lm 324 upgrade - Page 1
Forum section: electronics / projects

author: Kevin.D
author_rank: Frequent Contributor
timestamp: March 23, 2013, 09:38:46 pm
content: Does any one know a good upgrade replacement for the lm 324 op amp. ?Heres what im' looking forIt must be single supply capable upto at least 30Vlike LM324 common mode input MUST at least include GND ,And output must go to gnd .Have a decent input offset voltage < 0.5 mV (lm324 is 2 mV)Have good low input bias current spec . < 10nA max . (lm324 is 100nA)High speed is not so important ,as long as it's no slower than lm324 .Also it must be cheap and easily available .Could do with it being available in dual and quad versions.I am fed up with looking and not finding anything ,everything seems to be made for low voltage , these days .Been looking at the LT1014 which supposed to be an precision lm324 but ,it's not that much of an upgrade really ,the input bias current is 50nA which is still to high .

author: AndyC_772
author_rank: Super Contributor
timestamp: March 23, 2013, 10:21:14 pm
content: A few minutes on Linear Tech's parametric search yieldsthis:.Should get you started...

author: free_electron
author_rank: Super Contributor
timestamp: March 24, 2013, 12:33:43 am
content: lmc66xx series ?

author: amspire
author_rank: Super Contributor
timestamp: March 24, 2013, 04:28:47 am
content: There is no direct replacement for a LM324 family, since no other opamp family can safely handle voltages on the inputs well over the positive supply. The LT1014 is not a direct replacement. If you are replacing the LM324 opamp in an existing design, you need to check the circuit to see if the inputs are always below the positive supply.For new designs, you will be very much better off if you can redesign for a 5V supply. There are not a lot of options for 30V supply opamps, and I am not sure if any are cheap.The opa118/2188/4188 families are very nice but I wouldn't call them cheap. Same with the LT opamps.

author: konfu
author_rank: Contributor
timestamp: March 24, 2013, 07:14:46 am
content: LT6016 & LT6017.no direct replacements but great devices! might be a bit more costy but I haven't found ones with better specs for higher voltages yet. linear technology is quite easy to sample as well...

author: bingo600
author_rank: Super Contributor
timestamp: March 24, 2013, 04:28:52 pm
content: Are they that badI bought 1000 (SGS) in SO14 , for 55$ a few years ago on 'Bay...We ought to do a component exchange section/Bingo

author: Zlatko
author_rank: Newbie
timestamp: March 24, 2013, 10:57:38 pm
content: LT1491 Direct replecment much better performance

author: amspire
author_rank: Super Contributor
timestamp: March 25, 2013, 03:47:39 am
content: Quote from: Zlatko on March 24, 2013, 10:57:38 pmWow! Well done for spotting this chip.The inputs have an even better overvoltage then the LM324. Up to 44V positive (regardless of supply voltage) at a very low bias current and it can safely handle -22V below the negative rail through an internal 1K resistor to diodes to 0V rail.That is brilliant! It has two parallel input stages - NPN and PNP which I think give it ac active common mode range of probably 0.3V below the negative rail to 0.3V above the positive supply rail.Much slower then the LM324 so it is only a replacement for very slow LM324 circuits, but I will definitely keep this opamp on my short list.Richard

author: codeboy2k
author_rank: Super Contributor
timestamp: March 25, 2013, 06:03:57 am
content: I'll keep the LT1491 on my radar as well for when it's needed. It's quite pricey at $3.26 each for a reel of 2500 from Digikey so I'd have to be damn sure I needed it. You just can't beat the LM324 for it's price... $0.10 each for a reel of 2500, and when it fits the circuit and you can live with it's specs and/or calibrate them out, then it's a clear winner to choose the LM324, even for new designs (although many datasheets say not recommended for new designs, they are still producing them )

author: amspire
author_rank: Super Contributor
timestamp: March 26, 2013, 01:36:20 am
content: Quote from: AcHmed99 on March 25, 2013, 07:08:12 pmYes. If the inputs exceed the specified maximums, the opamp IC can latch that usually means it self destructs. So if your opamp circuit does connect to an externally power circuit that under some circumstances (eg power up) can drag an input more then 0.3V above the positive rail or 0.3V below the negative rail, then you do have to add a series resistor and a pair of external schottky diodes. You cannot rely on the inherent IC diode junctions as it it those junctions that cause the latchup in the first place.What this means is that if you use conventional opamps in a circuit with multiple supply rails, and assume the supplies power up at different rates, you have to make sure that on power up, an opamp input can never go above or below the supply rails. With a LM324, you do not have to worry about this for positive overvoltages. With the LT1491, a 1K series resistor with the input means it is safe for positive and negative overvoltages.As another example, I used LM324s in my power supply project. This means that I can have a 12V battery on the output, and switch off the power supply, and the LM324's can cope with the 12V from the battery fine without loading the battery. With almost all other opamps, I would have to add a series resistor, and the schottky diodes, and they would load the battery. In many supply designs, they get around this problem by using a reverse-biased diode that goes from the load output back to the supplies power rail which means that if the supply is off, and you attach a 12V battery, the battery is actually powering the power supply.It is a nice feature. If you do not have overvoltage, you just have to make different design choices. That is all.In the context of this thread, if you want to replace a LM324 in an existing design, you have to keep in mind that the designer of the original design may be using the LM324's overvoltage capability. If the design does not use this property, then replacement is probably not hard.Richard.

author: codeboy2k
author_rank: Super Contributor
timestamp: March 26, 2013, 07:01:56 pm
content: Quote from: AcHmed99 on March 25, 2013, 07:08:12 pmOh wow it's on sale at .097 for QTY 1Since I don't have a project at the moment where I need 2500, I'll have to add a few to my parts bin at this price

author: Kevin.D
author_rank: Frequent Contributor
timestamp: March 27, 2013, 01:23:07 pm
content: Quote from: Zlatko on March 24, 2013, 10:57:38 pmWell it's got some good specs , low power aswell , it's slow though , slower than LM324 .The LT1639 looks to be the higher speed version of this device ,roughly same speed as the lm324 ,but it also has a higher input bias current which lets it down,only 50% better than the LM324 ,it's seems to be a direct replacement I think. As long as the extra rail to rail capability is not going to cause a problem .Thanks for the replies guys

author: amspire
author_rank: Super Contributor
timestamp: March 27, 2013, 02:06:27 pm
content: If I understand the specs correctly, the LT1491 and the LT1639 will not only withstand overvoltage on the inputs, but they keep operating with overvoltage on the inputs.So they can still operate with both inputs at 44V with the opamp running from a +5V supply.The input bias current increases from 20nA to to 8uA (as the input NPN transistors saturate and so they are now just forward biased diodes into the emitters of the next PNP stage) and the offset voltage increases to 2mV, but the inputs are still fully functioning in differential mode.That is pretty amazing. I am more impressed now.One thing you have to watch is the changes in bias current. In a normal opamp, the bias current is always in one direction and is fairly constant. In these opamps, the bias current goes from -20nA for 0.8V below the +Vs rail to +40uA between +Vs - 0.5V to +Vs and then 8uA up to +44V.If you were using a 1M input resistor, this would correspond to voltage drops across the 1M input resistor of -0.02V, +0.04V and 8V (ouch!).Richard.

author: Zlatko
author_rank: Newbie
timestamp: March 29, 2013, 06:01:21 pm
content: I use LT1490 dual opamp at the moment in Dave Supply schematic rev.C because i cannot manage to make it work with LM358 (N and P versions). And works perfectly. If u need 1 or 2 for testing purposes u can order from Linear as free sample.

author: dotneck335
author_rank: Newbie
timestamp: November 26, 2015, 05:26:45 am
content: The LMC660 is pin-for-pin compatible with the LM324 and offers greater bandwidth and input resistance over the LM324. These featureswill improve the performance of many existing single-supply applications. Note, however, that the supply voltagerange of the LMC660 is smaller than that of the LM324.

author: Aeternam
author_rank: Unknown
timestamp: April 25, 2016, 03:39:15 pm
content: I'm digging out this thread because I need a noobie reality check on opamp datasheet grammar.Am I correct in assuming that I'm looking forVoh (output swing high) = V+ andVol (output swing low) = GNDwhen hunting for a rail-to-rail single-supply opamp? Further, that these values change (unfavorably) with load?

author: macboy
author_rank: Super Contributor
timestamp: April 26, 2016, 05:47:51 pm
content: Quote from: amspire on March 24, 2013, 04:28:47 amPlenty do this. Search for "Over the top" or OTT inputs.