Electronics > Beginners
LM358 from LT? (crossreference for an LTSpice simulation)
Ian.M:
Although that works, its a real mess on the schematic for all except short model files, and you cant include custom symbols, so it makes more sense to keep the files separate, make a folder and put them in it with the sim file then in the sim, .lib the model file to use it.
magic:
--- Quote from: David Hess on December 06, 2019, 08:26:05 pm ---I am not sure why the LM358/LM324 did not use a class-AB output stage to reduce or eliminate crossover distortion. At the time they were released, Fairchild had their own versions with different part numbers which did use a class-AB output stage.
--- End quote ---
I think I found it: µA798, and I suppose there is no particular mystery here, 4x higher supply current was the reason.
--- Quote from: Kleinstein on December 06, 2019, 09:10:58 pm ---The original LM358 has a class B output stage. The cross over error is clearly visible in many cases. AFAIR the dead range is more like 1 diode drop, so the 2 extra diodes give more cross over distortion.
--- End quote ---
The output uses a darlington on one side so it's 3 diode drops, actually. Given the 0.6V/µs slew rate, theory predicts some 3µs of Hi-Z before the output switches polarity.
edit
It's even worse, more like 10µs in (presumably) TI version here:
https://e2e.ti.com/support/amplifiers/f/14/t/698220
Zero999:
--- Quote from: Ian.M on December 07, 2019, 12:36:43 am ---Although that works, its a real mess on the schematic for all except short model files, and you cant include custom symbols, so it makes more sense to keep the files separate, make a folder and put them in it with the sim file then in the sim, .lib the model file to use it.
--- End quote ---
I agree, it is messy, although that can somewhat be mitigated by choosing the smallest font size. It does have the advantage of making it easier to post here, because some people are wary about opening a zip file, which can contain just about anything.
David Hess:
--- Quote from: magic on December 07, 2019, 09:11:21 am ---
--- Quote from: David Hess on December 06, 2019, 08:26:05 pm ---I am not sure why the LM358/LM324 did not use a class-AB output stage to reduce or eliminate crossover distortion. At the time they were released, Fairchild had their own versions with different part numbers which did use a class-AB output stage.
--- End quote ---
I think I found it: µA798, and I suppose there is no particular mystery here, 4x higher supply current was the reason.
--- End quote ---
There is quite a bit of variation between manufacturers of the LM358 and I doubt designers cared. Later Fairchild manufactured both the quad LM324 and uA3403 and the supply current difference was 1.5 and 2.8 milliamps typical.
David Hess:
Something else which is odd about the Fairchild parts is that they specify a single supply output however their unusually detailed schematics show only a PNP emitter follower for sinking current. Yet they specify 1 milliamp of sink current at 400 millivolts which is *better* than the LM358/LM324. Maybe the schematics are incomplete but there is also no detailed graph of sink current versus voltage. The outputs will work to ground as shown but an external pull-down would be required.
I might suspect that they never went into production however the part was listed in multiple editions of Fairchild's databooks. It might be interesting to find some on Ebay for testing.
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