I am a electronics hobbyist trying to make a linear power supply/phone charger. This is a schematic that I have created. Optimally, my load would be a phone charging at 1A and 5V from a usb jack with the D+/D- lines shorted. From some experimenting, a multimeter measurment of the voltage on the wire that gets filtered by the caps and goes into the 5V regulator is ~18VDC. I know that 1A current draw from a 7805 will need serious cooling so I figured a fan would be able to both provide a voltage drop that will reduce the wattage of the 7805 as well as provide some cooling for all the components. My fan is a 12vdc 70mA computer fan. I am stuck finding a way to safely run the fan from an 18V line. I figured a voltage divider would be a good way to create 12v and also take more wattage away from the regulator. I am simply stuck finding values for those resistors. I did some quick math and found that R1 should be ~3.6K for 5mA thru the LED and R2 should be ~1.3k. Does those numbers seem reasonable? Would running the fan straight off of the 18V line be a feasible alternative?
Update: Would something like this form a resistor divider, dropping the voltage going into the regulator?[![enter image description here]]
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