Electronics > Beginners
Understanding circuit for inrush current limiting
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AngraMelo:
Hey guys,
Im building a couple of linear PS and they are fairly beefy, both around 300W.
The capacitor bank is also pretty  hefty so ill need a inrush current limiting.

On the Texas Instruments website they have the attached circuit but I do not understand it.

The position of that zener holding the 12V point but at the same time tied to ground doesnt make sense to me. Also the way contacts 1 and 3 of the relay are tied up together seems very weird.
Im not criticizing the circuit I just dont understand it.

So why is diode 103 there? Wouldnt it be simpler to have the anode of the tied to ground (with a current limiting resistor)?
Can someone help me with this, please?

https://e2e.ti.com/blogs_/b/powerhouse/archive/2015/03/31/powertips-how-to-limit-inrush-current-in-an-ac-dc-power-supply
AngraMelo:
So this is my case:
I have a transformer that is rated at 25A and has 21V on the secondary. It has 30,000uF capacitor bank.
So the inrush current would be Vrms minus the diodo drops and that divided by my series resistance right?
Then we get 30V - 2V divided by 82R/10W resulting inrush a current of around 340mA. Now, I used that value because thats what I have for 10W resistors. Will that be enough? If I use the circuit above and after a couple seconds trigger the relay and bypass the resistors wont I have a huge current dump?
Or should I use a lower value like a 10R/10W (that I also have laying around) and use a 555 to wait one sec and then trigger the relay and ignore the power on the resistor given that it is just for 1 second?
That would give me still only 2.8A of inrush current and Im not convinced that bypassing the 10R resistor after one second wont give me a huge current spike.
Benta:
As it is not apparent what "GND2" and "12V2" is, impossible to say. More info is needed to answer your question.
AngraMelo:

--- Quote from: Benta on December 19, 2018, 06:36:55 pm ---As it is not apparent what "GND2" and "12V2" is, impossible to say. More info is needed to answer your question.

--- End quote ---

I cant, that is all it is provided on an article title"Power Tips: How to limit inrush current in an AC/DC power supply"

The link is here

https://e2e.ti.com/blogs_/b/powerhouse/archive/2015/03/31/powertips-how-to-limit-inrush-current-in-an-ac-dc-power-supply
AngraMelo:
But that is fine, I think the main idea of the circuit is to bypass the resistor after some time has passed and some current has raised the voltage of the caps.
So what am I searching for here? Is there a specific current that I should let pass or a minimum voltage for the caps to reach?
What is the science here?
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