Thursday 9 August 2018

operational amplifier - How to amplify and offset the voltage in an opamp?


I need to amplify a voltage, which comes from a DAC and is 0-2.5V and scale it 0-25V in an operational amplifier. After amplified, I need to offset it -1.25V, so the final voltage is -1.25 to 23.75V. In other words, being an operational amplifier, I want to do the y=ax+b operation. with a=10, and b=-1.25V


I thought of 2 different ways of doing this.




  1. The first idea I had is to use a second amplifier as a summing amplifier, with a fixed -1.25V voltage.





  2. The second idea is to use a 1.2V zener in series with the output, along with a biasing resistor to -V.




Why do I want this? I want to set the ADJ pin in an LM338 voltage regulator from an MCU. LM338 out is ADJ+1.25V. If ADJ is -1.25V then the output is 0V.




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