Yes thats it......and the TLV431 comes with 1.24V reference so that you can do , say 2 vout SMPS's......but as you know, many SMPS chips have an 0.8V reference......and indeed, some PFC chips have a 7V reference (LT1248)......with the LT1248, its a PFC chip, and vout is 390V....so your feedback signal is less drowned by noise if you only divide it down to 7V......so in that case, its a SNR thing.......but the cheap TL431 is the cheapest reference on the market, and its 2.48V(?).....its used for many other things other than SMPS...and because its so cheap, its gotten adopted into the world of SMPS.