Constant Current Diode

Introduction

Constant current diode is an electronic device that limits current to a maximum specified value for the device it is also known as current limiting diode (CLD) or current regulating diode (CRD). These diodes consist of an n-channel jfet transistor with the gate shorted to the source which functions like a two terminal current limiter or current source analogous to a voltage limiting Zener diode. These diodes allow a current through them to rise to a definite value and then level off at a specific value. These diodes keep the current constant instead of the voltage. These devices keep the current flowing through them unaffected even when the voltage changes. These diodes are operated in forward biasing condition use of voltage is from 1.5 volts to 6 volts. The current generated by forward biasing is known as forward current and it is denoted as Ip. Even if the variation occurs in input voltage and load resistance, the diode is able to maintain the current value.

Characteristic of Constant current diode

• In the above graph characteristics of Constant current diode is shown. This graph is divided into two different regions.
• In a shaded part of the graph diode is operating in forward biasing condition, the value of forward current is constant for voltage ranges from 1.5 volts to 6 volts.
• The forward current is also known as regulator current and denoted as Ip.
• The value of regulator current that the diode can handle is from 220 milliamperes to 4.7 milliamperes.
• To get a large value of current these diodes are used in parallel combination.
• These diodes have no specific reverse breakdown.
• These diodes do not operate in reverse biased conditions.
• The reverse current start to rise for the VAK of less than zero volts. In forward biased conditions the regulation process of diode start at limiting voltage VL, to the POV or peak operating voltage.
• From the graph we can examine that between the points Vk and POV the current is constant. VT is the test voltage for this voltage IP and ZT mentioned on the datasheet of a diode.
• The value of impedance ZT is 235 KΩ to 25 MΩ for diode series 1N5283 to 1N5314.

Advantages

• There is no need of any additional voltage source.
• Its circuit is very simple which exits in series combinations.

Application

• Constant current diodes can be used in devices such as power supply circuits, to Battery charging circuits, to LED drivers.
• Other applications where a fixed current needs to be regulated irrespective of the applied Load.