Transformer Snubbing

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Nick
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#1 Transformer Snubbing

Post by Nick »

I had a need to add some snubbers to the mosfet amp power supply. So I built up this very useful test rig

http://www.diyaudio.com/forums/power-su ... t-jig.html

It would have been silly to just get a single PCB made, so I have some spare blank boards. If anyone thinks they would make use of this, let me know and I will post one on. First come first served, etc.
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thomas
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#2 Re: Transformer Snubbing

Post by thomas »

Hi
If you have one spare after more ummm knowledgable folk have their share could I have one please?!
Thanks
T
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pre65
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#3 Re: Transformer Snubbing

Post by pre65 »

Hi Nick, I'm interested.
Last edited by pre65 on Tue Feb 21, 2017 1:09 pm, edited 1 time in total.
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#4 Re: Transformer Snubbing

Post by simon »

Yes please Nick
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#5 Re: Transformer Snubbing

Post by Nick »

pre65 wrote: Tue Feb 21, 2017 12:47 pm Hi Nick, I'm very interested, but would it be seen as greedy to ask for two ? :oops:

As you may know, my mosfet project is monoblocks.
Now I am certain you dont understand what the board if for.

If people PM me their address I will post them. Only a tiny board, so will fit in a letter envelope.

I got all the parts to populate it from RS, so I can post a parts list, but you will have to buy 5 of some parts that you only need 1 of, so maybe you could get together and spread the part cost out.
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#6 Re: Transformer Snubbing

Post by pre65 »

Nick wrote: Tue Feb 21, 2017 1:07 pm
pre65 wrote: Tue Feb 21, 2017 12:47 pm Hi Nick, I'm very interested, but would it be seen as greedy to ask for two ? :oops:

As you may know, my mosfet project is monoblocks.
Now I am certain you dont understand what the board if for.

If people PM me their address I will post them. Only a tiny board, so will fit in a letter envelope.

I got all the parts to populate it from RS, so I can post a parts list, but you will have to buy 5 of some parts that you only need 1 of, so maybe you could get together and spread the part cost out.
Sorry Nick, I was busy and had not read the explanatory posts. :oops: I have amended my previous post.
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#7 Re: Transformer Snubbing

Post by jack »

In Linear Audio, Volume 5, Morgan Jones did a great article all about rectifier ringing and snubbing - it's extremely rigorous - far more so that his high-level maths in "Valve Amplifiers" etc. A consequence of that is that for a while now, I always snub my PSUs - it's easy and removes almost all the ringing & switching crap from the diodes in the bridge.

Whilst the article needs a subscription if you want to read it, the follow on correspondence is public domain and quite interesting: https://linearaudio.net/sites/linearaud ... J%20V5.pdf

Abstract:
Morgan Jones Look inside almost any piece of commercial equipment having a linear power supply and you will find small capacitors across the rectifier diodes. Those capacitors are there to prevent the combination of mains transformer leakage inductance and diode capacitance from ringing when the diode switches off. But would ringing really occur, and if snubbers do work, how well do they work? To answer these questions, Morgan Jones first investigates transformer leakage inductance, then focusses on semiconductor diode capacitance and finally comes up with a surprisingly simple and effective snubbing method .

Mark Johnson, who wrote the post Nick references, published his results in Linear Audio, Volume 10:

In linear power supplies with solid state rectifiers, the diode switch-off transient generates a current rate-of-change, dI/dt; excellent diodes generate small dI/dt and poor diodes generate large dI/dt. When dI/dt is large, it produces substantial voltage spikes across the leakage inductance of the transformer secondary (V = L*dI/dt). These voltage spikes stimulate the secondary RLC resonant circuit into oscillatory ringing, wich in turn can have a detrimental effect on the audio quality.

In this article Mark Johnson presents measured data on power transformer secondary ringing, produced by 48 different semiconductor diodes. Diode performance is tabulated to facilitate selection for a particular purpose. A design procedure and equations are given for a secondary snubber that eliminates almost all ringing effects.


As I've probably rambled on about before, I love Linear Audio. Great read.
Last edited by jack on Tue Feb 21, 2017 5:43 pm, edited 2 times in total.
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#8 Re: Transformer Snubbing

Post by Nick »

As I've probably rambled on about before, I love Linear Audio. Great read.
Yes, this board is a simple way of finding the optimum resistor value for exactly the CRC snubber that Morgan talks about in that article. (and shows is better than caps across the diodes, which I have never liked as they look to me like easy paths for HF into the rest of the amp).
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#9 Re: Transformer Snubbing

Post by jack »

For those interested in Linear Audio:

https://linearaudio.net/volumes
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#10 Re: Transformer Snubbing

Post by Nick »

These are the parts I used from RS

403-840: 6A Single MOSFET Driver,MCP1407-E/P

725-9329: MOSFET N-Channel 30V 92A TO220AB

534-4002: CMOS timer, LMC555CN DIP8

486-4460: Schottky barrier diode,1N58191A 40V

521-9631: 3296W top adj cermet trimmer,1K 10mm

652-9743: Radial C0G ceramic cap,100pF 100V 2.5mm

108-2435: FKS2 Polyester Cap,100Vdc,1nF

108-2390: MKS2 Polyester Cap,63Vdc,150nF

839-9276: Al Electrolytic Capacitors 220uF 35V

214-1125: ROX1S metal oxide film resistor,820R 1W

683-2847: MRS16 Resistor A/P,0.4W,1%,39K

707-7745: Carbon Resistor, 0.25W ,5%, 10k

707-7697: Carbon Resistor, 0.25W ,5%, 2k

765-5474: Receptacle 2.54mm vertical 3+3way

670-5073: Header 2.54mm, single row, vertical, 1w

193-0564: 2 way std vertical terminal,5.08mm pitch

148-663: Metal film resistor,4K7 0.6W

765-5486: Receptacle 2.54mm vertical 4+4way

765-5483: Receptacle 2.54mm vertical 3way

877-2122: Switch DIP 4 pos raised act solder
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