amdx wrote:> > On 5/6/2013 11:01 AM, Uncle Steve wrote: > > Back again for some more abuse. > > Where's Phil when somebody really deserves abuse?Off abusing someone who doesn't deserve it.
Whole house fan motor
Started by ●May 5, 2013
Reply by ●May 7, 20132013-05-07
Reply by ●May 8, 20132013-05-08
On 07/05/13 10:57, Jim Thompson wrote:> On Mon, 06 May 2013 22:16:14 -0400, Uncle Steve <stevet810@gmail.com> > wrote: > >> On Mon, May 06, 2013 at 06:59:01PM -0700, Jim Thompson wrote: >>> On Mon, 06 May 2013 12:01:44 -0400, Uncle Steve <stevet810@gmail.com> >>> wrote: >>> >>>> Back again for some more abuse. >>>> >>>> I'm building a 12V battery charger that will be controlled by a small >>>> low-power microcontroller. I've not yet hooked up the >>>> microcontroller, but most of the code is written and I'm trying to >>>> finalize the charger electronics before I hook it up. >>>> >>> [snip] >>> >>> How is the charger "controlled"? >>> >>> Do you mean that the output CURRENT from the charger will be a >>> function of the "duty-cycle" from the micro-controller? >> >> The average current, yes. >> >>> Or do you have some other algorithm in mind? >> >> I've used a similar technique in other circumstances. In this >> instance the ADC measurements of the carger circuit will determine how >> much energy will be dumped into the battery at any given time, again >> /on average/. Lead acid battery chemistry has significant hysteresis, >> so I do not at this time expect any major problems with this strategy. >> The instantaneous current at any time will be limited by the power >> supply, so it's not as if there will be tens of amps rushing the >> battery while the power transistor is turned on. >> >> >> Regards, >> >> Uncle Steve > > How about something like this... > > http://www.analog-innovations.com/SED/ChargerForUncleSteve.pdf > > ...Jim Thompson >If Uncle is using a micro to control it, why not just control a mosfet with the PWM output ???
Reply by ●May 8, 20132013-05-08
On Wed, May 08, 2013 at 04:44:25PM +0800, Rheilly Phoull wrote:> On 07/05/13 10:57, Jim Thompson wrote: > >On Mon, 06 May 2013 22:16:14 -0400, Uncle Steve <stevet810@gmail.com> > >wrote: > > > >>On Mon, May 06, 2013 at 06:59:01PM -0700, Jim Thompson wrote: > >>>On Mon, 06 May 2013 12:01:44 -0400, Uncle Steve <stevet810@gmail.com> > >>>wrote: > >>> > >>>>Back again for some more abuse. > >>>> > >>>>I'm building a 12V battery charger that will be controlled by a small > >>>>low-power microcontroller. I've not yet hooked up the > >>>>microcontroller, but most of the code is written and I'm trying to > >>>>finalize the charger electronics before I hook it up. > >>>> > >>>[snip] > >>> > >>>How is the charger "controlled"? > >>> > >>>Do you mean that the output CURRENT from the charger will be a > >>>function of the "duty-cycle" from the micro-controller? > >> > >>The average current, yes. > >> > >>>Or do you have some other algorithm in mind? > >> > >>I've used a similar technique in other circumstances. In this > >>instance the ADC measurements of the carger circuit will determine how > >>much energy will be dumped into the battery at any given time, again > >>/on average/. Lead acid battery chemistry has significant hysteresis, > >>so I do not at this time expect any major problems with this strategy. > >>The instantaneous current at any time will be limited by the power > >>supply, so it's not as if there will be tens of amps rushing the > >>battery while the power transistor is turned on. > >> > >> > >>Regards, > >> > >>Uncle Steve > > > >How about something like this... > > > > http://www.analog-innovations.com/SED/ChargerForUncleSteve.pdf > > > > ...Jim Thompson > > > If Uncle is using a micro to control it, why not just control a mosfet > with the PWM output ???I have the app notes for the LM338 and such, which show simple charger circuits like that, but the fact of the matter is I have a couple of 3055s and this project is as much about learning some basics as it is about charging a battery. For my requirements it is easier to use what I have on hand than try to select among parts that I don't really understand. If there were a fundamental reason why the 3055 is bad for this application I might consider a mosfet, but I don't see why I should bother. Regards, Uncle Steve -- There should be a special word in the English language to identify people who create problems and then turn around and offer up their own tailor-made bogus non-solutions designed to completely avoid the root causes of the situation under consideration. 'Traitor' might be a good choice, but lacks the requisite specificity. One of the problems with contemporary English is it lacks many such words that would otherwise categorically identify certain kinds of person, place, or thing -- making it difficult or impossible to think analytically about such objects. These shortcomings of the English lexicon are representative of Orwellian linguistics at work in the real world.
Reply by ●May 8, 20132013-05-08
On Wed, 08 May 2013 10:36:21 -0400, Uncle Steve <stevet810@gmail.com> wrote:>On Wed, May 08, 2013 at 04:44:25PM +0800, Rheilly Phoull wrote: >> On 07/05/13 10:57, Jim Thompson wrote:[snip]>> > >> >How about something like this... >> > >> > http://www.analog-innovations.com/SED/ChargerForUncleSteve.pdf >> > >> > ...Jim Thompson >> > >> If Uncle is using a micro to control it, why not just control a mosfet >> with the PWM output ??? > >I have the app notes for the LM338 and such, which show simple charger >circuits like that, but the fact of the matter is I have a couple of >3055s and this project is as much about learning some basics as it is >about charging a battery. For my requirements it is easier to use >what I have on hand than try to select among parts that I don't really >understand. If there were a fundamental reason why the 3055 is bad >for this application I might consider a mosfet, but I don't see why I >should bother. > >Regards, > >Uncle SteveThe 3055 has a minimum beta of 20 at 4 Amps, which you spoke of at one point in this thread, which means the base current that must be supplied is 200mA... not a big deal EXCEPT the driving device will see considerable dissipation. You ought to go buy the TO-3 version of the LM317 for the circuit I suggested and avoid the magic smoke ;-) ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
Reply by ●May 8, 20132013-05-08
On Wed, May 08, 2013 at 02:19:05PM -0700, Jim Thompson wrote:> On Wed, 08 May 2013 10:36:21 -0400, Uncle Steve <stevet810@gmail.com> > wrote: > > >On Wed, May 08, 2013 at 04:44:25PM +0800, Rheilly Phoull wrote: > >> On 07/05/13 10:57, Jim Thompson wrote: > [snip] > >> > > >> >How about something like this... > >> > > >> > http://www.analog-innovations.com/SED/ChargerForUncleSteve.pdf > >> > > >> > ...Jim Thompson > >> > > >> If Uncle is using a micro to control it, why not just control a mosfet > >> with the PWM output ??? > > > >I have the app notes for the LM338 and such, which show simple charger > >circuits like that, but the fact of the matter is I have a couple of > >3055s and this project is as much about learning some basics as it is > >about charging a battery. For my requirements it is easier to use > >what I have on hand than try to select among parts that I don't really > >understand. If there were a fundamental reason why the 3055 is bad > >for this application I might consider a mosfet, but I don't see why I > >should bother. > > > >Regards, > > > >Uncle Steve > > The 3055 has a minimum beta of 20 at 4 Amps, which you spoke of at one > point in this thread, which means the base current that must be > supplied is 200mA... not a big deal EXCEPT the driving device will see > considerable dissipation.I'm starting to appreciate these factors. Yet, after removing the 4004 diode as superfluous and changing the .5 ohm sense resistor to .1 ohms, I'm seeing 3A output which is pretty much the capacity of the power supply. The 3055 runs cooler as well; not sure what that means. Now I have to use an op-amp comparator to measure the current to get decent resolution.> You ought to go buy the TO-3 version of the LM317 for the circuit I > suggested and avoid the magic smoke ;-)The literature doesn't specify the switching frequency, rise time, etc. for that part. Regards, Uncle Steve -- There should be a special word in the English language to identify people who create problems and then turn around and offer up their own tailor-made bogus non-solutions designed to completely avoid the root causes of the situation under consideration. 'Traitor' might be a good choice, but lacks the requisite specificity. One of the problems with contemporary English is it lacks many such words that would otherwise categorically identify certain kinds of person, place, or thing -- making it difficult or impossible to think analytically about such objects. These shortcomings of the English lexicon are representative of Orwellian linguistics at work in the real world.
Reply by ●May 8, 20132013-05-08
On Wed, 08 May 2013 17:55:36 -0400, Uncle Steve <stevet810@gmail.com> wrote:>On Wed, May 08, 2013 at 02:19:05PM -0700, Jim Thompson wrote: >> On Wed, 08 May 2013 10:36:21 -0400, Uncle Steve <stevet810@gmail.com> >> wrote: >> >> >On Wed, May 08, 2013 at 04:44:25PM +0800, Rheilly Phoull wrote: >> >> On 07/05/13 10:57, Jim Thompson wrote: >> [snip] >> >> > >> >> >How about something like this... >> >> > >> >> > http://www.analog-innovations.com/SED/ChargerForUncleSteve.pdf >> >> > >> >> > ...Jim Thompson >> >> > >> >> If Uncle is using a micro to control it, why not just control a mosfet >> >> with the PWM output ??? >> > >> >I have the app notes for the LM338 and such, which show simple charger >> >circuits like that, but the fact of the matter is I have a couple of >> >3055s and this project is as much about learning some basics as it is >> >about charging a battery. For my requirements it is easier to use >> >what I have on hand than try to select among parts that I don't really >> >understand. If there were a fundamental reason why the 3055 is bad >> >for this application I might consider a mosfet, but I don't see why I >> >should bother. >> > >> >Regards, >> > >> >Uncle Steve >> >> The 3055 has a minimum beta of 20 at 4 Amps, which you spoke of at one >> point in this thread, which means the base current that must be >> supplied is 200mA... not a big deal EXCEPT the driving device will see >> considerable dissipation. > >I'm starting to appreciate these factors. Yet, after removing the >4004 diode as superfluous and changing the .5 ohm sense resistor to >.1 ohms, I'm seeing 3A output which is pretty much the capacity of the >power supply. The 3055 runs cooler as well; not sure what that means. > >Now I have to use an op-amp comparator to measure the current to get >decent resolution. > >> You ought to go buy the TO-3 version of the LM317 for the circuit I >> suggested and avoid the magic smoke ;-) > >The literature doesn't specify the switching frequency, rise time, >etc. for that part. > > >Regards, > >Uncle SteveI'm curious why you need to "switch" it? Isn't your only concern the _average_ current, as determined by the PWM? All you need is a low-pass R/C between the micro and the base of Q1 (as noted in the text box on the schematic). I'll run a simulation of that and repost later (under this same link). http://www.analog-innovations.com/SED/ChargerForUncleSteve.pdf ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
Reply by ●May 8, 20132013-05-08
On Wed, 08 May 2013 15:56:44 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:>On Wed, 08 May 2013 17:55:36 -0400, Uncle Steve <stevet810@gmail.com> >wrote: > >>On Wed, May 08, 2013 at 02:19:05PM -0700, Jim Thompson wrote: >>> On Wed, 08 May 2013 10:36:21 -0400, Uncle Steve <stevet810@gmail.com> >>> wrote: >>> >>> >On Wed, May 08, 2013 at 04:44:25PM +0800, Rheilly Phoull wrote: >>> >> On 07/05/13 10:57, Jim Thompson wrote: >>> [snip] >>> >> > >>> >> >How about something like this... >>> >> > >>> >> > http://www.analog-innovations.com/SED/ChargerForUncleSteve.pdf >>> >> > >>> >> > ...Jim Thompson >>> >> > >>> >> If Uncle is using a micro to control it, why not just control a mosfet >>> >> with the PWM output ??? >>> > >>> >I have the app notes for the LM338 and such, which show simple charger >>> >circuits like that, but the fact of the matter is I have a couple of >>> >3055s and this project is as much about learning some basics as it is >>> >about charging a battery. For my requirements it is easier to use >>> >what I have on hand than try to select among parts that I don't really >>> >understand. If there were a fundamental reason why the 3055 is bad >>> >for this application I might consider a mosfet, but I don't see why I >>> >should bother. >>> > >>> >Regards, >>> > >>> >Uncle Steve >>> >>> The 3055 has a minimum beta of 20 at 4 Amps, which you spoke of at one >>> point in this thread, which means the base current that must be >>> supplied is 200mA... not a big deal EXCEPT the driving device will see >>> considerable dissipation. >> >>I'm starting to appreciate these factors. Yet, after removing the >>4004 diode as superfluous and changing the .5 ohm sense resistor to >>.1 ohms, I'm seeing 3A output which is pretty much the capacity of the >>power supply. The 3055 runs cooler as well; not sure what that means. >> >>Now I have to use an op-amp comparator to measure the current to get >>decent resolution. >> >>> You ought to go buy the TO-3 version of the LM317 for the circuit I >>> suggested and avoid the magic smoke ;-) >> >>The literature doesn't specify the switching frequency, rise time, >>etc. for that part. >> >> >>Regards, >> >>Uncle Steve > >I'm curious why you need to "switch" it? Isn't your only concern the >_average_ current, as determined by the PWM? > >All you need is a low-pass R/C between the micro and the base of Q1 >(as noted in the text box on the schematic). > >I'll run a simulation of that and repost later (under this same link). > > http://www.analog-innovations.com/SED/ChargerForUncleSteve.pdf >And you don't need to measure the current via a high-side OpAmp kludge, it's calculable from the voltage at the emitter of Q1. (If you want it to be super precise, just add an OpAmp between your micro and Q1.) ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
Reply by ●May 8, 20132013-05-08
On Wed, 08 May 2013 16:01:24 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:>On Wed, 08 May 2013 15:56:44 -0700, Jim Thompson ><To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote: > >>On Wed, 08 May 2013 17:55:36 -0400, Uncle Steve <stevet810@gmail.com> >>wrote: >> >>>On Wed, May 08, 2013 at 02:19:05PM -0700, Jim Thompson wrote: >>>> On Wed, 08 May 2013 10:36:21 -0400, Uncle Steve <stevet810@gmail.com> >>>> wrote: >>>> >>>> >On Wed, May 08, 2013 at 04:44:25PM +0800, Rheilly Phoull wrote: >>>> >> On 07/05/13 10:57, Jim Thompson wrote: >>>> [snip] >>>> >> > >>>> >> >How about something like this... >>>> >> > >>>> >> > http://www.analog-innovations.com/SED/ChargerForUncleSteve.pdf >>>> >> > >>>> >> > ...Jim Thompson >>>> >> > >>>> >> If Uncle is using a micro to control it, why not just control a mosfet >>>> >> with the PWM output ??? >>>> > >>>> >I have the app notes for the LM338 and such, which show simple charger >>>> >circuits like that, but the fact of the matter is I have a couple of >>>> >3055s and this project is as much about learning some basics as it is >>>> >about charging a battery. For my requirements it is easier to use >>>> >what I have on hand than try to select among parts that I don't really >>>> >understand. If there were a fundamental reason why the 3055 is bad >>>> >for this application I might consider a mosfet, but I don't see why I >>>> >should bother. >>>> > >>>> >Regards, >>>> > >>>> >Uncle Steve >>>> >>>> The 3055 has a minimum beta of 20 at 4 Amps, which you spoke of at one >>>> point in this thread, which means the base current that must be >>>> supplied is 200mA... not a big deal EXCEPT the driving device will see >>>> considerable dissipation. >>> >>>I'm starting to appreciate these factors. Yet, after removing the >>>4004 diode as superfluous and changing the .5 ohm sense resistor to >>>.1 ohms, I'm seeing 3A output which is pretty much the capacity of the >>>power supply. The 3055 runs cooler as well; not sure what that means. >>> >>>Now I have to use an op-amp comparator to measure the current to get >>>decent resolution. >>> >>>> You ought to go buy the TO-3 version of the LM317 for the circuit I >>>> suggested and avoid the magic smoke ;-) >>> >>>The literature doesn't specify the switching frequency, rise time, >>>etc. for that part. >>> >>> >>>Regards, >>> >>>Uncle Steve >> >>I'm curious why you need to "switch" it? Isn't your only concern the >>_average_ current, as determined by the PWM? >> >>All you need is a low-pass R/C between the micro and the base of Q1 >>(as noted in the text box on the schematic). >> >>I'll run a simulation of that and repost later (under this same link). >> >> http://www.analog-innovations.com/SED/ChargerForUncleSteve.pdf >> > >And you don't need to measure the current via a high-side OpAmp >kludge, it's calculable from the voltage at the emitter of Q1. > >(If you want it to be super precise, just add an OpAmp between your >micro and Q1.) > > ...Jim ThompsonReposted with those features added... http://www.analog-innovations.com/SED/ChargerForUncleSteve.pdf Non-linearity at low end is due to bias current from LM317 adjust pin. Scaling both R2 and R3, proportionately to lower values, will lower that break point. Diode is necessary as a safety in the case where battery is connected, but 18V supply is set to zero. Diode can be moved in front of LM317 if desired. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
Reply by ●May 8, 20132013-05-08
On Wed, May 08, 2013 at 03:56:44PM -0700, Jim Thompson wrote:> On Wed, 08 May 2013 17:55:36 -0400, Uncle Steve <stevet810@gmail.com> > wrote: > > >On Wed, May 08, 2013 at 02:19:05PM -0700, Jim Thompson wrote: > >> On Wed, 08 May 2013 10:36:21 -0400, Uncle Steve <stevet810@gmail.com> > >> wrote: > >> > >> >On Wed, May 08, 2013 at 04:44:25PM +0800, Rheilly Phoull wrote: > >> >> On 07/05/13 10:57, Jim Thompson wrote: > >> [snip] > >> >> > > >> >> >How about something like this... > >> >> > > >> >> > http://www.analog-innovations.com/SED/ChargerForUncleSteve.pdf > >> >> > > >> >> > ...Jim Thompson > >> >> > > >> >> If Uncle is using a micro to control it, why not just control a mosfet > >> >> with the PWM output ??? > >> > > >> >I have the app notes for the LM338 and such, which show simple charger > >> >circuits like that, but the fact of the matter is I have a couple of > >> >3055s and this project is as much about learning some basics as it is > >> >about charging a battery. For my requirements it is easier to use > >> >what I have on hand than try to select among parts that I don't really > >> >understand. If there were a fundamental reason why the 3055 is bad > >> >for this application I might consider a mosfet, but I don't see why I > >> >should bother. > >> > > >> >Regards, > >> > > >> >Uncle Steve > >> > >> The 3055 has a minimum beta of 20 at 4 Amps, which you spoke of at one > >> point in this thread, which means the base current that must be > >> supplied is 200mA... not a big deal EXCEPT the driving device will see > >> considerable dissipation. > > > >I'm starting to appreciate these factors. Yet, after removing the > >4004 diode as superfluous and changing the .5 ohm sense resistor to > >.1 ohms, I'm seeing 3A output which is pretty much the capacity of the > >power supply. The 3055 runs cooler as well; not sure what that means. > > > >Now I have to use an op-amp comparator to measure the current to get > >decent resolution. > > > >> You ought to go buy the TO-3 version of the LM317 for the circuit I > >> suggested and avoid the magic smoke ;-) > > > >The literature doesn't specify the switching frequency, rise time, > >etc. for that part. > > > > > >Regards, > > > >Uncle Steve > > I'm curious why you need to "switch" it? Isn't your only concern the > _average_ current, as determined by the PWM? > > All you need is a low-pass R/C between the micro and the base of Q1 > (as noted in the text box on the schematic). > > I'll run a simulation of that and repost later (under this same link). > > http://www.analog-innovations.com/SED/ChargerForUncleSteve.pdfYou're probably correct, except the rating of the LM317 is half of what I need. It's an interesting idea to use PWM to control a voltage regulator, but it's a completely different approach from what I intended to build. Perhaps it will be worthwhile to refactor your design and substitute a LM338, which has the requisite capacity. For now I think I will fool around with the existing arrangement. Even at 3A output, the 3055 doesn't appear to be saturated as Vce is only .9V. I picked up a couple of BC517 which have a beta of 30000 and 1A current capacity. Perhaps that will be more effective than the BC557 in the pseudo-Sziklai arrangement. Regards, Uncle Steve -- There should be a special word in the English language to identify people who create problems and then turn around and offer up their own tailor-made bogus non-solutions designed to completely avoid the root causes of the situation under consideration. 'Traitor' might be a good choice, but lacks the requisite specificity. One of the problems with contemporary English is it lacks many such words that would otherwise categorically identify certain kinds of person, place, or thing -- making it difficult or impossible to think analytically about such objects. These shortcomings of the English lexicon are representative of Orwellian linguistics at work in the real world.
Reply by ●May 10, 20132013-05-10
On 5/8/2013 9:49 PM, Uncle Steve wrote:> On Wed, May 08, 2013 at 03:56:44PM -0700, Jim Thompson wrote: >> On Wed, 08 May 2013 17:55:36 -0400, Uncle Steve <stevet810@gmail.com> >> wrote: >> >>> On Wed, May 08, 2013 at 02:19:05PM -0700, Jim Thompson wrote: >>>> On Wed, 08 May 2013 10:36:21 -0400, Uncle Steve <stevet810@gmail.com> >>>> wrote: >>>> >>>>> On Wed, May 08, 2013 at 04:44:25PM +0800, Rheilly Phoull wrote: >>>>>> On 07/05/13 10:57, Jim Thompson wrote: >>>> [snip] >>>>>>> >>>>>>> How about something like this... >>>>>>> >>>>>>> http://www.analog-innovations.com/SED/ChargerForUncleSteve.pdf >>>>>>> >>>>>>> ...Jim Thompson >>>>>>> >>>>>> If Uncle is using a micro to control it, why not just control a mosfet >>>>>> with the PWM output ??? >>>>> >>>>> I have the app notes for the LM338 and such, which show simple charger >>>>> circuits like that, but the fact of the matter is I have a couple of >>>>> 3055s and this project is as much about learning some basics as it is >>>>> about charging a battery. For my requirements it is easier to use >>>>> what I have on hand than try to select among parts that I don't really >>>>> understand. If there were a fundamental reason why the 3055 is bad >>>>> for this application I might consider a mosfet, but I don't see why I >>>>> should bother. >>>>> >>>>> Regards, >>>>> >>>>> Uncle Steve >>>> >>>> The 3055 has a minimum beta of 20 at 4 Amps, which you spoke of at one >>>> point in this thread, which means the base current that must be >>>> supplied is 200mA... not a big deal EXCEPT the driving device will see >>>> considerable dissipation. >>> >>> I'm starting to appreciate these factors. Yet, after removing the >>> 4004 diode as superfluous and changing the .5 ohm sense resistor to >>> .1 ohms, I'm seeing 3A output which is pretty much the capacity of the >>> power supply. The 3055 runs cooler as well; not sure what that means. >>> >>> Now I have to use an op-amp comparator to measure the current to get >>> decent resolution. >>> >>>> You ought to go buy the TO-3 version of the LM317 for the circuit I >>>> suggested and avoid the magic smoke ;-) >>> >>> The literature doesn't specify the switching frequency, rise time, >>> etc. for that part. >>> >>> >>> Regards, >>> >>> Uncle Steve >> >> I'm curious why you need to "switch" it? Isn't your only concern the >> _average_ current, as determined by the PWM? >> >> All you need is a low-pass R/C between the micro and the base of Q1 >> (as noted in the text box on the schematic). >> >> I'll run a simulation of that and repost later (under this same link). >> >> http://www.analog-innovations.com/SED/ChargerForUncleSteve.pdf > > You're probably correct, except the rating of the LM317 is half of > what I need.I would urge you to follow JT's advice. Build his circuit. It is easy to add a pass element to get higher current later on. Here's an example diagram to give you an idea how it's done: MJ2955 Vin ---+----> ------------------+-----------> Vout | e\ /c | [3R] --- | | | ----- | +------+---Vin|LM317|Vout---+-------+ | ----- | | | Adj [240R] | | | | | | +----------+ | | | | [.22uF] / [.1uF] | \ | | 5K /<---+ | | \ | | | / | | | | | | Gnd ----------+---------+----+-------------+ Current drawn from the 317 causes a voltage drop across the 3 ohm resistor. When that voltage drop is below about .6 volts, the 2955 conducts no e-c current. When the voltage drop rises to about .6 volts the 2955 begins to conduct e-c current. The more current drawn by the load, the greater the e-c current. The e-c current passes around (not through) the 317 so the 2955 is called a pass element or pass transistor. You can also do it with your 3055, but you need an inverting stage to its base. See "High Current Adjustable Regulator" diagram in the datasheet for the 317 for an example of using an NPN pass element. They use 3 195's in that diagram, but you need only the single 3055.> It's an interesting idea to use PWM to control a voltage > regulator, but it's a completely different approach from what I > intended to build.In reading your various posts it seems clear to me that you are expending a lot of effort and have a lot of interest in this, which is all to the good. But I also see that you are speeding by some points where you could benefit by working to understand them, rather than passing them by - which is what prompted me to reply.> Perhaps it will be worthwhile to refactor your > design and substitute a LM338, which has the requisite capacity.No perhaps about it, it is definitely worthwhile. The earlier part of my reply suggests how you can do it with parts on hand, then later on add a pass element, or, as you mention, substitute a 338.> For > now I think I will fool around with the existing arrangement. > > Even at 3A output, the 3055 doesn't appear to be saturated as Vce is > only .9V. I picked up a couple of BC517 which have a beta of 30000 > and 1A current capacity. Perhaps that will be more effective than the > BC557 in the pseudo-Sziklai arrangement. > >Well, you may get it to work, but you won't learn why it does, or why the previous attempts didn't. It is my impression that you are leap frogging some of the basics. Sometimes throwing bigger/better/stronger parts at a problem is not in your best interests. Ed> > Regards, > > Uncle Steve >
