A simple level converter. It assumes the +4V supply can sink current, so why not just have 2 resistors between +4 and +10 and use the opamp as a buffer?
+10V | | R | | |---------- | | | | R | | | | | GND | | | |---- + >------- +7V out +4V -----R------------- - | | | | | |------2R-----|-- Reply in group, but if emailing add one more zero, and remove the last word.
There are three different ways to do this with just two resistors.
-- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
I know what you mean. This was just someone's idea of an example but he should have thought of a better one. I wondered if there was any justification for using 4 resistors.
-- Reply in group, but if emailing add one more zero, and remove the last word.
The op-amp version has a -2 voltage gain for variations in the +4 line to the output. If you want that, you can't get it with passive components.
-- My liberal friends think I'm a conservative kook. My conservative friends think I'm a liberal kook. Why am I not happy that they have found common ground? Tim Wescott, Communications, Control, Circuits & Software http://www.wescottdesign.com
Yes, I know you can't get gain with passive components. :)
I wasn't suggesting resistors with no opamp. I just wanted to know if the
4-resistor approach had any advantage over the obvious 2-resistor equivalent.In the OP I said 'use the opamp as a buffer', so do you mean that it would have no gain (unity gain) with that approach?
-- Reply in group, but if emailing add one more zero, and remove the last word.
If you use a pair of resistors to get 7V out of the 10V and the 4V, then when the 4V changes by dV, the output will change by significantly less than dV and in the same direction.
If you use the setup you show and the 4V changes by dV, then the output will change by -2*dV. If what you need is to pick out and amplify some signal that's riding on the 4V, then the pictured circuit would be the way to go.
You don't say what the circuit is from or what you want to use it for, so it's impossible to answer your "why not". My suggestion was just that -- one possible reason "why not", which you then have take and exercise your own brain cells to see if it makes sense or not.
-- My liberal friends think I'm a conservative kook. My conservative friends think I'm a liberal kook. Why am I not happy that they have found common ground? Tim Wescott, Communications, Control, Circuits & Software http://www.wescottdesign.com
Thanks.
It was somebody's example of a 'basic opamp circuit' so I wondered if there was any reason to do that other than making an imaginary circuit.
-- Reply in group, but if emailing add one more zero, and remove the last word.
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.