2. Instead of a voltage doubler, a 'boost' supply is another way to get higher anode-supply voltage. One version (hvsupply.pdf) 'adds' a few volts to the AC line before it's rectified, though it's not isolated. I use this in my big clock to get around +220VDC. The other version (neondr_pwrsupp.jpg) accomplishes the same result, but it's isolated from the AC line and that's desirable for safety reasons.
For the non-isolated supply (hvsupply.pdf), I used a 36 V transformer. There's a full-wave section for 220VDC (D4 & C4). There's also a half-wave doubler (D1, D2, D3, C2, and C3) that generates +440V for the dekatron in this particular clock. R3, R12, and R4 are important for safety reasons: They discharge the capacitors. The role of R12 is subtle, but if you study the circuit you will see the discharge path thru the transformer. RESD2 is one of several high-value resistors in the overall design that provide a DC path between all supplies to reduce ESD susceptibility while the clock is being built. The isolated supply (neondr_pwrsupp.jpg) is from the clock I'm currently designing. This circuit has not been tested in actual usage yet, but I have run quite a few simulations on it. I still need to run it with transformer winding resistance. The rectifier (XD101) and filter cap (C101) provide about +180V. This clock has fourteen IN-18 tubes, each running at 5mA, so it's a fair amount of current. In order to get isolation, you need a dual-primary transformer. One of the primaries is connected to the AC line and supplies the energy; the other primary winding is used as a secondary winding. When using a transformer in this manner for isolation, you must be careful not to exceed the VA (volt-amps) rating and that means you must include the VA consumption for all secondary windings (which includes the primary winding that got re-purposed as a secondary). Assuming you use a diode-> capacitor rectifier, you will want to calculate the VA rating based on peak current, which is higher than the load current. If you pick a transformer with a VA rating that's too low, you will see more losses (heat). Some will be I-squared-R losses in the windings, and most will probably be from core saturation. The easiest way to determine peak current is with a circuit simulation (LTspice and ngspice are excellent simulators available for free). Or, you can just try it out and see if the transformer gets warm; if it does, get a higher VA rating. I'll post another article about designing the correct filter cap value. -- 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 [email protected]. To post to this group, send an email to [email protected]. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/a7b6bab1-eb4f-4b67-b19c-69e5528d9f57%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
