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I am currently having an voltage output that differs with time and is about 35 V at maximum. I am looking for a solution to decrease the voltage to 3.3 V without changing the signal. I am looking into using a voltage buffer and a voltage divider, but the op amps I found has a maximum voltage of 32 V. Is there another way to decreasing the voltage without affecting the signal?

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  • \$\begingroup\$ Divide it and then buffer it. \$\endgroup\$ – Rohat Kılıç Jun 7 '17 at 20:56
  • \$\begingroup\$ Why do you think you need to buffer it? What is the load's input impedance? What will your 3.3V signal be coupled to? \$\endgroup\$ – atmnt Jun 7 '17 at 21:09
  • \$\begingroup\$ I don't want to decrease the signal as well, the reason for the buffer I thought. The voltage of 3.3 V I want to connect that to a teensy 3.2 micro-controller. @user134429 \$\endgroup\$ – user123 Jun 7 '17 at 21:28
  • \$\begingroup\$ what kind of signal is that? what is the freq. range? 0 to 3.3V digital or varying analog from 0 to 3.3V? Will it be coupled to ADC or digital input? \$\endgroup\$ – atmnt Jun 7 '17 at 21:55
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If you put your 35 V waveform through a potential divider of 10 K upper and 600 ohm lower, you'll get the scaling to 3.3 V that you need. The resistor values can be made larger or smaller to adjust the current drawn, providing the ratio of the two stay the same.

You can then buffer the potential divider output with a rail-to-rail op-amp connected as a voltage follower (signal to + input, output to - input). As this op-amp is only driven with a 0..3.3 V signal, it can be powerful from a supply rails of this range or greater e.g. 0 and 3.3 V, 0 V and 5 V.

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If you need high input impedance (G ohms or nA/pA bias current) you can simply use a higher voltage op-amp (which will generally require a high supply voltage. For example, an LT1006 with a +40V supply voltage (it needs to be a couple volts higher than the maximum input voltage). Note that the maximum differential input voltage is 30V so it would be wise to add some series resistance and put back-to-back diodes across the inputs. Not all op-amps may require that.

Otherwise, you may be able to use a high impedance divider and buffer that with an op-amp that has suitable characteristics (eg. low input bias current). It's probably not a problem to achieve a 10M input impedance- depending on all the many details such as temperature range, desired accuracy and so on.

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