I want to use a 24Volts DC power supply to power the my spark core / spark photon, according to the previous posts, I will provide a 5VDC power to the VIN pin. However the thing now is how to design a small circuit to regulate the 24V to 5V, which I think I need to know what is range of the min and max working current? and anyone who has the schematic for regulating 24DV to 5DC
Here’s some information: http://docs.particle.io/photon/hardware/#2-2-power
Buying an off the shelf 5V DC supply works well too 
Something like this should also work: https://www.pololu.com/product/2107
What are you planning to use the 24V for, if I may ask?
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Hi，@Moors7，The reason I am using the 24 v is because the spark core are connecting to three peripherals through the relays, those peripherals are all in 24V DC
I’d go for one of those off-the-shelve down regulators, rather than making something of my own. They’re proven to work, and are relatively efficient.
As far as current goes; I know the Core could use up to 300mA when there was active wifi going on. That’s the minimum you need for operation. Any additional hardware needs to be accounted for as well. Do keep in mind that the onboard regulator on the Core has a maximum output of 500mA, of which 300mA can go to powering the board itself. So if you need more than the remaining 200mA, you’ll need to get that externally through transistors for example.
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