> I notice that the RDS on value is higher on the 720. 1.8ohms instead of .28 > ohms. Could this be contributing to the problem?
That's about seven times as much, so with a higher current inductor, it'll start to impact your efficiency. > Last question. From reading Nicks webpage: Switcher rate was approximately > 62kHz > > This doesn't seem to be a problem but I was wondering since this is an audio > application if there would be a lot involved in moving this up to 100 -120K > or even more and still get 200v/50ma out. The main problem with higher frequency switching is the FET turn on/off time. The higher the frequency, the shorter the period, and therefore the larger proportion of the time you'll be spending turning the FET on and off. During the turn on/off period, the FET is in its linear region and is dissipating more power. Ideally, the FET is all the way off (dissipating no power) or all the way on (dissipating only the power from its RDS on resistance times the current flowing through it). The limiting factor in how fast you can turn the FET on and off is its gate capacitance divided by the available gate drive current. To speed up the switching time, you can either choose a FET with a small gate capacitance, or increase the gate drive current. To increase the gate drive current, you can either build a transistor booster or use a dedicated FET gate driver chip such as a MAX627. - 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/7859A303-74A9-423F-9CAF-8F832A065285%40mac.com. For more options, visit https://groups.google.com/d/optout.
