On 15 sty 2012, at 00:37, Jon wrote: > On Jan 14, 10:24 pm, Jan Rychter <jrych...@gmail.com> wrote: >> On 14 sty 2012, at 18:37, marta_kson wrote: >> >> I think I'll need to redesign the board without the potentiometer, thus >> bringing the FB resistors much closer to the chip. >> > > I can't speak to the arcane world of the 1771 circuit, never having > used it. But if it's important to you to have an easily variable > output voltage and it's the pot which is killing you, then there is a > completely different strategy which works well. You can make very > satisfactory nixie and dekatron power supplies using microcontrollers > with on-board ADC and PWM modules.The PWM pin drives the switching > element in a standard boost SMPS circuit, and the HV feedback line > comes from a fixed potential divider into the ADC pin. You then > process the ADC output in firmware to determine the PWM duty cycle, > which gives you a continuously variable, programmable HV supply which > is great for playing around with things. Want to test the nixie at > 160V or 200V? Just tell the microcontroller what you want the output > to be, and let the magic of negative feedback sort it out. > > The downside is that it costs you some time overhead in the > microcontroller to keep the HV going, but with the right chip you can > do this, run a USB link and still have plenty of cycles left for a > funky user program. You probably don't get as good efficiency as > Nick's beautifully optimised 1771 circuit, but that is rarely a > terminal design issue in my experience. The efficiency drop has never > required me to heatsink the FET or anything like that. > > I've run this strategy up to about 12W output - no doubt less than you > could get out of a thoroughly tweaked 1771 or John Taylor's awesome > modules - but plenty enough for most purposes.
I develop software for a living, and I know how difficult it is to make reliable software. In the solution above I'd worry what would happen if my software went astray and the PWM controller happily continued to pump the voltage without any control whatsoever. I'd much rather use solutions which are self-balancing. As for other suggested solutions (555 timers, etc) -- I learned already that a switching PSU is a complex beast, even though it might seem superficially simple. There are many corner cases that I'd rather have covered, such as: how does the circuit behave when the output gets shorted? When the short gets released? Is there overcurrent/overvoltage protection? Does it start reliably? Does it start when input voltage ramps up slowly? How does it react to sudden load changes? There are many things which one can get wrong, so I prefer an IC-based solution, where someone thought about all the corner cases. --J. -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To post to this group, send an email to neonixie-l@googlegroups.com. To unsubscribe from this group, send email to neonixie-l+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/neonixie-l?hl=en-GB.
