The voltage is not regulated, but it is adjustable via a variac. Nixies really dont need regulated voltage; it's the current that controls the brightness. Many common sources of light (incandescent, LED) operate the same way.
The 500V current-limiter (right-half of regulator.ps) uses a non-precise reference voltage ( a 24 volt DC-DC converter that provides isolation) across a pot. The pot is diagrammed in the schematic at the connector P5. The voltage at the wiper of the pot is applied to the gate of a NMOS device. Once the voltage at the gate is high enough to turn the MOSFET on, there is negative feedback across R12+R13. The voltage across R12+R13 is 1V per mA of load-current. The load is connected to DCOUT500 and ACISO1 (the common gnd for the high-voltage section). As more load current is drawn, the voltage at the NMOS source increases, which tends to shut-off the NMOS. Equilibrium is reached and the current is essentially constant. Note that the Vgs of the NMOS device affects the load-current, but it's essentially constant over the range of currents being used (0-20mA). The voltage produced by the DC-DC converter directly affects the output current, but it too is mostly constant and it has a constant load as well. Though I could have used a 0-20mA meter to monitor the load-current, there were none available for low-cost but there are plenty of 0-20V meters, so that is why I chose that approach. The preliminary testing I've done so far shows current holds-steady as indicated on the panel meter; at most it dithers only on the lowest digit. For example, when running at 2mA, the current varies only +/- 10uA which is much steadier than a nixie requires. Some of the 'extra' components are there for filtering, spike protection, ESD, reverse-polarity applied *into* the power supply, etc (zener diode, R11, C7, D19). They have no functional purpose. The 0-170V output, which is adjustable from 0-100mA, operates similarly except it has a real ammeter (0-200mA). The 100 ohm / 2Watt resistor provides current-limiting in case the NMOS has failed-shorted; in normal operation it will 'penalize' the output as much as 10 volts. Lastly, there is a voltmeter at the DC output jacks that measures the voltage actually delivered to the load; there are relays to switch the meter accordingly. -- 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/46c93d9a-c392-44b2-b8e5-3c9b797487ae%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
