- [R1] role of these low value resistors is to sense - the peak inductor current within each operating cycle - ... if current exceeds ... determined by these resistors, - ... the current cycle is quickly terminated. - - For some reason on the linked schematic ... capacitor C1 - is connected after the current sensing resistors. ... - resistors are no longer measuring ... peak but mean value
Its a compromise. C1's primary purpose is to provide a very localized source of power to be fed into the coil. It can be relocated just prior to the sense resistors (R1), but that adds a little more resistance before getting to L1. More importantly, it will increase the routing length, of the actual physical circuit layout. Putting after R1, simplifies, and decreases trace routing. In practice, by detecting "mean" (average), as opposed to "peak", means you just have to adjust the R1 value, to trip at some lower current level. The sense circuit still protects this unit against shorts. If you need maximum output, then leave R1 completely out; zero ohms (short). If you want 185V at 10mA, the output power is 1.85W. At 75% efficiency, the input power is ~2.5W. That's 9V at 0.28A (280mA). R1 set to 0.33 ohms (3 1ohms in parallel), will give you more than enough. The efficiency is determined by parts used, and physical layout. 75% is usually a safe, conservative, level for this circuit. Squeezing proper parts, onto a small PCB board, with healthy fat, but short, traces, has gotten me levels just over 80%. - understand the equations surrounding R3 and R4 for - determining Vout. ... the default values shown, but end up - 185V requiring me to adjust R3/R4 to get my desired 180V. - would I decide which R to adjust "first"? Unless my calculator is broken, I get 180V. For nixies, however, an exact value isn't required. 180V could mean 170V or 190V, and that's a +/-5% variation. In the old days, +/-10% would be considered pretty damn good. If you want 185V, leave R4 alone at 3.32K (3K32), and get a new value for R3. 488K ideally. 487K 1% available. Note, 1% variance is still +/-1.9V, or 183V to 187V. You really don't need that kind of precision for a supply. If your circuit does, then consider another circuit. If an app needs that kind of precision for its supply, you're asking for trouble. -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To post to this group, send an email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/neonixie-l?hl=en-GB.
