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Why is the Constant Current Circuit Important?

During analog circuit design engineers often encounter current source and voltage source. Voltage sources like a 12V adapter or USB standard 5V output usually have a constant voltage. However, there is more to say about current sources. Some circuit designs require engineers to make use of a constant current source, particularly those involving switching circuits and Op-Amps.

These designs require a supply of constant current with fewer or no interruptions. So, what is the function of a constant current circuit and what are its uses?

What is a Constant Current Circuit?

A constant current circuit ensures a constant current gets to a load regardless of the variances and changes in a load resistance. This means that a constant current source provides a consistent output current everytime.

Irrespective of the variations in resistance, this source must supply a constant current. A constant current source is a requirement for circuits with regular current.

A constant current source is a very valuable component in a constant current circuit because it offers steady current even if the resistance changes. Also, a constant current circuit requires a steady supply of current without any form of fluctuations.

What is the Function of a Constant Current Source?

A constant current source functions as a power generator with higher internal resistance than the load resistance it supplies power to. Due to its high internal resistance, it ensures a steady current to a load which has a varying resistance value, even above a high range.

A constant current source works based on the principle of current division. Since it has a high internal resistance and low load resistance, the current passes through the path with least resistance, comes out of the current source and goes into the load resistance. Power generators with constant current sources can keep supplying a steady current for a fluctuating load resistance since it has a high internal resistance.

A constant current source is one of the best ways to ensure constant power driving especially for a number of devices where there can be variation of load like LED strings. These circuits generate an I-V characteristics which is denoted by a straight line.

What is the Difference Between a Constant Current Source and Constant Voltage Source?

Current Circuit
Current Circuit

Constant current source is different from  constant voltage source, although they sound similar. Each of these power supplies differs in terms of their functions and applications. Therefore, it is important you choose the suitable power supply.

A constant current is a type of direct current which maintains its intensity regardless of the resistance value. If an electrical load varies, a constant current source will help in regulating the load to a constant current. Furthermore, a constant current source keeps a current at a constant level, no matter the changes in voltage supply.

A constant current power supply is applicable in LED lighting systems. The brightness of the LED changes in response to the current value.

On the other hand, a constant voltage regulates the output voltage to a constant level. This type of power supply offers constant voltage irrespective of the electrical load. Constant voltage is commonly used in most DC benchtop power supplies and power supplies in electronic circuits.

Good examples of constant voltage sources include regulated power supplies and batteries, although batteries need charging or replacement.

What is the Constant Current Source Circuit of LM334, TL431, and LM317?

The constant current source circuit is a source connected to the load it is powering. The LM344 is a very stable constant current source that comes with three terminals. This current source can function at current levels ranging from 1uA to 10mA. The operation level of this current source depends on an external resistor Reset.

With LM317, it is possible to use three pins to create a current of 1 amp. Also, there are TO-92 packages that feature TL431 part. You can consider a TL431A as a temperature-compensated variable that can serve as a voltage source and a constant current source. Always ensure the input voltage, output voltage, and switch nodes are measured properly.

Electronic Circuits that work on Constant Currents

Simple resistor current source circuit

There is only one resistor in a simple current source circuit.  The output current is independent of the load when the voltage that needs current is lower compared to the source voltage. Furthermore, the voltage source has an infinite voltage and the resistors have limitless resistance.

Constant current source circuit using transistor

It is possible to get a constant current source when you use a transistor with other components such as resistors.

Simple stabilized active current source circuit

Also, you can change some electronic components in a circuit to add some regulations. Therefore, it is possible to get rid of current fluctuations as a result of changes in voltage supply.

What are the Applications of Constant Current Circuit?

Constant current circuits are widely used in many applications since they ensure steady constant current source. For example, LED lighting systems and battery charging circuits require a steady constant source. Also, constant current source is an important consideration for portable devices need There are other applications which use a constant current source include:

  • Solar energy system
  • Electromagnetic fields
  • Hall Effect sensors
  • Amplifying audio system
  • Zener diode biasing regulator circuit

What are Variable Power Supplies?

Variable power supplies are components or devices that feature a means to adjust the output voltage and as well as the output current. It is possible perform this adjustment via a control panel and a switch. For instance, you can use the control panel to adjust some settings and also make some changes between CV and CC modes.

The voltage of the original power source transferred to the circuit can be regulated by a variable power. For example, a model train requires you to use a switch to increase its speed and minimize the voltage supply.


Constant current circuit relies on a constant current source which connects to a load that it is running. This source ensures there is a continuous flow of current regardless of the voltage or resistance.

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