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.
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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