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Clarify "reverse-voltage protection"?

#1

Hi All,

I’m hoping this is a quick one. Can someone clarify what “reverse-voltage protection” is, on the Pololu 7.5V, 2.4A Step-Down Voltage Regulator D24V22F7?

Is that protection against a reverse polarity applied to the input, or protection against someone connecting an unspecified voltage (of an unspecified polarity) to VOUT & GND?

Thanks,

Greig.

#2

Hello Greig.

The reverse voltage protection on our products only protects against reverse polarity applied to the inputs. Connecting a voltage above the maximum operating voltage for the device in any polarity could damage it. For many devices, the reverse voltage protection will work up to at least the maximum operating voltage of that device, though please note that some products have a reduced maximum for reversed connections (this is called out on the web pages for these products).

For the product you linked to, the reverse voltage protection will protect the regulator if up to 36 V is connected with reverse polarity.

-Patrick

#3

Thanks for the prompt and detailed response Patrick.

Do you know if they have any protection against someone accidentally connecting the Vin supply to the Vout pin - or to put it another way, if the voltage on Vout should exceed Vin?

I’m guessing a power diode (1N4004 or similar) from Vout back to Vin would provide sufficient protection (if there’s none inherent)? That wouldn’t do anything to upset the switch-mode regulation would it (in both normal operation and this fault condition)?

I realise I can test this myself pretty easily, but I’d rather save the $10 and not generate unnecessary eWaste in the process.

Thanks,

G.

#4

Our regulators generally do not have protection for your VIN supply getting connected to the VOUT pin. There’s a lot more in play than just VOUT being greater than VIN. For instance, on the regulator you initially asked about, you can see there is a 10V rated capacitor on the output. If you connect some higher voltage to the output, you’re going to destroy that, regardless of if you manage to get VIN to be high, too.

There’s not an easy electrical way we know of for offering the kind of protection you are asking about. Perhaps you can do it mechanically, by using connectors that cannot be interchanged. If you can accept worse regulation, you could put a big diode on the output and not expose the regulator output directly, so the higher voltage could only be applied past the diode. That would waste power in the diode the whole time it’s in use, though, and the output voltage would vary depending on how much of a drop you get on the diode. Something like 1N4004 is not appropriate since it cannot handle enough current, and you would want a schottky diode with a lower forward voltage drop than a standard diode.

-Patrick

#5

Thanks Patrick. Awesome response again, even though you’ve killed my cunning protection plan.

We’ll be adopting at least one of your suggestions for our next iteration of PCB.

- G.