You don't need to limit the current, the relay will only draw as much power as it needs.
If your power supply is only rated to supply 100mA and the relay requires 250mA, then you're out of luck. You either need to get a power supply which can provide 250mA or get a relay which uses less power.
It isn't my desired solution, becauce i want to use relay out of my designed circuit. my circuit have 3 wires: IN ,GND,OUT
but i think transistors are good idea.
pls another way .
Hero's circuit is the best way to do this. Hero's circuit does not have any relay contacts though which could be where you are getting confused. What Hero's circuit is doing is energising a coil (the inductor) that then closes the relay contacts. These contacts are a completely isolated set of contacts and can be though of as just a normal switch that close when the relay coil is energised (when the transistor is ON) and open when the relay is de-energised.
He probably means he has far more power available on the 24 volt circuit than what is likely to be needed.
Mains source Vs a 9 volt battery type situation.
He probably means he has far more power available on the 24 volt circuit than what is likely to be needed.
Mains source Vs a 9 volt battery type situation.