Where Does a Solid State Relay Draw Power From?

[booxcar]

Hello,

I am not an electrical engineer but I do have a slight background in some electrical engineering concepts. My question is a general one about relays (more specifically solid state relays but I don't think that really changes my question). I understand that a relay gets a small input signal which is used to control the output voltage of the relay. My question is, where does the relay draw the extra power from? All relays must need some external power supply in order to output power that is much greater than the input signal correct? Maybe I am not understanding things about relays because when I am shopping for them, it seems as though no brands suggest a power supply or anything to provide the extra power for the relay output. Any information would be awesome!

Thanks,
Boox

 

[technician]

A relay is a switch rather than an 'output voltage'.
Electro-mechanical relays consist of an electromagnet (a coil) which operates a switch when it is energised. The switch can be used to control a separate electrical circuit with its own power supply.
Solid state relays do much the same job but do not use an electro-magnet.
A 'reed relay' is a small switch sometimes operated by a small permanent magnet brough close to the switch.