EEVblog #1104 - Omicron Labs Bode 100 Teardown

[sorin]

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?

Please can you post a photo of your final product

[Jay_Diddy_B]

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 mu_r 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]

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]

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

[jmw]

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]

Hi Jay_Diddy_B, I repeated the test to your procedure:

(Attachment Link)

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

[Roland_W]

Hi, All,

I read the all about the Injection Transformer.

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.

[MilkmanCDN]

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?

Hey there.    Are you sure you bought the L2040?  There are a few posts on this thread stating that the L2030 is the transformer used in the BWIT-100.    I first purchased the L2030 and had the same problem as you (I could only get about 29-30 turns around the thing).   It was then that I realized that the L2040 is a larger core and in fact the one used in the BWIT-100, which will accommodate the required 40 turns.

See reply #216 in the thread for details.   I've since purchased a used Bode100 and verified performance of the transformer (which is identical to the original).

[jmw]

I bought it from Mouser, and part # from the order history checks out, but there is the small chance they did a bad pick. I'll make a note to check the dimensions on it tomorrow at the lab, and the datasheet for T60006-L2040-W424 says it is 40 mm OD / 25 mm ID.