simple cheap (power-wasting) voltage step-down regulator from 3.3V to 1.2V using zener & led

circuit-20250128-0142.svg

<svg version="1.1" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" width="412" height="292"><defs><linearGradient id="iBObEuOKuAZe" x1="0px" x2="32px" y1="0px" y2="0px" gradientUnits="userSpaceOnUse"><stop offset="0" stop-color="#639c63"/><stop offset="1" stop-color="#57a757"/></linearGradient><linearGradient id="PmLRqlFWwvNP" x1="0px" x2="32px" y1="0px" y2="0px" gradientUnits="userSpaceOnUse"><stop offset="0" stop-color="#639c63"/><stop offset="1" stop-color="#807f7f"/></linearGradient></defs><g><rect fill="#000000" stroke="none" x="0" y="0" width="412" height="292"/><g transform="scale(1,1) translate(-906,-334)"><path fill="none" stroke="#2cd22c" paint-order="fill stroke markers" d=" M 1072 384 L 993 384" stroke-linecap="round" stroke-miterlimit="10" stroke-width="3" stroke-dasharray=""/><g><text fill="#ffffff" stroke="none" font-family="sans-serif" font-size="10px" font-style="normal" font-weight="normal" text-decoration="normal" x="962" y="384" text-anchor="start" dominant-baseline="central">+3.3V</text></g><path fill="none" stroke="#807f7f" paint-order="fill stroke markers" d=" M 1072 560 L 1072 520" stroke-linecap="round" stroke-miterlimit="10" stroke-width="3" stroke-dasharray=""/><path fill="none" stroke="#639c63" paint-order="fill stroke markers" d=" M 1072 504 L 1072 464" stroke-linecap="round" stroke-miterlimit="10" stroke-width="3" stroke-dasharray=""/><path fill="#807f7f" stroke="none" paint-order="stroke fill markers" d=" M 1064 520 L 1080 520 L 1072 504 Z"/><path fill="none" stroke="#639c63" paint-order="fill stroke markers" d=" M 1064 504 L 1080 504" stroke-linecap="round" stroke-miterlimit="10" stroke-width="3" stroke-dasharray=""/><path fill="none" stroke="#639c63" paint-order="fill stroke markers" d=" M 1061 512 L 1064 504" stroke-linecap="round" stroke-miterlimit="10" stroke-width="3" stroke-dasharray=""/><path fill="none" stroke="#639c63" paint-order="fill stroke markers" d=" M 1083 496 L 1080 504" stroke-linecap="round" stroke-miterlimit="10" stroke-width="3" stroke-dasharray=""/><path fill="none" stroke="#639c63" paint-order="fill stroke markers" d=" M 1072 464 L 1072 464" stroke-linecap="round" stroke-miterlimit="10" stroke-width="3" stroke-dasharray=""/><path fill="none" stroke="#57a757" paint-order="fill stroke markers" d=" M 1072 432 L 1072 432" stroke-linecap="round" stroke-miterlimit="10" stroke-width="3" stroke-dasharray=""/><g transform="matrix(0,-1,1,0,1072,464)"><path fill="none" stroke="url(#iBObEuOKuAZe)" paint-order="fill stroke markers" d=" M 0 0 L 2 6 L 6 -6 L 10 6 L 14 -6 L 18 6 L 22 -6 L 26 6 L 30 -6 L 32 0" stroke-linecap="round" stroke-miterlimit="10" stroke-width="3" stroke-dasharray=""/></g><text fill="#ffffff" stroke="none" font-family="sans-serif" font-size="12px" font-style="normal" font-weight="normal" text-decoration="normal" x="1082" y="454" text-anchor="start" dominant-baseline="alphabetic">100</text><path fill="none" stroke="#807f7f" paint-order="fill stroke markers" d=" M 1072 560 L 1072 576" stroke-linecap="round" stroke-miterlimit="10" stroke-width="3" stroke-dasharray=""/><path fill="none" stroke="#807f7f" paint-order="fill stroke markers" d=" M 1082 576 L 1062 576" stroke-linecap="round" stroke-miterlimit="10" stroke-width="3" stroke-dasharray=""/><path fill="none" stroke="#807f7f" paint-order="fill stroke markers" d=" M 1078 581 L 1066 581" stroke-linecap="round" stroke-miterlimit="10" stroke-width="3" stroke-dasharray=""/><path fill="none" stroke="#807f7f" paint-order="fill stroke markers" d=" M 1074 586 L 1070 586" stroke-linecap="round" stroke-miterlimit="10" stroke-width="3" stroke-dasharray=""/><g><g><text fill="#ffffff" stroke="none" font-family="sans-serif" font-size="14px" font-style="normal" font-weight="normal" text-decoration="normal" x="1248" y="464" text-anchor="middle" dominant-baseline="central">1.195 V</text></g><path fill="none" stroke="#639c63" paint-order="fill stroke markers" d=" M 1152 464 L 1215 464" stroke-linecap="round" stroke-miterlimit="10" stroke-width="3" stroke-dasharray=""/></g><path fill="none" stroke="#639c63" paint-order="fill stroke markers" d=" M 1008 464 L 1008 508" stroke-linecap="round" stroke-miterlimit="10" stroke-width="3" stroke-dasharray=""/><path fill="none" stroke="#639c63" paint-order="fill stroke markers" d=" M 1020 508 L 996 508" stroke-linecap="round" stroke-miterlimit="10" stroke-width="3" stroke-dasharray=""/><path fill="none" stroke="#807f7f" paint-order="fill stroke markers" d=" M 1008 560 L 1008 516" stroke-linecap="round" stroke-miterlimit="10" stroke-width="3" stroke-dasharray=""/><path fill="none" stroke="#807f7f" paint-order="fill stroke markers" d=" M 1020 516 L 996 516" stroke-linecap="round" stroke-miterlimit="10" stroke-width="3" stroke-dasharray=""/><text fill="#ffffff" stroke="none" font-family="sans-serif" font-size="12px" font-style="normal" font-weight="normal" text-decoration="normal" x="1022" y="518" text-anchor="start" dominant-baseline="alphabetic">470μF</text><path fill="none" stroke="#807f7f" paint-order="fill stroke markers" d=" M 1008 560 L 1008 576" stroke-linecap="round" stroke-miterlimit="10" stroke-width="3" stroke-dasharray=""/><path fill="none" stroke="#807f7f" paint-order="fill stroke markers" d=" M 1018 576 L 998 576" stroke-linecap="round" stroke-miterlimit="10" stroke-width="3" stroke-dasharray=""/><path fill="none" stroke="#807f7f" paint-order="fill stroke markers" d=" M 1014 581 L 1002 581" stroke-linecap="round" stroke-miterlimit="10" stroke-width="3" stroke-dasharray=""/><path fill="none" stroke="#807f7f" paint-order="fill stroke markers" d=" M 1010 586 L 1006 586" stroke-linecap="round" stroke-miterlimit="10" stroke-width="3" stroke-dasharray=""/><path fill="none" stroke="#639c63" paint-order="fill stroke markers" d=" M 1008 464 L 1072 464" stroke-linecap="round" stroke-miterlimit="10" stroke-width="3" stroke-dasharray=""/><text fill="#ffffff" stroke="none" font-family="sans-serif" font-size="12px" font-style="normal" font-weight="normal" text-decoration="normal" x="1040" y="458" text-anchor="start" dominant-baseline="alphabetic"></text><path fill="none" stroke="#2cd22c" paint-order="fill stroke markers" d=" M 1072 384 L 1072 396" stroke-linecap="round" stroke-miterlimit="10" stroke-width="3" stroke-dasharray=""/><path fill="none" stroke="#57a757" paint-order="fill stroke markers" d=" M 1072 420 L 1072 432" stroke-linecap="round" stroke-miterlimit="10" stroke-width="3" stroke-dasharray=""/><path fill="none" stroke="#808080" paint-order="fill stroke markers" d=" M 1083.76 408 A 11.76 11.76 0 1 1 1083.7599941200006 407.98824000196" stroke-linecap="round" stroke-miterlimit="10" stroke-width="3" stroke-dasharray=""/><path fill="#d10000" stroke="none" paint-order="stroke fill markers" d=" M 1080 408 A 8 8 0 1 1 1079.9999999998872 407.9999575425633 Z"/><path fill="none" stroke="#639c63" paint-order="fill stroke markers" d=" M 1152 464 L 1152 496" stroke-linecap="round" stroke-miterlimit="10" stroke-width="3" stroke-dasharray=""/><path fill="none" stroke="#807f7f" paint-order="fill stroke markers" d=" M 1152 528 L 1152 560" stroke-linecap="round" stroke-miterlimit="10" stroke-width="3" stroke-dasharray=""/><g transform="matrix(0,1,-1,0,1152,496)"><path fill="none" stroke="url(#PmLRqlFWwvNP)" paint-order="fill stroke markers" d=" M 0 0 L 2 6 L 6 -6 L 10 6 L 14 -6 L 18 6 L 22 -6 L 26 6 L 30 -6 L 32 0" stroke-linecap="round" stroke-miterlimit="10" stroke-width="3" stroke-dasharray=""/></g><text fill="#ffffff" stroke="none" font-family="sans-serif" font-size="12px" font-style="normal" font-weight="normal" text-decoration="normal" x="1162" y="518" text-anchor="start" dominant-baseline="alphabetic">50k</text><path fill="none" stroke="#807f7f" paint-order="fill stroke markers" d=" M 1152 560 L 1152 576" stroke-linecap="round" stroke-miterlimit="10" stroke-width="3" stroke-dasharray=""/><path fill="none" stroke="#807f7f" paint-order="fill stroke markers" d=" M 1162 576 L 1142 576" stroke-linecap="round" stroke-miterlimit="10" stroke-width="3" stroke-dasharray=""/><path fill="none" stroke="#807f7f" paint-order="fill stroke markers" d=" M 1158 581 L 1146 581" stroke-linecap="round" stroke-miterlimit="10" stroke-width="3" stroke-dasharray=""/><path fill="none" stroke="#807f7f" paint-order="fill stroke markers" d=" M 1154 586 L 1150 586" stroke-linecap="round" stroke-miterlimit="10" stroke-width="3" stroke-dasharray=""/><path fill="none" stroke="#639c63" paint-order="fill stroke markers" d=" M 1152 464 L 1072 464" stroke-linecap="round" stroke-miterlimit="10" stroke-width="3" stroke-dasharray=""/><text fill="#ffffff" stroke="none" font-family="sans-serif" font-size="12px" font-style="normal" font-weight="normal" text-decoration="normal" x="1112" y="458" text-anchor="start" dominant-baseline="alphabetic"></text><path fill="#ffffff" stroke="none" paint-order="stroke fill markers" d=" M 1075 464 A 3 3 0 1 1 1074.9999999999577 463.99998407846124 Z"/><path fill="#ffffff" stroke="none" paint-order="stroke fill markers" d=" M 1155 464 A 3 3 0 1 1 1154.9999999999577 463.99998407846124 Z"/></g></g></svg>

sim

Instead could use two 7660 ICs two divide a 5.0 V supply twice to produce a 2.5 V supply and a 1.25 V supply. Note that 1.25 V is within the ice40's 1.2 V core supply tolerance range of 1.14 V to 1.26 V.

And a similar really cheap way to get 3.3V from 5V using red (-1.7V) LED into 3.3 V zener:

regarding the very first image, turns out 1.2V zeners don't really exist...seems lower limit is 2.0V zeners. So an alternative could be to use a 2.1V zener to subtract 2.0V from 3.3V:

assuming that don't already have a stable high voltage to start with, then could drop down to the lowest zener (lowest I can find cheaply are 2.0V) and then from that 2.0V do a simple resistor-divider:

Takes about 5us for the 1.2V level to get close enough to be considered "on", since just needs to charge up the 1nF and 10nF capacitors through the somewhat low-valued resistors:

sim