[neonixie-l] Re: MC34063 SMPS questions
Good day, No scope sadly. Its on the list of things to get, I seldom do SMPS black art so I haven't had a real use for one. I guess I will get friendly with the Spice emulation software. My input is 11.5V wallcube. Originally I had my timing cap at 1000pf, Wich gave me about 150V area. After taking it to 2000-3000pf things really sarted to show up in terms of voltage, 180-185V but it seems that's where it capped out. Not to mention the FET was burning and the coil was getting warm. Mike Morreess doesn't have a heat sink and proposes his unit will pull 35mA at 190V. So I don't think a heat sink is needed. Just need to know what to tweak. Thanks for the reply yet again! On Monday, June 16, 2014 6:32:23 PM UTC-6, greg...@hotmail.com wrote: > > Do you have a scope ? If not, your only other solution is to run extensive > simulations. We really need to see what's happening in the circuit. > > The large voltage droop (25V) at 15-20mA load-current suggests your > converter is running at a really low frequency, maybe 150Hz. > > What Vcc are you running ? Hard for me to determine if your inductor is > getting saturated (Isat is 1.2 amps from the website) > > When you changed the timing capacitor, did you increase it or decrease it > ? I would expect that decreasing the capacitance value would increase the > converter's frequency and produce less droop/ripple at the +180V output. > Switching losses increase at higher frequencies, but my gut feeling is that > the temperature increase you saw is not caused by this, unless the > frequency was too high for Q1 & Q3 to handle, in which case the MOSFET > might not be turning-on or shutting-off completely. This is where the scope > would really help. > > If you increased the timing-capacitor value, and reduced the frequency of > operation, you have to be careful about dumping too much current into the > inductor, which leads to saturation and also higher conduction losses in > Q2. You should be able to keep the IRF740 cool enough with a small heatsink > once the design is tweaked. > > > > > -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To unsubscribe from this group and stop receiving emails from it, send an email to neonixie-l+unsubscr...@googlegroups.com. To post to this group, send an email to neonixie-l@googlegroups.com. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/d3b4de45-f87f-4323-9959-d02ee5a5926a%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: [neonixie-l] MC34063 SMPS questions
Hi Philip, A friend suggested that extra cap just before the coil. Surprise surprise :) The explanation for the voltage ripple on the 540V line makes sense, With no real feedback there can't be any regulation. I have much bigger issue on of heavy sag on the 180V line. I removed the tripler all together for testing. I plan to have identical caps @ 600V when I figure out this sagging issue. Thanks for the tips and your time! On Tuesday, June 17, 2014 5:47:42 AM UTC-6, Philip Pemberton wrote: > > On 15/06/14 17:23, Chris Stalin wrote: > > 1. I also added a 220uF cap near the coil. I noticed the voltage jump > > about 3 volts. I have kept the 220uF cap near the IC. Does any one > > recommend I keep the IC cap or remove it o adjust its value? When > > removed the voltage drops about 1 volt. So clearly adding or removing > > caps adjust the voltage - just not sure why. None of my caps are low ESR > > yet. > > From the circuit, it's probably providing an alternate source of > current for L1 which bypasses R3..R6. What you're seeing is the > capacitor charging while Q2 is off then discharging into L2 when Q2 is > on, supplementing the current coming from R3..R6. > > The 34063 notices that there's less voltage going through the current > sense resistors (via Ipk Sense) and reacts by increasing the power > through Q2 by increasing the duty cycle. (if I remember correctly the > 34063 is an "almost-PWM" controller). > > > 2. When my system is not loaded and just idling I see about 182.5V on > > the 180V line and 535V on the 540V line. > > When I load down my 180V line with 5mA of resistance my voltage jumps > > 555V on the 540 line. 180V line stays the same. Can any one explain why > > this is happening? I would assume a load on the system would make > > voltage sag not drop. > > You have a Cockroft-Walton divider comprised of C6, D2, D3, and the > other unnamed parts. What you're probably seeing is the divider > responding differently to a change in input frequency and/or voltage. > > In short, The 34063 is regulating the 180V rail, but not the 540V rail. > If your feedback was coming from the 540V rail you'd expect to see the > 180V rail jumping around while the 540V remains stable. > > Are you loading down the 540V rail at all? > > > 3. Are the cap values critical? I need to pick up a couple more caps as > > I ran out of HV caps. I currently have 2.2uF caps x 2 and the rest are > > 4.7uF and 10uF 450V caps - Just for testing purposes only. ( cap values > > from 1-2.2uF throughout the HV section is acceptable ? ) > > I'll let someone else field this one as I don't have an answer. Sorry! :( > > Though ideally for a C-W multiplier all the capacitors and all the > diodes should be identical. If they're not, this might be why you're > seeing the voltage rise slightly. > > Thanks, > -- > Phil. > phi...@philpem.me.uk > http://www.philpem.me.uk/ > -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To unsubscribe from this group and stop receiving emails from it, send an email to neonixie-l+unsubscr...@googlegroups.com. To post to this group, send an email to neonixie-l@googlegroups.com. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/059bb0ea-1845-480b-9212-4845015596c3%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: [neonixie-l] MC34063 SMPS questions
On 15/06/14 17:23, Chris Stalin wrote: 1. I also added a 220uF cap near the coil. I noticed the voltage jump about 3 volts. I have kept the 220uF cap near the IC. Does any one recommend I keep the IC cap or remove it o adjust its value? When removed the voltage drops about 1 volt. So clearly adding or removing caps adjust the voltage - just not sure why. None of my caps are low ESR yet. From the circuit, it's probably providing an alternate source of current for L1 which bypasses R3..R6. What you're seeing is the capacitor charging while Q2 is off then discharging into L2 when Q2 is on, supplementing the current coming from R3..R6. The 34063 notices that there's less voltage going through the current sense resistors (via Ipk Sense) and reacts by increasing the power through Q2 by increasing the duty cycle. (if I remember correctly the 34063 is an "almost-PWM" controller). 2. When my system is not loaded and just idling I see about 182.5V on the 180V line and 535V on the 540V line. When I load down my 180V line with 5mA of resistance my voltage jumps 555V on the 540 line. 180V line stays the same. Can any one explain why this is happening? I would assume a load on the system would make voltage sag not drop. You have a Cockroft-Walton divider comprised of C6, D2, D3, and the other unnamed parts. What you're probably seeing is the divider responding differently to a change in input frequency and/or voltage. In short, The 34063 is regulating the 180V rail, but not the 540V rail. If your feedback was coming from the 540V rail you'd expect to see the 180V rail jumping around while the 540V remains stable. Are you loading down the 540V rail at all? 3. Are the cap values critical? I need to pick up a couple more caps as I ran out of HV caps. I currently have 2.2uF caps x 2 and the rest are 4.7uF and 10uF 450V caps - Just for testing purposes only. ( cap values from 1-2.2uF throughout the HV section is acceptable ? ) I'll let someone else field this one as I don't have an answer. Sorry! :( Though ideally for a C-W multiplier all the capacitors and all the diodes should be identical. If they're not, this might be why you're seeing the voltage rise slightly. Thanks, -- Phil. phil...@philpem.me.uk http://www.philpem.me.uk/ -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To unsubscribe from this group and stop receiving emails from it, send an email to neonixie-l+unsubscr...@googlegroups.com. To post to this group, send an email to neonixie-l@googlegroups.com. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/539DE01E.7030901%40gmail.com. For more options, visit https://groups.google.com/d/optout.
