On Thu, 18 Jul 2013 10:53:53 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>On 07/18/2013 10:49 AM, Jim Thompson wrote: >> On Thu, 18 Jul 2013 10:39:22 -0400, Phil Hobbs >> <pcdhSpamMeSenseless@electrooptical.net> wrote: >> >>> On 07/18/2013 10:32 AM, Jim Thompson wrote: >>>> On Thu, 18 Jul 2013 08:32:13 -0400, Phil Hobbs >>>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>>> >>>>> On 07/17/2013 11:01 PM, John K wrote: >>>>>> Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote: >>>>>> >>>>>>> Okay, thanks all--I think I've got it figured out. I'm already using >>>>>>> a Simple Switcher buck to make -15 from +16-20, and I'll piggyback off >>>>>>> the free AC and then use regulated cap multipliers to make a nice >>>>>>> quiet +-40ish volts. >>>>>>> >>>>>>> Cartoon attached. >>>>>>> >>>>>>> Cheers >>>>>>> >>>>>>> Phil Hobbs >>>>>> >>>>>> Very nice. You got rid of the horrible ringing at the drain on most of >>>>>> the other versions posted here. That is very nice. >>>>>> >>>>>> I was wondering why you want to dump 2.25 watts into R2, the 100 ohm >>>>>> going from -15V to ground. >>>>>> >>>>> >>>>> That's the load, i.e. it represents the circuit that needs the -15V. >>>>> >>>>>> I couldn't see why it was needed, so I removed it. Circuit works fine. >>>>>> >>>>>> There may be some loading effect on either or both supplies that require >>>>>> it, but as currently shown, the reason is not apparent. >>>>>> >>>>>> Similarly, D6 which was in parallel with R2 doesn't seem to be needed >>>>>> either. Removed it also. Circuit works fine. >>>>> >>>>> That was there to get rid of a weird polarity reversal at power-on. The >>>>> power-on transient isn't representative of what the real circuit will >>>>> do--the chip has built-in current limiting, whereas this version goes up >>>>> to like 7A on power-up--but putting +3V on a -15V rail isn't usually >>>>> considered too healthy for the rest of the circuitry. >>>> >>>> Running it on LTspice: The current thru M1 goes up to 12A, with a half >>>> sinusoidal envelope, base width of nearly a millisecond. What is the >>>> actual schematic/chip that "has built-in current limiting"? >>>> >>>> [snip] >>>> >>>> ...Jim Thompson >>>> >>> >>> I'll probably hang it on the output of an LM2594. >>> >>> >>> Cheers >>> >>> Phil Hobbs >> >> 0.5A Limit, or is there a way to set it lower? >> >> ...Jim Thompson >> > >No, there isn't, but half an amp isn't awful. The current limit on that >chip is a bit squishy, as well--the datasheet limits are pretty wide, >but it's guaranteed to be less than 1.25A iirc. > >Cheers > >Phil HobbsSpice voltage sources are infinitely powerful; wall warts aren't. Lots of switchers have soft-start, too. -- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
Flyback vs half-bridge
Started by ●July 16, 2013
Reply by ●July 18, 20132013-07-18
Reply by ●July 18, 20132013-07-18
On Friday, 19 July 2013 00:37:44 UTC+10, Phil Hobbs wrote:> On 07/18/2013 10:06 AM, Joerg wrote:=20 > > George Herold wrote:=20 > >> On Wednesday, July 17, 2013 7:56:00 PM UTC-4, Bill Sloman wrote:=20 > > [...] =20 > >>>=20 > >>> When Siemens became EPCOS, and the magnetic business was eventually > >>> sold off to TDK the situation got a bit confused, and I've lost > >>> touch with the relevant web-sites.=20 > >>>=20 > >>> If Winfield Hill ever does get around to releasing the third=20 > >>> edition of "The Art of Electronics" it may include a decent section==20> >>> on magnetics - I certainly put in a personal plea for one a few > >>> years ago.=20 > >>>> >> OK thanks Bill, So I should go looking for the Siemens book. I'll=20 > >> see what the web has to offer.<snip>> > It's probably long gone. If you want to also learn about switcher desig=n=20> > you might want to take a look at a book by Pressman. I don't have i b=ut=20> > heard it being lauded by lots of engineers. Maybe someone can shed ligh=t=20> > as to the exact title or ISBN. On some online stores you can take a > > preview before buying. > =20 > Pressman, Billings, & Morey, "Switching Power Supply Design" 3rd Ed,=20 > McGraw Hill. > =20 > I bought a copy the other day but haven't spent much time with it yet.I've got a copy of the second edition ISBN 0-07-052236-7 The chapter on magnetics is comprehensive, and even covers the skin effect,= and the "proximity effect" which I've never heard of before. Pedagogically= , it's rubbish - almost as bad as Snelling. The author assumes that the rea= der understands the basics, and concentrates on the complicated detail. --=20 Bill Sloman, Sydney
Reply by ●July 18, 20132013-07-18
On 07/18/2013 11:28 AM, John Larkin wrote:> On Thu, 18 Jul 2013 10:53:53 -0400, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> On 07/18/2013 10:49 AM, Jim Thompson wrote: >>> On Thu, 18 Jul 2013 10:39:22 -0400, Phil Hobbs >>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>> >>>> On 07/18/2013 10:32 AM, Jim Thompson wrote: >>>>> On Thu, 18 Jul 2013 08:32:13 -0400, Phil Hobbs >>>>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>>>> >>>>>> On 07/17/2013 11:01 PM, John K wrote: >>>>>>> Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote: >>>>>>> >>>>>>>> Okay, thanks all--I think I've got it figured out. I'm already using >>>>>>>> a Simple Switcher buck to make -15 from +16-20, and I'll piggyback off >>>>>>>> the free AC and then use regulated cap multipliers to make a nice >>>>>>>> quiet +-40ish volts. >>>>>>>> >>>>>>>> Cartoon attached. >>>>>>>> >>>>>>>> Cheers >>>>>>>> >>>>>>>> Phil Hobbs >>>>>>> >>>>>>> Very nice. You got rid of the horrible ringing at the drain on most of >>>>>>> the other versions posted here. That is very nice. >>>>>>> >>>>>>> I was wondering why you want to dump 2.25 watts into R2, the 100 ohm >>>>>>> going from -15V to ground. >>>>>>> >>>>>> >>>>>> That's the load, i.e. it represents the circuit that needs the -15V. >>>>>> >>>>>>> I couldn't see why it was needed, so I removed it. Circuit works fine. >>>>>>> >>>>>>> There may be some loading effect on either or both supplies that require >>>>>>> it, but as currently shown, the reason is not apparent. >>>>>>> >>>>>>> Similarly, D6 which was in parallel with R2 doesn't seem to be needed >>>>>>> either. Removed it also. Circuit works fine. >>>>>> >>>>>> That was there to get rid of a weird polarity reversal at power-on. The >>>>>> power-on transient isn't representative of what the real circuit will >>>>>> do--the chip has built-in current limiting, whereas this version goes up >>>>>> to like 7A on power-up--but putting +3V on a -15V rail isn't usually >>>>>> considered too healthy for the rest of the circuitry. >>>>> >>>>> Running it on LTspice: The current thru M1 goes up to 12A, with a half >>>>> sinusoidal envelope, base width of nearly a millisecond. What is the >>>>> actual schematic/chip that "has built-in current limiting"? >>>>> >>>>> [snip] >>>>> >>>>> ...Jim Thompson >>>>> >>>> >>>> I'll probably hang it on the output of an LM2594. >>>> >>>> >>>> Cheers >>>> >>>> Phil Hobbs >>> >>> 0.5A Limit, or is there a way to set it lower? >>> >>> ...Jim Thompson >>> >> >> No, there isn't, but half an amp isn't awful. The current limit on that >> chip is a bit squishy, as well--the datasheet limits are pretty wide, >> but it's guaranteed to be less than 1.25A iirc. >> >> Cheers >> >> Phil Hobbs > > Spice voltage sources are infinitely powerful; wall warts aren't. Lots of > switchers have soft-start, too. > >I think the torture-test is powering up the wall wart and then plugging it into the box. There'll be the usual polyfuse, whose cold resistance helps a bit, and I suppose I could do something fancier like a resistor parallelled by a MOSFET controlled by the POR chip, but that's way too fancy for just a few watts. It's really the 1N4148s or BAV99s or whatever little diode I use that will be the issue--the turn-on surge will divide between the main -15V reservoir cap and the charge pump caps more or less proportionally with the size of the caps (neglecting ESR and diode drops). So I may use a much bigger reservoir cap and smaller charge pump caps, followed by RC filters ahead of the cap multipliers. Alternatively, just putting 50 or 100 ohms in series with the charge pumps will protect them OK, and will only cost a volt or two. It's better from a certification standpoint if the voltages inside the box never exceed 60V even in fault conditions, so I'll need to put zeners on the +-45V outputs, so that even with an out-of-spec input voltage and the transzorb at its upper spec limit, I don't get over 60V. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●July 18, 20132013-07-18
Bill Sloman wrote:> On Friday, 19 July 2013 00:37:44 UTC+10, Phil Hobbs wrote: >> On 07/18/2013 10:06 AM, Joerg wrote:[...]>>> It's probably long gone. If you want to also learn about switcher >>> design you might want to take a look at a book by Pressman. I >>> don't have i but heard it being lauded by lots of engineers. >>> Maybe someone can shed light as to the exact title or ISBN. On >>> some online stores you can take a preview before buying. >> >> Pressman, Billings, & Morey, "Switching Power Supply Design" 3rd >> Ed, McGraw Hill. >> >> I bought a copy the other day but haven't spent much time with it >> yet. > > I've got a copy of the second edition ISBN 0-07-052236-7 > > The chapter on magnetics is comprehensive, and even covers the skin > effect, and the "proximity effect" which I've never heard of before. > Pedagogically, it's rubbish - almost as bad as Snelling. The author > assumes that the reader understands the basics, and concentrates on > the complicated detail. >That's what most books about advanced technologies do. If they didn't then most of the forests on this planet would be depleted by now :-) But seriously, a person with lacking EE basics should not be designing switchers without first becoming proficient enough, that's something the pros should do. -- Regards, Joerg http://www.analogconsultants.com/
Reply by ●July 18, 20132013-07-18
Phil Hobbs wrote:> On 07/18/2013 10:32 AM, Jim Thompson wrote: >> On Thu, 18 Jul 2013 08:32:13 -0400, Phil Hobbs >> <pcdhSpamMeSenseless@electrooptical.net> wrote: >> >>> On 07/17/2013 11:01 PM, John K wrote: >>>> Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote: >>>> >>>>> Okay, thanks all--I think I've got it figured out. I'm already using >>>>> a Simple Switcher buck to make -15 from +16-20, and I'll piggyback off >>>>> the free AC and then use regulated cap multipliers to make a nice >>>>> quiet +-40ish volts. >>>>> >>>>> Cartoon attached. >>>>> >>>>> Cheers >>>>> >>>>> Phil Hobbs >>>> >>>> Very nice. You got rid of the horrible ringing at the drain on most of >>>> the other versions posted here. That is very nice. >>>> >>>> I was wondering why you want to dump 2.25 watts into R2, the 100 ohm >>>> going from -15V to ground. >>>> >>> >>> That's the load, i.e. it represents the circuit that needs the -15V. >>> >>>> I couldn't see why it was needed, so I removed it. Circuit works fine. >>>> >>>> There may be some loading effect on either or both supplies that >>>> require >>>> it, but as currently shown, the reason is not apparent. >>>> >>>> Similarly, D6 which was in parallel with R2 doesn't seem to be needed >>>> either. Removed it also. Circuit works fine. >>> >>> That was there to get rid of a weird polarity reversal at power-on. The >>> power-on transient isn't representative of what the real circuit will >>> do--the chip has built-in current limiting, whereas this version goes up >>> to like 7A on power-up--but putting +3V on a -15V rail isn't usually >>> considered too healthy for the rest of the circuitry. >> >> Running it on LTspice: The current thru M1 goes up to 12A, with a half >> sinusoidal envelope, base width of nearly a millisecond. What is the >> actual schematic/chip that "has built-in current limiting"? >> >> [snip] >> >> ...Jim Thompson >> > > I'll probably hang it on the output of an LM2594. >That's a buck. If you already have a -15V switcher in there, why not hook into that as you had outlined earlier? -- Regards, Joerg http://www.analogconsultants.com/
Reply by ●July 18, 20132013-07-18
On 07/18/2013 12:23 PM, Joerg wrote:> Phil Hobbs wrote: >> On 07/18/2013 10:32 AM, Jim Thompson wrote: >>> On Thu, 18 Jul 2013 08:32:13 -0400, Phil Hobbs >>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>> >>>> On 07/17/2013 11:01 PM, John K wrote: >>>>> Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote: >>>>> >>>>>> Okay, thanks all--I think I've got it figured out. I'm already using >>>>>> a Simple Switcher buck to make -15 from +16-20, and I'll piggyback off >>>>>> the free AC and then use regulated cap multipliers to make a nice >>>>>> quiet +-40ish volts. >>>>>> >>>>>> Cartoon attached. >>>>>> >>>>>> Cheers >>>>>> >>>>>> Phil Hobbs >>>>> >>>>> Very nice. You got rid of the horrible ringing at the drain on most of >>>>> the other versions posted here. That is very nice. >>>>> >>>>> I was wondering why you want to dump 2.25 watts into R2, the 100 ohm >>>>> going from -15V to ground. >>>>> >>>> >>>> That's the load, i.e. it represents the circuit that needs the -15V. >>>> >>>>> I couldn't see why it was needed, so I removed it. Circuit works fine. >>>>> >>>>> There may be some loading effect on either or both supplies that >>>>> require >>>>> it, but as currently shown, the reason is not apparent. >>>>> >>>>> Similarly, D6 which was in parallel with R2 doesn't seem to be needed >>>>> either. Removed it also. Circuit works fine. >>>> >>>> That was there to get rid of a weird polarity reversal at power-on. The >>>> power-on transient isn't representative of what the real circuit will >>>> do--the chip has built-in current limiting, whereas this version goes up >>>> to like 7A on power-up--but putting +3V on a -15V rail isn't usually >>>> considered too healthy for the rest of the circuitry. >>> >>> Running it on LTspice: The current thru M1 goes up to 12A, with a half >>> sinusoidal envelope, base width of nearly a millisecond. What is the >>> actual schematic/chip that "has built-in current limiting"? >>> >>> [snip] >>> >>> ...Jim Thompson >>> >> >> I'll probably hang it on the output of an LM2594. >> > > That's a buck. If you already have a -15V switcher in there, why not > hook into that as you had outlined earlier? >I'm using it as an inverter, i.e. grounding the far end of the inductor and letting it pump its ground pin down to -15V. Works fine. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●July 18, 20132013-07-18
On Thu, 18 Jul 2013 10:53:53 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>On 07/18/2013 10:49 AM, Jim Thompson wrote: >> On Thu, 18 Jul 2013 10:39:22 -0400, Phil Hobbs >> <pcdhSpamMeSenseless@electrooptical.net> wrote: >> >>> On 07/18/2013 10:32 AM, Jim Thompson wrote: >>>> On Thu, 18 Jul 2013 08:32:13 -0400, Phil Hobbs >>>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>>> >>>>> On 07/17/2013 11:01 PM, John K wrote: >>>>>> Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote: >>>>>> >>>>>>> Okay, thanks all--I think I've got it figured out. I'm already using >>>>>>> a Simple Switcher buck to make -15 from +16-20, and I'll piggyback off >>>>>>> the free AC and then use regulated cap multipliers to make a nice >>>>>>> quiet +-40ish volts. >>>>>>> >>>>>>> Cartoon attached. >>>>>>> >>>>>>> Cheers >>>>>>> >>>>>>> Phil Hobbs >>>>>> >>>>>> Very nice. You got rid of the horrible ringing at the drain on most of >>>>>> the other versions posted here. That is very nice. >>>>>> >>>>>> I was wondering why you want to dump 2.25 watts into R2, the 100 ohm >>>>>> going from -15V to ground. >>>>>> >>>>> >>>>> That's the load, i.e. it represents the circuit that needs the -15V. >>>>> >>>>>> I couldn't see why it was needed, so I removed it. Circuit works fine. >>>>>> >>>>>> There may be some loading effect on either or both supplies that require >>>>>> it, but as currently shown, the reason is not apparent. >>>>>> >>>>>> Similarly, D6 which was in parallel with R2 doesn't seem to be needed >>>>>> either. Removed it also. Circuit works fine. >>>>> >>>>> That was there to get rid of a weird polarity reversal at power-on. The >>>>> power-on transient isn't representative of what the real circuit will >>>>> do--the chip has built-in current limiting, whereas this version goes up >>>>> to like 7A on power-up--but putting +3V on a -15V rail isn't usually >>>>> considered too healthy for the rest of the circuitry. >>>> >>>> Running it on LTspice: The current thru M1 goes up to 12A, with a half >>>> sinusoidal envelope, base width of nearly a millisecond. What is the >>>> actual schematic/chip that "has built-in current limiting"? >>>> >>>> [snip] >>>> >>>> ...Jim Thompson >>>> >>> >>> I'll probably hang it on the output of an LM2594. >>> >>> >>> Cheers >>> >>> Phil Hobbs >> >> 0.5A Limit, or is there a way to set it lower? >> >> ...Jim Thompson >> > >No, there isn't, but half an amp isn't awful. The current limit on that >chip is a bit squishy, as well--the datasheet limits are pretty wide, >but it's guaranteed to be less than 1.25A iirc. > >Cheers > >Phil HobbsThat's what I was noticing... it's a switch current limit, not an output current limit. But probably safe. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 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 ●July 18, 20132013-07-18
On Thu, 18 Jul 2013 12:05:13 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>On 07/18/2013 11:28 AM, John Larkin wrote: >> On Thu, 18 Jul 2013 10:53:53 -0400, Phil Hobbs >> <pcdhSpamMeSenseless@electrooptical.net> wrote: >> >>> On 07/18/2013 10:49 AM, Jim Thompson wrote: >>>> On Thu, 18 Jul 2013 10:39:22 -0400, Phil Hobbs >>>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>>> >>>>> On 07/18/2013 10:32 AM, Jim Thompson wrote: >>>>>> On Thu, 18 Jul 2013 08:32:13 -0400, Phil Hobbs >>>>>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>>>>> >>>>>>> On 07/17/2013 11:01 PM, John K wrote: >>>>>>>> Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote: >>>>>>>> >>>>>>>>> Okay, thanks all--I think I've got it figured out. I'm already using >>>>>>>>> a Simple Switcher buck to make -15 from +16-20, and I'll piggyback off >>>>>>>>> the free AC and then use regulated cap multipliers to make a nice >>>>>>>>> quiet +-40ish volts. >>>>>>>>> >>>>>>>>> Cartoon attached. >>>>>>>>> >>>>>>>>> Cheers >>>>>>>>> >>>>>>>>> Phil Hobbs >>>>>>>> >>>>>>>> Very nice. You got rid of the horrible ringing at the drain on most of >>>>>>>> the other versions posted here. That is very nice. >>>>>>>> >>>>>>>> I was wondering why you want to dump 2.25 watts into R2, the 100 ohm >>>>>>>> going from -15V to ground. >>>>>>>> >>>>>>> >>>>>>> That's the load, i.e. it represents the circuit that needs the -15V. >>>>>>> >>>>>>>> I couldn't see why it was needed, so I removed it. Circuit works fine. >>>>>>>> >>>>>>>> There may be some loading effect on either or both supplies that require >>>>>>>> it, but as currently shown, the reason is not apparent. >>>>>>>> >>>>>>>> Similarly, D6 which was in parallel with R2 doesn't seem to be needed >>>>>>>> either. Removed it also. Circuit works fine. >>>>>>> >>>>>>> That was there to get rid of a weird polarity reversal at power-on. The >>>>>>> power-on transient isn't representative of what the real circuit will >>>>>>> do--the chip has built-in current limiting, whereas this version goes up >>>>>>> to like 7A on power-up--but putting +3V on a -15V rail isn't usually >>>>>>> considered too healthy for the rest of the circuitry. >>>>>> >>>>>> Running it on LTspice: The current thru M1 goes up to 12A, with a half >>>>>> sinusoidal envelope, base width of nearly a millisecond. What is the >>>>>> actual schematic/chip that "has built-in current limiting"? >>>>>> >>>>>> [snip] >>>>>> >>>>>> ...Jim Thompson >>>>>> >>>>> >>>>> I'll probably hang it on the output of an LM2594. >>>>> >>>>> >>>>> Cheers >>>>> >>>>> Phil Hobbs >>>> >>>> 0.5A Limit, or is there a way to set it lower? >>>> >>>> ...Jim Thompson >>>> >>> >>> No, there isn't, but half an amp isn't awful. The current limit on that >>> chip is a bit squishy, as well--the datasheet limits are pretty wide, >>> but it's guaranteed to be less than 1.25A iirc. >>> >>> Cheers >>> >>> Phil Hobbs >> >> Spice voltage sources are infinitely powerful; wall warts aren't. Lots of >> switchers have soft-start, too. >> >> > >I think the torture-test is powering up the wall wart and then plugging >it into the box. There'll be the usual polyfuse, whose cold resistance >helps a bit, and I suppose I could do something fancier like a resistor >parallelled by a MOSFET controlled by the POR chip, but that's way too >fancy for just a few watts. > >It's really the 1N4148s or BAV99s or whatever little diode I use that >will be the issue--the turn-on surge will divide between the main -15V >reservoir cap and the charge pump caps more or less proportionally with >the size of the caps (neglecting ESR and diode drops). So I may use a >much bigger reservoir cap and smaller charge pump caps, followed by RC >filters ahead of the cap multipliers. Alternatively, just putting 50 or >100 ohms in series with the charge pumps will protect them OK, and will >only cost a volt or two. > >It's better from a certification standpoint if the voltages inside the >box never exceed 60V even in fault conditions, so I'll need to put >zeners on the +-45V outputs, so that even with an out-of-spec input >voltage and the transzorb at its upper spec limit, I don't get over 60V. > >Cheers > >Phil HobbsYup. It's the inrush that tests your specifications ;-) ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 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 ●July 18, 20132013-07-18
Phil Hobbs wrote:> On 07/18/2013 12:23 PM, Joerg wrote: >> Phil Hobbs wrote: >>> On 07/18/2013 10:32 AM, Jim Thompson wrote: >>>> On Thu, 18 Jul 2013 08:32:13 -0400, Phil Hobbs >>>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>>> >>>>> On 07/17/2013 11:01 PM, John K wrote: >>>>>> Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote: >>>>>> >>>>>>> Okay, thanks all--I think I've got it figured out. I'm already >>>>>>> using >>>>>>> a Simple Switcher buck to make -15 from +16-20, and I'll >>>>>>> piggyback off >>>>>>> the free AC and then use regulated cap multipliers to make a nice >>>>>>> quiet +-40ish volts. >>>>>>> >>>>>>> Cartoon attached. >>>>>>> >>>>>>> Cheers >>>>>>> >>>>>>> Phil Hobbs >>>>>> >>>>>> Very nice. You got rid of the horrible ringing at the drain on >>>>>> most of >>>>>> the other versions posted here. That is very nice. >>>>>> >>>>>> I was wondering why you want to dump 2.25 watts into R2, the 100 ohm >>>>>> going from -15V to ground. >>>>>> >>>>> >>>>> That's the load, i.e. it represents the circuit that needs the -15V. >>>>> >>>>>> I couldn't see why it was needed, so I removed it. Circuit works >>>>>> fine. >>>>>> >>>>>> There may be some loading effect on either or both supplies that >>>>>> require >>>>>> it, but as currently shown, the reason is not apparent. >>>>>> >>>>>> Similarly, D6 which was in parallel with R2 doesn't seem to be needed >>>>>> either. Removed it also. Circuit works fine. >>>>> >>>>> That was there to get rid of a weird polarity reversal at >>>>> power-on. The >>>>> power-on transient isn't representative of what the real circuit will >>>>> do--the chip has built-in current limiting, whereas this version >>>>> goes up >>>>> to like 7A on power-up--but putting +3V on a -15V rail isn't usually >>>>> considered too healthy for the rest of the circuitry. >>>> >>>> Running it on LTspice: The current thru M1 goes up to 12A, with a half >>>> sinusoidal envelope, base width of nearly a millisecond. What is the >>>> actual schematic/chip that "has built-in current limiting"? >>>> >>>> [snip] >>>> >>>> ...Jim Thompson >>>> >>> >>> I'll probably hang it on the output of an LM2594. >>> >> >> That's a buck. If you already have a -15V switcher in there, why not >> hook into that as you had outlined earlier? >> > > I'm using it as an inverter, i.e. grounding the far end of the inductor > and letting it pump its ground pin down to -15V. Works fine. >Yes, that's the old MC34063 method. But watch out for noise and loop stability. -- Regards, Joerg http://www.analogconsultants.com/
Reply by ●July 18, 20132013-07-18
On Thu, 18 Jul 2013 10:06:17 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:>On Thu, 18 Jul 2013 10:53:53 -0400, Phil Hobbs ><pcdhSpamMeSenseless@electrooptical.net> wrote: > >>On 07/18/2013 10:49 AM, Jim Thompson wrote: >>> On Thu, 18 Jul 2013 10:39:22 -0400, Phil Hobbs >>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>> >>>> On 07/18/2013 10:32 AM, Jim Thompson wrote: >>>>> On Thu, 18 Jul 2013 08:32:13 -0400, Phil Hobbs >>>>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>>>> >>>>>> On 07/17/2013 11:01 PM, John K wrote: >>>>>>> Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote: >>>>>>> >>>>>>>> Okay, thanks all--I think I've got it figured out. I'm already using >>>>>>>> a Simple Switcher buck to make -15 from +16-20, and I'll piggyback off >>>>>>>> the free AC and then use regulated cap multipliers to make a nice >>>>>>>> quiet +-40ish volts. >>>>>>>> >>>>>>>> Cartoon attached. >>>>>>>> >>>>>>>> Cheers >>>>>>>> >>>>>>>> Phil Hobbs >>>>>>> >>>>>>> Very nice. You got rid of the horrible ringing at the drain on most of >>>>>>> the other versions posted here. That is very nice. >>>>>>> >>>>>>> I was wondering why you want to dump 2.25 watts into R2, the 100 ohm >>>>>>> going from -15V to ground. >>>>>>> >>>>>> >>>>>> That's the load, i.e. it represents the circuit that needs the -15V. >>>>>> >>>>>>> I couldn't see why it was needed, so I removed it. Circuit works fine. >>>>>>> >>>>>>> There may be some loading effect on either or both supplies that require >>>>>>> it, but as currently shown, the reason is not apparent. >>>>>>> >>>>>>> Similarly, D6 which was in parallel with R2 doesn't seem to be needed >>>>>>> either. Removed it also. Circuit works fine. >>>>>> >>>>>> That was there to get rid of a weird polarity reversal at power-on. The >>>>>> power-on transient isn't representative of what the real circuit will >>>>>> do--the chip has built-in current limiting, whereas this version goes up >>>>>> to like 7A on power-up--but putting +3V on a -15V rail isn't usually >>>>>> considered too healthy for the rest of the circuitry. >>>>> >>>>> Running it on LTspice: The current thru M1 goes up to 12A, with a half >>>>> sinusoidal envelope, base width of nearly a millisecond. What is the >>>>> actual schematic/chip that "has built-in current limiting"? >>>>> >>>>> [snip] >>>>> >>>>> ...Jim Thompson >>>>> >>>> >>>> I'll probably hang it on the output of an LM2594. >>>> >>>> >>>> Cheers >>>> >>>> Phil Hobbs >>> >>> 0.5A Limit, or is there a way to set it lower? >>> >>> ...Jim Thompson >>> >> >>No, there isn't, but half an amp isn't awful. The current limit on that >>chip is a bit squishy, as well--the datasheet limits are pretty wide, >>but it's guaranteed to be less than 1.25A iirc. >> >>Cheers >> >>Phil Hobbs > >That's what I was noticing... it's a switch current limit, not an >output current limit. But probably safe. > > ...Jim ThompsonYou might want to reconsider and add soft-start to your "cartoon".... Subject: Hobb's Cartoon (SED) - HobbsCartoon-with_CL.png Date: Thu, 18 Jul 2013 11:19:26 -0700 Message-ID: <abcgu89uf09kt8l0n55pvm5su9c7ct6li6@4ax.com> Using the LM2594, you're sort of caught between a rock and a hard-place... large load (on LM2594) capacitor, huge peak currents on your add-on inverter, smaller capacitor... sag your 16V. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 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.
