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Old 4th May 2004, 08:48 PM   #1
haldor is offline haldor  United States
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Default Inrush Current Limiting Circuit

I found this passive inrush current limiting circuit in a back issue of EDN and thought somebody might be interested in it.

http://www.reed-electronics.com/ednm...es/92602di.pdf

What's interesting to me about this circuit is that it doesn't require a timer (it automatically switches out once the cap has reached a certain charge voltage) plus the relay contacts don't carry the full supply current (just the capacitor currents). Another benefit of this circuit is that it automatically bleeds off voltage from the caps without seperate bleeder resistors constantly wasting power and generating heat any time the amp is in use.

Phil
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Old 4th May 2004, 10:49 PM   #2
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I'd be interested but there was a size mismatch error when I downloaded. Besides, the file size is way to big for the small schematic and text needed to explain the circuit. Did you create this file yourself out of a super high resolution scanned page?
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Old 4th May 2004, 10:51 PM   #3
Magura is offline Magura  Denmark
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It worked fine for me 10 min ago.

Magura
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Old 5th May 2004, 01:08 AM   #4
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Here's a circuit from Promitheus that also does not require a timer and the relay contacts are on the primary side so the currents are much lower (deepending on the secondary voltage).
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Old 5th May 2004, 01:10 AM   #5
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Hi,

Quote:
Besides, the file size is way to big for the small schematic and text needed to explain the circuit.
It's a series of articles on design ideas, that's why it's so big.

Download it, it don't bite...

Cheers,
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Old 5th May 2004, 01:15 AM   #6
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Quote:
Originally posted by Bill Fitzpatrick
I'd be interested but there was a size mismatch error when I downloaded. Besides, the file size is way to big for the small schematic and text needed to explain the circuit.
Broad Band
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Old 5th May 2004, 03:04 AM   #7
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Quote:
Originally posted by roddyama

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Old 5th May 2004, 03:24 AM   #8
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Quote:
Originally posted by Bill Fitzpatrick


Is that the name of an all girl rock group?
No, it's 5-6-7-8
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Old 5th May 2004, 04:56 AM   #9
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Default Re: Inrush Current Limiting Circuit

Quote:
Originally posted by haldor
I found this passive inrush current limiting circuit in a back issue of EDN and thought somebody might be interested in it.

http://www.reed-electronics.com/ednm...es/92602di.pdf

What's interesting to me about this circuit is that it doesn't require a timer (it automatically switches out once the cap has reached a certain charge voltage) plus the relay contacts don't carry the full supply current (just the capacitor currents). Another benefit of this circuit is that it automatically bleeds off voltage from the caps without seperate bleeder resistors constantly wasting power and generating heat any time the amp is in use.

Phil
One disadvantage I see is that both the load ripple current and the cap charging ripple current (in normal operations) go through the switch contact. These currents will be less than the initial inrush current, but they may be high enough to be aware of when selecting the relay.

Jan Didden
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Old 5th May 2004, 06:41 AM   #10
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Default Re: Inrush Current Limiting Circuit

Quote:
Originally posted by haldor
I found this passive inrush current limiting circuit in a back issue of EDN and thought somebody might be interested in it.

http://www.reed-electronics.com/ednm...es/92602di.pdf

What's interesting to me about this circuit is that it doesn't require a timer (it automatically switches out once the cap has reached a certain charge voltage) plus the relay contacts don't carry the full supply current (just the capacitor currents). Another benefit of this circuit is that it automatically bleeds off voltage from the caps without seperate bleeder resistors constantly wasting power and generating heat any time the amp is in use.
I have tested ideas like that but you don't need them, unless, you have rather weak diodes and HUGE capacitors.

Normally you only want to save fuses and be able to have "normal" primary fuses and for this the circuit above has the disadvantage of long reset time. I think an electronical device with a < 1 sec delay is better and it works with prediction. What happens if you have short power interrupts? = burned fuses!
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