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Calculating inductance, Datasheet says AsubL =75 (nH)

I know and use the formulas for calculating turns on a core. For Ferrite cores N=1000 x sqrt of (your desired L (in mH) / AsubL (mH/1000turns) For Iron Cores N=100 x sqrt of (your desired L (in uH) / AsubL (uH/100)

Now I have a core that says AsubL is 75 (nH) Assuming that is 75nH for one turn, that is the same as For Ferrite cores N=1000 x sqrt of (your desired L (in mH) / AsubL (mH/1000turns)

That needs verification, an error her could explain my misunderstanding.

I'm having a problem relating that to an inductor used in an oscillator. From this article, >

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It says, "the VCO coil, which uses seven turns of 30 gauge wire on a Ferroxcube core (P/N: 135T050-4C4)"

P/N: 135T050-4C4 is a 1/2" toroid of 4C4 material.

The oscillator has a frequency range of 20MHz to 150MHz. What I don't understand is 30 turns on a AsubL 75(nH) core is 76.8 uH. I assume that is way to high for a 20MHz to 150MHz oscillator.

What have I missed?

A couple of somewhat educated leaps of faith I have made are the following. From 25 years ago, I know that 4C4 material was replaced with

4C6 material. And now searching data sheets I see 4C6 has been replaced by 4C65. So I'm assuming a 1/2" toroid of 4C65 which the datasheet says has AsubL if 75 (nH) is the same as a 1/2" core of 4C4. If it helps, 4C4 and 4C65 both have an Initial Permeability of 125.

I have not been able to find any datasheet of the original 4C4 and any catalogs I have with 4C4 do not include toroids.

Thanks, Mikek

Reply to
amdx
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No doubt the 30-turn spec is for a core with a gap, which greatly reduces A_L. Ungapped cores have very unstable A_L values.

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 Thanks, 
    - Win
Reply to
Winfield Hill

Good grief, what a mess. Just memorize L = A_l N^2. Express everything in SI base units and forget about all these factors of 1000.

Seven (not 30!) turns on this core gives 75nH * 7^2 = 3.5uH. That's still a lot for 150MHz, but probably manageable.

Jeroen Belleman

Reply to
Jeroen Belleman

It's a toroid! No mention of any gap. Mikek

Reply to
amdx

Probably iron powder, the gap is distributed. The Al value is normally pretty accurate on these 'gapped' low Al cores, so 30 turns should give

30*30* 75nH = 67.5uH which is a bit far out really. Maybe you misread 76.8uH as 67.8uH or you miscounted and wound 32 turns. 32*32*75nH = 76.8uH

Cheers

--
Clive
Reply to
Clive Arthur

Except most of the data books I have specify A_L in mH/1000 turns. Yes, I could multiply the databook A_l in mH/1000 value my 100,000,000 and use L = A_l N^2. It works probably easier.

Ah, that make a big difference although their cap is 3pf or 1.5pf I don't know if the variable caps are series in the LC circuit. Still 3.5uH and 1.5pf is... ya, never mind, they are adjusting L and C so I'm not sure what values are. 7 turns instead of 30 solved my dilemma. Also tells me I need a lot more turns for 100uh! (37 Turns)

Thank you for helping, Mikek

Reply to
amdx

Ya, mixed up some other calcs in with this thought.

The article as pointed out by Jeroen said 7 turns not 30. Mikek

Reply to
amdx

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