resistor.

Designing a current regulator for an LED with a constant current of 50mA using the LM317 variable voltage regulator.

How the LM317 voltage regulator can be repurposed as a current regulator by adding a resistor in series.

The importance of the 1.25V drop across the series resistor in maintaining a constant current.

Calculation of the resistor value needed for the desired output current using the formula R = 1.25 / Iout.

Calculation of power dissipation for the circuit components, including the regulator, LED, and series resistor.

Demonstration of the circuit's ability to maintain a constant current output even with changes in input voltage or load.

Advantages of using a voltage regulator like the LM317 for constant current applications, including simplicity and built-in protection features.

Disadvantages of using a voltage regulator for small current requirements, such as potential bulkiness and power losses.

The potential for future videos to explore other methods of designing current regulators using discrete components.

The inclusion of simulation results to validate the circuit's performance and the constant current output.

The use of filter capacitors to improve the design and performance of the constant current regulator circuit.

The wide input voltage range of voltage regulators, making them versatile for various applications.

Encouragement for viewers to revisit the video for clarification, ask questions, and engage with the content.

Transcripts

Hey guys, welcome to another video from foolish engineer. Last time we saw how we can design

voltage regulator using discrete components like BJT and zener diodes. This time we will

see the design of a constant current regulator with simple circuits, so let’s go for a

ride. The very 1st thing we need to ask is what

is a constant current regulator. Well, any source which provides constant current irrespective

of any change in output load or input voltage is known as constant current regulator.

Let’s see the basics of current and voltage. When we connect a normal voltage source, say

a battery to a resistor, then the current flowing through a resistor will be the division

between voltage applied to it and it’s resistance. Well, this is nothing but the basic ohm’s

law, right? So, with this logic, the constant current regulator changes its own resistance

in order to give the constant output current, which may result in changing output voltage

to pump the current in the load. So when the load current is supposed to be increased the

regulator decreases its resistance & when the load current is supposed to be decreased

the regulator increases its resistance. Well, keeping that in mind, let’s see a

circuit which can provide constant current to a load. Let’s consider we need to power

an LED, for that it needs to be given constant current of 50mA. So we can design a current

regulator which will provide the 50mA constant current irrespective of it’s changing input

voltage or even if we change the LED. The very basic circuit that we can design is using

LM317. Well, LM317 is a variable voltage regulator. The output voltage of this regulator can be

adjusted by a resistor which is supposed to be connected at the adjustable pin of the

IC. So, how can a voltage regulator be used as a current regulator? This regulator is

designed such that the voltage between its output pin & adjustable pin is regulated at

1.25V. In voltage regulator application, we need to use a voltage divider using some resistors.

But, for current regulator things get super easy, we just need to add a resistor in series

between the output & adjustable pin. So, the LM317 tries to maintain 1.25V drop across

this resistor and to do that it needs to source constant current to the output branch.

Let’s take an example, we need to provide 50mA at the output, the input voltage is 8V

& the forward voltage drop across LED is 2.2V so we will select this resistor. The value

of this resistor can be calculated with this formula

R = 1.25 / 50m R = 25ohm

Now, the power dissipation of the components used in the circuit can be calculated as voltage

drop across the component and current flowing through it.

So, Pr = 1.25*0.05 = 0.0625W

Pled = 2.2*0.05 = 0.11W Pq across LM317 = (8-2.2-1.25)*0.05 = 0.2275W

So if we change the input voltage, the power dissipation across this regulator will change

which will keep power dissipation across LED & resistor constant. Because current flowing

through both of them and voltage drop is constant. And we can add some filter capacitors to this

design as well. so that’s how this circuit is able to provide a constant current of 50mA.

Let’s check the simulation of this circuit. I have connected a LED at the output, in the

input I am giving 8VDC, now when we simulate this we get the constant current output of

50mA, now if I change input voltage from 8V to 10V still the output current is 50mA. If

we add one more LED, that means if we change the load still the output current remains

the same. (ref) There are some advantages of this circuit,

We need very less components to get constant current out of this voltage regulator

There is an overtemperature protection in such ICs, so it could come handy when more

load current is required and it tries to increase the junction temperature of the IC.

Voltage regulators have a wide input voltage range, so we can use them very easily.

But there are some disadvantages also For small current requirement applications,

these regulators might be very bulky. Due to quiescent current from the regulator.

There will be some power losses. Well that was just one way of designing a

current regulator, in the next video we will see how we can design a current regulator

using discrete components like transistor & zener diode. I hope you got something from

this. If you haven't, you can watch the video again. still If you don’t you can ask your

doubts in the comment box below, hit the like button if you liked the video subscribe to

my channel and finally thanks for watching.