Hi, my name's Tom and this is my first post here. I'm really in to saltwater aquariums and have been busy building Arduino and Esp32 based gadgets to control and automate various aspects of my tanks. Right now I'm working on a PCB for auto water changes using an ESP32. I'll need both 5VDC and 3.3VDC on the board. VIN will be 12VDC. As I am an absolute newbie when it comes to circuit design, I scoured the internet and put what I found into the circuit shown below.

I'd like to ask whether you feel the circuit (assuming all voltage, current limits, etc. are within specs) will function, as shown. Thanks.

 

Welcome to AAC!

Looks fine at first glance. What is your current requirement for 5V and 3.3V?

 

Thanks for the welcome! The 5V is for driving a 20x4 LCD display (tried converting it to 3.3V using a charge pump etc. but, I couldn't get the backlight evenly lit). The 5V will also power the ESP32. The 3.3V will handle 4 water level sensors (photo diodes) and a bank of 3V relays. The relays have opto-couplers to separate the circuits. Other that that, 5 or 6 3v LEDs. I doubt if I'll ever encounter more than 500mA.

 

The 3.3V will handle 4 water level sensors (photo diodes) and a bank of 3V relays. The relays have opto-couplers to separate the circuits. Other that that, 5 or 6 3v LEDs. I doubt if I'll ever encounter more than 500mA.

That could be problematic. That half amp will be going through the 5V regulator; increasing it's power dissipation and using half of it's current capacity.

 

The 500mA was just a guess (and coming from a newbie). I'll finish hooking up the entire circuit to a breadboard tonight - hook up everything possible and post the results.

 

OK. Tested everything. Turned on all sensors and activated 5 relays and 5 leds. Total mA varies around a value of 133mA. A lot less than I thought it would be.

 

Total mA varies around a value of 133mA. A lot less than I thought it would be.

The current draw is determined by the load, so that's fine, right? Having overhead capacity is a good thing.