48V to 12v to 5 v buck converter

[Badstraw]

Hey! I’m planning to design a pcb for high power Leds, I want to use 12 V fans and a 5v microcontroller (esp32). I would like to make my own buck converter.
So the question is, how do I reduce the voltage from 48 to 12 v and then 5v for the microcontroller using the same 48V 7A power supply?

I was trying to use a 12v adapter and then decrease the voltage to 5v using an LM2596S but it didn’t work (I’m getting 12v on the output). I got the values from Webench power design tool for Texas Instruments.
Here’s the schematic

48 to 12 (4A)

12 to 5 (1A)

I’d like to know if you guys can point me to the right direction please.

 

[ronsimpson]

I was trying to use a 12v adapter and then decrease the voltage to 5v using an LM2596S but it didn’t work (I’m getting 12v on the output). I got the values from Webench power design tool for Texas Instruments.
Here’s the schematic

It should work. Is Rfb2 missing or wrong value. Also check Rfb1. You could measure the FB voltage.
OR The IC might be dead.
Can you send pictures?

 

[AnalogKid]

What is the peak load current on the 5 V? I've been down this road, and sometimes a switching converter isn't worth the complexity. If the system is not critically dependent on battery life and the 5 V current is low, getting rid of that little bit of extra heat in a linear regulator will save significant development time (which ultimately is paid for by someone), and probably some component cost.

ak

 

[ronsimpson]

getting rid of that little bit of extra heat in a linear regulator will

12V to 5V 1A linear will have 7 watts of heat. And draw 1A from a battery.
12V to 5V 1A switcher will have 0.5 watts of heat. And draw 0.4A from the battery.

 

[Pommie]

Note that the max voltage for an ESP32 is 3.6V. A lot of boards have a 3.3v regulator to supply the ESP, however, if you use just a module 5V will destroy it.

Mike.

 

[AnalogKid]

12V to 5V 1A linear will have 7 watts of heat.

As I said, if the 5 V current is low and if battery life isn't an issue ... I missed the "12 to 5 (1A) " note. oops.

Still, if the conditions are right ... I did a 6 kW VME chassis that had lots of aluminum surfaces and a ton of air flow. The system monitor was powered by the +5.1 V, +12 V, and +18 V (specialty chassis), diode-ORed into a 5 V linear regulator at around 1 A.

ak