On Nov 2, 10:51=A0pm, John Larkin <jjlar...@highNOTlandTHIStechnologyPART.com> wrote:> This > > http://www.panoramio.com/photo/61564837 > > might work for powering a thing I'm doing. I can use a standard cheap > Coiltronix dual-coil inductor as the transformer. The complementary > emitter followers will have no shoot-through and can have controllably > slow switching edges, since they will just follow the base drive. > > Anybody got ideas for the base driver device? Ideally it would be > self-oscillating, set with some R-C; have a moderate slew rate; swing > to the rails. I'm thinking roughly 150 KHz maybe, a few watts output. > > Maybe an LM8261 opamp? I'd have to see if it winds up when it rails. > It might not. > > Some sort of fet gate driver would be OK, but few go to 24 volts.> > Something discrete maybe, like a 2N7002 to 24-, and maybe a > bootstrapped pullup?That's my 1rst impulse. Hard to ensure 50% duty with the self- oscillator + slew rate stuff. Linear's got quiet slew-rate limited switcher chips. -- Cheers, James Arthur
isolated DC/DC converter
Started by ●November 3, 2011
Reply by ●November 4, 20112011-11-04
Reply by ●November 4, 20112011-11-04
On 03/11/11 19:00, John Larkin wrote:> I want to avoid custom magnetics, and I want it to be cheap, in case > we build a lot of them. I'd like to trade off efficiency for switching > noise, which this topology allows. There will be a 12-bit, 250 Ms/s > ADC a couple of inches away.Check out the LT3439 (slew rate limited). I found it worked very well as a DC transformer (its datasheet shows you how) with an off-the-shelf transformer. Couple of points - - wrap a shorting turn round the transformer to reduce radiated flux - use a transformer with about 500-1000uH primary inductance to avoid wasting power / heating the IC unecessarily. If you have one of those standard 6 coil types, you can put 2 coils in series for 4 times the L (not twice, 'cos they are on the same core) - you can get by with 10uF ceramics for the output, it switches around 120kHz - follow up with C-multipliers on the output for an unregulated but very quiet rail. Nemo
Reply by ●November 4, 20112011-11-04
Vladimir Vassilevsky wrote:> > > John Larkin wrote: > >> This >> >> http://www.panoramio.com/photo/61564837 >> >> might work for powering a thing I'm doing. I can use a standard cheap >> Coiltronix dual-coil inductor as the transformer. The complementary >> emitter followers will have no shoot-through and can have controllably >> slow switching edges, since they will just follow the base drive. >> >> Anybody got ideas for the base driver device? Ideally it would be >> self-oscillating, set with some R-C; have a moderate slew rate; swing >> to the rails. I'm thinking roughly 150 KHz maybe, a few watts output. >> >> Maybe an LM8261 opamp? I'd have to see if it winds up when it rails. >> It might not. >> >> Some sort of fet gate driver would be OK, but few go to 24 volts. >> >> Something discrete maybe, like a 2N7002 to 24-, and maybe a >> bootstrapped pullup? > > You might want to check IR2085S >But I am sure John won't want to spend the two bux in the BOM :-) -- Regards, Joerg http://www.analogconsultants.com/
Reply by ●November 4, 20112011-11-04
On 4 Nov., 23:57, Joerg <inva...@invalid.invalid> wrote:> Vladimir Vassilevsky wrote: > > > John Larkin wrote: > > >> This > > >>http://www.panoramio.com/photo/61564837 > > >> might work for powering a thing I'm doing. I can use a standard cheap > >> Coiltronix dual-coil inductor as the transformer. The complementary > >> emitter followers will have no shoot-through and can have controllably > >> slow switching edges, since they will just follow the base drive. > > >> Anybody got ideas for the base driver device? Ideally it would be > >> self-oscillating, set with some R-C; have a moderate slew rate; swing > >> to the rails. I'm thinking roughly 150 KHz maybe, a few watts output. > > >> Maybe an LM8261 opamp? I'd have to see if it winds up when it rails. > >> It might not. > > >> Some sort of fet gate driver would be OK, but few go to 24 volts. > > >> Something discrete maybe, like a 2N7002 to 24-, and maybe a > >> bootstrapped pullup? > > > You might want to check IR2085S > > But I am sure John won't want to spend the two bux in the BOM :-) >if it sits next to a 12bit 250MHz adc I'm not sure 1-2$ will make such a big difference -Lasse
Reply by ●November 4, 20112011-11-04
On Fri, 04 Nov 2011 15:57:28 -0700, Joerg <invalid@invalid.invalid> wrote:>Vladimir Vassilevsky wrote: >> >> >> John Larkin wrote: >> >>> This >>> >>> http://www.panoramio.com/photo/61564837 >>> >>> might work for powering a thing I'm doing. I can use a standard cheap >>> Coiltronix dual-coil inductor as the transformer. The complementary >>> emitter followers will have no shoot-through and can have controllably >>> slow switching edges, since they will just follow the base drive. >>> >>> Anybody got ideas for the base driver device? Ideally it would be >>> self-oscillating, set with some R-C; have a moderate slew rate; swing >>> to the rails. I'm thinking roughly 150 KHz maybe, a few watts output. >>> >>> Maybe an LM8261 opamp? I'd have to see if it winds up when it rails. >>> It might not. >>> >>> Some sort of fet gate driver would be OK, but few go to 24 volts. >>> >>> Something discrete maybe, like a 2N7002 to 24-, and maybe a >>> bootstrapped pullup? >> >> You might want to check IR2085S >> > >But I am sure John won't want to spend the two bux in the BOM :-)Actually, I ordered some IRS2153D's, a very simlar part. Maybe if I use biggish gate resistors and keep the frequency down I can get tolerable efficiency and low noise. It may need a snubber, not sure. I'll build one on Monday. My little emitter follower thing seems to work, but it's not very efficient. A couple of bux of parts cost is not a big deal here. Getting it to work the first time is. John
Reply by ●November 5, 20112011-11-05
On Thu, 03 Nov 2011 11:42:10 -0500, John S <sophi.2@invalid.org> wrote:>On 11/3/2011 11:51 AM, legg wrote: >> On Wed, 02 Nov 2011 23:45:15 -0700, miso<miso@sushi.com> wrote: >> >>> Given base charge storage, if the driver rise/fall time is fast, the >>> design could have shoot through. >> >> ...and given magnetizing energy, emitters will be pulled above and >> below the rails. > >But only by one Vbe above or below.... just enough to cause the transistor to conduct the magnetising current to the opposing rail - clamping the winding in the lossiest way possible, Imag x VCC losses being absorbed by the bipolar transistor that is supposed to be 'off'. RL
Reply by ●November 5, 20112011-11-05
On 5 Nov., 02:09, John Larkin <jjlar...@highNOTlandTHIStechnologyPART.com> wrote:> On Fri, 04 Nov 2011 15:57:28 -0700, Joerg <inva...@invalid.invalid> > wrote: > > > > > > > > > > >Vladimir Vassilevsky wrote: > > >> John Larkin wrote: > > >>> This > > >>>http://www.panoramio.com/photo/61564837 > > >>> might work for powering a thing I'm doing. I can use a standard cheap > >>> Coiltronix dual-coil inductor as the transformer. The complementary > >>> emitter followers will have no shoot-through and can have controllably > >>> slow switching edges, since they will just follow the base drive. > > >>> Anybody got ideas for the base driver device? Ideally it would be > >>> self-oscillating, set with some R-C; have a moderate slew rate; swing > >>> to the rails. I'm thinking roughly 150 KHz maybe, a few watts output. > > >>> Maybe an LM8261 opamp? I'd have to see if it winds up when it rails. > >>> It might not. > > >>> Some sort of fet gate driver would be OK, but few go to 24 volts. > > >>> Something discrete maybe, like a 2N7002 to 24-, and maybe a > >>> bootstrapped pullup? > > >> You might want to check IR2085S > > >But I am sure John won't want to spend the two bux in the BOM :-) > > Actually, I ordered some IRS2153D's, a very simlar part. Maybe if I > use biggish gate resistors and keep the frequency down I can get > tolerable efficiency and low noise. It may need a snubber, not sure. > I'll build one on Monday. > > My little emitter follower thing seems to work, but it's not very > efficient. > > A couple of bux of parts cost is not a big deal here. Getting it to > work the first time is. > > Johnjust wait till jf hears you are playing with what is basically a 555 and a halfbridge driver :P -Lasse
Reply by ●November 5, 20112011-11-05
John Larkin wrote:> On Fri, 04 Nov 2011 15:57:28 -0700, Joerg <invalid@invalid.invalid> > wrote: > >> Vladimir Vassilevsky wrote: >>> >>> John Larkin wrote: >>> >>>> This >>>> >>>> http://www.panoramio.com/photo/61564837 >>>> >>>> might work for powering a thing I'm doing. I can use a standard cheap >>>> Coiltronix dual-coil inductor as the transformer. The complementary >>>> emitter followers will have no shoot-through and can have controllably >>>> slow switching edges, since they will just follow the base drive. >>>> >>>> Anybody got ideas for the base driver device? Ideally it would be >>>> self-oscillating, set with some R-C; have a moderate slew rate; swing >>>> to the rails. I'm thinking roughly 150 KHz maybe, a few watts output. >>>> >>>> Maybe an LM8261 opamp? I'd have to see if it winds up when it rails. >>>> It might not. >>>> >>>> Some sort of fet gate driver would be OK, but few go to 24 volts. >>>> >>>> Something discrete maybe, like a 2N7002 to 24-, and maybe a >>>> bootstrapped pullup? >>> You might want to check IR2085S >>> >> But I am sure John won't want to spend the two bux in the BOM :-) > > Actually, I ordered some IRS2153D's, a very simlar part. Maybe if I > use biggish gate resistors and keep the frequency down I can get > tolerable efficiency and low noise. It may need a snubber, not sure. > I'll build one on Monday. > > My little emitter follower thing seems to work, but it's not very > efficient. > > A couple of bux of parts cost is not a big deal here. Getting it to > work the first time is. >But yesterday you wrote that you wanted it cheap in case you build lots of them :-) Reminds me of a time when I was designing something for the guys where things must have cast-iron robustness. I sat there in agony and a manager asked me whether I had problems with my design. "Not technical ones but these multipliers are over $6, a piece". A whole group of people around me had listened in. They and the manager burst into thundering laughter ... -- Regards, Joerg http://www.analogconsultants.com/
Reply by ●November 5, 20112011-11-05
John Larkin wrote:>>Vladimir Vassilevsky wrote: >>>John Larkin wrote: >>> >>>>This >>>> >>>>http://www.panoramio.com/photo/61564837 >>>> >>>>might work for powering a thing I'm doing. >>>>Anybody got ideas for the base driver device?>>>You might want to check IR2085S > Actually, I ordered some IRS2153D's, a very simlar part.So, getting a self oscillating thing to work seems too complicated ? (http://www.abvolt.com/misc/self_osc.jpg)> A couple of bux of parts cost is not a big deal here. Getting it to > work the first time is.Use a PIC. Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com
Reply by ●November 5, 20112011-11-05
On Sat, 05 Nov 2011 10:59:48 -0500, the renowned Vladimir Vassilevsky <nospam@nowhere.com> wrote:> > >John Larkin wrote: > >>>Vladimir Vassilevsky wrote: >>>>John Larkin wrote: >>>> >>>>>This >>>>> >>>>>http://www.panoramio.com/photo/61564837 >>>>> >>>>>might work for powering a thing I'm doing. >>>>>Anybody got ideas for the base driver device? > >>>>You might want to check IR2085S >> Actually, I ordered some IRS2153D's, a very simlar part. > >So, getting a self oscillating thing to work seems too complicated ? >(http://www.abvolt.com/misc/self_osc.jpg) > >> A couple of bux of parts cost is not a big deal here. Getting it to >> work the first time is. > >Use a PIC.It should be pretty easy to throw some randomness into the frequency with a PIC for a spread-spectrum converter. Best regards, Spehro Pefhany -- "it's the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
