Relay vs Transistor-Difference between Relay and Transistor

This page compares Relay vs Transistor and mentions difference between Relay and Transistor.

What is Relay?

• The relay is controlled device which opens and closes contacts in order to effect operation of other devices in the same or another electric circuit.
• The relay is used in circuits with lower ampere capacity i.e. Max. 20A.
• They are smaller in size.
• They have at least two NO/NC contacts.
• They are used in control circuits, automation circuits, protection circuits and switching circuits.

Relay vs Transistor

What is Transistor?

• There are two types of transistors viz. NPN and PNP. It can be used as amplifier as well as switch.
• The terminals of transistors are known as Base, Emitter and Collector.
• Transistor can function as switch. There are two modes in a transistor cut-off and saturation. In cut-off mode, transistor is said to be open switch. In saturation mode, it is said to be closed switch.
• In NPN, when negative DC bias voltage is applied to base, it operates in cut-off mode and when positive voltage is applied to base, it operates in saturation mode.
• Refer Application Note on Transistor as switch >>.

Following table mentions difference between relay and transistor.

Specifications Relay Transistor
Power supply It can work with AC and DC. It can work with DC only.
Power loss It has zero closed resistance. It has forward voltage drop. Due to this reason, lots of power gets wasted.
Resistance Relay has infinite open resistance. Transistor has leakage which can affect attached electronic circuits.
Temperature Relay can operate at extreme temperatures. Transistor can operate upto 95oC and little below 0oC.
Speed of operation Relay is much slower and operates at 200 Hz speed. Transistor can operate at MHz speed.
Damaged by Relay is primarily damaged due to over current. Transistor is damaged due to voltage peaking, over current etc.
Isolation It has very high isolation from control coil. It is not isolated from Base, Gate or Trigger.
Wear out It has much shorter mechanical wear out contact life. Transistor switches almost never wear out.
Application It can used only to open and close circuits. Transistor can amplify analog signals as well as functions as switch.


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