What is Constant Current Diode : Working & Its Applications

A diode is a polarized two-terminal electronic component that conducts the current within a single direction & blocks the flow of current in another direction because, in one direction, its resistance is ideally zero whereas in another direction it is infinite. These components include two terminals an anode and a cathode. There are different kinds of diodes available that are used in various electrical and electronic projects based on requirements like PN junction diode, Zener diode, constant current diode, Schottky diode, light-emitting diode, and many more. So, this article discusses one of the types of diode constant current diode and its working with applications.

What is Constant Current Diode?

The diode which is used to restrict or change the current to the highest value for the device is called a constant current diode or CCD. This diode is also known as the current regulating diode or CRD and the current limiting diode or CLD. The constant current diode symbol is shown below. The function of a constant current diode is to provide protection to the circuit from short circuits.

Constant Current Diode Symbol
Constant Current Diode Symbol

Constant Current Diode Construction & Working

The internal structure of the constant current diode is shown below. This diode includes an N-channel JFET transistor where the transistor’s gate terminal is shorted to the source so that it works like a two-terminal current limiter or current source which is equivalent to a voltage limiting Zener diode.

Diode Construction
Diode Construction

Not like Zener diodes, these types of diodes will maintain the current stable rather than the voltage constant. Once voltage changes, these diodes don’t change the flow of current throughout them. In forward biasing conditions, these diodes are operated by using voltage from 1.5 volts to 6 volts. The current which is generated from this biasing is called forward current (Ip). Even if the difference takes place within input voltage as well as the load resistance, then this diode is capable of maintaining the current value.


The features of a constant current diode include the following.

  • Its tolerance is ± 10%.
  • Its operating voltage ranges from 1V to 100V.
  • Its behavior is stable when temperature values vary.
  • Its peak functioning voltage is 100 volts.
  • The value of Thermal resistance is 100 C/w.
  • Its storage temperature rating ranges from -55 to 200 degrees centigrade.
  • Its power dissipation is 30 mW.
  • The current ranges from 0.192mA to 5.6mA.
  • Peak voltage rating ranges from 50V to 100V.
  • Its impedance ranges from 20Mega ohms to several kilo-ohms.
  • This diode does not need any biasing & offers good temperature stability.

Constant Current Diode Circuit

As the name suggests, this diode regulates the flow of current throughout it to some highest levels. If you apply more current throughout this diode than its current-regulation point, then it fights back simply by reducing more voltage. The application circuit of the constant current diode is shown below. This diode is applicable in LED or Laser diode circuits to limit the current flow throughout LED or Laser diodes.

The following circuit is built with a battery, constant current diode, and a Laser diode or LED. In the following circuit, the constant current diode is connected in series with a laser diode. Once the voltage is applied to this diode through a voltage source, then this diode limits the flow of current and supplies the required voltage to the laser diode so that the laser diode or LED diode in the circuit will be turned ON.

Constant Current Diode Circuit
Constant Current Diode Circuit

Here, the regulation point of this diode must be selected to match the LED (light-emitting diode) otherwise optimum forward current of the laser diode. This is particularly significant for the laser diode, but not so much for the LED because normal LEDs tend to be more tolerant of forward current variations. Another application of this diode is to charge a small secondary cell battery.

Constant Current Diode Characteristics

The characteristics of a constant current diode include the following.

Constant Current Diode Characteristics
Constant Current Diode Characteristics
  • The above constant current diode characteristic curve is separated into different regions.
  • In the above diagram, the right portion of the curve operates in forward biasing condition. So, the forward current value is stable for voltage that ranges between 0V to 6V.
  • Here, this current is called regulator current and it is denoted with ‘Ip’. For example, the regulator current values for 1N5283 to 1N5314 series diodes range from 220 mA to 4.7 mA.
  • These diodes are utilized within the parallel combinations to obtain a large current value.
  • As compared to other diodes, this diode functions in reverse biased conditions. In forward bias, the diode’s regulation procedure will begin at ‘VL’ (limiting voltage) to the ‘POV’ (peak operating voltage).
  • From the above curve, we can observe that the current in between two points like Vk & POV is stable.
  • For the IP & ZT voltages, VT is the test voltage.
  • The impedance value like ‘ZT’ ranges from 235 KΩ to 25 MΩ for 1N5283 to 1N5314 diodes.

Advantages and Disadvantages

The advantages of a constant current diode include the following.

  • There is no requirement for any extra voltage source.
  • This circuit is very easy to design.
  • These diodes maintain a stable current flow even there is voltage fluctuation.
  • Available in small size & lightweight.
  • The diode operation is continuous for low voltage & provides safety for high voltage harmonics.

The disadvantages of a constant current diode include the following.

  • These diodes operate in forward biasing conditions.
  • These diodes are sensitive to high temperatures.
  • It provides a poor response.
  • At high frequencies, the noise level is high.


The applications of constant current diode or current limiting diode include the following.

  • The current limiting diodes are used in different circuits like battery chargers, timing & waveform generator circuits.
  • These diodes can also be used as constant current sources mainly for driving LEDs.
  • These diodes replace holding coils within telephone connection devices.
  • These diodes are applicable in circuits wherever a large LED string length is used & in voltage variable sources like bulbs.
  • The current regulator diode is mainly used for regulating the current like the Zener diode limits the voltage.
  • These diodes are used to provide input to the solid-state relays.
  • It is used to give protection to circuits from overvoltage.

Thus, this is all about an overview of a constant current diode and its working with applications. This is an electronic device that limits or regulates the flow of current to a maximum value. So this is a very essential diode in the circuit because it protects from the short-circuits or harmful effects. Here is a question for you, what is the Zener diode?