Dylan, First off, treat the power circuits for the "HT" and heaters separately. otherwise any circuit that you might come up with is going to be a compromise, and loading on one voltage rail is going to effect the other. One problem at a time is best!
Each IV 11 tube has a 1.5V(100ma) heater. So there is your first challenge - how to drive those? Put all the filaments in parallel and then design a 1.5V 600mA power supply? Don't think so! Put them all in series, so now you have to feed your tubes with a 9V 100mA supply? That starts to sound more likely. But now each tube is "sitting on" a different heater voltage, so tubes at one end of your array are going to see a different voltage step of from their heaters to the HT. This then causes those tubes at the "high" end of your heater chain to glow less brightly. This is noticeable on multidigit arrays like the IV18 (8 digit mux tube) for example. You might get away with it where you've got shorter strings of heaters in series - how about two strings of three heaters each, driven via a diode dropper (0.6V) from a handy 5V supply? That might work well. This brightness gradient across an array is also exasperated when the tubes are directly driven, since the HT voltage is lower, when compared to the total voltage across your heater chain. Another way around any brightness gradient is to drive the heaters via AC. if you don't already have it from your power supply, you have to make it! And that's what the MAX 628 is all about - you use it a bit like a four diode bridge rectifier in reverse - DC in, AC out (with a square wave control signal, of course). That was, over the AC cycle, each tube "sees" the same average HT voltage. There are lots of small SMPS designs out there, either using 555's or something a little more esoteric. Personally, I favour the UC3483 switcher. I've used it for years, and it's bullet-proof. But pick one that you've worked with before, and try that. And Yes, 1000uH is going to be WAY too big - come down to something nearer 100uH, that can handle about 1A peak. your choice of FET looks fine. Have a look at other designs out there, and experiment! WARNING! Want to know the QUICKEST way to fry a VFD? Put 5V DC across the 1.5V heater... marvel at the LIGHT BULB you have just discovered (briefly), before the filament POPS. Conversely, it is hard to blow up a VFD with too much HT voltage (within reason!) at least for short periods of time. DOUBLE CHECK your heater circuits to make sure they cannot over-volt, or I will be back to say "I told you so..." Laurence www.MrNixie.com On Dec 19, 9:43 am, Grahame Marsh <[email protected]> wrote: > I am interested in building a IV-11 clock from scratch, and have Maxim 1771s, > inductors around 1000 uH, and IRFD220s on hand but am open to ordering > whatever parts I need. I'm most interested in solutions for generating the > grid voltage, but ideally am looking for a nice circuit for both grid and > filament. > > > > But it is true that you and drive the filament with DC but you get a > brightness gradient across tubes in series or long multisegment VFDs? > I've never seen how severe the gradient is. The anode/grid voltage can > be generated with a simple power supply by selecting the transformer > voltage correctly. > > Grahame -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To post to this group, send an email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/neonixie-l?hl=en-GB.
