ok - looks like about 150kHz frequ for the 555 boost - this might work better at a higher frequ, just adjust the C1, the 1nF that's the 555 timing cap (maybe 330pF for about 3x freq). With the pair of 50uH in parallel, there's about 600mA peak current - kinda whopping at start-up. Prob can use just a single inductor there - that helps with peak inductor current also. Hmm. All the "real-adult SMPS chips" have some "soft-start" mechanism and R, C adjustments. Now I see why ... Michael Beach, 29 min the "7.5V" looks like it might be closer to 9V with the R8 and R9 settings and a 3Vzener ref. I'll assume most "adjust to taste" component value changes are all OK and what's needed during debug of the first built units. Don't make a batch of 100 right away .. Michael Beach, 25 min unused op-amps - I usually tie the Vout to the neg feedback pin - makes a voltage follower. No need to tie the input to anything - you have these avail for some future TBD hack, and they should not cause havoc. Michael Beach, 22 min the LED_CONTROL signal - I see an incompatible level here, with the 555 providing a 5V square wave, and the R3, R4 implies a 3V micro-level control for 20mA to the LED. There's a bunch of ways to adjust this ... if the future micro could be either 3V or 5V then we should make use of the 3V zener that's back at the 555-boost stage! Michael Beach, 14 min for debug, or for DMM use, we might really like having a pin that has the +2.5V available to use humans, somewhere - that would help the "rect" value to be more trustworthy. I noticed this when I noticed there might be some errors (DC errors, not likely troubles here due to process) at the "detect" signal output due to any R mismatch for R9, R10, R11, R12. We could use a genuine differential amp here (more pricey and slightly exotic, but not very) or precision R's ... prob not worth the troubles here. Oh, look - that +2.5V goes to pin 3 at the output! I should have scrolled down before I complained! And there's a spare I/O pin at pin 10! Glory! Michael Beach, 8 min OK - that's all I got! There's likely to be some component value adjustments at the detector, to adjust the gain, but otherwise I like this! I like that quad op-amp, the OPA4340, from what I see. DigiKey says TI has a new updated version. It's odd that TI has a fetish for making annoyingly similar parts with incompatible pin-outs, prob for some specific mfg of some crap product built on a cheap single sided pcb ...