Difference between Diode and Transistor

Both diodes and transistors are types of semiconductor devices that find a wide range of applications in different electronic circuits such as clippers, clampers, oscillators, rectifiers and amplifiers, etc. Go through this article to get an overview of how diodes and transistors function and how they are different from each other.

What is a Diode?

A diode is a semiconductor switching device which is constructed by combining two layers of N-type and P-type semiconductor materials. For this reason, a diode is also called as PN junction diode. The circuit symbol of the diode is shown in Figure-1.

A diode has only one PN-junction and two terminals viz. anode (positive terminal of the diode) and cathode (negative terminal). There are two modes of operation of diode, i.e. forward bias and reverse bias.

  • Forward biasing of diode means the anode is connected to positive terminal of battery and cathode to the negative terminal battery and in the forward biased mode, the diode acts as a closed switch.

  • While in the reverse biased mode, the anode is connected to the negative terminal and cathode is connected to the positive terminal of source. In the reverse bias mode, the diode works an open switch.

Therefore, a diode is a unidirectional semiconductor switch which allows current only in forward direction and blocks in the current in the reverse direction. Thus, it is widely used in rectification, i.e., for the conversion of AC into DC.

What is a Transistor?

A transistor is also a semiconductor switching device consists of three layers of P-type and N-type semiconductor materials. The transistor has two PN junctions and three terminals named emitter, base and collector. The symbolic representation of the transistor is shown in the figure-2.

A transistor is formed by sandwiching either a P-type semiconductor between two N-type semiconductors or an N-type semiconductor between two P-type semiconductors. Thus, based on the construction, the transistors are of following two types −

  • NPN Transistor
  • PNP Transistor

A transistor is widely used in the different electronic circuits as amplifier and digital switch etc.

Difference between Diode and Transistor

The following table compares and contrasts the various features of diodes and transistors −

Point of DifferenceDiodeTransistor
DefinitionA diode is two terminal semiconductor switching device which allows current flow only in one direction.A transistor is three terminal semiconductor device which is capable of switching and amplifying the signals.
ConstructionA diode is constructed by joining a P-type semiconductor material with an N-type semiconductor material.A transistor is constructed by sandwiching either a P-type semiconductor between two N-type semiconductors or an N-type semiconductor between two P-type semiconductors.
Number of PN junctionsDiode has one PN junction.Transistor has two PN junctions.
TerminalsDiode has two terminals named anode and cathode.Transistor has three terminals, i.e. emitter, base and collector.
TypesThere are various types of diodes such as signal diode, power diode, Zener diode, LED, etc.Transistor are mainly of two types: BJT (Bipolar Junction Transistors) and FET (Field Effect Transistors).
Depletion regionThere is only one depletion region in a diode at the PN junction.There are two depletion regions in a transistor.
Type of elementThe diode is a passive circuit element.Transistor is an active circuit element as it can provide amplification in the circuit.
Modes of operationDiode can operate only as a switch. Where closed switch in forward bias and open switch in reverse bias.Transistor can be operated as switch as well as amplifier. In active region, it operates as an amplifier. While in saturation region as closed switch and in cut-off region as open switch.
SwitchingA diode performs uncontrolled switching.A transistor performs controlled switching. Where the controlling is provided by base signal.
ApplicationsDiode finds application in electronic circuits such as clipping, clamping, rectifiers, voltage multipliers, etc.Transistors are used as electronic switches, amplifiers, oscillators, regulators, etc.


From the above discussion, it can be concluded that there are various differences between a diode and a transistor. Hence, it is important to have a good understanding of the way diodes and transistors function in order to be able to use either of them as per the exact requirements.