Linear Regulator - reverse voltage protection

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Wolframore

Joined Jan 21, 2019
1,797
Did some research thought I would share:

I know it's good practice to put reverse voltage protection diode on your regulator.. but is it always required?

According to Infineon if there is a PNP pass transistor it would limit the reverse current and therefore not always needed. if you can dissipate the heat and working at lower voltages you might be ok without reverse protection. Remember that thermal protection will not work in reverse polarity situations.
https://www.infineon.com/cms/en/product/promopages/aim-mc/Selecting-a-linear-voltage-regulator/Voltage-Regulator-Reverse-Polarity.html

For this AZ1117 5V - it looks like there is an NPN pass transistor and needs some sort of reverse polarity protection such as a diode, polarized connectors or permanent wiring that won't allow this to happen or risk being toast...
https://static6.arrow.com/aropdfconversion/82d5a41dde8764b091e2d8c0ea5ee766f168f1d/az1117c.pdf

Block Diagram
upload_2019-4-25_8-31-40.png
 

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crutschow

Joined Mar 14, 2008
25,460
I know it's good practice to put reverse voltage protection diode on your regulator.. but is it always required?
It depends on what conditions may cause the reverse voltage.
If the power is just removed from the input with no other input load, then the load on the output will simply drain the voltage from the input and nothing ever gets reversed biased.
If there is another load on the input that pulls the input rapidly low, before the output can follow, then you need reverse protection.
 

ian field

Joined Oct 27, 2012
6,539
It depends on what conditions may cause the reverse voltage.
If the power is just removed from the input with no other input load, then the load on the output will simply drain the voltage from the input and nothing ever gets reversed biased.
If there is another load on the input that pulls the input rapidly low, before the output can follow, then you need reverse protection.
I'd hang a reverse flow diode across it regardless - there's always the unexpected.
 
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