Discussion in 'Homework Help' started by Cerkit, Apr 23, 2009.

  1. Cerkit

    Thread Starter Active Member

    Jan 4, 2009
    Is it fair to say that in general relays are more reliable than bjt as switches??
  2. StayatHomeElectronics

    Well-Known Member

    Sep 25, 2008
    Not really.

    They each have their uses. One negative for relays is that they also have a mechanical end of life. It may be 1,000,000 operations but the mechanical parts do wear out.

    Let's hear others opinions on this...
  3. cumesoftware

    Senior Member

    Apr 27, 2007
    In my opinion, relays are more durable, but not as efficient. About the reliability, a relay at a given point might get stuck. BJT are temperature sensitive, and are not in the league for durability. That's why relays are used more often in industrial and heavy appliances.
  4. etuzuner


    Mar 21, 2009
    I agree with cumesoftware. Although I'm an electronics engineer, I trust mechanics more than electronics. There are so many assumptions in electronics. When you see the theoretical schemes of the devices that are part of our lives, you're having some doubts about them. As a friend of mine said: " I can understand anything I can see, I can touch, so I love mechanics. On the other hand, I can't say the same things about electronics, for example the current flowing through a wire."

    Anyway, in my opinion relays are more reliable than bjt's. Once I had read a paper. It was told that 2 bjt's can not be produced with having the exact properties and characterizations. They differ decimally from each other because of the junctions.

    Of course these are my opinions.

  5. bertus


    Apr 5, 2008

    It also depends on the speed of switching.
    A relay may wear out at fast switching.
    A bjt will work upto many kHz or even MHz.

  6. mik3

    Senior Member

    Feb 4, 2008
    I wouldn't say that. It really depends on the application and the way you use them. If you use both a relay and a transistor as specified in their datasheet then they will work fine (unless something causes their failure).
    Relays are more efficient to switch high currents but they work at low speeds. On the other hand, transistors can switch very fast but the carry low currents. Some expensive transistors can conduct high currents too.