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7.08 = 15 * (R4 / (R4 + R3 + R2 + R1))
7.1 = 15 * ((R4 + R3) / (R4 + R3 + R2 + R1))
7.12 = 15 * ((R4 + R3 + R2) / (R4 + R3 + R2 + R1))
Rtotal = 150K
R1 = 78K8
R2 = 200R
R3 = 200R
R4 = 70K8
(R2 + R3 + R4)/(R1 + R2 + R3 + R4) * Vin = 0.4746r* 15V = 7.12V
(R3 + R4)/(R1 + R2 + R3 + R4) * Vin = 0.473r * 15V = 7.1V
(R4/ R1 + R2 + R3 + R4) * Vin = 0.472 * 15V = 7.08V
Maybe not so much, because there is only 0.04V span between lowest and highest out value.Also note, that the range of values you are trying to create with this divider is only about +/ 2%, so if you use this approach, you must use precision resistors, or simply the normal variations in resistor values will cause you to miss these specifc voltage values.
I wonder what's the idea behind writing 30+ digits? Nonsense.0.47466666666666666666666666666667
Here is one another such calculator. This one supports configurable stock, which could be useful.On obvious way to get any arbitrary resistor values is to put two 1% resistors in series or parallel of the proper value.
That way the worst-case arbitrary value will be within 1% of the desired.
This website will calculate the optimum values for any desired resistance.
Using this same example, my tool recommends putting 5.9k and 64.9k in series to obtain exactly 70.8k. Of course subject to the tolerance of the resistors used. I think 143k is an E96 value, but both 5.9k and 64.k are from E48 series, so I prefer this combination.Thus, for example, to get the 70.8k resistor value calculated for R4 in the first part of post #3, you can put 140k in parallel with 143k to give 70.8k within 0.08% (±1% of course).
Hi,
I wonder what's the idea behind writing 30+ digits? Nonsense.
For a 1% tolerated resistor 3 digits are sufficient, maybe write 4 digits (integer + fractional). Everything above 4 digits makes no sense.
Klaus
...choose 10 ppm Vref at 7V and pullup to 120mV offset easily with taps..
No.Would a TL431 accomplish this?
I vote for tolerance....;-)No Tolerance makes your spec INCOMPLETE.
your 15V supply error will quickly dominate your results.
Hi,
Is it for a LiIon battery charge status detector?
(if so, then I doubt it will give meaningful results)
Klaus
Is it for a LiIon battery charge status detector?
I use an LM3915 to drive the LEDs in my sound level indicator that also has a peak detector. The LM3915 has the resistor ladder and 10 comparators that drive the LEDs with an adjustable constant current. Its detection points are 3dB (0.707 times or 1.414 times) apart which is a small but noticeable change in level. Nobody will be able to hear the tiny change in level (less than 1%) with your resistors.It's just a simple audio peak detector, doesn't have to be super accurate. The tap voltages are just what I measured at where I wanted the LEDs to come on at.
I use an LM3915 to drive the LEDs in my sound level indicator that also has a peak detector. The LM3915 has the resistor ladder and 10 comparators that drive the LEDs with an adjustable constant current. Its detection points are 3dB (0.707 times or 1.414 times) apart which is a small but noticeable change in level. Nobody will be able to hear the tiny change in level (less than 1%) with your resistors.