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Inrush current into ACDC power module?

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cupoftea

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This concerns TUNS500F 500W ACDC power supply (100-265VAC).

Pg 7 (top) of this...

....is calling for a 4.7-22 Ohm inrush resistor into the PFC output caps of this ACDC module (TUNS500F). The page also calls for PFC output capacitance of 390uF to 2200uF.
Do you know where this inrush resistor is getting connected?, since if in series with the AC input, we are talking inursh resistor dissipation of 88-415W at max power, 115VAC input.
If its not in the power path, then how is it doing proper inrush limitation? (no internal relay is mentioned)

TUNS500F datasheet (page 8)
 

Hi,
Do you know where this inrush resistor is getting connected?
There are two optioons for inrush current limiting:
* a thermistor in series with the mains input (named "TH1" in Fig. 2.1 on page "TUNS-20")
* use of an external resistor connected between pin "R" and pin "+BC" (named "TFR1" in Fig. 1.1 on page "TUNS-23" and Fig. 2.1 on page "TUNS-24" and other figures)

sadly the datasheet has two times "Fig. 2.1"

Klaus
 
use of an external resistor connected between pin "R" and pin "+BC" (named "TFR1" in Fig. 1.1 on page "TUNS-23" and Fig. 2.1 on page "TUNS-24" and other figures)
Thanks KlausST, the relay shown there is in series with the inrush resistor....as you know, this is very odd, usually an inrush resistor shorts out the inrush resistor and is in parallel with it....so i am wondering how they have connected this resistor/relay combo into the SMPS itself?

I suspect that the "R" connection is the DC positive output of the mains Rectifier...and the "B+" connection is of course the pos terminal of the PFC output caps....as you know, such a connection gives totally insufficient inrush current limiting....as the attached LTspice sim and PDF schem clearly shows...
 

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  • Boost PFC inrush.zip
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Last edited:

I see no relay...
..woops yes, its not a relay, its an inrush resistor with internal thermal disconnect.
Anyway, i assume there is a relay inside the module which switches out this inrush resistor? (ie shorts it out)

Why dont they give the details of this relay? (if it even exists), eg the time after switch ON when the realy operates?
 

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