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I am measuring the slew rate of an LM358 op amp running +/-15V using both unity-gain (+/- 10V input signal = 2/3 full scale) and 'comparator mode' (+/- 1V input to noninv input, inv input grounded). I've made the measurement in situ as well, with a circuit whose output depends directly on the slew rate. In all experiments, the slew rate of the humble '358 notoriously slow) comes out to be roughly 18 V/us, with a lowest measurement in the range of 11 V/us. I've tested multiple 358s and found the same result. In all tests, the other op amp (dual package) has its inputs tied together, output is open.

TI brand LM358 page is here. SR should be 0.3 V/us typ.; I'm measuring over an order of magnitude faster response. Datasheet here [pdf]. SR recently updated to 0.5 V/us at G = +1.

In all calculations, a square wave output is measured on a scope, the slew rate is calculated as $$SR = \frac{\Delta V}{ \Delta t}= \frac{V_{end}-V_{start}}{t_{end}-t_{start}}$$ Example calculation: 10x probe measures a rise time (linear voltage ramp) of 1.34us, voltages are -1.36V up to 1.12V, thus $$ SR = \frac{2.48 \text{ V} \times 10}{1.4\ \mu\text{s}} = 17.7 \text{ V}/\mu\text{s}$$ Now it's perfectly alright with me if the 358 has a faster slew rate. But I had actually hoped for something slower; not only that, but having an op amp be that far out of spec (as a 'typical value' nonetheless) caught me off guard.

Can anyone verify the 358 slew rate? Or explain why the rate is so much faster when I'm measuring it?

EDIT

Image of one of the LM358s I'm measuring.

enter image description here

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    \$\begingroup\$ Are you sure it's actually an LM358 and not, say, an LT1358? Were the parts acquired via franchised distributors? \$\endgroup\$
    – Spehro 'speff' Pefhany
    Commented Nov 11, 2020 at 19:50
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    \$\begingroup\$ Can't say where these op amps came from now. Probably bought in bulk from an ebay seller years ago. Adding a picture in case it helps identify a fake. \$\endgroup\$
    – Sam Gallagher
    Commented Nov 11, 2020 at 19:58
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    \$\begingroup\$ The TI logo doesn't look right. \$\endgroup\$
    – vofa
    Commented Nov 11, 2020 at 20:36
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    \$\begingroup\$ Here's a photo of a TI chip that is genuine: 74LS590. (Don't have any LM358s handy.) \$\endgroup\$
    – jonk
    Commented Nov 11, 2020 at 20:37
  • \$\begingroup\$ @jonk I remember all those old TI 74 series DIP's pins going black with age. That one is well preserved. \$\endgroup\$
    – Unimportant
    Commented Nov 11, 2020 at 20:43

1 Answer 1

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Given the dubious eBay source and somewhat dodgy markings, they're probably something similarly cheap like TL071 remarked.

Suggest you discard them and get known parts from a reliable source.

Real clone LM358s are 2.8 cents apiece in 1K from LCSC, for example, and ON ones are only slightly more.

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    \$\begingroup\$ Pulled some 358s that I knew were genuine, and the measured slew rates were 0.6 V/us or so. Grabbed some TL072s, slew rate matched 18 V/us. I'd certainly say this makes for a convincing picture! \$\endgroup\$
    – Sam Gallagher
    Commented Nov 11, 2020 at 20:42
  • \$\begingroup\$ 0.3 to 0.6 could be process variations. \$\endgroup\$
    – user16324
    Commented Nov 11, 2020 at 21:32
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    \$\begingroup\$ Looking at the photo in the question, this seems like a clearly blacktopped part. It looks like there is a bit of the black paint flaking off just below the "83" in the bottom row, plus the inner edge of the round dent seems to be "rounded off" with paint as well. \$\endgroup\$
    – TooTea
    Commented Nov 12, 2020 at 10:49

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