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staric
Joined: 26 Sep 2003
Posts: 80
Helped: 1
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 07 Aug 2005 2:31 inrush current calculation |
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| I don't know whether the inrush current can be calculated and how to calculate.
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Btrend
Joined: 26 Dec 2003
Posts: 424
Helped: 55
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09 Aug 2005 11:29 calculate inrush current |
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inrush current estimation:
assumption: Vin apply to C with Resr only, can view as a simple R+C network.
i(t)=(V-Vc)/Resr
Vc(t)=V(1-exp(-t/τ)), where τ=Resr*C
===> i(t)=V/Resr*exp(-t/τ)
===> i_inrush= i_max=lim_t->0 i(t)=V/Resr
usually Resr is small, (e.g. 50m ohm)
if V=5V, Resr=50m, then i_inrush=5/50m=100 A
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09 Aug 2005 11:29 Ads |
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babbage
Joined: 15 Aug 2005
Posts: 38
Helped: 5
Location: China
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17 Aug 2005 14:21 calculating inrush current |
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I think this equation is too simple, and it doesn't the real case.
I don't know this question yet, but if the inrush current from this equation is too far from the real one, then that is no use for designer. OK?
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scottieman
Joined: 08 Aug 2005
Posts: 134
Helped: 11
Location: On Top of Silicon
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17 Aug 2005 17:29 how to calculate inrush current |
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| staric wrote: |
| I don't know whether the inrush current can be calculated and how to calculate. |
I assume a non-isolated buck converter. During start-up, the PWM signal can be assumed to be 100% (in real case, it may be 95% only). Therefore, looking from the input of the buck converter, there is a inductor, a resistor (the on-resistance of MOS switch) and a output capacitor connected in series. From this model, you can solve the differential equation and get the maximum inrush current quring start-up.
Scottie
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Btrend
Joined: 26 Dec 2003
Posts: 424
Helped: 55
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19 Aug 2005 9:04 capacitor inrush current calculation |
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| babbage wrote: |
I think this equation is too simple, and it doesn't the real case.
I don't know this question yet, but if the inrush current from this equation is too far from the real one, then that is no use for designer. OK? |
u can refer to section 10.5.2.1 in this book
http://www.edaboard.com/viewtopic.php?t=61948&highlight=power+electronics
or I had snapshotted it.
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