Building a Regulated 9-Volt, 20-mA or 10-mA Power Supply

I am looking for a circuit for an active antenna circuit that requires 9 Volts, 20 mA. But I cannot find anything that will meet my needs. I see other power supplies that are more than 20 mA.

Hi Adam. You are brave to ask such a question as it does indeed show you dont know that much at this time. Never mind. A good place for you to start is to purchase a three terminal 100mA regulator type 78L09. Just abut any electronics catalogue or hobby magazine will have something in one or other issue. The internet is more than likely to have something as well. You will need about 12 volts or more for the input of the regulator as it needs about 2 volts minimum drop acros it from memory.

Your load requires a MINIMUM of 20ma. Your power supply must be able to provide at least that. Your power supply will only provide what the load calls for, so if you have a power supply that can provide 300ma, but the load only asks for 20ma, then it will only provide 20ma.

I solved it and I added a 4700 uF and 6800 uF electrolytic capacitor for better filtering and for clean RF signals.. I am now using a power supply that came from a old cordless phone answering system that uses 9 volts 210 mA. I know I it's not hard for find a power supply @ 9 volts 200 mA than it is to find a 9 volts @ 20 mA. I just realized that 20 mA is a minimum. I even tried a simple experiment that used a 470 ohm resistor in series of a Green LED and it lit up nicely. So I know that this power supply will not burn up the coil or transistor. Thanks for your support.

Thanks for the input. Yes, I am not that strong in ohms law. It's kinda complicated so I have to use calculators and a multimeter. I have to try to study and practice with it.