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Old 31st October 2013, 01:10 PM   #1
gtrmkr is offline gtrmkr  United States
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Default Power supply question:twin choke input?

Hello,

I was scrounging through my junk box yesterday looking for power supply parts and, not finding chokes with a high enough current rating for my intended application, got to wondering ...

I know that placing a choke in both the positive and negative legs in a full-wave bridge, cap input supply works.

Will it work with a full-wave, choke input arrangement?

In either case, how is the load current distributed between the two chokes?

I've attached a crude schematic of the latter case for reference.

Thanks very much!
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Old 31st October 2013, 04:10 PM   #2
DF96 is offline DF96  England
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Each choke carries the full load current, but only half the AC voltage swing. OK for chokes which are beefy enough for the current but can't cope with the voltage. The opposite of what you need?
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Old 31st October 2013, 04:26 PM   #3
gtrmkr is offline gtrmkr  United States
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Thanks. That's what I suspected, and yes, opposite of what I need.

I did find a swinging choke with a current rating large enough (2H-12H @ 300ma) but am unsure if it's appropriate to use for a choke input, class A circuit. I think not ... correct?
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Old 31st October 2013, 04:54 PM   #4
rongon is offline rongon  United States
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Shouldn't it be possible to parallel a pair of chokes to get half the value in Henries, but at twice the current capacity?

For example, if I had two 7H 150mA (140 ohms DCR) chokes, and I wire the pair of them in parallel, wouldn't that work the same as a single 3.5H 300mA (70 ohms DCR) choke?

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Old 31st October 2013, 05:39 PM   #5
gtrmkr is offline gtrmkr  United States
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Both chokes are from the same manufacturer and within a couple Ohms DCR, so that should work fine, and what I will likely wind up doing. Thanks for the suggestion.

Is there a reasonably simple way to guesstimate the inductance of a swinging choke at a particular current?

Thanks again. I really appreciate the info.
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Old 31st October 2013, 06:41 PM   #6
DF96 is offline DF96  England
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Swinging chokes are commonly used for choke input supplies. Your best bet is to rig it up and measure it e.g. see how output voltage varies with load.
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Old 1st November 2013, 09:25 PM   #7
gtrmkr is offline gtrmkr  United States
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Thanks. Will do ... My weekend project!
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Old 2nd November 2013, 08:52 AM   #8
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Hi!

Quote:
Originally Posted by rongon View Post
Shouldn't it be possible to parallel a pair of chokes to get half the value in Henries, but at twice the current capacity?
Yes you can do that

Thomas
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Old 2nd November 2013, 08:54 AM   #9
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Hi!

Quote:
Originally Posted by gtrmkr View Post
I did find a swinging choke with a current rating large enough (2H-12H @ 300ma) but am unsure if it's appropriate to use for a choke input, class A circuit. I think not ... correct?
Yes, swinging chokes are meant for choke input duty. I don't have much experience with swinging chokes. As far as I understand they might be mechanically noisy (buzzing) since they are driven into saturation.

You can try and see if they work for you

Thomas
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