I have an AC power source that when rectified with 470 µF capacitor gives 38 V DC with no load. I have a 7805 (TO-220) which the data sheet says has a maximum input of 35 VDC. I'm trying to power an ESP8266 module that when connected to a bench power supply indicates that it's using less than 100 mA and maybe 100 mA when it powers a relay. There might be current spikes that the power supply meters aren't fast enough to show.
When feeding the 38 V directly into the 7805 I do get 5 V DC, but when powering the 8266 something happens and the output falls to about 2.5 V. I think the regulator is shutting down. When I put a resistor in series with the input voltage (50 to 120 ohms, small light bulbs actually) the module does operate properly until I activate the relay.
If instead of using the AC source I use a bench power supply to feed DC into the bridge I can crank the power supply up to the max of 30 V and the module works fine, the 5 V DC is stable.
Do I need to look at another way to generate 5 V DC from this AC source, maybe a switching power supply module of some sort, or can I do something other than using a huge wattage resistor to get the input voltage under control?