Brian's LM3875 REV C boards

[homer09]

Brian's out of stock with the current REV B boards and is working on the REV C boards for shipping mid Jan (according to his site).

Any info on what changes the new revision is going to bring? I'm sure we're in for a treat as usual...

[Greg Erskine]

Oh no homer09, I have both Rev A and Rev B now I'll have to buy Rev C to keep my collection of BrianGT PCBs complete.

BTW: What I'd really like is a experiementers PCB. Similar to the existing board as far as the LM3875 and caps are concerned but the connectors to the sides and a prototyping area in the middle. I wish I had a tenth of Brian's skills to design and make one. It would be nice if a LM3886 chip could fit as well. Hey, this is probably a good idea for digi01.

[wigginjs]

We could always turn this thread into a Revision C wishlist. Perhaps Brian and PD could get some ideas from it. I would personally like to see the ability to add in the snubber caps CarlosFM has been talking so much about.

[steenoe]

I would personally like to see the ability to add in the snubber caps CarlosFM has been talking so much about.

That is easely done on the rev.B boards! You actually have four holes for the caps 'onboard'. The zobel network would in either case be mounted at the output of the PSU. Assuming you are talking about the 'high-cap' PSU. See the pic.

Steen.

[jackinnj]

Originally posted by m0tion
We could always turn this thread into a Revision C wishlist. Perhaps Brian and PD could get some ideas from it. I would personally like to see the ability to add in the snubber caps CarlosFM has been talking so much about.

the snubber caps belong on the diode board --

[widman]

That is easely done on the rev.B boards! You actually have four holes for the caps 'onboard'. The zobel network would in either case be mounted at the output of the PSU. Assuming you are talking about the 'high-cap' PSU. See the pic.

steenoe,

What size/type cap did you use with the snubber?

widman

[jackinnj]

Originally posted by widman


steenoe,

What size/type cap did you use with the snubber?

widman

the size of the capacitor is related to the inductance of the secondary of the transformer, and the capacitance of the diode itself (this can be obtained from the manufacturer's data sheet).

when you measure the inductance make sure to short the primary leads.

[steenoe]

What size/type cap did you use with the snubber?

The value of the caps is 100nF as recommended by CarlosFM.
It is generic polyesterfilm caps. You could ofcourse consider more excotic parts, but how much is gained by that?
It is the same type 1oonF caps used at the output of the psu for the Zobelnetwork, as well as for bypass for the 100uF electrolytics on the board. Hope this helps
The small caps are not at all implementet as diode-snubbers.

Steen.

[jackinnj]

Originally posted by steenoe

The value of the caps is 100nF as recommended by CarlosFM.
It is generic polyesterfilm caps. You could ofcourse consider more excotic parts, but how much is gained by that?
It is the same type 1oonF caps used at the output of the psu for the Zobelnetwork, as well as for bypass for the 100uF electrolytics on the board. Hope this helps
The small caps are not at all implementet as diode-snubbers.

Steen.

100nF is a number pulled out of thin air -- with any value this high you dissipate energy through the snubber according to E= 1/2 (C*V^2) -- (not that it's a lot of joules, it's just a pointless waste of energy).

here's a homework assignment: using 100 uH for the secondary inductance and 100pf for the diode capacitance of an MUR860 at 30V determine the correct value of a snubber --

http://www.hagtech.com/pdf/snubber.pdf

[carlosfm]

I'm getting consistently good results with the values I recommend for the snubber, no matter what trafo or diodes I use.

Just found out another happy diyer:
http://gainclone.com/phpBB2/viewtopi...er=asc&start=0