Hi, I bought this module for my RPi Hat to provide power to RPi 5V rail.
Im using this with 24VDC PSU and it works well. 24VDC from connector has inditcator led, and some 100uF capacitor.
Strange thing happens when I do not have 24VDC connected, instead I power RPi from USB connector. Extremely Bright LED at 24VDC input brought my attention to this, and I measured 67 Volts DC at module inputs. Its not excatly floating, loaded by 22k and green LED.
Somehow my 35VDC cap is not blowing up. Somehow D36V28F5 is surviving all that and i can even hot-swap power source and it will still work… but what is going on? I’d understand that it can maybe backfeed 5V to the inputs but somehow it manages to pump that voltage up to 67V… Im not familiar with D36V28F5 application note, but this is very strange behavior.
Also, I used 2 separate meters to check this, because I started doubting brymen…
Any clues?
Hello.
Unfortunately, seems like that behavior is a characteristic of the particular regulator IC used on this the D36V28Fx boards. We tested a unit here by applying slightly over 5V to VOUT and saw similar results; it would generate high voltages (over 60V) on VIN. So, if you decide to keep using this regulator, we recommend you avoid backfeeding power through VOUT such as by adding one of our ideal diode reverse voltage protectors between the regulator and your Raspberry Pi.
Alternatively, we also tested our similar D30V30F5 regulator, which handles backfed power much better. (Applying 5V to VOUT passed basically the same 5V to VIN, though we also observed that at 5.5V on VOUT, VIN jumps to around 11V.) If you are interested in either of those solutions, please email us with your order information and a reference to this thread, and we can probably help you out with a discount.
- Patrick
Thanks for checking!
I’ll continue to use it as is as I designed this thing to run from 24V DIN PSU not to be used with USB adapters, so should not be an issue.
For the sake of electrolytic cap safety I decided to put resistor to ground which clamps the voltage, I just hope that IC itself survives that long term.
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