On 4 Aug 2016 20:07:05 -0700, Winfield Hill <hill@rowland.harvard.edu> wrote:> > I've created all kinds of HV circuits in the last > 5 years,** and each one needs an external HV supply. > So I really need some simple HV-supply circuits to > plop onto these PCB's to make them self-sufficient. > > Today's circuit is a basic flyback, to convert a > 12V,1A wallwort source to 500V max, at 5-10W load. > > I used a UC3843B running at 100kHz driving a MOSFET > switching a 47uH inductor (dI = dt V/L = 2A in 8us). > This can provide up to 100uJ each cycle, to charge > a say 2000uF storage cap to 400V in 16 seconds. > > I settled on an ES1J fast-recovery output diode > (after rejecting an MRA4007), After rejecting > an STP7NB60 as too lossy, I experimented and > picked an Infineon IPP65R225C7 superjunction > MOSFET: Rds(on) = 0.2 ohms (0.5 ohms max at Tj > = 150C), and Coss = 14pF at 400V (20pF at 100V). > Nice. > > But the flyback inductor was an issue. See photo >https://www.dropbox.com/s/cwo10wm5upehvrw/PWR-741_flyback_350V-inductors_small.jpg?dl=0 > > I started with an older 1A part from the drawer: > a Mouser 47uH, 0.1 ohms, rated 1.3A, see photo, > lower right. With this part my circuit had 2.2W > of wasted power at 5W out. Heating was bad, the > inductor melted a soldered lead and disconnected > itself from the circit! Whew, ugly! I needed a > beefier part. Enter a Coilcraft PCV-0-473-05L, > photo lower left. Those fat wires, this had to > be the answer. Rated 0.035 ohms and 6A. But it > increased my wasted power to 3.7W, double ouch! > > Giving up on my commercial inventory, I made > an inductor using an RM8 bobbin and core. > (See photo, upper part, mounted on the PCB.) > > I selected a large gap core, A_L = 100nH/t^2. > N = sqrt(L / A_L) = 22 turns. With #20 wire, > Rdc=0.036 ohms. I measured Q=39 at 100kHz, > esr = 2pi f L/Q = 0.75 ohms. Q=80 at 1MHz. > Looking pretty good, ignoring coreloss at > full power (the ckt uses 40mW at no load). > > Yeah! With the RM8 inductor, total losses > dropped to 1.1 watts. Note, the MOSFET, > sense resistor, diode and capacitor share > in the loss generation, so I don't know > the inductor loss. Everything runs cool, > which wasn't the case at the beginning. > > ** more on that later ...I have posted this before, but... I've found that high-ratio boosts can have problems, so I like to use dual-winding inductors as autotransformer flybacks. Lots of people make these things in various sizes. They are cheap enough that you could even parallel some. https://dl.dropboxusercontent.com/u/53724080/Circuits/HV/T840_A13_PS.pdf https://dl.dropboxusercontent.com/u/53724080/Circuits/HV/HV_Proto_2.JPG https://dl.dropboxusercontent.com/u/53724080/PCBs/T840_E1.jpg I pushed that inductor some, and did get a little warm, so I added some copper to heat sink it. -- John Larkin Highland Technology, Inc lunatic fringe electronics
inductor for HV flyback supply
Started by ●August 5, 2016
Reply by ●August 5, 20162016-08-05
Reply by ●August 5, 20162016-08-05
On Friday, 5 August 2016 16:37:43 UTC+2, John Larkin wrote:> On 4 Aug 2016 20:07:05 -0700, Winfield Hill <hill@rowland.harvard.edu> > wrote: > > > > > I've created all kinds of HV circuits in the last > > 5 years,** and each one needs an external HV supply. > > So I really need some simple HV-supply circuits to > > plop onto these PCB's to make them self-sufficient. > > > > Today's circuit is a basic flyback, to convert a > > 12V,1A wallwort source to 500V max, at 5-10W load. > > > > I used a UC3843B running at 100kHz driving a MOSFET > > switching a 47uH inductor (dI = dt V/L = 2A in 8us). > > This can provide up to 100uJ each cycle, to charge > > a say 2000uF storage cap to 400V in 16 seconds. > > > > I settled on an ES1J fast-recovery output diode > > (after rejecting an MRA4007), After rejecting > > an STP7NB60 as too lossy, I experimented and > > picked an Infineon IPP65R225C7 superjunction > > MOSFET: Rds(on) = 0.2 ohms (0.5 ohms max at Tj > > = 150C), and Coss = 14pF at 400V (20pF at 100V). > > Nice. > > > > But the flyback inductor was an issue. See photo > >https://www.dropbox.com/s/cwo10wm5upehvrw/PWR-741_flyback_350V-inductors_small.jpg?dl=0 > > > > I started with an older 1A part from the drawer: > > a Mouser 47uH, 0.1 ohms, rated 1.3A, see photo, > > lower right. With this part my circuit had 2.2W > > of wasted power at 5W out. Heating was bad, the > > inductor melted a soldered lead and disconnected > > itself from the circit! Whew, ugly! I needed a > > beefier part. Enter a Coilcraft PCV-0-473-05L, > > photo lower left. Those fat wires, this had to > > be the answer. Rated 0.035 ohms and 6A. But it > > increased my wasted power to 3.7W, double ouch! > > > > Giving up on my commercial inventory, I made > > an inductor using an RM8 bobbin and core. > > (See photo, upper part, mounted on the PCB.) > > > > I selected a large gap core, A_L = 100nH/t^2. > > N = sqrt(L / A_L) = 22 turns. With #20 wire, > > Rdc=0.036 ohms. I measured Q=39 at 100kHz, > > esr = 2pi f L/Q = 0.75 ohms. Q=80 at 1MHz. > > Looking pretty good, ignoring coreloss at > > full power (the ckt uses 40mW at no load). > > > > Yeah! With the RM8 inductor, total losses > > dropped to 1.1 watts. Note, the MOSFET, > > sense resistor, diode and capacitor share > > in the loss generation, so I don't know > > the inductor loss. Everything runs cool, > > which wasn't the case at the beginning. > > > > ** more on that later ... > > I have posted this before, but... > > I've found that high-ratio boosts can have problems, so I like to use > dual-winding inductors as autotransformer flybacks. Lots of people > make these things in various sizes. They are cheap enough that you > could even parallel some. > > https://dl.dropboxusercontent.com/u/53724080/Circuits/HV/T840_A13_PS.pdf > > https://dl.dropboxusercontent.com/u/53724080/Circuits/HV/HV_Proto_2.JPG > > https://dl.dropboxusercontent.com/u/53724080/PCBs/T840_E1.jpg > > I pushed that inductor some, and did get a little warm, so I added > some copper to heat sink it. >Perhaps a half-bridge forward converter. The 12V will be easy to drive into the primary, and turns ratio of 1:40 is not a problem in a forward Cheers Klaus
Reply by ●August 5, 20162016-08-05
On Thursday, August 4, 2016 at 11:07:26 PM UTC-4, Winfield Hill wrote:> I've created all kinds of HV circuits in the last > 5 years,** and each one needs an external HV supply. > So I really need some simple HV-supply circuits to > plop onto these PCB's to make them self-sufficient. > > Today's circuit is a basic flyback, to convert a > 12V,1A wallwort source to 500V max, at 5-10W load. > > I used a UC3843B running at 100kHz driving a MOSFET > switching a 47uH inductor (dI = dt V/L = 2A in 8us). > This can provide up to 100uJ each cycle, to charge > a say 2000uF storage cap to 400V in 16 seconds. > > I settled on an ES1J fast-recovery output diode > (after rejecting an MRA4007), After rejecting > an STP7NB60 as too lossy, I experimented and > picked an Infineon IPP65R225C7 superjunction > MOSFET: Rds(on) = 0.2 ohms (0.5 ohms max at Tj > = 150C), and Coss = 14pF at 400V (20pF at 100V). > Nice. > > But the flyback inductor was an issue. See photo > https://www.dropbox.com/s/cwo10wm5upehvrw/PWR-741_flyback_350V-inductors_small.jpg?dl=0 > > I started with an older 1A part from the drawer: > a Mouser 47uH, 0.1 ohms, rated 1.3A, see photo, > lower right. With this part my circuit had 2.2W > of wasted power at 5W out. Heating was bad, the > inductor melted a soldered lead and disconnected > itself from the circit! Whew, ugly! I needed a > beefier part. Enter a Coilcraft PCV-0-473-05L, > photo lower left. Those fat wires, this had to > be the answer. Rated 0.035 ohms and 6A. But it > increased my wasted power to 3.7W, double ouch! > > Giving up on my commercial inventory, I made > an inductor using an RM8 bobbin and core. > (See photo, upper part, mounted on the PCB.) > > I selected a large gap core, A_L = 100nH/t^2. > N = sqrt(L / A_L) = 22 turns. With #20 wire, > Rdc=0.036 ohms. I measured Q=39 at 100kHz, > esr = 2pi f L/Q = 0.75 ohms. Q=80 at 1MHz. > Looking pretty good, ignoring coreloss at > full power (the ckt uses 40mW at no load). > > Yeah! With the RM8 inductor, total losses > dropped to 1.1 watts. Note, the MOSFET, > sense resistor, diode and capacitor share > in the loss generation, so I don't know > the inductor loss. Everything runs cool, > which wasn't the case at the beginning. > > ** more on that later ... > > > -- > Thanks, > - WinJohn beat me to suggesting coupled inductors ... I got distracted simulating one. An boost inductor charged for 8uS @ 12V, will discharge into 500V in 8uS * 12V/(500V-12V) = 200nS. That's pretty fast! And quite a whack for your rectifier and filter components. Driving the tap of two coupled inductors in series lets you double the discharge time, halve the discharge current, and halve the switch's voltage rating. It's kind of a nice option for low-power high-ratio dc-dc converters, short of resorting to a forward converter with a custom transformer. They're jelly-bean, e.g.: http://www.mouser.com/ds/2/597/msd1278-220442.pdf http://www.mouser.com/Passive-Components/Inductors/Coupled-Inductors/_/N-afrbk?Rl=afrbkZer9dZ1z0wqgnZ1z0wqavSGTafrbkZgjdhkrZ1yzcffhZ1yc9bmgSGT Cheers, James Arthur
Reply by ●August 5, 20162016-08-05
On Fri, 5 Aug 2016 07:50:46 -0700 (PDT), klaus.kragelund@gmail.com wrote:>On Friday, 5 August 2016 16:37:43 UTC+2, John Larkin wrote: >> On 4 Aug 2016 20:07:05 -0700, Winfield Hill <hill@rowland.harvard.edu> >> wrote: >> >> > >> > I've created all kinds of HV circuits in the last >> > 5 years,** and each one needs an external HV supply. >> > So I really need some simple HV-supply circuits to >> > plop onto these PCB's to make them self-sufficient. >> > >> > Today's circuit is a basic flyback, to convert a >> > 12V,1A wallwort source to 500V max, at 5-10W load. >> > >> > I used a UC3843B running at 100kHz driving a MOSFET >> > switching a 47uH inductor (dI = dt V/L = 2A in 8us). >> > This can provide up to 100uJ each cycle, to charge >> > a say 2000uF storage cap to 400V in 16 seconds. >> > >> > I settled on an ES1J fast-recovery output diode >> > (after rejecting an MRA4007), After rejecting >> > an STP7NB60 as too lossy, I experimented and >> > picked an Infineon IPP65R225C7 superjunction >> > MOSFET: Rds(on) = 0.2 ohms (0.5 ohms max at Tj >> > = 150C), and Coss = 14pF at 400V (20pF at 100V). >> > Nice. >> > >> > But the flyback inductor was an issue. See photo >> >https://www.dropbox.com/s/cwo10wm5upehvrw/PWR-741_flyback_350V-inductors_small.jpg?dl=0 >> > >> > I started with an older 1A part from the drawer: >> > a Mouser 47uH, 0.1 ohms, rated 1.3A, see photo, >> > lower right. With this part my circuit had 2.2W >> > of wasted power at 5W out. Heating was bad, the >> > inductor melted a soldered lead and disconnected >> > itself from the circit! Whew, ugly! I needed a >> > beefier part. Enter a Coilcraft PCV-0-473-05L, >> > photo lower left. Those fat wires, this had to >> > be the answer. Rated 0.035 ohms and 6A. But it >> > increased my wasted power to 3.7W, double ouch! >> > >> > Giving up on my commercial inventory, I made >> > an inductor using an RM8 bobbin and core. >> > (See photo, upper part, mounted on the PCB.) >> > >> > I selected a large gap core, A_L = 100nH/t^2. >> > N = sqrt(L / A_L) = 22 turns. With #20 wire, >> > Rdc=0.036 ohms. I measured Q=39 at 100kHz, >> > esr = 2pi f L/Q = 0.75 ohms. Q=80 at 1MHz. >> > Looking pretty good, ignoring coreloss at >> > full power (the ckt uses 40mW at no load). >> > >> > Yeah! With the RM8 inductor, total losses >> > dropped to 1.1 watts. Note, the MOSFET, >> > sense resistor, diode and capacitor share >> > in the loss generation, so I don't know >> > the inductor loss. Everything runs cool, >> > which wasn't the case at the beginning. >> > >> > ** more on that later ... >> >> I have posted this before, but... >> >> I've found that high-ratio boosts can have problems, so I like to use >> dual-winding inductors as autotransformer flybacks. Lots of people >> make these things in various sizes. They are cheap enough that you >> could even parallel some. >> >> https://dl.dropboxusercontent.com/u/53724080/Circuits/HV/T840_A13_PS.pdf >> >> https://dl.dropboxusercontent.com/u/53724080/Circuits/HV/HV_Proto_2.JPG >> >> https://dl.dropboxusercontent.com/u/53724080/PCBs/T840_E1.jpg >> >> I pushed that inductor some, and did get a little warm, so I added >> some copper to heat sink it. >> > >Perhaps a half-bridge forward converter. The 12V will be easy to drive into the primary, and turns ratio of 1:40 is not a problem in a forward > >Cheers > >KlausI think Win is charging a capacitor. Forward converters are very inefficient when heavily loaded, namely when the capacitor voltage is low. Most of the voltage drop is in the mosfets or the transformer copper. An ideal flyback can be 100% efficient over the entire charging curve. -- John Larkin Highland Technology, Inc lunatic fringe electronics
Reply by ●August 5, 20162016-08-05
On Fri, 5 Aug 2016 08:10:24 -0700 (PDT), dagmargoodboat@yahoo.com wrote:>On Thursday, August 4, 2016 at 11:07:26 PM UTC-4, Winfield Hill wrote: >> I've created all kinds of HV circuits in the last >> 5 years,** and each one needs an external HV supply. >> So I really need some simple HV-supply circuits to >> plop onto these PCB's to make them self-sufficient. >> >> Today's circuit is a basic flyback, to convert a >> 12V,1A wallwort source to 500V max, at 5-10W load. >> >> I used a UC3843B running at 100kHz driving a MOSFET >> switching a 47uH inductor (dI = dt V/L = 2A in 8us). >> This can provide up to 100uJ each cycle, to charge >> a say 2000uF storage cap to 400V in 16 seconds. >> >> I settled on an ES1J fast-recovery output diode >> (after rejecting an MRA4007), After rejecting >> an STP7NB60 as too lossy, I experimented and >> picked an Infineon IPP65R225C7 superjunction >> MOSFET: Rds(on) = 0.2 ohms (0.5 ohms max at Tj >> = 150C), and Coss = 14pF at 400V (20pF at 100V). >> Nice. >> >> But the flyback inductor was an issue. See photo >> https://www.dropbox.com/s/cwo10wm5upehvrw/PWR-741_flyback_350V-inductors_small.jpg?dl=0 >> >> I started with an older 1A part from the drawer: >> a Mouser 47uH, 0.1 ohms, rated 1.3A, see photo, >> lower right. With this part my circuit had 2.2W >> of wasted power at 5W out. Heating was bad, the >> inductor melted a soldered lead and disconnected >> itself from the circit! Whew, ugly! I needed a >> beefier part. Enter a Coilcraft PCV-0-473-05L, >> photo lower left. Those fat wires, this had to >> be the answer. Rated 0.035 ohms and 6A. But it >> increased my wasted power to 3.7W, double ouch! >> >> Giving up on my commercial inventory, I made >> an inductor using an RM8 bobbin and core. >> (See photo, upper part, mounted on the PCB.) >> >> I selected a large gap core, A_L = 100nH/t^2. >> N = sqrt(L / A_L) = 22 turns. With #20 wire, >> Rdc=0.036 ohms. I measured Q=39 at 100kHz, >> esr = 2pi f L/Q = 0.75 ohms. Q=80 at 1MHz. >> Looking pretty good, ignoring coreloss at >> full power (the ckt uses 40mW at no load). >> >> Yeah! With the RM8 inductor, total losses >> dropped to 1.1 watts. Note, the MOSFET, >> sense resistor, diode and capacitor share >> in the loss generation, so I don't know >> the inductor loss. Everything runs cool, >> which wasn't the case at the beginning. >> >> ** more on that later ... >> >> >> -- >> Thanks, >> - Win > >John beat me to suggesting coupled inductors ... I got distracted simulating >one. > >An boost inductor charged for 8uS @ 12V, will discharge into 500V in >8uS * 12V/(500V-12V) = 200nS. That's pretty fast! And quite a whack >for your rectifier and filter components. > >Driving the tap of two coupled inductors in series lets you double the >discharge time, halve the discharge current, and halve the switch's voltage >rating. > >It's kind of a nice option for low-power high-ratio dc-dc converters, >short of resorting to a forward converter with a custom transformer. > >They're jelly-bean, e.g.: >http://www.mouser.com/ds/2/597/msd1278-220442.pdf > >http://www.mouser.com/Passive-Components/Inductors/Coupled-Inductors/_/N-afrbk?Rl=afrbkZer9dZ1z0wqgnZ1z0wqavSGTafrbkZgjdhkrZ1yzcffhZ1yc9bmgSGT > >Cheers, >James ArthurThose dual-winding coils are good for all sorts of things. I should test a few for breakdown voltage. Oops, I posted a pre-release version of that HV supply. Here's the real thing: https://dl.dropboxusercontent.com/u/53724080/Circuits/HV/28S840A_3.pdf I did the PCB layout myself! The HV clearances and thermal issues added some interesting complexities. I have the Spice file for that one if anybody is interested. -- John Larkin Highland Technology, Inc lunatic fringe electronics
Reply by ●August 5, 20162016-08-05
On Friday, 5 August 2016 17:57:31 UTC+2, John Larkin wrote:> On Fri, 5 Aug 2016 07:50:46 -0700 (PDT), klaus.kragelund@gmail.com > wrote: > > >On Friday, 5 August 2016 16:37:43 UTC+2, John Larkin wrote: > >> On 4 Aug 2016 20:07:05 -0700, Winfield Hill <hill@rowland.harvard.edu> > >> wrote: > >> > >> > > >> > I've created all kinds of HV circuits in the last > >> > 5 years,** and each one needs an external HV supply. > >> > So I really need some simple HV-supply circuits to > >> > plop onto these PCB's to make them self-sufficient. > >> > > >> > Today's circuit is a basic flyback, to convert a > >> > 12V,1A wallwort source to 500V max, at 5-10W load. > >> > > >> > I used a UC3843B running at 100kHz driving a MOSFET > >> > switching a 47uH inductor (dI = dt V/L = 2A in 8us). > >> > This can provide up to 100uJ each cycle, to charge > >> > a say 2000uF storage cap to 400V in 16 seconds. > >> > > >> > I settled on an ES1J fast-recovery output diode > >> > (after rejecting an MRA4007), After rejecting > >> > an STP7NB60 as too lossy, I experimented and > >> > picked an Infineon IPP65R225C7 superjunction > >> > MOSFET: Rds(on) = 0.2 ohms (0.5 ohms max at Tj > >> > = 150C), and Coss = 14pF at 400V (20pF at 100V). > >> > Nice. > >> > > >> > But the flyback inductor was an issue. See photo > >> >https://www.dropbox.com/s/cwo10wm5upehvrw/PWR-741_flyback_350V-inductors_small.jpg?dl=0 > >> > > >> > I started with an older 1A part from the drawer: > >> > a Mouser 47uH, 0.1 ohms, rated 1.3A, see photo, > >> > lower right. With this part my circuit had 2.2W > >> > of wasted power at 5W out. Heating was bad, the > >> > inductor melted a soldered lead and disconnected > >> > itself from the circit! Whew, ugly! I needed a > >> > beefier part. Enter a Coilcraft PCV-0-473-05L, > >> > photo lower left. Those fat wires, this had to > >> > be the answer. Rated 0.035 ohms and 6A. But it > >> > increased my wasted power to 3.7W, double ouch! > >> > > >> > Giving up on my commercial inventory, I made > >> > an inductor using an RM8 bobbin and core. > >> > (See photo, upper part, mounted on the PCB.) > >> > > >> > I selected a large gap core, A_L = 100nH/t^2. > >> > N = sqrt(L / A_L) = 22 turns. With #20 wire, > >> > Rdc=0.036 ohms. I measured Q=39 at 100kHz, > >> > esr = 2pi f L/Q = 0.75 ohms. Q=80 at 1MHz. > >> > Looking pretty good, ignoring coreloss at > >> > full power (the ckt uses 40mW at no load). > >> > > >> > Yeah! With the RM8 inductor, total losses > >> > dropped to 1.1 watts. Note, the MOSFET, > >> > sense resistor, diode and capacitor share > >> > in the loss generation, so I don't know > >> > the inductor loss. Everything runs cool, > >> > which wasn't the case at the beginning. > >> > > >> > ** more on that later ... > >> > >> I have posted this before, but... > >> > >> I've found that high-ratio boosts can have problems, so I like to use > >> dual-winding inductors as autotransformer flybacks. Lots of people > >> make these things in various sizes. They are cheap enough that you > >> could even parallel some. > >> > >> https://dl.dropboxusercontent.com/u/53724080/Circuits/HV/T840_A13_PS.pdf > >> > >> https://dl.dropboxusercontent.com/u/53724080/Circuits/HV/HV_Proto_2.JPG > >> > >> https://dl.dropboxusercontent.com/u/53724080/PCBs/T840_E1.jpg > >> > >> I pushed that inductor some, and did get a little warm, so I added > >> some copper to heat sink it. > >> > > > >Perhaps a half-bridge forward converter. The 12V will be easy to drive into the primary, and turns ratio of 1:40 is not a problem in a forward > > > >Cheers > > > >Klaus > > I think Win is charging a capacitor. Forward converters are very > inefficient when heavily loaded, namely when the capacitor voltage is > low. Most of the voltage drop is in the mosfets or the transformer > copper. > > An ideal flyback can be 100% efficient over the entire charging curve. >Forward converters are not inefficient. It's just a transformer fed buck converter, so in the beginning of Wins charge cycle, he of course needs to start with 0 duty cycle The halfbridge MOSFETs never see more than the supplied voltage, so they can be selected to have low RDSon, whereas the flyback has a reflected voltage so the primary side MOSFET must be selected for a 2-3 times higher voltage The flyback is a power per cycle topology, so boosting more current is not possible without changing the transformer Cheers Klaus
Reply by ●August 5, 20162016-08-05
On 5 Aug 2016 05:53:42 -0700, Winfield Hill <hill@rowland.harvard.edu> wrote:>bill.sloman@ieee.org wrote... >> >> Too many people make a habit of avoiding custom magnetics. >> The Rowland Institute ought to have a simple coil winder - >> there are cheap ones available from China if it doesn't - >> and you don't need much of a range of RM cores, formers, >> mylar tape and enamelled wire to do useful stuff. > > We have a winder, but need an fixture for small bobbins. > I have the full range of materials, including my favorite > Kapton tape, in various widths. It's the painful magnet- > wire enamel removal and soldering to tiny bobbin pins > that slows me down. That'd be an even worse issue with > extra windings. But I heard a rumor about a special > magnet wire with disappearing enamel at soldering temps.Beldsol, thermal strip. I got a high-temp Metcal clone tip from Amazon, https://www.amazon.com/Thermaltronics-S75CH015-Chisel-interchangeable-SSC-738A/dp/B00NS4E0YW that solders this stuff great. https://dl.dropboxusercontent.com/u/53724080/Parts/Inductors/TEM1_Xfmr_Proto.JPG I hate custom magnetics. Expensive, boring hassle. The technical challenge of designing transformers is to NOT design transformers. -- John Larkin Highland Technology, Inc lunatic fringe electronics
Reply by ●August 5, 20162016-08-05
dagmargoodboat@yahoo.com wrote...> > John beat me to suggesting coupled inductors ... I got > distracted simulating one. > > An boost inductor charged for 8us @ 12V, will discharge > into 500V in 8us * 12V/(500V-12V) = 200ns. That's pretty > fast! And quite a whack for your rectifier and filter > components.Well, even my poor inductors can do that well, the issue is high-frequency core loss. I'd rather use commercial inductors than a custom. Looking over available stuff, I've been discouraged by a lack of the right info. But newly-designed parts tend to work better, maybe because the newer smps ICs are running faster, to over 1MHz. Anyway, yes, coupled inductors are awesome. I've used a few in recent designs and have been accumulating a collection of candidate parts for experimenting.> Driving the tap of two coupled inductors in series lets > you double the discharge time, halve the discharge > current, and halve the switch's voltage rating. > > It's kind of a nice option for low-power high-ratio > dc-dc converters, short of resorting to a forward > converter with a custom transformer. > They're jelly-bean, e.g.: > http://www.mouser.com/ds/2/597/msd1278-220442.pdf >http://www.mouser.com/Passive-Components/Inductors/Coupled-Inductors/_/N-afrbk?Rl=afrbkZer9dZ1z0wqgnZ1z0wqavSGTafrbkZgjdhkrZ1yzcffhZ1yc9bmgSGTRight. My test universal-supply PCB layout predated my interest in coupled inductors, but I'll shoehorn one in there to see how it works. -- Thanks, - Win
Reply by ●August 5, 20162016-08-05
On Fri, 5 Aug 2016 09:16:03 -0700 (PDT), klaus.kragelund@gmail.com wrote:>On Friday, 5 August 2016 17:57:31 UTC+2, John Larkin wrote: >> On Fri, 5 Aug 2016 07:50:46 -0700 (PDT), klaus.kragelund@gmail.com >> wrote: >> >> >On Friday, 5 August 2016 16:37:43 UTC+2, John Larkin wrote: >> >> On 4 Aug 2016 20:07:05 -0700, Winfield Hill <hill@rowland.harvard.edu> >> >> wrote: >> >> >> >> > >> >> > I've created all kinds of HV circuits in the last >> >> > 5 years,** and each one needs an external HV supply. >> >> > So I really need some simple HV-supply circuits to >> >> > plop onto these PCB's to make them self-sufficient. >> >> > >> >> > Today's circuit is a basic flyback, to convert a >> >> > 12V,1A wallwort source to 500V max, at 5-10W load. >> >> > >> >> > I used a UC3843B running at 100kHz driving a MOSFET >> >> > switching a 47uH inductor (dI = dt V/L = 2A in 8us). >> >> > This can provide up to 100uJ each cycle, to charge >> >> > a say 2000uF storage cap to 400V in 16 seconds. >> >> > >> >> > I settled on an ES1J fast-recovery output diode >> >> > (after rejecting an MRA4007), After rejecting >> >> > an STP7NB60 as too lossy, I experimented and >> >> > picked an Infineon IPP65R225C7 superjunction >> >> > MOSFET: Rds(on) = 0.2 ohms (0.5 ohms max at Tj >> >> > = 150C), and Coss = 14pF at 400V (20pF at 100V). >> >> > Nice. >> >> > >> >> > But the flyback inductor was an issue. See photo >> >> >https://www.dropbox.com/s/cwo10wm5upehvrw/PWR-741_flyback_350V-inductors_small.jpg?dl=0 >> >> > >> >> > I started with an older 1A part from the drawer: >> >> > a Mouser 47uH, 0.1 ohms, rated 1.3A, see photo, >> >> > lower right. With this part my circuit had 2.2W >> >> > of wasted power at 5W out. Heating was bad, the >> >> > inductor melted a soldered lead and disconnected >> >> > itself from the circit! Whew, ugly! I needed a >> >> > beefier part. Enter a Coilcraft PCV-0-473-05L, >> >> > photo lower left. Those fat wires, this had to >> >> > be the answer. Rated 0.035 ohms and 6A. But it >> >> > increased my wasted power to 3.7W, double ouch! >> >> > >> >> > Giving up on my commercial inventory, I made >> >> > an inductor using an RM8 bobbin and core. >> >> > (See photo, upper part, mounted on the PCB.) >> >> > >> >> > I selected a large gap core, A_L = 100nH/t^2. >> >> > N = sqrt(L / A_L) = 22 turns. With #20 wire, >> >> > Rdc=0.036 ohms. I measured Q=39 at 100kHz, >> >> > esr = 2pi f L/Q = 0.75 ohms. Q=80 at 1MHz. >> >> > Looking pretty good, ignoring coreloss at >> >> > full power (the ckt uses 40mW at no load). >> >> > >> >> > Yeah! With the RM8 inductor, total losses >> >> > dropped to 1.1 watts. Note, the MOSFET, >> >> > sense resistor, diode and capacitor share >> >> > in the loss generation, so I don't know >> >> > the inductor loss. Everything runs cool, >> >> > which wasn't the case at the beginning. >> >> > >> >> > ** more on that later ... >> >> >> >> I have posted this before, but... >> >> >> >> I've found that high-ratio boosts can have problems, so I like to use >> >> dual-winding inductors as autotransformer flybacks. Lots of people >> >> make these things in various sizes. They are cheap enough that you >> >> could even parallel some. >> >> >> >> https://dl.dropboxusercontent.com/u/53724080/Circuits/HV/T840_A13_PS.pdf >> >> >> >> https://dl.dropboxusercontent.com/u/53724080/Circuits/HV/HV_Proto_2.JPG >> >> >> >> https://dl.dropboxusercontent.com/u/53724080/PCBs/T840_E1.jpg >> >> >> >> I pushed that inductor some, and did get a little warm, so I added >> >> some copper to heat sink it. >> >> >> > >> >Perhaps a half-bridge forward converter. The 12V will be easy to drive into the primary, and turns ratio of 1:40 is not a problem in a forward >> > >> >Cheers >> > >> >Klaus >> >> I think Win is charging a capacitor. Forward converters are very >> inefficient when heavily loaded, namely when the capacitor voltage is >> low. Most of the voltage drop is in the mosfets or the transformer >> copper. >> >> An ideal flyback can be 100% efficient over the entire charging curve. >> > >Forward converters are not inefficient. It's just a transformer fed buck converter, so in the beginning of Wins charge cycle, he of course needs to start with 0 duty cycleThe forward converter needs an additional load-side inductor, and input current limiting, to be efficient. And two mosfets. A current-mode flyback switcher is simpler. Forwards are usually used for higher-power apps.> >The halfbridge MOSFETs never see more than the supplied voltage, so they can be selected to have low RDSon, whereas the flyback has a reflected voltage so the primary side MOSFET must be selected for a 2-3 times higher voltage > >The flyback is a power per cycle topology, so boosting more current is not possible without changing the transformer > >Cheers > >Klaus-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●August 5, 20162016-08-05
On Fri, 05 Aug 2016 09:24:31 -0700, John Larkin <jjlarkin@highlandtechnology.com> wrote:>On 5 Aug 2016 05:53:42 -0700, Winfield Hill <hill@rowland.harvard.edu> >wrote: > >>bill.sloman@ieee.org wrote... >>> >>> Too many people make a habit of avoiding custom magnetics. >>> The Rowland Institute ought to have a simple coil winder - >>> there are cheap ones available from China if it doesn't - >>> and you don't need much of a range of RM cores, formers, >>> mylar tape and enamelled wire to do useful stuff. >> >> We have a winder, but need an fixture for small bobbins. >> I have the full range of materials, including my favorite >> Kapton tape, in various widths. It's the painful magnet- >> wire enamel removal and soldering to tiny bobbin pins >> that slows me down. That'd be an even worse issue with >> extra windings. But I heard a rumor about a special >> magnet wire with disappearing enamel at soldering temps. > >Beldsol, thermal strip. I got a high-temp Metcal clone tip from >Amazon, > >https://www.amazon.com/Thermaltronics-S75CH015-Chisel-interchangeable-SSC-738A/dp/B00NS4E0YW > >that solders this stuff great. > >https://dl.dropboxusercontent.com/u/53724080/Parts/Inductors/TEM1_Xfmr_Proto.JPG > > >I hate custom magnetics. Expensive, boring hassle. The technical >challenge of designing transformers is to NOT design transformers.Search ebay for Beldsol wire I got my #28 cheap from that antique dealer in Virginia. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
