### Author Topic: EEVblog #1104 - Omicron Labs Bode 100 Teardown  (Read 43205 times)

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#### sorin

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##### Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
« Reply #275 on: April 20, 2020, 12:21:46 pm »
We have tested a different option and found that two huge chinese MnZn cores (search for "Cores Green 75mm x 39mm x 13mm") stacked on top of each other and afterwards wound in a similar fashion (not in the number of turns, but in terms of covering the core with windings, style of twisted wire and connection) to the Bode 100 transformer gives the attatched result. Seems like a lot of wideband transformer for about 10€ for the cores. The much increased volume of core material might also help with saturation?

#### Jay_Diddy_B

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##### Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
« Reply #276 on: April 21, 2020, 02:29:05 pm »
We have tested a different option and found that two huge chinese MnZn cores (search for "Cores Green 75mm x 39mm x 13mm") stacked on top of each other and afterwards wound in a similar fashion (not in the number of turns, but in terms of covering the core with windings, style of twisted wire and connection) to the Bode 100 transformer gives the attatched result. Seems like a lot of wideband transformer for about 10€ for the cores. The much increased volume of core material might also help with saturation?

Hi,

Can you post a schematic showing how this transformer was measured?

If I calculate the inductance:

for one core:

Area = Thickness x (D - d)/2

Where
D= outside diameter = 75mm

d= inside diameter = 39mm

Thickness = 13mm

Area = 13 x (75-39) /2 = 234E-6 m2

Mean magnetic Path length

Pi x (D + d)/2 = PI x (75 +39) /2 = 180E-3

Assume that this core is a power grade of ferrite with a relative permeability of 2000.

AL= mu0 x mur x Area/length

AL = 4E-7 x Pi x 2000 x 234E-6 / 180E-3

= 3.28uH per turn2

Assume 50 turns

Lmag = 502 x 3.3uH

= 8mH

and two cores stacked would be 16mH

50 Ohm test circuit

The LF -3dB for this configuration is calculated

R1 // R2 = R

LF(-3db) = 1/(2 x Pi x L/R)

= 250 Hz

It just seems too good …

Regards,

Jay_Diddy_B

#### jmw

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##### Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
« Reply #277 on: April 28, 2020, 04:23:58 am »
I bought a VAC T60006-L2040-W424 and used a 23AWG pair from a plenum CAT6 cable. For the life of me, I could not get more than 29 turns on the core. Maybe the original uses 24AWG or something smaller?

I don't have a two-port VNA but I used the Bode function on my scope (with a 50 ohm feed-thru term on the sec. side). Flat and phase response below 5 deg until just below 1 MHz, good enough for my needs.

#### Jay_Diddy_B

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##### Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
« Reply #278 on: April 28, 2020, 12:36:26 pm »
Hi,

I suspect that you are not measuring the transformer correctly.

To test the transformer in a 50 environment you need to use the top circuit here:

I suspect that you are using the bottom one. In this configuration you should read -6dB in the flat portion.

If you use the bottom one you don't see the impact of the magnetizing inductance.

Regards,
Jay_Diddy_B

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#### jmw

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##### Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
« Reply #279 on: April 28, 2020, 09:33:25 pm »
Hi Jay_Diddy_B, I repeated the test to your procedure:

So it seems by 3 dB points it is good from 40 Hz - 2 MHz, and by 5° phase limit from 500 Hz - 200 kHz. Not spectacular by others' work, but still adequate for evaluating the feedback look on many switchers. I'm still puzzled on the turns count and why I'm topping out at 29 if people got 40 using 23 AWG... but my expectation is that more turns would help at the low frequency and not so much the high end.

#### Jay_Diddy_B

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##### Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
« Reply #280 on: April 28, 2020, 10:07:38 pm »
Hi Jay_Diddy_B, I repeated the test to your procedure:

So it seems by 3 dB points it is good from 40 Hz - 2 MHz, and by 5° phase limit from 500 Hz - 200 kHz. Not spectacular by others' work, but still adequate for evaluating the feedback look on many switchers. I'm still puzzled on the turns count and why I'm topping out at 29 if people got 40 using 23 AWG... but my expectation is that more turns would help at the low frequency and not so much the high end.

Hi,

40Hz means that the magnetizing inductance is about 100mH.

I am not sure that other people measured them correctly.

It is very useable.

Regards,
Jay_Diddy_B

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#### Roland_W

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##### Re: EEVblog #1104 - Omicron Labs Bode 100 Teardown
« Reply #281 on: July 01, 2020, 12:48:31 pm »
Hi, All,

I need one, and as Wolfgang I build one using the same core VAC T60006-L2030-W514 :
https://pl.mouser.com/ProductDetail/Vacuumschmelze/T60006-L2030-W514?qs=ePbE9GiMmvVKrWoTvqBaIQ==

I use a RJ45 cable twisted pair 10 m long.

I wind first layer and I measure using the Diligent Waveforms Analog Discovery 2 to measure frequency response.

I make first measurement when I done the first layer of the winding – orange one, second layer winding – blue one, and the third – yellow one.
More turns move lower the working frequency.
« Last Edit: July 03, 2020, 07:21:58 pm by Roland_W »

Smf