I have plan to create a switch ON-ON, this switch will be activated or become ON if there is a supplied current. There is a common (C) connection point to A/B, in initial no current supplied by the switch, the connection would be C to A, and if there is a current supplied to the switch to make it ON, the connection would be C to B. I know that it can be handled by 2 Transistors (A),(B) and can be handled also by relay, but I want your expert point of view and suggentions. Here is the critical issue to make a decision which is the exact medium to use as a switch either transistor or relay.. the critical issue is the current/signal including all the properties (voltage, frequencies, etc...) connected to (C) should be exactly will be thesame to the output(A) or (B).

     C o------
  • \$\begingroup\$ You are missing too much relevant information to provide a useful answer. \$\endgroup\$ – Olin Lathrop Oct 8 '11 at 17:55
  • \$\begingroup\$ @Jun2x, Russel has put a decent bit of question about detail in his answer. Please try to give some detail and update your question. I can think of 8million solutions, but only a few are perfect based on details I do not have. \$\endgroup\$ – Kortuk Oct 8 '11 at 17:58

NB - this could be a good question if you take note of the points below. If you don't the question will die.

This is the sort of answer that Google can be used to answer well.
People have been making this decision since about 1956 :-) - and had been looking forwards to making it since about 1905. However -

There are many many many issues. Which ones matter most and how important they are depend on your requirements, and you have not provided enough information to allow an excellent answer to be provided.

You should try and provide much much much more information or the men with the long knives will come an cast your question into outer darkness in no time flat.

What voltage?
What current?
What power level?
Are you switching AC or DC. What is being controlled?
Resistive/inductive/capacitive load?
How often switched?
How fast does it need to switch? How long is it on for, shortest time?
How long is it off for, shortest time?
How many switching actions in life time ?
Do you want isolation of output and input eg person and mains electricity.
What voltages do you have available for powering?
Why use a relay anmd not just a switch?
What is controlling this? (person, Arduino, cat, Water Buffalo ...?)
More information! More! More ! ... ;-)



  • A relay has a finite life. Maybe 1000, 10,000, 100,000 or 1,000,000 operations. More in a few cases.

    Relays tend to take more power than a transistor circuit for the same job.

    If you want very many operations or very long life times or very low operating power then relays may not be your best solution.

    Relays provide low loss connections, don't need power on their output circuit, conduct AC currents easily are reasonably robust and blowup proof on the input side and OK on the output side if designed well.


  • Transistors can be operated with almost zero power if necessary, can switch very fast and can have extremely long lifetimes.

    If switching AC special care is needed to provide bidirectional switching, - this is not hard but needs to be done. Decisions about when to switch compared to the AC voltage level can be made (but not with a relay).

    Transistors tend to be less robust than relays in extreme conditions BUT can be designed to handle any eventuality that can be predicted.

Which is best for you depends very much on your answers to the questions at the top.

  • \$\begingroup\$ Actually I will create a stompbox switch by footswitch, for my electric guitar, I have 1 guitar but 2 guitar amplifier, I dont want to unplug the guitar chord and plug to the other in transfering... I wan't to create a switch that will manage it with 1 input from my guitar and the output will be to first guitar amplifier or second amplifier by pressing the switch... but I don't want the signal current including the properties from my guitar to be affected or changed... \$\endgroup\$ – Jun2x Oct 9 '11 at 8:10
  • \$\begingroup\$ based on the theory and my understanding regarding transistor that there is a voltage from base to emitter so maybe the voltage or signal from to collector to emitter will be different output... \$\endgroup\$ – Jun2x Oct 9 '11 at 8:31
  • \$\begingroup\$ @Jun2x - that's the sort of information that would help a great amount if provided initially. A relay will work well for you and will be far less trouble to get going for you. \$\endgroup\$ – Russell McMahon Oct 9 '11 at 10:54

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