Hardware design issue

Author	Message
Mixtel90 Guru Joined: 05/10/2019 Location: United Kingdom Posts: 8964	Posted: 08:33am 04 Dec 2024       If you have AC in then rectify it as shown in the circuit the DC is *very, very* rough and will drop to zero on every half cycle as there is no reservoir capacitor from pin 1 of the 7812 to GND. I'd be very surprised if this power supply will work. Also, the output capacitor from the 7812 is high for those chips. Move the 220uF to the input of the regulator. That will give you about (12*1.4)-1.2= 15.5V DC. Dropout voltage on these is about 2V, so you should be ok for a 12V regulator if the current isn't too high. Normally you'd want to see around 18-19V here. Now use about 22-47uF capacitor for the output. It only really needs 0.1uF for stability, but I like a bit more for pulling relays in.