Hi Spehro, > Sometimes you can trick the LM324 into doing what you want by > loading it > with a resistor to one of the supply pins (usually "GND"), thus > keeping the > output in the class A mode. Can you please explain this. Thanks, Mohit. ----- Original Message ----- From: "Spehro Pefhany" To: "Microcontroller discussion list - Public." Sent: Monday, November 20, 2006 9:26 AM Subject: Re: [EE] Op-Amp Recommendations > At 08:38 PM 11/19/2006, you wrote: >>Content-Type: text/plain; format=flowed >>X-MIME-Autoconverted: from 8bit to quoted-printable by pch.mit.edu >>id kAK1cVeA025855 >> >> >> Spehro, >> >>>The requirement for high voltage operation *and* R-R operation is >>>quite >>>rare, in fact I suggest it might be an error to add that >>>constraint. Usually >> >> Yeah, don't I know it! >> Unfortunately it's just one application. This particular part is >> being used for doing some analog math on control voltages to some >> CCA gain blocks. The greater the rail voltages, the greater the >> headroom in the system. >>The gain blocks are set up to be "off" when the CV is at the >>negative rail, hence the negative rail requirement. The positive >>rail would be nice, too, but getting close to the negative rail is a >>lot more important or else there'll be bleed-through. >> >> I've used the 324 lots of times and like it fine, but it has this >> goofy output stage (well, not really goofy -- it's designed for >> low-power consumption, which I don't care about) that has a >> noticable glitch at the crossover point into high-ish impedance >> loads. It's really visible on a scope and audible if the signal in >> question is audio. But the 324 does go down to 20mV or so of the >> negative rail, and it's cheap, and has a wide range of operating >> voltages. As for the other specs, any parameter I didin't list >> isn't something I'm overly concerned with. >> >> If I can't find a part that works, I'll just use the 324 or bring >> down the rails and recalculate the biasing. But I'd like to not >> have to. Even a R-R (or just the negative rail) part that was okay >> with +/- 10 would be pretty great. > > Okay. > > The LT1013 Dwayne mentioned is a pretty good precision bipolar dual > op-amp. > It handles common mode input voltage down to ground and the output > swings to > ground. It can also do +/-15V supplies with ease. Try looking for > "single > supply" op-amps rather than R-R types and you'll find lots of others > that > should work for you, if you can live without the inputs/outputs > going to > the positive rail (there are other problems associated with the > inputs > if there's a lot of common mode voltage anyway). > > Sometimes you can trick the LM324 into doing what you want by > loading it > with a resistor to one of the supply pins (usually "GND"), thus > keeping the > output in the class A mode. > >>Best regards, > > Spehro Pefhany --"it's the network..." "The Journey is > the reward" > speff@interlog.com Info for manufacturers: > http://www.trexon.com > Embedded software/hardware/analog Info for designers: > http://www.speff.com > ->>Test equipment, parts OLED displys > http://search.ebay.com/_W0QQsassZspeff > > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist