Wi-Fi controlled light; 230VAC – 12VDC/3.3VDC

esp8266safetytransformer

I try to connect an ESP8266-12 and a 12V RGB LED strip to 230V AC. Based on this link, I've came to the following scheme. This will also be the first time I will etch a PCB myself.
enter image description here

The partlist will be as following:

Part      Value          

C2        0.1uF        
C3        0.1uF         
C4        0.1uF          
C5        0.1uF     
D1        1N4004    
D2        1N4004       
D3        1N4004       
D4        1N4004        
F1        1A will be sufficient?             
JP1       screw connectors for 230V AC
JP2       jumper for connecting GPIO15 to ground
LED_STRIP the rgb leddstrip               
Q1        TIP120         
Q2        TIP120        
Q3        TIP120         
R1        220 Ohms            
R2        220 Ohms       
R3        220 Ohms      
S1        switch to reset ESP8266-12               
SERIAL    header pins for connecting over serial 
TR1       transfo
U$1       ESP12          
U1        L7812              
U2        LD1117V33

I'm still unsure about what transfo to use? I was thinking about the MYRRA 44090 TRANSFORMER 1.5VA 24V. I'd like to get some feedback on this pick.

Also I'd like to gain some feedback if this scheme is safe to use. I assume the ESP8266-12 will be isolated from the net since I'm using a transfo?

For completeness I add a link here to my GitHub repo where the eagle files can be found.

Best Answer

You're using a 7812 to make 12V from the DC voltage from the bridge rectifier. You need approximately 2V more than 12V to make that work (officially 1.5 or 1.25 I think, but this is safe to use). That means you need 14V from the bridge rectifier.

When rectifying an AC voltage of \$x\$ volt, you get a DC voltage of \$x\cdot\sqrt2\$ volt. That means you will need an AC voltage of \$14/\sqrt2\approx10V\$. With a 24V AC transformeter, you will get a very high DC voltage, about 34V, much higher than necessary. All the other Volts, 34-14=20, will need to be disippated as heat by the regulator. This is not only a waste of energy, but also may cause issues when the regulator gets overheated. A heatsink is a solution, but a transformator that gives you, say, 12V AC would be better.

Related Topic