DIY 22uH Choke using Torroid Core?

[Charmed Snark]

If I have a junk box of smallish (1/2 inch dia say)
torroid cores, of some unknown T-#, how many
turns of wire should I guestimate for a >= 22 uH
choke (for use with a MAX762 switching supply)?

I know you can't give a precise answer to that,
with that information, but I just need a
ballpark answer.

I simply need to exceed 22 uH for this
junk-box application. I am guessing, that it
is going to be somewhere in the ballpark of
30 to 50 turns.

Comments, besides suggesting that I order a choke?

The only other idea I had was perhaps paralleling
that with some suitable cap and trying to find
resonance with my grid dip meter. But that sounds
too much like work. ;-)

Warren.

 

[Rich Webb]

If I have a junk box of smallish (1/2 inch dia say)
torroid cores, of some unknown T-#, how many
turns of wire should I guestimate for a >= 22 uH
choke (for use with a MAX762 switching supply)?

I know you can't give a precise answer to that,
with that information, but I just need a
ballpark answer.

Hop on over to http://www.dl5swb.de/html/software_for_amateur_radio.htm
and download their free ring-core calculator. Not much help if you don't
know the material, though it does show color codes for iron powder.

I simply need to exceed 22 uH for this
junk-box application. I am guessing, that it
is going to be somewhere in the ballpark of
30 to 50 turns.

Comments, besides suggesting that I order a choke?

The only other idea I had was perhaps paralleling
that with some suitable cap and trying to find
resonance with my grid dip meter. But that sounds
too much like work. ;-)

Depends on what test equipment you've got handy; I'm guessing not an LCR
meter. But with sine wave source, some resistors, and a DMM you should
be able to get pretty close to the 3 dB-down point for an LR filter by
adjusting the frequency or resistance, or both.

 

[DJ Delorie]

http://en.wikipedia.org/wiki/Inductor has formulas for calculating
inductance from turns, area, etc, near the bottom of the page.

Wild guess (I don't know the length of your core or it's K factor) is
42 turns.

 

[Charmed Snark]

Rich Webb expounded in

Hop on over to http://www.dl5swb.de/html/software_for_amateur_radio.htm
and download their free ring-core calculator. Not much help if you don't
know the material, though it does show color codes for iron powder.

Hey, that is perfect, thanks.

Between the dimension information and the colours, I think I have what I
need.

Warren

Depends on what test equipment you've got handy; I'm guessing not an LCR
meter.

No. A grid dip meter is a coil+meter unit brought close to a tuned
circuit. By sweeping frequency, you can find where the "dip" occurs (hence
resonance). If you know C and f, you can determine L. But the software
approach above, is more to my liking as a starting point at least.

But with sine wave source, some resistors, and a DMM you should
be able to get pretty close to the 3 dB-down point for an LR filter by
adjusting the frequency or resistance, or both.

Ya, I should try that out and see how close I got.

Warren.

 

[Phil Allison]

"Charmed Snark"

If I have a junk box of smallish (1/2 inch dia say)
torroid cores, of some unknown T-#, how many
turns of wire should I guestimate for a >= 22 uH
choke (for use with a MAX762 switching supply)?

** The choke for use with a DC-DC converter had to pass DC current - so any
old ferrite ring with a few turns on it will NOT do.

Cos it will saturate the core.

I simply need to exceed 22 uH for this
junk-box application.

** No - you need a choke that can pass up to 1 amp without core saturation.

Read the section on "Selecting the Inductor L " in the data sheet.

I am guessing, that it
is going to be somewhere in the ballpark of
30 to 50 turns.

Comments, besides suggesting that I order a choke?

** Piss off.


....... Phil

 

[Charmed Snark]

Phil Allison expounded in

** The choke for use with a DC-DC converter had to pass DC current -
so any old ferrite ring with a few turns on it will NOT do.

Cos it will saturate the core.


** No - you need a choke that can pass up to 1 amp without core
saturation.

Read the section on "Selecting the Inductor L " in the data sheet.

But the output of what I have in mind is < 1 amp.

 

[Phil Allison]

"Charmed Snark"

Phil Allison


But the output of what I have in mind is < 1 amp.

** So he still has not read the data sheet.

Must be out of his mind.


.... Phil

 

[Eeyore]

If I have a junk box of smallish (1/2 inch dia say)
torroid cores, of some unknown T-#, how many
turns of wire should I guestimate for a >= 22 uH
choke (for use with a MAX762 switching supply)?

I know you can't give a precise answer to that,
with that information, but I just need a
ballpark answer.

Not possible. Note the use of the word 'unknown' !

Graham

 

[Eeyore]

Hop on over to http://www.dl5swb.de/html/software_for_amateur_radio.htm
and download their free ring-core calculator. Not much help if you don't
know the material, though it does show color codes for iron powder.

Conceivably this may help. Identify the core and it'll calculate it for you.

http://www.micrometals.com/

Graham

 

[Eeyore]

Hop on over to http://www.dl5swb.de/html/software_for_amateur_radio.htm
and download their free ring-core calculator. Not much help if you don't
know the material, though it does show color codes for iron powder.

http://www.micrometals.com/software_index.html

Graham

 

[Charmed Snark]

Phil Allison expounded in

"Charmed Snark"


** So he still has not read the data sheet.

Must be out of his mind.

... Phil

That's right. You're taking this way too seriously.

 

[Phil Allison]

"Charmed Snark"

That's right.

** **** off - IMBECILE.



... Phil

 

[Charmed Snark]

Phil Allison expounded in

"Charmed Snark"


** **** off - IMBECILE.

.. Phil

I'm not the one with the "problem". <snicker>