100 ohm resistor between 24V and 0V?

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naughtyTed2020-12-30 14:57:33

Electronics

naughtyTed, 2020-12-30 14:57:33

I studied the power circuit on the board of a purchased active USB hub. Powered by an external power supply unit 24V. Then there is a converter to 5V and then these 5 V diverge across the board. I am attaching the diagram.
Question - why is there a 100-ohm resistor directly parallel to the input? Its size is 0805, why hasn't it burned out yet?

UPD: Added a photo of the board. The resistor in question is R168. One of its outputs through a 0 Ohm resistor R165 goes to the power circuit, its other output rings with the ground (the photo shows that it is connected to the side output of the input connector - a standard coaxial power connector 2.5x5.5). The microcircuit in the photo is SC4525ESETRT.

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4 answer(s)

V

VT100, 2020-12-30
@naughtyTed

It seems to me that it is necessary to check the connection of the third contact of the connector used to switch "battery-network":
https://static.chipdip.ru/lib/507/DOC001507919.pdf
Discharging the input capacitor when the power is turned off.

A

Alexander Gusev, 2020-12-30
@Sanchogus

So this is not a 100 ohm resistor, but someone intended some garbage. Attach a photo of the patient.
Or at least it's turned on wrong.

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VkolV, 2020-12-30
@VkolV

Even this bothers me

between 24V and 0V

: )
Is the scheme correct?

O

oslikia, 2020-12-30
@oslikia

Couldn't this resistor be connected in series with the zener diode?
Then you get a parametric stabilizer.
Well, if the green F1 is PPTC, then no, this is a self-resetting fuse F1.