| Electronics > Beginners |
| LM741 as comparator 1.9V problem |
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| Lee Leduc:
Wikipedia has a very nice write up of 741 op amp. It walks you through the device explaining how each stage of the circuit works. Very educational. https://en.wikipedia.org/w/index.php?title=Operational_amplifier&direction=next&oldid=436142906 |
| PerranOak:
Beaut, thanks, I'll have a look. |
| Zero999:
--- Quote from: PerranOak on May 04, 2018, 01:24:23 pm ---Thanks all. I was just experimenting with comparators and found a circuit online. I had an LM741 so I gave it a go. When I used an LM393 all was well but I just wanted to understand what was happening. I looked on the datasheet for "input common voltage range" but can't find it nor anything that mentions the 2V headroom. I do have difficulty with datasheets though: it says that for my LM741C it says that the supply voltage can be +/-18V but doesn't mention that it only works properly at the higher values. Oh well, new stuff learned and thanks all. --- End quote --- Page 5, section 6.5, "input voltage range ±13V". It's specified with +/-15V supplies, which implies it's 2V of headroom from either supply rail. Note it also says ±13V typical, ±12V minimum, you you'll need to allow 3V of headroom to ensure it works over the entire temperature range. http://www.ti.com/lit/ds/symlink/lm741.pdf |
| viperidae:
--- Quote from: PerranOak on May 04, 2018, 01:24:23 pm ---it says that for my LM741C it says that the supply voltage can be +/-18V but doesn't mention that it only works properly at the higher values. --- End quote --- It says the recommended minimum supply voltage is +/- 10V. All the values in the tables are only valid when running at +/- 15V |
| David Hess:
--- Quote from: PerranOak on May 05, 2018, 01:07:38 pm --- --- Quote from: David Hess on May 04, 2018, 05:33:48 pm ---It also includes an equivalent schematic from which it is possible to derive the input and output voltage ranges without too much trouble. --- End quote --- Really. How is this done? --- End quote --- Just add up the transistor Vce (about 0.2 volts) and Vbe (about 0.6 volts) saturation values. |
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