ESP32 Forum

Hi
I'm developing a PCB with the ESP32-DEVKITC-32D with Can Bus, two GPS, ADS1115 for wheel position and MMA8452.
My challenge is the power supply on the PCB. The PCB will be installed in an old tractor, normally the power supply is 12V. But it can go down to 7V and op to 17v with short spikes.
I have used the AMS1117-3.3_C165482 and AMS1117-5.0_C165483 but im not sure that is the best way to go. I better like to use a R-78C5.0-1.0 but im not sure about the LDO to 3V3 and about the 5V supply to the ADS1115
I hope someone can guide me on that one.

PS I'm a programmer, not an electronics so circuit design isn't an area I'm familiar with.

That sounds like you are having a fair amount of potential peak power... are you sure those LDOs can supply that, and additionally, if they can cope with the heat they generate burning up the voltage difference? I'd personally prefer to have a buck converter of sorts to get the battery power down to 5V, then perhaps use a LDO to generate the 3.3V from that; that or 2 separate buck converters.

ESP_Sprite wrote: ↑

Mon Jun 08, 2020 1:25 pm

That sounds like you are having a fair amount of potential peak power... are you sure those LDOs can supply that, and additionally, if they can cope with the heat they generate burning up the voltage difference? I'd personally prefer to have a buck converter of sorts to get the battery power down to 5V, then perhaps use a LDO to generate the 3.3V from that; that or 2 separate buck converters.

I changed the design to this now. But still i would love to go for a buck converter i just not sure how and what to select. i'm really nervous about to get a stable supply for the ADC and the ESP32.

Not sure if I would go that way with LDOs... issue is that your 7805 now dissipates the load from both the 5V line as well as the 3.3V line.

Wrt buck converters: I can't really advise you on any designs there, but there are buck converter modules that work pretty well, some even in the same form factor as a 7805. If you put a 3.3V LDO behind that, that should already remove some of the potential noise a buck like that could put out; you can add chokes, ferrites and decoupling in the scenario you have problems afterwards. Or solve it in software: if the signals you need to ADC are slow enough, you can just take a thousand samples and average them; if the time period you do this over is comfortably longer than the period of any noise, you cancel it out. (Oversampling like that is a good idea anyway if you use the internal ESP32 ADCs; they're a bit noisy.)

Why do you have the rectifier in series with the capacitor on the output of the regulator?

D1 and D2 should be removed and shorted out. Leaving those diodes will likely cause instability in the output of the linear regulators.

a Linear Reg works at 12V and if the PCB is large enough to cool.
this is a Automotive one from Infineon.

for 24V this is not recommended.
for Traktor it is 12V, so no issue.

Thanks,
Franz