What is main difference between diode , thyristor AND transistor ?

A Diode is1N with a PN junction, use for rectifcation (allow only positive cycle of the current to pass and block the negative).

A Transistor is a2N with NPN or PNP junction, can be used as switch or voltage regulator.

A Thyristor is a3N with PNPN junctions, works as an ideal switch & also used for rectification.

All the three are type of Switches.

• A Switch is a device for making and breaking the connection in an electric circuit.

Transistor: Full controlled Switch.Thyristor: Semi-controlled Switch.

Diode: Uncontrolled Switch.

• transistor are used as a switch, amplification and in inverter and cant be used for rectification.
• Diode is used for uncontrolled rectification.
• tyristors are used for controlled rectification and also for switches in circuit like fire/ emergency Alarm.

Diodes are uncontrolled devices, ie. they are turned on by applying forward bias to their PN junction. Whereas thyristor has gate terminal apart from the anode and cathode terminals. The turn on and off can be controlled using the voltage applied to gate terminal. In a thyristor gate terminal voltage is necessary only to initiate it to conduction state, once the thyristor is in conduction state the gate pulse can be removed. Whereas a transistor contains a third terminal called the base through which voltage has to be applied throughout for the transistor to continue in conduction state.

DIODE" is a1N device with PN junction. It acts like a valve, and allows current flow in only one direction, but not the reverse. It is used to convert a.c. into DC current using the Bridge rectifier circuit. TRANSISTOR is a2N device with NPN and PNP junctions. The central one is called the base in a bipolar or current biased transistor and is called the Gate in a field effect transistor. A small current or potential on the base or Gate causes a large current across the transistor. Thus the transistor acts like a switch to on and off current and also to regulate the potential. THYRISTOR is a3N device with PNPN junctions. It is used to switch a.c. current at volts and more than4 amperes, thus being a high voltage high power device.

Diode is uncontrolled switch, thyristor is semi-controlled switch and transistor is fully controlled switched.

All are semiconductor devices with difference in PN-Junction layers.  Diode is a two layer device while transistor and thyristor are three and four layer devices respectively.

Diode is uncontrollable while transistor and thyristor are controllable devices.

Diode and Thyristor has only difference of controllable function of thyristor.

diode is a two terminal semiconductor device while thyristor and transistor are four terminal and three terminal devices respectively.

Diode is consist of onlye one PN junction which allow current to flow only in one direction while thyristor is 4 layers 3 junction semiconductor device which can also allow current in both direction. Trnasistor is consist of two PNP or NPN junction. Which is current control device.

Simple words

Transistor is a fully controllable switching device.

Thyristor is a semi-controlled switching device.

Diode is a uncontrollable switching device.

Diode is a one p_n junction device having two terminals, diodes main function is to rectifying the signals, where as transistor  is a two p_n junction device, having three terminal. Basic function of the transistor are switching amplifying the signal.

thyristor is a four layer device with three terminals. they are semi-control devices