inverting dc-dc converter circuit
in [Design]
|
Prev: Very low frequency 100 microvolt/sec triangle ramp with adjustable limits and slope
Next: DIY studio strobe
From: Joerg on 2 Feb 2010 19:21 Tim Williams wrote: > "Hammy" <spam(a)spam.com> wrote in message > news:kpbhm5tdt8aeu5dp1cofgu395583h2r0ju(a)4ax.com... >> Have you seen the UCC25600 LLC Resonant mode controller.Can only sink >> source 0.4A-0.8A . The absolute minimum guaranteed gate drive output >> is 9V >> >> http://focus.ti.com/docs/prod/folders/print/ucc25600.html > > Ooh, I should revise my induction heater design with one of those. That's > basically what I'm doing, except the transformer secondary is a hunk of > metal. ;-) > And next time you demo it with a piece of tube held upwards into the coil at least wear welders gloves :-) Man, just looking at the video scared me. A guy in the army told me about a similar experiment except that in his case a chunk of white-hot metal decided to follow gravity. Missed his hands but landed right onto one of his shoes ... phssssss ... through the shoe ... -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Tim Williams on 2 Feb 2010 19:22 "John Larkin" <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in message news:ptehm559ud9m2ok9eqvn39hm4a3k11lenr(a)4ax.com... > But "storage scope"? Is there any other kind? Y...no, I guess not: http://webpages.charter.net/dawill/Images/Photoflash_Discharge2_sm.jpg Although to be fair, the camera's 10 second exposure really gets all the credit. Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
From: Tim Williams on 2 Feb 2010 19:31 "Joerg" <invalid(a)invalid.invalid> wrote in message news:7srtseF692U1(a)mid.individual.net... > And next time you demo it with a piece of tube held upwards into the coil > at least wear welders gloves :-) Pssh... I ruined my last pair of welding gloves handling the still-hot electrochemical cell when I was cooking up chlorate one summer: http://webpages.charter.net/dawill/tmoranwms/Chem_Chlorate3.html That square stainless tank is a little too hot to handle bare, but inevitable spills result in sodium chlorate soaking into the gloves. Needless to say I kept the gloves well away from welding after that. ;-) > Man, just looking at the video scared me. A guy in the army told me about > a similar experiment except that in his case a chunk of white-hot metal > decided to follow gravity. Missed his hands but landed right onto one of > his shoes ... phssssss ... through the shoe ... Nice one! A classic welding incident, too. I'll keep that in mind when I get the 10kW beast running. For now, I know exactly how much power I'm delivering, and fortunately, it's not enough to melt steel. So I've been staying out of the hot convection instead. Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
From: JosephKK on 2 Feb 2010 23:26 On Tue, 02 Feb 2010 16:14:58 -0800, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >On Tue, 2 Feb 2010 12:02:27 -0800 (PST), "miso(a)sushi.com" ><miso(a)sushi.com> wrote: > > >>> >>> >> Here's my inverter, sort of similar. >>> >>> >>ftp://jjlarkin.lmi.net/Inverter.jpg >>> >>> >> The thevenin impedance seen by the emitter determines loop gain. I >>> >> needed the ESR of the tantalum in the output to get good loop >>> >> stability; startup dV/dT is low enough that a tantalum appears safe >>> >> here. >>> >>> >> Load regulation is surprisingly good, about a tenth of a volt from 80 >>> >> to 500 mA. >>> >>> >> John >>> >>> >I see a start up problem here. Look at the UVL of the LM5112. Won't >>> >this circuit whack the inductor while starting up? >>> >>> It's designed to start up at about 70% duty cycle. When the output >>> gets close to -12, the transistor turns on and backs off the duty >>> cycle to whatever it needs, which should be a bit over 50%. >>> >>> John >> >>I'm talking about the first pulse. The P-fet will be on because of the >>UVL being designed with a N-fet in mind. You should be able to see >>this on a storage scope. > >Good point, except that it seems to work fine, even from a >current-limited bench supply. The UVLO is typically 3 volts, and that >klunky old NDT2955 has a 2.6 volt threshold, so it's barely on before >the oscillator starts. > >But "storage scope"? Is there any other kind? > Absolutely. I have heard that you have a Tek 2465 or similar in working condition. The instant you think it is a storage scope or do not find it valuable let me know; i will be there to relieve you of it just as fast as i can get there. >>I see a lot of people rolling their own converters and have read the >>justifications, but seriously, controller chips have (or should have >>if done well) every contingency in mind. The first pulse, the initial >>ramp up (soft start), etc. Linear Tech, Maxim, etc parts have been >>tied to the whipping post and flogged without mercy. If you sell >>millions of a component, even problems with 1% of them is a total >>disaster. > >There aren't many inverting switchers around. The trick of having a >regular buck wind its own "ground" rail negative is OK, but usually >gets into trouble at higher output voltages. This circuit soft-starts >because the +5 reference comes up fairly slowly, by design. That >protects the tantalum on the output. > >And designing circuits is fun. > >But we've had a lot of problems with LDOs and switchers, way more than >1% of the various parts we've used. > >National did this to us, LM3102: > >ftp://jjlarkin.lmi.net/SwitcherRise.JPG > >which cost a whole board spin. > >John >
From: John Larkin on 2 Feb 2010 23:41
On Tue, 02 Feb 2010 20:26:28 -0800, "JosephKK"<quiettechblue(a)yahoo.com> wrote: >On Tue, 02 Feb 2010 16:14:58 -0800, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: > >>On Tue, 2 Feb 2010 12:02:27 -0800 (PST), "miso(a)sushi.com" >><miso(a)sushi.com> wrote: >> >> >>>> >>>> >> Here's my inverter, sort of similar. >>>> >>>> >>ftp://jjlarkin.lmi.net/Inverter.jpg >>>> >>>> >> The thevenin impedance seen by the emitter determines loop gain. I >>>> >> needed the ESR of the tantalum in the output to get good loop >>>> >> stability; startup dV/dT is low enough that a tantalum appears safe >>>> >> here. >>>> >>>> >> Load regulation is surprisingly good, about a tenth of a volt from 80 >>>> >> to 500 mA. >>>> >>>> >> John >>>> >>>> >I see a start up problem here. Look at the UVL of the LM5112. Won't >>>> >this circuit whack the inductor while starting up? >>>> >>>> It's designed to start up at about 70% duty cycle. When the output >>>> gets close to -12, the transistor turns on and backs off the duty >>>> cycle to whatever it needs, which should be a bit over 50%. >>>> >>>> John >>> >>>I'm talking about the first pulse. The P-fet will be on because of the >>>UVL being designed with a N-fet in mind. You should be able to see >>>this on a storage scope. >> >>Good point, except that it seems to work fine, even from a >>current-limited bench supply. The UVLO is typically 3 volts, and that >>klunky old NDT2955 has a 2.6 volt threshold, so it's barely on before >>the oscillator starts. >> >>But "storage scope"? Is there any other kind? >> >Absolutely. I have heard that you have a Tek 2465 or similar in working >condition. The instant you think it is a storage scope or do not find >it valuable let me know; i will be there to relieve you of it just as >fast as i can get there. I have 60 or so oscillscopes, but no 2465s. I rarely use an analog scope. The only one I occasionally use is a Tek 7104, the 1 GHz scope with the microchannel plate CRT. It's not a storage scope. The old Tek storage CRTs don't hold up very well. My favorite scope is probably my 11802, a 20 GHz sampler. It's digital, but actually uses a magnetic-deflection CRT for waveform display. John |