Actually my 555 output at 10 V is greater than 5V and I used 50K POT to adjust it to the required level at load. For example take output from 4.5V leg of ladder and adjust the 50K POT to get 4.5V across the load. Without disturbing the set value of POT take output at all other voltage positions. One time adjustment is applicable for all voltage levels.MrAl wrote: If you want more accurate steps then you have to clamp the 5v going to the divider. A way to do this is through another op amp set up to clamp the output at 5v, or if a zener diode is good enough you can use a resistor plus zener. Im wondering how did you expect to get 5v out of the 555 when it is powered by a 10v supply line? Wouldnt that mean it puts out close to 10 volts for the peak? A resistor and zener would clamp that to 5v or near that. If you want really accurate then maybe an op amp and reference diode to buffer the 555 output and clamp the output to 5.00 volts.
If I have exact 5V at top of ladder then this one time 50K adjustment is not required. For that I can use the cases you said, or 74121 / 74123 ICs as they can output exact 5V.
If I have exact 5V at top of ladder then resistors of the ladder should be have 0.01% tolerance levels for equal divisions of this 5V.
My doubt is then the 50K in parallel with them could change the balanced condition of the ladder. Thus no equal voltage divisions takes place. Can I avoid this by placing 100K or 1M ohms (>> 1K ladder) in place of 50K without disturbing both ladder and the op-amp.
If I avoid POT and connect op-amp directly to ladder , then floating condition would be resulted between switching intervals of ladder outs.