LM393 - Page 1
Forum section: electronics / beginners

author: Unknown
author_rank: Unknown
timestamp: April 18, 2014, 08:07:38 pm
content: POST REMOVED AT USERS REQUEST

author: Rudane
author_rank: Regular Contributor
timestamp: April 18, 2014, 08:54:17 pm
content: Could you post a schematic?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 18, 2014, 09:45:58 pm
content: Circuits that are rated for 5V are to be used at 5V

author: c4757p
author_rank: Super Contributor
timestamp: April 18, 2014, 10:40:33 pm
content: It's not a stupid question (though you really need to give more information next time!). The LM393 indeed should be able to handle up to 36V, and I don't really see what the problem is.At 12V, the 1k resistors will dissipate about 100mW - a bit high, but shouldn't be enough to pop them. That was my first thought, maybe they're burning open circuit. But no.Are you sure it's actually anLM393, and they didn't use another similar chip on your board that might not be rated for 36V? The LMV393, for example, is only rated to 5V.Are you sure you didn't do anything else to mess it up? You'll piss it off if you connect a voltage directly to the output, for instance.As for the MOSFET - 12V at 1A is hardly anything for a modern FET, just about any TO-220 MOSFET will do. Just make sure the gate threshold is low enough for it to switch on at 5V (keyword: "logic level"), and obviously, check all the ratings in the datasheet.

author: David_AVD
author_rank: Super Contributor
timestamp: April 18, 2014, 10:45:09 pm
content: Keep in mind that the output from the LM393 is open collector, not push pull. This means that it can't "output 12V" as such. It can only pull it's output pin to ground.Have you read the data sheet for the LM393? Lots of example circuits in the National (now TI) one.

author: kizzap
author_rank: Unknown
timestamp: April 18, 2014, 10:47:10 pm
content: did you draw over the rated output current? might have fried something that way.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 19, 2014, 02:35:08 am
content: Quote from: kizzap on April 18, 2014, 10:47:10 pm(A "nodding" emote would be even better here)

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 20, 2014, 04:00:51 pm
content: Note the short circuit duration is not "unlimited" (another frequent difference between op-amps and comparators). Actually... what they say is sneaky. Read the statement, and the note, carefully...The output saturation voltage curve shows typical current over a range of voltages.Tim

author: David_AVD
author_rank: Super Contributor
timestamp: April 20, 2014, 09:52:09 pm
content: Quote from: pereczes on April 20, 2014, 11:53:22 amDo you really mean 1 Ohm or 1K (1000) Ohms ?If you meant 1K, I doubt you'd kill the LM393 by having it sink a little over 10mA of LED current.

author: David_AVD
author_rank: Super Contributor
timestamp: April 20, 2014, 10:09:29 pm
content: Quote from: pereczes on April 18, 2014, 09:19:07 pmAfter looking at the circuit in that link, I noticed that the 2nd comparator is left floating. From the National data sheet:Quote

author: c4757p
author_rank: Super Contributor
timestamp: April 20, 2014, 10:26:30 pm
content: Quote from: pereczes on April 20, 2014, 10:20:02 pmIt won't hurt itgenerally*. Some comparators (digital stuff in general) don't like to be left floating or left in a "halfway" state. LM393 doesn't mind, you can even use it as an op amp if you like (it's just hard to tame, because there's no internal compensation capacitor). The TI datasheet notes that ESD protection is "limited".*Itwillbe more sensitive to static discharge. Positive voltages especially will be "trapped" on the emitter of Q1 or Q4. Negative voltages will hit the current sources, which probably won't be pleased either.

author: David_AVD
author_rank: Super Contributor
timestamp: April 20, 2014, 10:28:45 pm
content: In general, floating inputs can lead to oscillation or latchup. This may result in either incorrect operation or permanent damage. If the maker says to ground them, you do it.