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A PIC based boost converter

Started by Jan Panteltje November 22, 2011
On a sunny day (Wed, 23 Nov 2011 20:58:44 -0800 (PST)) it happened Tim
Williams <tmoranwms@gmail.com> wrote in
<72c931c1-6e16-4224-aa12-1756c9f14cd4@m7g2000vbc.googlegroups.com>:

>On Nov 23, 5:09&#2013266080;am, Jan Panteltje <pNaonStpealm...@yahoo.com> wrote: >> Any drift in the current transformer is regulated out by the output volta= >ge >> sense loop. >> The current form is the current form in the inductor, and that is a TRIAN= >GLE >> waveform, not a peak. >> As drawn in the diagram. > >So, you aren't doing peak current mode switching, as every switching >circuit with a current sense and comparator does? > >So, you don't mind that you have no DC current reference? > >So in short, you've created a voltage-mode boost converter with >current feedback that...just kind of sits there? > >Yuuuuck. > >> There is no difference with the drain current, >> as the comparator looks at the top of the upgoing side of the triange. > >Yes there is. The drain current stops for about half a cycle on >average. Current transformers don't happen to work at DC. > >Tim
OK, you may be right, but I can assure you that current transformers have no problem with a DC bias, as long as it does not saturate the transformer. I think the input regulation specs, and the efficiency for this design that now is at 69% at nominal input, speak for themselves. Only the AC component of the triangle wave form is used (passed by the CT). the actual value is highly irrelevant, you can think of the current transformer's winding ratio + your losses as part of the open loop gain of the system. The voltage feedback sees perhaps a slightly changing open loop gain, but that is why it is there, the feedback, to keep the output stable. You can test this by reducing the load resistor on the CT by half, the effect on the output is neglible. Plenty of open loop gain. In fact I just grabbed a resistor, thought it could be a bit lower, and added a second in parallel. Most non-critical thing you can imagine. Just like a shunt value, higher more open loop gain. Just do not make it too close to zero, or leave it open ;-) Same for the CT winding ratio. The PIC comparator has an offset around 10 mV IIRC, and its gain is huge, so 100 mV on the CT output is already plenty if not too much. Personally I am very happy with this circuit, as it is a zillion times better than the 'Joule Thieve', that one would not even start with a capacitive load, leading to destruction of the switching transistor due to overheating. You need some introspection. :-)
John S wrote:

> On 11/23/2011 6:27 PM, Jamie wrote: > >> Jan Panteltje wrote: >> >>> On a sunny day (Tue, 22 Nov 2011 19:15:07 -0500) it happened Jamie >>> <jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote in >>> <cUWyq.117643$Cr1.1733@newsfe03.iad>: >>> >>> >>>> The problem looks obvious from here. >>> >>> >>> >>> It works fine. >>> >>> >>> >>>> You are using a Xformer by the looks of it for your current sense? >>>> That would be fine when there is >>>> actual moving current how ever, in the case where output load is >>>> nulling this factor, I guess you're not going to see much effects. >>> >>> >>> >>> Sorry I cannot decrypt that. >>> Study switch mode design. >> >> >> Ha, you're so funny. >> >> Have fun with your endeavors.. >> >> Jamie > > > He has been. > > He has supplied something of substance especially compared to your posts > of almost indecipherable verbiage. What have you posted of any value > other than your ill-informed criticism? Please point to something. > > > >
Don't be such a putz, it only serves to deepen the wound. I don't criticize any one here, except maybe SLow-Man, I merely try to assist in observations I make with experience of my own. Unlike a few un-named here, I try not to second guess before sticking my neck out. If you find it difficult to understand my explanations of things I point out, so be it. We all can't be mind readers how ever, I find that those that really know their business do not seem to have any issues with it. And btw John, I don't recall seeing much of anything out of you that impressed me, if at all. Jamie
Nico Coesel wrote:

> "langwadt@fonz.dk" <langwadt@fonz.dk> wrote: > > >>On 23 Nov., 22:05, Jan Panteltje <pNaonStpealm...@yahoo.com> wrote: >> >>>On a sunny day (Wed, 23 Nov 2011 12:18:44 -0800 (PST)) it happened >>>"langw...@fonz.dk" <langw...@fonz.dk> wrote in >>><761a9bb1-4083-4555-afa8-eef6d073f...@h3g2000yqa.googlegroups.com>: >>> >>> >>>>On 23 Nov., 12:08, Jan Panteltje <pNaonStpealm...@yahoo.com> wrote: >>> >>>>snip >>>> >>>>>It would be short circuit proof IF it was not for the >>>>>boost configuration where the diode would conduct from input to output. >>>>>So for that in this sort of regulator you need a normal fuse. >>>>>For the rest of loads it nicely current limits. >>> >>>>I remember seeing some put a cap in series with the diode to make it >>>>short >>>>circuit proof >>> >>>mm but caps do not conduct DC? >>> >> >>in normal operation the switch node is not DC >> >>but when there's no dc path from input to output, current flow stops >>when you >>stop switching > > > Even though its pulsed, it still is DC. Hint: current flows in one > direction. >
Give it up. You'll save more hair :) Jamie
On 11/24/2011 11:29 AM, Jamie wrote:
> John S wrote: > >> On 11/23/2011 6:27 PM, Jamie wrote: >> >>> Jan Panteltje wrote: >>> >>>> On a sunny day (Tue, 22 Nov 2011 19:15:07 -0500) it happened Jamie >>>> <jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote in >>>> <cUWyq.117643$Cr1.1733@newsfe03.iad>: >>>> >>>> >>>>> The problem looks obvious from here. >>>> >>>> >>>> >>>> It works fine. >>>> >>>> >>>> >>>>> You are using a Xformer by the looks of it for your current sense? >>>>> That would be fine when there is >>>>> actual moving current how ever, in the case where output load is >>>>> nulling this factor, I guess you're not going to see much effects. >>>> >>>> >>>> >>>> Sorry I cannot decrypt that. >>>> Study switch mode design. >>> >>> >>> Ha, you're so funny. >>> >>> Have fun with your endeavors.. >>> >>> Jamie >> >> >> He has been. >> >> He has supplied something of substance especially compared to your >> posts of almost indecipherable verbiage. What have you posted of any >> value other than your ill-informed criticism? Please point to something. >> >> >> >> > Don't be such a putz, it only serves to deepen the wound. > > I don't criticize any one here, except maybe SLow-Man, I merely > try to assist in observations I make with experience of my own. Unlike > a few un-named here, I try not to second guess before sticking my neck > out. If you find it difficult to understand my explanations of things > I point out, so be it. We all can't be mind readers how ever, I find > that those that really know their business do not seem to have any > issues with it. > > And btw John, I don't recall seeing much of anything out of you that > impressed me, if at all. > > Jamie
That's because you don't recall.