MC34063 with small inductors
in [Design]
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From: John Devereux on 9 Apr 2010 13:03 John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> writes: > On Fri, 9 Apr 2010 09:01:36 -0700 (PDT), dagmargoodboat(a)yahoo.com > wrote: > >>On Apr 9, 10:36 am, John Larkin >><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >>> On Fri, 9 Apr 2010 05:00:10 -0700 (PDT), dagmargoodb...(a)yahoo.com >>> wrote: >>> >>> >On Apr 8, 2:41 pm, Joerg <inva...(a)invalid.invalid> wrote: >> >>> >> On the 34063? I have simulated the dickens out of that and the >>> >> comparator never shuts off the switch at onset, just occasionally in the >>> >> middle of a ramp-up which it ain't supposed to be able to do. And in >>> >> Hammy's case doesn't do. >>> >>> >Propagation delay? When the ramp comparator trips, it'll take a >>> >minute or two to turn the timing ramp current source around. So to >>> >speak. :-) >>> >>> We're using some tiny 3 MHz switchers now. >> >>Two orders of magnitude faster than the MC34063. Sweet. Aren't core >>and skin losses deadly? > > The compensation is that you need very little copper and ferrite at 3 > MHz. Much easier to filter the ripple too. -- John Devereux
From: John Larkin on 9 Apr 2010 14:40 On Fri, 09 Apr 2010 18:03:50 +0100, John Devereux <john(a)devereux.me.uk> wrote: >John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> writes: > >> On Fri, 9 Apr 2010 09:01:36 -0700 (PDT), dagmargoodboat(a)yahoo.com >> wrote: >> >>>On Apr 9, 10:36�am, John Larkin >>><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >>>> On Fri, 9 Apr 2010 05:00:10 -0700 (PDT), dagmargoodb...(a)yahoo.com >>>> wrote: >>>> >>>> >On Apr 8, 2:41�pm, Joerg <inva...(a)invalid.invalid> wrote: >>> >>>> >> On the 34063? I have simulated the dickens out of that and the >>>> >> comparator never shuts off the switch at onset, just occasionally in the >>>> >> middle of a ramp-up which it ain't supposed to be able to do. And in >>>> >> Hammy's case doesn't do. >>>> >>>> >Propagation delay? �When the ramp comparator trips, it'll take a >>>> >minute or two to turn the timing ramp current source around. �So to >>>> >speak. :-) >>>> >>>> We're using some tiny 3 MHz switchers now. >>> >>>Two orders of magnitude faster than the MC34063. Sweet. Aren't core >>>and skin losses deadly? >> >> The compensation is that you need very little copper and ferrite at 3 >> MHz. > >Much easier to filter the ripple too. Yup. All 0805 ceramic caps. John
From: dagmargoodboat on 9 Apr 2010 14:48 On Apr 9, 12:03 pm, John Devereux wrote: > John Larkin writes: > > dagmargoodb...(a)yahoo.com wrote: > > >> John Larkin wrote: > >>> We're using some tiny 3 MHz switchers now. > > >>Two orders of magnitude faster than the MC34063. Sweet. Aren't core > >>and skin losses deadly? > > > The compensation is that you need very little copper and ferrite at 3 > > MHz. > > Much easier to filter the ripple too. True. Smaller, too. Especially nifty when you can use ceramic caps. But, ripple's pretty easy even at 50-100KHz. Methinks there's probably a voltage dependence--optimal 5-to-3.3v and 48-to-5v converters won't look the same. (E.g., (1/2) f*c*v^2 switching loss isn't a big deal for low-voltage switchers, so they can really scream.) I'm too lazy to calculate numbers for a real supply just now. Hmmm. I try to keep total switching time under roughly 10% of the PWM period. At 3MHz that's 17nS per transition. Pretty do-able at 5v, actually. But that's supply's so generic you might as well just buy it. -- Cheers, James Arthur
From: Tim Williams on 9 Apr 2010 17:59 <dagmargoodboat(a)yahoo.com> wrote in message news:e0e92d93-d2be-4502-ab3b-cf7d28723790(a)q23g2000yqd.googlegroups.com... > I've done 300KHz, discrete, but 50KHz-ish is usually more efficient. I've done 1MHz discrete. Didn't come out all that efficient though, needs work... http://webpages.charter.net/dawill/Images/Fast_Forward.gif (note the output filter cap specifically *isn't* tantalum... ESR compensates the loop) Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
From: Tim Williams on 9 Apr 2010 18:06
<dagmargoodboat(a)yahoo.com> wrote in message news:f55d370d-36ac-4bf7-835e-c2b1938594d1(a)r18g2000yqd.googlegroups.com... > Hmmm. I try to keep total switching time under roughly 10% of the PWM > period. At 3MHz that's 17nS per transition. Pretty do-able at 5v, > actually. But that's supply's so generic you might as well just buy > it. Seems to me, D from BC was working on some 1MHz offline switcher. Something about big loads of EMC from the transistor-to-heatsink capacitance. I'm going to try an induction heater at 1MHz sooner or later. C0G tank cap: http://myweb.msoe.edu/williamstm/Images/1MHz_Ind_Cap.jpg Inverter board: http://myweb.msoe.edu/williamstm/Images/1MHz_Ind_Top.jpg (the whole high side is top and bottom ground plane floating at the 1MHz output) Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms |