Vout Lo in LM324

Schematic?

By the data sheet it should go down to 100mV, but only if the load is around 500uA -- are you pulling the output high with anything?

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com

LM324 needs a pulldown load to go really low. Also to avoid crossover distortion where required

Grant.

"Shmitt" trigger sounds like there are pull-up loads. Thus, in the LM324, the output is dominated by a PNP device (there's only around

50uA of pull-down current available... read the data sheet :-)

While you're reading data sheets read the LM317 data sheet for the proper way to make current limiters ;-) ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
I love to cook with wine.     Sometimes I even put it in the food.

Hi Tim,

well this is what I had expected too. But there is a stable level of few under 700 mV at the lowest potential on the output of all real LM324 I have.

I'll give you a LTSpice file i drawed, because I wanted to see, what Spice guesses, but Spice would also expect lower voltages. The same LM324 in amplifier mode (impedance converter f.ex.) works totally correct by the way. So they are not broken. Did anyone noticed similar on LM324?

Marte

_____ Version 4 SHEET 1 1988 3788 WIRE 208 -432 144 -432 WIRE 832 -432 208 -432 WIRE 144 -384 144 -432 WIRE 832 -224 832 -432 WIRE 416 -192 336 -192 WIRE 496 -192 416 -192 WIRE 640 -192 576 -192 WIRE 832 -112 832 -144 WIRE 832 -112 736 -112 WIRE 976 -112 832 -112 WIRE 992 -112 976 -112 WIRE 416 -48 416 -192 WIRE 448 -48 416 -48 WIRE 480 -48 448 -48 WIRE 608 -32 544 -32 WIRE 640 -32 640 -192 WIRE 640 -32 608 -32 WIRE 688 -32 640 -32 WIRE 224 -16 224 -128 WIRE 416 -16 224 -16 WIRE 448 -16 416 -16 WIRE 480 -16 448 -16 WIRE 224 48 224 -16 WIRE 416 112 416 -16 WIRE 496 112 416 112 WIRE 640 112 640 -32 WIRE 640 112 576 112 FLAG 144 -80 5v FLAG 144 0 0 FLAG 224 -208 5v FLAG 512 -64 5v FLAG 512 0 0 FLAG 224 128 0 FLAG 336 -128 0 FLAG 608 -32 A FLAG 448 -48 i FLAG 448 -16 ni FLAG 144 -304 0 FLAG 208 -432 In FLAG 832 -32 0 FLAG 736 -16 0 FLAG 976 -112 OUT SYMBOL voltage 144 -96 R0 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V1 SYMATTR Value 5 SYMBOL Opamps\\opamp2 512 -96 R0 WINDOW 0 16 32 Invisible 2 WINDOW 3 24 95 Left 2 SYMATTR InstName U1 SYMATTR Value LM324 SYMATTR Value2 LM324 SYMBOL res 208 -224 R0 SYMATTR InstName R1 SYMATTR Value 15k SYMBOL res 208 32 R0 SYMATTR InstName R2 SYMATTR Value 10k SYMBOL res 592 96 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R3 SYMATTR Value 10k SYMBOL res 592 -208 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R4 SYMATTR Value 12k SYMBOL cap 320 -192 R0 WINDOW 0 31 15 Left 2 WINDOW 3 29 57 Left 2 SYMATTR InstName C1 SYMATTR Value 10n SYMBOL voltage 144 -400 R0 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V2 SYMATTR Value SINE(0 5 50) SYMBOL nmos 688 -112 R0 SYMATTR InstName M1 SYMATTR Value 2N7002 SYMBOL res 816 -240 R0 SYMATTR InstName R8 SYMATTR Value 910 SYMBOL res 816 -128 R0 SYMATTR InstName R9 SYMATTR Value 100 TEXT -768 -608 Left 2 !*//////////////////////////////////////////////////////////\n*LM324 Low Power Quad OPERATIONAL AMPLIFIER MACRO-MODEL\n*//////////////////////////////////////////////////////////\n*\n* connections: non-inverting input\n* | inverting input\n* | | positive power supply\n* | | | negative power supply\n* | | | | output\n* | | | | |\n* | | | | |\n.SUBCKT LM324 1 2 99 50

28\n*\n*Features:\n*Eliminates need for dual supplies\n*Large DC voltage gain = 100dB\n*High bandwidth = 1MHz\n*Low input offset voltage = 2mV\n*Wide supply range = +-1.5V to +-16V\n*\n*NOTE: Model is for single device only and simulated\n* supply current is 1/4 of total device current.\n* Output crossover distortion with dual supplies\n* is not modeled.\n*\n****************INPUT STAGE**************\n*\nIOS 2 1 5N\n*^Input offset current\nR1 1 3 500K\nR2 3 2 500K\nI1 99 4 100U\nR3 5 50 517\nR4 6 50 517\nQ1 5 2 4 QX\nQ2 6 7 4 QX\n*Fp2=1.2 MHz\nC4 5 6 128.27P\n*\n***********COMMON MODE EFFECT***********\n*\nI2 99 50 75U\n*^Quiescent supply current\nEOS 7 1 POLY(1) 16 49 2E-3 1\n*Input offset voltage.^\nR8 99 49 60K\nR9 49 50 60K\n*\n*********OUTPUT VOLTAGE LIMITING********\nV2 99 8 1.63\nD1 9 8 DX\nD2 10 9 DX\nV3 10 50 .635\n*\n**************SECOND STAGE**************\n*\nEH 99 98 99 49 1\nG1 98 9 POLY(1) 5 6 0 9.8772E-4 0 .3459\n*Fp1=7.86 Hz\nR5 98 9 101.2433MEG\nC3 98 9 200P\n*\n***************POLE STAGE***************\n*\n*Fp=2 MHz\nG3 98 15 9 49 1E-6\nR12 98 15 1MEG\nC5 98 15 7.9577E-14\n*\n*********COMMON-MODE ZERO STAGE*********\n*\n*Fpcm=10 KHz\nG4 98 16 3 49 5.6234E-8 \nL2 98 17 15.9M\nR13 17 16 1K\n*\n**************OUTPUT STAGE**************\n*\nF6 50 99 POLY(1) V6 300U 1\nE1 99 23 99 15 1\nR16 24 23 17.5\nD5 26 24 DX\nV6 26 22 .63V\nR17 23 25 17.5\nD6 25 27 DX\nV7 22 27 .63V\nV5 22 21 0.27V\nD4 21 15 DX\nV4 20 22 0.27V\nD3 15 20 DX\nL3 22 28 500P\nRL3 22 28 100K\n*\n***************MODELS USED**************\n*\n.MODEL DX D(IS=1E-15)\n.MODEL QX PNP(BF=1.111E3)\n*\n.ENDS\n*$ TEXT 0 3288 Left 2 !.tran 25m

I missed that -- I was just seeing the 10k load. I assume, then, that the 10k is to Vee?

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com

...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
I love to cook with wine.     Sometimes I even put it in the food.

Eww. Top-posting. Ick. I mean -- it makes sense in this case, but still.

I'm pretty sure there's a model in there, and that the '\n' means "put a linefeed here". It was probably one line of text in the original file, and the newsreader put in line breaks.

But I tried editing it back to a real deal, and all LTSpice did was complain about the .SUBCKT command.

\n*\n*

--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?

Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com

ng

th

The output load is too large for the LM324 pull to 0v.

Multiply R1-4 values x10, C1 / 10, and it'll work as intended.

-- Cheers, James Arthur

Got your schematic to play in LTspice. Use an LM339 instead... it has an NPN pull-down. ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
I love to cook with wine.     Sometimes I even put it in the food.

Hi Tim, hi Jim,

No just a simple RC-oscillatorwith RC in the inverting path and RR-network in the non inverting feedback. See my LTSpice file in the other message.

OK, there is a c missing... Schmitt-trigger ,-)

OK, It seems to be true, that the feedback resistors of 10 k are too low. Well I see, that all examples in the datasheets use 100 k instead. I'll try this monday...

Marte

Hi Jim,

I know. I'd prefer the LM324 because I need two impedanceconverter in the project, too. With additional 1 kOhm between gate and source of the

2N7002 all works fine. I just wondered why this is as it is. Now I saw the graph Voutlow vs Iout. The plateau there is what I see. the 10 k I used for feedback seem to be too low. I just have to tune all one decade up.

Thanks for thinking

Marte

Poster didn't turn off line wrapping before copy-and-paste. The "\n" are newlines, you need to go in with a text editor and get rid of all the CRLFs starting with the line that starts "!*/////". Leave the \n in.

When will they learn?

--
"For a successful technology, reality must take precedence 
over public relations, for nature cannot be fooled."
                                       (Richard Feynman)

How about an LM393 and an LM358? About the same board space, easier to route, similar price?

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot net
http://electrooptical.net

Hi fred,

I'm so sorry, I never knew this. I always used it this way just copy and paste it.

Marte

Hi Phil,

??? at least double price, two more wires for powersupply needed, and additional two types of ICs in stock...? Are you sure?

Marte

You're not the only one to do this. Don't feel too bad ;-)

It's better, when you've got a big .SUBCKT file, not to include it on the schematic, but to post it as a separate file, with a .lib directive on the schematic, then post the model along with the schematic, but as a separate file. It's then up to the recipient to put the model somewhere his LTSpice can find it such as /lib/sub.

I've unraveled your listing to give this subcircuit file. For Jim's benefit, as well. E.&O.E, as always.

LM324.sub:

*////////////////////////////////////////////////////////// *LM324 Low Power Quad OPERATIONAL AMPLIFIER MACRO-MODEL *////////////////////////////////////////////////////////// *

• connections: non-inverting input

• | inverting input

• | | positive power supply

• | | | negative power supply

• | | | | output

• | | | | |

• | | | | | .SUBCKT LM324 1 2 99 50 28

* *Features: *Eliminates need for dual supplies *Large DC voltage gain = 100dB *High bandwidth = 1MHz *Low input offset voltage = 2mV *Wide supply range = +-1.5V to +-16V * *NOTE: Model is for single device only and simulated

• supply current is 1/4 of total device current.

• Output crossover distortion with dual supplies

• is not modeled.

* ****************INPUT STAGE**************

• IOS 2 1 5N

*^Input offset current R1 1 3 500K R2 3 2 500K I1 99 4 100U R3 5 50 517 R4 6 50 517 Q1 5 2 4 QX Q2 6 7 4 QX *Fp2=1.2 MHz C4 5 6 128.27P * ***********COMMON MODE EFFECT***********

• I2 99 50 75U

*^Quiescent supply current EOS 7 1 POLY(1) 16 49 2E-3 1 *Input offset voltage.^ R8 99 49 60K R9 49 50 60K * *********OUTPUT VOLTAGE LIMITING******** V2 99 8 1.63 D1 9 8 DX D2 10 9 DX V3 10 50 .635 * **************SECOND STAGE**************

• EH 99 98 99 49 1 G1 98 9 POLY(1) 5 6 0 9.8772E-4 0 .3459

*Fp1=7.86 Hz R5 98 9 101.2433MEG C3 98 9 200P * ***************POLE STAGE*************** * *Fp=2 MHz G3 98 15 9 49 1E-6 R12 98 15 1MEG C5 98 15 7.9577E-14 * *********COMMON-MODE ZERO STAGE********* * *Fpcm=10 KHz G4 98 16 3 49 5.6234E-8 L2 98 17 15.9M R13 17 16 1K * **************OUTPUT STAGE**************

• F6 50 99 POLY(1) V6 300U 1 E1 99 23 99 15 1 R16 24 23 17.5 D5 26 24 DX V6 26 22 .63V R17 23 25 17.5 D6 25 27 DX V7 22 27 .63V V5 22 21 0.27V D4 21 15 DX V4 20 22 0.27V D3 15 20 DX L3 22 28 500P RL3 22 28 100K

* ***************MODELS USED**************

• .MODEL DX D(IS=1E-15) .MODEL QX PNP(BF=1.111E3)

• .ENDS

--
"For a successful technology, reality must take precedence 
over public relations, for nature cannot be fooled."
                                       (Richard Feynman)

It's generally easier to route duals than quads. Stock is pretty cheap for a few-cent IC. Cost depends on everything under the sun.

On Findchips, I see LM324s and LM339s for about 8 cents in 100k quantities. LM358s are there for as low as 6 cents in 10k's, and LM393s as low as 5.6 cents. So it would be about four cents more, it looks like, plus whatever the delta in pick & place is.

Applications where that's even noticeable are way outside my experience, though obviously there are some.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot net
http://electrooptical.net

The upper left graph on page 6 explains it:

As long as there is any sink current in excess of 60-80uA the voltage will remain around 700mV. When it is less then it'll drop down to under

100mV. In your case R4 supplies that sink current. Don't fully trust simulator models.

The schematic on page 2 explains why: There is a Q13 Vbe drop left over at the last stage even if Q12 pulls hard down (and Q12 won't go much below 100mV Vce anyhow so that adds in).

So what could be done? All the resistors would need to be larger. You have roughly 2.5V at C1 and 12k gives 200uA. R3 adds about the same on top of that. Way too much. If you made C1 a 620pF cap, R4 a 200k resistor, and increase R1, R2 and R3 also by a factor of 20 you should be home for free :-)

You can be extra good and add a 10k pulldown.

BTW, the LM324 isn't a very happy camper when fed from 5V single-supply. It'll work, sort of, and probably pull up to a little under 4V. Not much to write home about.

--
Regards, Joerg

http://www.analogconsultants.com/

uA

I suggested multiplying the resistors x10, which, I calculate, gets your circuit from needing 290uA down to needing ~29uA sink current.

Typical LM324 sink current is around 50uA, but, looking at the datasheet, only 12uA @ 25C is guaranteed. So, better multiply those resistors by x25, minimum.

The LM393 Phil suggested (and the LM339 per Jim) drives low a lot harder--use that and you might be able to eliminate the 2n7002, load permitting.

-- Cheers, James Arthur