A low pemeability toroidal core is the easiest solution since this requires neither gapping nor special interference precautions (well, laying the core down on top of a ground plane is never wrong). If you go for a gapped RM-core (I use an RM-12 with 1.35mm center leg gap) you better make sure you keep the sensitive parts of your electronics perpendicular to the magnetic flux leakage since RM-cores radiate when gapped.
A 3mm gap is huge! Normally the biggest gap, even if it is only in the middle leg is only up to 1.5mm or so.
For example, an RM10 core using 3C91 ferrite has an AL of 160nH with a 0.98mm gap in the centre lag only; an AL of 630nH with an air gap of 0.19mm; and with no gap the AL is 1550nH.
The lower the AL, the more turns needed for a particular inductance, but also the more current it can take without saturating.
The best bet is for you to download the Ferroxcube data book (it's 6.5 meg bytes) called 'Soft Ferrites and accessories'. It's got everything in there you'll need to know.
For example, an RM10 core using 3C91 ferrite has an AL of 160nH with a 0.98mm gap in the centre lag only; an AL of 630nH with an air gap of 0.19mm; and with no gap the AL is 1550nH.
The lower the AL, the more turns needed for a particular inductance, but also the more current it can take without saturating.
The best bet is for you to download the Ferroxcube data book (it's 6.5 meg bytes) called 'Soft Ferrites and accessories'. It's got everything in there you'll need to know.
Hi, Zilog,
Thanks for the advice. There are some things that are not clear to me.
- toroidal core has less flux leakage than RM cores? (that can radiate)? If I see a toroidal core, I can see the wires, and when I see RM cores, I can see only small part of the wires (most of the wires are blocked by the ferrites). How come toroidal core has less flux radiation?
-
-
Thanks for the advice. There are some things that are not clear to me.
- toroidal core has less flux leakage than RM cores? (that can radiate)? If I see a toroidal core, I can see the wires, and when I see RM cores, I can see only small part of the wires (most of the wires are blocked by the ferrites). How come toroidal core has less flux radiation?
-
How to place toroidal in PCB? Like in this photograph, I call it horizontal (towards the surface). Or is it should be vertical (like IRaudAmp or Fumac's toroid)?
-
I think this is important, but I don't understand at what direction the flux is leaking. Do you have a simple drawing explaining the direction of flux leakage relative to RM core gap?
Attachments
The pictures here -> http://gnuffel.googlepages.com/pictures depict my placement of the core/pcbs, the small vertical pcb carries the modulator while the large board only houses mosfets/drivers and protection.
I might be in over my head here, but I think that the wires on a toroid couple capacitively to the resistive core, and cause a current to circulate inside the core, thus radiating both perpendicular from the toroidal plane AND tangentially from the leakage field caused by the leagage inductance from the windings, thus radiating in all directions. Placing the toroid as you showed over a ground plane will help reduce the field at least in one direction.
A RM-core should radiate less than a toroid, but when you add a gap, the magnetic field is no longer confined to the core material as you use air to strore magnetic energy, and as magnetic flux lines repell each other, you have leakage from the magnetic flux in the center leg gap. This poses no problem as long as you know how to deal with this.
I might be in over my head here, but I think that the wires on a toroid couple capacitively to the resistive core, and cause a current to circulate inside the core, thus radiating both perpendicular from the toroidal plane AND tangentially from the leakage field caused by the leagage inductance from the windings, thus radiating in all directions. Placing the toroid as you showed over a ground plane will help reduce the field at least in one direction.
A RM-core should radiate less than a toroid, but when you add a gap, the magnetic field is no longer confined to the core material as you use air to strore magnetic energy, and as magnetic flux lines repell each other, you have leakage from the magnetic flux in the center leg gap. This poses no problem as long as you know how to deal with this.
Lumanaw,
This link: http://focus.ti.com/lit/ml/slup105/slup105.pdf must have what you want.
Best regards,
This link: http://focus.ti.com/lit/ml/slup105/slup105.pdf must have what you want.
Best regards,
I havent made any measurements to prove this statement, but I recall the output ripple voltage being higher when using a toroid in the output filter of my last UcD prototype (at the same frequency) than it is with my current RM-12 core. That should indicate lower parasitic capacitance of the output coil.
I have also somehow got rid of HF spikes riding on the output.
I have also somehow got rid of HF spikes riding on the output.
hey....
my 1st ever working diy UCD... just the modu + mosfet drivers... no input buffers/ protections... and the horrible filter COIL....
ahhhh the good 'ol days.....
An externally hosted image should be here but it was not working when we last tested it.
my 1st ever working diy UCD... just the modu + mosfet drivers... no input buffers/ protections... and the horrible filter COIL....
ahhhh the good 'ol days.....
Hi, Zilog,
So it is better only make 1 totem pole for all parrareled mosfets?
I'm thinking about 3pcs of IRFP250N. This device is hard to turn-off.
Do you have any trick or totem pole design trick that with only 1 totem pole can drive these 3 parrareled mosfets properly switching about 500khz?
So it is better only make 1 totem pole for all parrareled mosfets?
I'm thinking about 3pcs of IRFP250N. This device is hard to turn-off.
Do you have any trick or totem pole design trick that with only 1 totem pole can drive these 3 parrareled mosfets properly switching about 500khz?
lumanauw said:
I didnt mean that the totem pole driver must consist of one pair only, I meant that you should drive the paralleled mosfets as if they were one monolith. Im sorry but I dont know of any fast driver for that combination straight from my head as I have invested money in easy to drive mosfets instead. I guess BD139/BD140 or BC639/BC640 would do a nice totem pole buffer since they handle a bit of Ic with sustained hfe.
R14-R15
Back again to R14-R15.
http://www.diyaudio.com/forums/showthread.php?postid=431959#post431959
What is the mechanism, that putting R from rail to inverting input is actually improve (not worsen) the PSRR?
Back again to R14-R15.
http://www.diyaudio.com/forums/showthread.php?postid=431959#post431959
What is the mechanism, that putting R from rail to inverting input is actually improve (not worsen) the PSRR?
Re: R14-R15
I'd like to know that too - and why R14 and R15 have different values on the Philips circuit, if the supply rails are the same?
Also, do you still need them if the input and feedback are differential?
I've not been able to find any reference to the detail of the mechanism in any of the UCD threads I've read - although I must confess to not having read them all - I did read all 2000+ posts in the Ucd180 questions thread though -- I obviously need to get out more!
lumanauw said:
I'd like to know that too - and why R14 and R15 have different values on the Philips circuit, if the supply rails are the same?
Also, do you still need them if the input and feedback are differential?
I've not been able to find any reference to the detail of the mechanism in any of the UCD threads I've read - although I must confess to not having read them all - I did read all 2000+ posts in the Ucd180 questions thread though -- I obviously need to get out more!
Hi, Rogs,
From the above link :
What I don't understand is the mechanism of putting resistors there. In a glance, putting resistors from rails to differential base will worsen the PSRR, not making it better. What is the mechanism?
From the above link :
The values are different, maybe it is because +rail and -rail PSRR are different?
What I don't understand is the mechanism of putting resistors there. In a glance, putting resistors from rails to differential base will worsen the PSRR, not making it better. What is the mechanism?
Hi, Fumac,
I found something strange. I've readjust the tracks following your drawing, thanks
Now I can use 10R gate resistors without blowing the mosfets at high volume.
But I can only do this with 200V mosfets, IRF630 and IRF640, they are fine.
But when I put 100V mosfets, IRF530, IRF540, FDP3672, they all blow in a few second.
The rails +/-45V.
What is making all the 100V mosfets blown away?
I found something strange. I've readjust the tracks following your drawing, thanks
Now I can use 10R gate resistors without blowing the mosfets at high volume.
But I can only do this with 200V mosfets, IRF630 and IRF640, they are fine.
But when I put 100V mosfets, IRF530, IRF540, FDP3672, they all blow in a few second.
The rails +/-45V.
What is making all the 100V mosfets blown away?
lumanauw said:Hi, Fumac,
I found something strange. I've readjust the tracks following your drawing, thanks
Now I can use 10R gate resistors without blowing the mosfets at high volume.
But I can only do this with 200V mosfets, IRF630 and IRF640, they are fine.
But when I put 100V mosfets, IRF530, IRF540, FDP3672, they all blow in a few second.
The rails +/-45V.
What is making all the 100V mosfets blown away?
20% is the best design, (100V -20%)/2=40v even 38V is the good chioce. 
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