> I would like to adapt the design found here > <http://www.desmith.net/NMdS/Electronics/NixiePSU.html> for a variable 300V > max output, instead of around 180–220V:
Unfortunately, these flyback supplies can only boost a voltage so far in a single step, and getting 300V out isn't really going to work with that circuit topology. The easiest modification is to run it with 30V in (with a separate supply for the MAX1771). The second easiest modification is to add a voltage doubler on the output. > > I understand that the output voltage is adjusted by the resistors R1 and R2, > per the MAX1771 datasheet > <https://datasheets.maximintegrated.com/en/ds/MAX1771.pdf>: > > > and that in this case a potentiometer is used to vary the voltage of R1. > However, I'm not sure how the above equations are used to arrive at the > voltage bounds specified in the schematic. Could someone explain? Using those > equations, what value of R2 should I substitute in for the one used in the > schematic to arrive at my desired maximum voltage of 300V? With a little algebra, the equations from the data sheet become: Vout = Vref(R2 + R1) / R1 In the circuit, the upper limit would be reached with VR1 at minimum, so the lower resistor would be 10k and the upper resistor would be 1.5M, so Vout = 226.5V. The lower limit would be with VR1 at maximum, which would make the lower resistor 15k, making Vout = 151.5V. Making R2 higher might lead to noise problems, so raising the output voltage is probably better done by reducing R1. Reducing R1 to 7.5k would give a maximum voltage of 301.5V, but again if you did that with the existing circuit, it would need to run on a higher input voltage (if you tried to get 300V out from 12V in, you'd probably end up just burning some parts). The note in the schematic is true: board layout is critical, not just for high efficiency, but to get it to work at all. For beginning builders, I recommend the more robust 555 based circuit, even though it's less elegant and efficient, it's more tolerant to layout issues. The fancier MAX1771 and MC34063 circuits are much less forgiving. - 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 [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/6960BBB3-EC26-4A0A-B235-6E3CF63C32C6%40mac.com. For more options, visit https://groups.google.com/d/optout.
