[neonixie-l] smps protection question
I have been playing with a couple of HV smps's I have purchased from alibaba with an audio circuit and have found a problem I was wondering if anyone had any suggestions for fixing. Essentially they get very unhappy if one plugs in an rca line level input while the amp is turned on. Here is an example of one of them. http://www.aliexpress.com/snapshot/6849909268.html?orderId=68754413558174 The unit doesn't die outright and still puts out the HV it was set to but it gets very noisy. You can see the power led flicker consistently, as soon as you put a load on it. Any thoughts on this are appreciated. Bob -- 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/7298412e-3db3-48ee-ba15-b3f7216de9fd%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: [neonixie-l] Nick Desmith smps board question
Thanks a ton for comments! The board as is, is stable and cool and apparently noise free, and has run 1 12AX7 at 300 volts with a 9v supply in the field for long periods of time in a audio application. Of course 1 12AX7 draws very little current. I dont know why RSense was left off but thats the next thing im going to try. And I will find someone with a bench capable of doing a proper high frequency oscillation test. In the meantime I going to try a couple of Taylor edge boards for this new project, assuming the switching freq. is high enough for an audio application. Thanks again, if you folks think of anything else to check please post! :) Bob On Thursday, April 16, 2015 at 2:24:53 PM UTC-4, taylorjpt wrote: Here's a PDF from 2004 on probe connections: http://www.tayloredge.com/reference/Electronics/TestBench/ScopeGrounding.pdf Especially when testing power supplies the ground wire acts as a single turn magnetic pickup. -- 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/c0f9cab0-fa01-40ba-bc3a-600a6c4a2a4e%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: [neonixie-l] Nick Desmith smps board question
Since I put up this thread I have since upgraded the coil, fet and diode but Im still having the problem. With 9v/3a power supply the output drops from 300 volts no load to 70 volts at around 45ma. I was wondering if anyone might comment of this: https://docs.google.com/spreadsheets/d/1KDNKAQ2sZJch5CYoSZMCEc1vGZVVrP8h2sKTUL66Opw/edit?usp=sharing If they see anything that might be causing the the problem. Thanks! Bob On Wednesday, January 14, 2015 at 5:05:55 PM UTC-5, gregebert wrote: For a MOSFET, there is no static drive-current except for a few nanoamps of leakage, which can usually be ignored. The gate-drive-current is whatever is needed to slew the gate-source capacitance (aka input capacitance). Using i=Cdv/dt, you can calculate how much drive-current your gate-driver needs to provide. From the datasheet, you need at least 4.5V for the gate-voltage. If you want a turn-on time around 250nsec, you would need about 25mA. Remember this is not continuous current; it's just there when turning the MOSFET on or off. Take note of the gate-charge graph (Fig 6 on the datasheet) if you are using more than 5V for the gate; it's a non-linear capacitance which is typical for MOS devices. If you really want to do an accurate assessment, a SPICE simulation is best though that might be overkill in this application. You can get-by with a smaller gate-driver, but that will increase your switching loss; it's a tradeoff. -- 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/a4fb0563-21f0-4459-8a87-8cbaa7e881a2%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
[neonixie-l] Re: Wanted: Nick de Smith SMPS board.
Thanks for all your responses. I thought I had this group set up to email me if there were any responses, but I messed up somewhere and just discovered these today. Bob On Sunday, March 1, 2015 at 3:58:07 PM UTC-5, threeneurons wrote: I made a one off MAX1771 supply following Nick's guidelines, as best I could using thru-hole parts, and got very impressive results. Not quite, what Nick got, but still a lot of power.. The Taylor Edge 1363/1364 are well regarded, as are those by Mike Moorrees (aka. threeneurons) - many others out there! Taylor's supplies can kick out a lot of power. I haven't compared them with the MAX1771 design, so I can't say if its more or less. They can still output significant current from just a 5V in, if that's needed. Taylor's day job, is designing supplies, and he uses a custom transformer. The claim to fame, on my units, is that the kits are cheap ! Its not the most efficient design, its max output is less than the ones above. It still, however, can power a 6 tube IN18 direct drive clock. Thanks to the Chinese for using the MC34063 in the millions, in USB car chargers, that chip's price continues to fall. Mine are kitted from all off the shelf parts. Of course my supply is a better design than the first supplies, I encountered, that used the MC34063. With the optimal coil (which doesn't come with the kit), my MC34063 can output close to 10W. I think the MAX1771 can do 20W (120mA @ 170V). Those are the max numbers. -- 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/7735a020-e8c3-4339-94c8-ae19277faef5%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
[neonixie-l] Wanted: Nick DeSmith SMPS board.
Hi Im looking for a Nick Desmith smps board http://desmith.net/NMdS/Electronics/NixiePSU.html preferably stuffed, but will take a blank. If you have one you would be willing sell please private email me. thanks Bob -- 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/0658a370-8c18-461c-bb10-fc86527fed8b%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: [neonixie-l] Nick Desmith smps board question
John thanks for the follow up, you have really been helpful. Im sure what specific specs gate capacitance and gate drive current are. So for example on this spec sheet http://www.vishay.com/docs/91039/91039.pdf is gate capacitance = input capacitance 1300pf and im not sure what gate drive current = ? Bob On Friday, December 26, 2014 at 10:46:27 AM UTC-5, jrehwin wrote: I notice that the RDS on value is higher on the 720. 1.8ohms instead of .28 ohms. Could this be contributing to the problem? That's about seven times as much, so with a higher current inductor, it'll start to impact your efficiency. Last question. From reading Nicks webpage: Switcher rate was approximately 62kHz This doesn't seem to be a problem but I was wondering since this is an audio application if there would be a lot involved in moving this up to 100 -120K or even more and still get 200v/50ma out. The main problem with higher frequency switching is the FET turn on/off time. The higher the frequency, the shorter the period, and therefore the larger proportion of the time you'll be spending turning the FET on and off. During the turn on/off period, the FET is in its linear region and is dissipating more power. Ideally, the FET is all the way off (dissipating no power) or all the way on (dissipating only the power from its RDS on resistance times the current flowing through it). The limiting factor in how fast you can turn the FET on and off is its gate capacitance divided by the available gate drive current. To speed up the switching time, you can either choose a FET with a small gate capacitance, or increase the gate drive current. To increase the gate drive current, you can either build a transistor booster or use a dedicated FET gate driver chip such as a MAX627. - John -- 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/14f45d99-014e-4e62-8dde-dd50c986fa70%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: [neonixie-l] Nick Desmith smps board question
I think I may have figured out the problem based on John's comment. This is from Nick Desmith's web page. - For 50mA+ output, L1 should be DC rated at about 2A. The chosen inductor, an EPCOS B82479, fits this bill and works very well in this circuit. If you use a shielded inductor, you will get less RFI, but the efficiency will also drop by about 3%. Small surface mount, high current, shielded inductors are not common! You could try a Sumida CDRH127-101 which works ok even though it starts to saturate at about 1.7A. - For lower output currents up to 25mA, you can use a 1A inductor and change Rsense to 0R100 Ω. A good inductor here would be a Sumida CDRH125-101. Select an inductor with a low DC resistance as straight resistive losses will effect efficiency and lead to heating. Sure enough my board is using the 1A Sumida. Also I notice my friend used a different vishay FET, I assume to get the 300v (I only need 200) Nick specified this one. http://www.vishay.com/docs/91039/91039.pdf My friend is using this one. http://www.vishay.com/docs/91043/sihf720.pdf I notice that the RDS on value is higher on the 720. 1.8ohms instead of .28 ohms. Could this be contributing to the problem? Last question. From reading Nicks webpage: Switcher rate was approximately 62kHz This doesn't seem to be a problem but I was wondering since this is an audio application if there would be a lot involved in moving this up to 100 -120K or even more and still get 200v/50ma out. I really appreciate all your help. Bob On Thursday, December 25, 2014 1:00:23 PM UTC-5, jrehwin wrote: I have been playing with an smps a friend built which is supposed to be identical to Nick Desmith's board http://desmith.net/NMdS/Electronics/NixiePSU.html with the exception that its a through hole board rather than smd. Im an audio guy btw not a nixie builder. With a 12ax7a at 300v/1ma it works well. Noise free, stable, sounds great. But when I tried it with a circuit that drew 20ma of current, both the voltage and current output collapsed to 78v/4ma. I tried changing the resistor that sets the output voltage to 200v and got similar results. Im using a 9v 3amp wall wart supply. I know its impossible to really diagnose anything without a circuit which is the next thing Im going to come up with, but I thought it couldn't hurt to post this and see if there is anything obvious those of you much more familiar with these supplies than me, might suggest as possibly the problem or what to look for. Does the switching FET get hot? If so, you probably need a lower resistance one. What's the DC current rating on the inductor? The efficiency and effectiveness of these single-inductor boost supplies starts to really fall off at large voltage ratios (like you'd have with 300V out). You might consider going to 24V or more on the input side (with appropriate modifications to correctly power the control chip), using a transformer, or adding a voltage doubler. - John -- 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/134d1b03-d345-408c-9f12-6454f0a800a1%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
[neonixie-l] Nick Desmith smps board question
Hi all I have been playing with an smps a friend built which is supposed to be identical to Nick Desmith's board http://desmith.net/NMdS/Electronics/NixiePSU.html with the exception that its a through hole board rather than smd. Im an audio guy btw not a nixie builder. With a 12ax7a at 300v/1ma it works well. Noise free, stable, sounds great. But when I tried it with a circuit that drew 20ma of current, both the voltage and current output collapsed to 78v/4ma. I tried changing the resistor that sets the output voltage to 200v and got similar results. Im using a 9v 3amp wall wart supply. I know its impossible to really diagnose anything without a circuit which is the next thing Im going to come up with, but I thought it couldn't hurt to post this and see if there is anything obvious those of you much more familiar with these supplies than me, might suggest as possibly the problem or what to look for. thanks! Bob -- 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/ac58b038-6fa4-45a8-87a5-8793b97d6ca7%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
