Voltage Current Characteristic of Diode

Hello, fellows, I hope all of you are enjoying your life. In today’s tutorial, we will have a look at the Voltage Current Characteristic of Diode. The diode is 2 terminal semiconductor devices that used to rectify alternating current into the direct current. If it converts half-wave of alternating current into direct than this process called half-wave rectification. If convert both parts of alternating current into direct current this process is known as full-wave rectification. In almost every electronic device and engineering project, a diode is used such as ups and some other electronic projects. There are different types of a diode according to their construction and working such as LED, OLED, Zener, etc.

There are normally 2 methods are used to provides input supply to the diode first is forward biasing and the second is reverse biasing. If the positive terminal of battery is connected with the anode and negative terminal is connected with the cathode this type of bias is known as forwarding bias. If negative terminal of battery is connected with the anode of diode and positive is connected with the cathode this called reverse biasing. By using these to biasing we will discuss the effect of current and voltage across the diode and find different characteristics. So let’s get started with the Voltage Current Characteristic of Diode.

Voltage Current Characteristic of Diode

• For a practical understanding of V-I characteristic of a diode, we discuss the forward biasing and reverse biasing conditions one by one.

V-I Characteristic for Forward Bias

Note: In this post, there are 2 types of voltage will be discussed the first one is froward biased voltage and the second is forward voltage (VF). The difference is that forward biased voltage across the complete circuit provided by the external voltage source. While forward voltage (VF) is the only value of voltage across the diode in a circuit. Lets start.

• The current flows when the diode is forward is called forward current. In the given figure this current is denoted as IF.
• In the given below figure, there are 2 circuits shown for forward biased arrangements

• In this circuit, we will increase the value of voltage from the 0 across the diode and will find the effect on it.
• In the circuit, resistance is connected in series it used to limit the value of current passing through the circuit to save a value that will not damage the diode.
• At the start, there is no voltage across the diode as we increase the forward-biased voltage value the current IF and voltage across diode increases the value of forward current and voltage across the diode can be seen in ammeter and voltmeter connected in a circuit.
• This arrangement is shown in the above circuit denoted as a.
• Some value of forward biased voltage is loss across the limiting resistance.

• In the above figure, the circuit denoted as b explains the condition when the value of forward biased voltage is such that the voltage across the diode is almost 0.7 volts or potential barrier while the increment in value of forward current is very fast
• As we continuously increase the forward-biased voltage-current also increases very fast with the forward-biased voltage, but the voltage about the dido increase very slowly after the 0.7 volts that are potential barriers.
• The less increment in the voltage across the diode after 0.7 volts is due to the voltage loss across the internal resistance of the semiconductor material by which diode is constructed.

V-I characteristic curve for a forward-biased diode

• If show above circuit measurements on the graph this graphical representation is called the V-I characteristics curve for a forward-biased diode.
• In the below figure this graphical representation is shown.

• You can see in the graph that is denoted as a that VF forward voltage or voltage across the diode is along the x-axis and (IF) forward current is along the Y-axis.
• In the graph (a) you can see that there is very less increment in forward current (IF) till value of forward voltage is 0.7 volts.
• After the 0.7 volts of forward voltage the increment in the forward current is very fast and (VF) is almost constant.
• The increment in forward voltage is less due to internal resistance or dynamic resistance voltage drop and forward continuously increases.
• In the curve (a) you can see three different points  A, B, and C.  First point ‘A’ explains the zero biasing condition.
• ‘B’ is a point where the value of forward voltage or VF is less than the potential barrier or 0.7 volts.
• While point ‘C’ defines the position where the forward voltage equals the potential barrier or 0.7 volts.
• After point C or knee of the curve, the increment in forward current is large while in forward voltage increment is minor.
• In practical, the value or forward voltage is almost one volt according to the value of forward current.

Dynamic Resistance

• The given figure is the expended form of V-I curve for forward bias diode and it explains the dynamic resistance.

• As linear resistance has constant value but the value of resistance offered by the diode in forward biasing does not remain same throughout the forward biasing diode.
• This resistance is known as ac resistance or dynamic resistance.
• Interior resistances of electronic components are generally labeled by lowercase italic r with a prime, in its place of the R.
• The dynamic resistor of the diode before the knee of the curve is high since the increment in current is very less with the increment in the voltage.
• As the voltage approaches to knee of curve resistance start to decreases and after the knee point it becomes very less and current start to increase.

V-I Characteristic of Diode for Reverse Bias

• When the diode is in reverse biasing condition then the current (IR) flow is very less.
• When the voltage across the diode is zero the IR is also zero.
• With the increment in reverse-biased voltage then very less value of reverse current flows through the diode and voltage across diode is also less.
• If we continuously increase the voltage applied then if the value of reverse voltage across the diode is equal to the breakdown voltage (VBR)  then the reverse current flows very rapidly.
• With the further increment in the reversed biased voltage, the reverse current also increases continuously but the increment in the voltage across the diode is very less.

V-I Curve for Reverse Biased Diode

• If we make a graphical representation of reversed biasing of a diode. The curve obtains called V-I characteristic curve for a reverse-biased diode.
• In the given figure, you can see the graphical representation.

• In curve, you can see that the reverse voltage (VR) across the diode is drawn on the negative x-axis and reverse current (IR) on the negative Y-axis.
• The increment in the reverse current is very less till the point where reverse voltage is at knee point.
• After the knee of curve reverse voltage is almost same but reverse current increases very fast.

• If the value of reverse current is not controlled then it can overheat or damage the diode.
• The doping level of decides the breakdown voltage of the diode, the doping level of the diode is set by the diode’s manufacturer.
• Normally general purpose diode has breakdown voltage value larger than fifty volts and some special diodes have breakdown voltage almost five volts only.

Complete V-I Characteristic Curve of Diode

• If we combine both forward biased and reverse biased curves of dido than we have a complete V-I characteristic curve. It is shown in the below figure.

Temperature effect on diode V-I characteristic

• If a diode is forward biased and we increase the temperature then there will be an increment in the forward current IF at a specified value of forward voltage.
• With the increment of temperature forward voltage decreases at a certain value of current.
• The effect on diode V-I curve is shown in a given figure.

• You can see there are 2 curves in graph blue is at room temperature (25 centigrade) and the red curve is for increment in the temperature (25C +ΔT).
• With the increment in one-degree Celsius, the potential barrier decreases by two millivolts.
• If the diode is in reverse biasing conditions then the increment in temperature the reverse current (IR) also increases.

So friends that is the detailed post on the Voltage Current Characteristic of Diode if you have any further query ask in comments. Thanks for reading. See you in the next post. Have a good day.