Hello. In my "high current" MAX1771 PSU design I made several years ago, the best results I got when I used a toroidal inductor with a current rating of 10.3 A (Bourns 2200LL-470-RC), and a RSENSE peak current setting of 5.33 A. I tried other inductors, including a physically smaller 2100LL series inductor (with a smaller current limit), but the efficiency was not good as the 2200LL. I don't know why.
Several notes that may help (based on my personal experience only): - The FET drain tab is the source of a great amount of noise. The FET drain should be placed as far away from the FB pin trace as reasonably possible. An SMD (D2PAK) FET may be better than a TO-220 one because of the horizontal placement on the PCB (also for better cooling of the FET). - I have never observed any interference from the inductor, but then I use toroidal inductors which are supposed to be self-shielding. I once did get good results with an unshielded Bourns 1110 series inductor, however. - For RSENSE I use several 0.075 Ohm 1/4 W resistors in parallel. They are cheaper than a single larger resistor, and it's easier to adjust the peak current value. - A diode between the REF and FB pins may help if the MAX1771 has trouble starting up. The MAX1771 can enter 12 V fixed output mode if the supply voltage is larger than 12 volts and the voltage at the FB pin is too low (because of the high input:output ratio of the voltage divider). On the other hand, many other people's designs seem to be working fine without this diode. My present design uses a Bourns 2200LL-470-V-RC inductor and an FDB28N30TM FET (0.129 Ohm ON resistance). The maximum power output in a testbench situation was 24.9 W at 85 % efficiency with 14 V input and 220 V output. Board size is 50 mm x 40 mm. I use three of these units in parallel to provide 40 watts at 250 V in a (non-Nixie) project. -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To post to this group, send an email to neonixie-l@googlegroups.com. To unsubscribe from this group, send email to neonixie-l+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/neonixie-l?hl=en-GB.
