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Constant Current Circuit: Ways To Build And Utilize Constant Current Circuits

We had often encountered voltage source and current source in a circuit design when we worked with analog circuits. Voltage sources are anything that provides a constant voltage, like a USB standard 5V output or a 12V adapter; however, current sources are a bit more mysterious. Several circuit designs, especially those involving Op-Amps and switching circuits, would require you to use a constant current source. What is a constant current circuit? What does it do, and why do we need it?

Below we will answer these questions and a few others that you might have, such as the temperature changes, circuits with a transistor, and applications for this specific current. 


1. What Is A Constant Current Circuit?


The circuit drives the resistor and creates voltage

(The circuit drives the resistor and creates voltage)



It is a power source that maintains a constant current to a load despite changes and variances in the load resistance. Another way of putting it is that a constant current source supplies a steady output current regardless of load resistance.

In this way, a constant current source is precious for supplying steady current regardless of any variations in resistance, even a significant variance in resistance. In circuits with regular current requirements, this is useful.


2. How Does A Constant Current Source Work?


LED light source

( LED light source)


Power generators with constant current sources have high internal resistance compared to their loads with high resistance. It can maintain a continuous current even for a load whose resistance fluctuates within a wide range since its internal resistance is high.

Accordingly, the constant current source operates according to the current division. Due to the high internal and low load resistance, the current takes the shortest path of least resistance. Current flows from the (high internal resistance) current source to the lower resistance load.


3. Ways To Build Constant Current Circuits


Transistor Active Constant Current Source Basics


Equation For The circuit solution example below using a battery voltage of 5

(Equation For The circuit solution example below using a battery voltage of 5)


With the equation above, we are using the mA value of 100. The circuit provides a constant current supply of 100mA using a 5V power supply. Additionally, it will have a potentiometer to control the recent output from one to a hundred mA. Despite the changes in load resistance, it will maintain a steady current. Circuits that need a constant supply of current without fluctuations can use this.


Simple Stabilised Working Current Source Circuit


This is a Transistor active current source circuit

(This is a Transistor active current source circuit.)


It is a simple matter to fix any problems with current arising from changes in the source voltage by changing a few electronic components in the primary circuit of the active device. Alternatively, you can use a voltage reference diode or Zener in place of R1.


Constant current circuit of LM334, TL431, and LM317


This is a constant current source circuit that uses the LM317 voltage regulator

(This is a constant current source circuit that uses the LM317 voltage regulator)


One of the most stable sources of constant current is the LM344. This current source has three terminals and can operate at current levels from 1uA to 10mA, as determined by an external resistor Reset. As a trustworthy two-terminal current source, it requires no extra components power connections. In addition, it is capable of operating as a temperature sensor. Unfortunately, the LM334 is only capable of supplying 10mA.

In addition to being a voltage regulator, the LM317 is also a stable constant current source. One can create a maximum current of 1 amp using only three pins. 

Small TO-92 packages commonly contain the TL431 part. A TL431A can be considered a temperature-compensated variable, and this device can also function as a constant current source and a voltage reference/source.

Remember always to measure the input voltage, switch nodes as well as output voltage before use.


4. Constant Current Circuit Dependant on Temperature


(Above is a Temperature-compensated transistor active current source circuit)


Active current sources are dependent to some extent on temperature, which is one of their main disadvantages. While this is likely not significant in many applications, temperature performance will be crucial to control the environment. 

Variations occur in two main ways:


The effects of temperature on variations of Vbe 


The temperature on Vbe is approximately -2 mV/°C, and a variation of Vce is due to this. The following relation is approximate: *Vbe equals approximately -0.0001ΔVce. Keep in mind that the circuit is sensitive to changes in the ambient temperature. 

It is advisable to use an emitter resistor value that is large enough. It is because the deal will guarantee changes in emitter voltage smaller than tens of millivolts. And that also influences only a proportion of the emitter voltage total.  For the collections to still have enough voltage between them, it is essential that both currents flow through and that the variations in the supply voltage are adequately absorbed.


Temperature and the Variations of β


When a transistor has the value of β / Hfe, this may not be a significant problem. By doing so, the influence on the emitter current by the base current decreases, and the variation reduces to the greatest extent.


5. Constant Current Circuit Application


For LED driving-related operations in an LED lighting system, there must be a continuous current source. You use a constant current source in battery charging circuits as well as in portable devices. You will use a constant current source in several applications, including:

  • Systems for amplifying audio.
  • System of solar energy.
  • Electromagnetic fields.
  • An engine that maintains a constant speed.
  • Sensors that measure the Hall Effect.
  • The Zener diode biasing regulator circuit


Final Thoughts


The constant current source circuit consists of a constant current source connected to the load that it powers, and it is a temperature dependence circuit. A continuous current will always flow, no matter what resistance or voltage the bag is.

Furthermore, we discussed the ins and outs of operating a constant current. 

We are happy to answer any further questions you may have and provide you with specific guidance as needed. Please feel free to contact us with any concerns.