ESP32 Forum

Hello.
I am using a 24V SMPS power source to power a custom pcb board with a Lolin D32.
The 24V is going directly to a few mosfets and the Lolin has a D24V5F5 buck converter from Pololu which I am converting to 5V and powering via the USB pin.
This works fine, but when I connect the usb cable to the lolin D32, I have a problem. When 24V is supplied and the usb is plugged in, there is no problem, but when the 24V is switched off and the usb cable is plugged in, that buck converter overheats and fails instantly.
I think it's the reverse current protection diode in D24V5F5, which works when 24V is supplied, but not when 24V is not supplied, causing it to be destroyed by the reverse current.



To solve this problem, I am going to place a Schottky diode between the buck converter and the lolin D32. The problem is that there is a voltage drop of about 0.5V, but according to the schematic of the lolin D32, it is converted to 3.3V, which powers the ESP32. I am not connecting any other devices such as batteries, so I think that the 4.5V will be converted to 3.3V and the supply to the ESP32 will be fine, but I was wondering what you think.

One more question, I was thinking of using an SS24 or MBRS340 as a Schottky diode. I haven't used them so I'm not sure, but would they be okay? Or if you have a better one, would you recommend it?

(FYI, those things are called Schottky diodes, after Walter H. Schottky, the guy who invented them.)

The ME6211 has a fairly low dropout voltage; it doesn't really state what it is at high currents, but it looks like it's less than 0.5V. So if you feed the device 4.5V, it should still work fine.

For a purpose like this, you can use almost any Schottky diode that is rated for the current. Since the ME6211 LDO is rated at 500mA, your Schottky should be capable of handling that or more. The SS24 can do 2A and the MBRS340 even 3A, so they're both suitable.