witches' brew
in [Design]
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From: John Larkin on 19 Jul 2010 15:19 On Mon, 19 Jul 2010 11:17:07 -0400, Spehro Pefhany <speffSNIP(a)interlogDOTyou.knowwhat> wrote: >On Mon, 19 Jul 2010 08:08:22 -0700, John Larkin ><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: > >>On Mon, 19 Jul 2010 07:35:56 -0700 (PDT), whit3rd <whit3rd(a)gmail.com> >>wrote: >> >>>On Jul 18, 2:29�pm, "Tim Williams" <tmoran...(a)charter.net> wrote: >>>> Yuck, hard switching into a capacitor, too? >>> >>>Maybe not; series inductance might be designed into the >>>transformer-looking gizmo. >> >>It's a tiny toroid in the CUI thing, so I'd suspect insignificant >>leakage inductance. >> >>John > >Does it conduct much switching noise back into the supply? I didn't measure that. I did include a ferrite bead in the +12 input and an extra cap in the converter side. Since I'm doing isolated channels, I care more about common-mode noise current. The unloaded output shows about 600 mv p-p common-mode noise on a grounded scope, not bad. It has 83 pF input to output, OK but higher than I'd like. John
From: Grant on 19 Jul 2010 17:11 On Mon, 19 Jul 2010 08:54:40 -0700, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >On Mon, 19 Jul 2010 10:19:54 -0500, "Tim Williams" ><tmoranwms(a)charter.net> wrote: > >>"Spehro Pefhany" <speffSNIP(a)interlogDOTyou.knowwhat> wrote in message news:n2r84658pa40h7cvejjbvceenamlu6fndv(a)4ax.com... >>>>It's a tiny toroid in the CUI thing, so I'd suspect insignificant >>>>leakage inductance. >>>> >>>>John >>> >>> Does it conduct much switching noise back into the supply? >> >>Funny, I made a chopper recently, having need of isolating a few hundred milivolts. Quite noisy, but it's low bandwidth so it all filters away. >> >>http://myweb.msoe.edu/williamstm/Images/Shunt_Isolator_Schem.pdf >>http://myweb.msoe.edu/williamstm/Images/Shunt_Isolator.jpg >> >>Off topic: doesn't use toroids. > >They are small, efficient, and apparently cheap. But harder to wind at >home. I once worked for a company that had a small toroid winding >machine, and we could make our own. That was sort of cool. I can't >imagine how they wind those tiny bifalar ones in the dc/dc bricks, or >Ethernet magnetics. Maybe by hand with starvation-pay suicide-prone >labor? Opened up a 1Gbps combined ethernet connector/line interface (like what's on a PC mobo)? Seven or eight little toroids, some fancy connections, all interconnected... Hard to imagine them being made by a machine. There must be some really boring jobs out there :( > > >>The interesting thing is, since the chopper is shorting-mode commutated, it *doesn't* work with a bypassed supply. It astonishes me how many of these circuits are out there, with 2N3055s and iron core transformers, and they'd work *so much better* with just a little series inductance in the supply! > >Yikes! Interesting if ones thinks of improving the thing by slapping a big cap on input? Oops. Grant. > >John
From: krw on 19 Jul 2010 20:12 On Mon, 19 Jul 2010 00:47:16 -0700, Robert Baer <robertbaer(a)localnet.com> wrote: >John Larkin wrote: >> We blew up a couple more of the SIP dc/dc converters, CUI type VASD1. >> This one is 12 volts in, +-15 out, rated 1 watt. I don't totally blame >> the bricks, since certain un-named parties likely shorted the outputs >> while probing channels, but it would be nice if they could stand a >> load short. >> >> There are 12 on this board... >> >> ftp://jjlarkin.lmi.net/V220_top.jpg >> >> >> Anyway, I took one home and tore off the potting shell. It's potted >> with something soft and a bit gritty, maybe a filled soft epoxy. >> Looking around the garage, I had some Jasco paint remover (methylene >> chloride mostly) some acetone, and some MEK, so I mixed them all in a >> glass jar and soaked the thing overnight. The potting swelled up and >> got really soft. I did lose the transformer, which stayed in the epoxy >> glob when I ripped it off the board. >> >> ftp://jjlarkin.lmi.net/VASD1_top.JPG >> >> This looks like a simple 2-transistor forward converter on the left, >> and a couple of dual diodes and caps on the right. The substrate is a >> pc board, unlike the Muratas which are ceramic. >> >> Maybe we'll add a polyfuse or something to protect them, although >> things like this tend to quit failing when people quit probing. >> >> With another part or two, they could have made this short-resistant. >> But these are only about $4 each and work very nicely otherwise. >> >> John >> >> > It has been said, for a car, that addition of a 50 cent part >increases the consumer price by 5 dollars. > So...the addition "of another part or two" would almost double the price. > "QED" In the real world there is no correlation between them, other than price > cost. Put another way, if I shave $.50 off the cost of a product there is no corresponding drop in our price. Price is set by a completely different set of equations than cost.
From: John Larkin on 19 Jul 2010 20:33 On Mon, 19 Jul 2010 19:12:32 -0500, "krw(a)att.bizzzzzzzzzzzz" <krw(a)att.bizzzzzzzzzzzz> wrote: >On Mon, 19 Jul 2010 00:47:16 -0700, Robert Baer <robertbaer(a)localnet.com> >wrote: > >>John Larkin wrote: >>> We blew up a couple more of the SIP dc/dc converters, CUI type VASD1. >>> This one is 12 volts in, +-15 out, rated 1 watt. I don't totally blame >>> the bricks, since certain un-named parties likely shorted the outputs >>> while probing channels, but it would be nice if they could stand a >>> load short. >>> >>> There are 12 on this board... >>> >>> ftp://jjlarkin.lmi.net/V220_top.jpg >>> >>> >>> Anyway, I took one home and tore off the potting shell. It's potted >>> with something soft and a bit gritty, maybe a filled soft epoxy. >>> Looking around the garage, I had some Jasco paint remover (methylene >>> chloride mostly) some acetone, and some MEK, so I mixed them all in a >>> glass jar and soaked the thing overnight. The potting swelled up and >>> got really soft. I did lose the transformer, which stayed in the epoxy >>> glob when I ripped it off the board. >>> >>> ftp://jjlarkin.lmi.net/VASD1_top.JPG >>> >>> This looks like a simple 2-transistor forward converter on the left, >>> and a couple of dual diodes and caps on the right. The substrate is a >>> pc board, unlike the Muratas which are ceramic. >>> >>> Maybe we'll add a polyfuse or something to protect them, although >>> things like this tend to quit failing when people quit probing. >>> >>> With another part or two, they could have made this short-resistant. >>> But these are only about $4 each and work very nicely otherwise. >>> >>> John >>> >>> >> It has been said, for a car, that addition of a 50 cent part >>increases the consumer price by 5 dollars. >> So...the addition "of another part or two" would almost double the price. >> "QED" > >In the real world there is no correlation between them, other than price > >cost. Put another way, if I shave $.50 off the cost of a product there is no >corresponding drop in our price. Price is set by a completely different set >of equations than cost. If we add a part, the price goes up 4x the part cost. If we delete a part, the price doesn't change. John
From: krw on 19 Jul 2010 20:47
On Mon, 19 Jul 2010 17:33:23 -0700, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >On Mon, 19 Jul 2010 19:12:32 -0500, "krw(a)att.bizzzzzzzzzzzz" ><krw(a)att.bizzzzzzzzzzzz> wrote: > >>On Mon, 19 Jul 2010 00:47:16 -0700, Robert Baer <robertbaer(a)localnet.com> >>wrote: >> >>>John Larkin wrote: >>>> We blew up a couple more of the SIP dc/dc converters, CUI type VASD1. >>>> This one is 12 volts in, +-15 out, rated 1 watt. I don't totally blame >>>> the bricks, since certain un-named parties likely shorted the outputs >>>> while probing channels, but it would be nice if they could stand a >>>> load short. >>>> >>>> There are 12 on this board... >>>> >>>> ftp://jjlarkin.lmi.net/V220_top.jpg >>>> >>>> >>>> Anyway, I took one home and tore off the potting shell. It's potted >>>> with something soft and a bit gritty, maybe a filled soft epoxy. >>>> Looking around the garage, I had some Jasco paint remover (methylene >>>> chloride mostly) some acetone, and some MEK, so I mixed them all in a >>>> glass jar and soaked the thing overnight. The potting swelled up and >>>> got really soft. I did lose the transformer, which stayed in the epoxy >>>> glob when I ripped it off the board. >>>> >>>> ftp://jjlarkin.lmi.net/VASD1_top.JPG >>>> >>>> This looks like a simple 2-transistor forward converter on the left, >>>> and a couple of dual diodes and caps on the right. The substrate is a >>>> pc board, unlike the Muratas which are ceramic. >>>> >>>> Maybe we'll add a polyfuse or something to protect them, although >>>> things like this tend to quit failing when people quit probing. >>>> >>>> With another part or two, they could have made this short-resistant. >>>> But these are only about $4 each and work very nicely otherwise. >>>> >>>> John >>>> >>>> >>> It has been said, for a car, that addition of a 50 cent part >>>increases the consumer price by 5 dollars. >>> So...the addition "of another part or two" would almost double the price. >>> "QED" >> >>In the real world there is no correlation between them, other than price > >>cost. Put another way, if I shave $.50 off the cost of a product there is no >>corresponding drop in our price. Price is set by a completely different set >>of equations than cost. > >If we add a part, the price goes up 4x the part cost. If we delete a >part, the price doesn't change. That's because you have no idea where to price your products. |