hybridfree/eevblog-posts huggingface dataset:
LM317 voltage regulator linearity - Page 1
Forum section: electronics / beginners

author: Mandelbrot
author_rank: Regular Contributor
timestamp: June 10, 2013, 07:14:34 am
content: Hello again!I'm still working on a linear power supply and I just noticed something that seems strange to me, but I'm probably being really stupid. According to the datasheethttp://www.ti.com/lit/ds/symlink/lm117.pdfon page 2, the formula for Vout is 1.25(1 + R1 / R2). If R1 is constant and R2 is a potentiometer, then the equation is very non linear and the regulator would only be useful for a very small range of the potentiometer and far from linear.I know I'm missing something simple, but I can't figure it out. Do I need a logarithmic potentiometer?Thanks for the help, I'd be even more lost without this forum.-Ryan

author: David_AVD
author_rank: Super Contributor
timestamp: June 10, 2013, 07:23:25 am
content: You have R1 and R2 flipped around. It actually says 1.25(1 + R2 / R1).

author: Mandelbrot
author_rank: Regular Contributor
timestamp: June 10, 2013, 07:27:15 am
content: Yep, I knew I did something stupid, I just wish it wasn't that! I typed it into my calculator wrong the first time and I used what I typed in as a reference from there on. Thanks.I know how a voltage divider works I swear! Next time I'll try not to blindly follow formulas I guess.

author: TerminalJack505
author_rank: Super Contributor
timestamp: June 10, 2013, 07:37:29 am
content: And, yes, with the correct formula, it is linear. It is linear also when you factor-in the error term.
LM324 as buffer conundrum (single supply) - Page 1
Forum section: electronics / beginners

author: VogonJelc
author_rank: Newbie
timestamp: January 06, 2019, 01:14:01 pm
content: Hello friends. This one is interesting. I decided to build dummy load to test dc power adapters. I decided to rip off Dave's design using lm324 and mosfets. I bought couple of lm324 (quad) since 741 I had were some 26+ years old and I figured they are either dead or soon to be. I use no2 op amp (pin 5 + pin 6 - and 7 output) as buffer and no 3 (pin 10+ pin 9- 8 output) to drive MOSFET . I tested setup with POT before hooking everything to arduino nano. I want to use 2 not used op amps as buffers for input Voltage measurement and to measure voltage across resistors connected to source of MOSFETS.And the problem is LM324 is having huge problems when voltage on non inverting input is close or 0v when working with single supply voltage (in test case it was 6v but I will use 12v when I finish ironing "issues"). Everything works fine (except v-1.5v max output voltage but its ok Ill use 12V for supply). GOing into mV range gets strange first at about 300 mV output stops following input by few hundred mV. But as soon as I drop to 0V input I get 4.75 output voltage. Which kind of isn't good for buffer nor as output of voltage divider to measure input voltage. Anyone had similar problems and possibly suggestion on how to solve the problem or maybe replacement op amp that has same pinout - the problem of lm324.I see that dave is using sam op amp on his dummy load but I also noticed on video he didn't start from 0 V but from 80mV.There is no schematics attached because its literary the same as Daves quad op amp mosfet couple of resistors (6 x 3.3 ohm 5w resistors).

author: orbanp
author_rank: Regular Contributor
timestamp: January 06, 2019, 02:31:49 pm
content: The LM324 is an early op-amp, and it could do funny things when you are getting close to the rail voltages.Do study the datasheet!To verify if that is the reason, do add some negative supply to the op-amp(s), and redesign your circuit with a more modern rail-to-rail op-amp, if proven so.PS: Do include the schematics!I (and probably the others) do not keep that at my fingertips!Regards, Peter

author: VogonJelc
author_rank: Newbie
timestamp: January 06, 2019, 04:55:25 pm
content: Found the reason for it behaving weird. It seems TI is not what it was or my dealer sold me broken op amp. Op amp no 2 is "partially" dead (?) and no 3 is totally dead outputting 600mV no matter the input voltage is. I have to test it again but after replacing it with another chip everything works ok. But out of the 4 of the lm324 I have that are working there are 2 that behave same outputting 5v at no 3 op amp no matter what and 2 where op amp no 3 outputs from 2.2v to 5v.
LM324 inverting amplifier, works but shouldn't? - Page 1
Forum section: electronics / beginners

author: MikeK
author_rank: Super Contributor
timestamp: March 25, 2013, 07:54:44 pm
content: Okay, so a while ago I built a display for my Elenco xp-720 power supply. It uses an LM324, a PIC, and an LCD. It works well as it quite accurate.But after going through the LM324 datasheet again recently, I'm wondering why part of it works at all. Specifically, I used one of the op-amps in the LM324 to invert and scale the power supply's negative output. This ranges from 0 down to -17V.Since I power the LM324 with +5V and 0V, and the datasheet says that the minimum common mode input voltage is 0V, aren't I exceeding the spec by a large amount by allowing the input to be negative?Or am I misreading the datasheet?

author: c4757p
author_rank: Super Contributor
timestamp: March 25, 2013, 08:18:55 pm
content: With an inverting amplifier, theinput to the inverting amplifierandinput to the op ampare not the same thing.See the attached schematic. -15V is applied to the input, +15V at the output, and the op amp only sees 0V and +15V. Remember that the op amp tries to make both inputs equal - by applying the opposite voltage to the other end of a voltage divider, the center will be zero.Of course, using different resistors can scale the -15V to something under 5V. If you use R1=75k and R2=20k, than -15V becomes 4V.One bad side to this approach is that the op amp will be unhappy if accidentally powered down. The LM324 is unique in being able to handle inputs up to +32V even when not powered, but that does not apply for negative inputs, only positive.

author: MikeK
author_rank: Super Contributor
timestamp: March 25, 2013, 08:23:59 pm
content: Ohhhhh.Great. Thanks for explaining that. I did forget about the inputs being made equal. I thought I was on to some cold fusion hyperspace thing there for a second.This is why I love op-amps...They're bloody awesome!

author: c4757p
author_rank: Super Contributor
timestamp: March 25, 2013, 08:29:42 pm
content: Quote from: MikeK on March 25, 2013, 08:23:59 pmYes, they are. Probably the single most useful active component in analog electronics. There's not much you can't do with some op amps, resistors, and caps.
LM324 IR detector circuit - Page 1
Forum section: electronics / beginners

author: cosminnci
author_rank: Regular Contributor
timestamp: May 03, 2016, 05:53:11 am
content: Hello,In my project I need to create 2 ir beams that are fed into a uc digital input and analyzed. So far I found a gate automation module and recreated the schematic in the idea to duplicate for the other channel as well, but somehow there is timing difference between the 2.My knowledge in op amps is not very good, from the schematic I deduced it has a band-pass filter and amplifier level, a comparator level and an logic inverter level, but not sure if they are applied properly in my design.The input of the circuit is from a fototransistor or photodiode I presume the first, the type is unknown.I already made a few revisions, but it`s like the 2 identical circuits do not behave the same way, like the treshold values varies and the uc receives incorect order of feeds and messes the logic.is my approach incorrect by using 2 identical circuits or should be used 1 with identical reference?also I noticed that the dividers are very sensitive to voltage changes so I should also have a ldo regulator also included.regards,Cosmin

author: oldway
author_rank: Super Contributor
timestamp: May 03, 2016, 01:27:14 pm
content: Easier to read

author: Audioguru
author_rank: Super Contributor
timestamp: May 04, 2016, 01:42:04 am
content: The lousy old LM324 works poorly above only 2kHz. Modern audio opamps like the OPA4134 work perfectly to above 200kHz.

author: cosminnci
author_rank: Regular Contributor
timestamp: May 04, 2016, 05:52:18 am
content: The ir modulation is regular pwm somewhere from 500Hz to 1,2Khz this is the sensitivity range I found.it should be safe from high freq remote control ir.I tried to understand the stagesic2c and ic2d should be the bandpass filter with amplificationic2b should be the comparator and ic2a only an signal inverter.the 2 rectifier diodes and the caps should filter the pwm input and allow the comparator to have a steady high or low.am I correct about the above?regards,Cosmin
LM324 Soldering Station - Page 1
Forum section: electronics / beginners

author: mike_mike
author_rank: Super Contributor
timestamp: April 01, 2020, 08:19:24 pm
content: Hello. I built the attached soldering station and I am encountering the following issue: on the attached screenshots I got the pins 7 (blue) and 8 (yellow). I don't know what is that impulse type of signal on the blue trace. The yellow trace is showing the signal to the driver of the triac (MOC3021) and the blue trace is showing the pin 7 output of the LM324 (differential amplifier).The inputs of the differential amplifier are in the 0024 (pin 5) and 0026.jpg (pin 6) screenshots.I am also attaching the signal coming from the triangle wave generator (0028.jpg). The triangle wave output does not look as a triangle, even if I rotate the 1M trimmer.Could you please clarify this situation ? Is there a problem in the circuit ?

author: magic
author_rank: Super Contributor
timestamp: April 02, 2020, 06:14:35 am
content: Given the almost 50Hz repetition rate of those pulses it's probably something mains-related, although I'm not sure why the pulses from the diffamp output are so sharp.Perhaps the diffamp output is a result of heater power turning on and coupling a pulse of noise into the sensor wires. As for the turning on of the heater, it would be due to peaks of mains noise received by the sensor wires.Zoom in and see whether the blue pulse comes before or after the first yellow pulse.

author: mike_mike
author_rank: Super Contributor
timestamp: April 02, 2020, 07:59:25 am
content: It looks like the yellow (pin 8 ) pulse is coming first or at the same time with the blue pulse (pin 7).

author: mikerj
author_rank: Super Contributor
timestamp: April 02, 2020, 11:47:52 am
content: How clean is the output from your triangle generator? You might want to consider a little bit of hysteresis on U1C to ensure clean switching.
LM336: How does it work in this circuit? - Page 1
Forum section: electronics / beginners

author: alpha_rolf
author_rank: Newbie
timestamp: June 22, 2022, 01:49:59 pm
content: Hi,I try to understand how this LM336 can generate 5V out of the 12V regulator.So I looked into the datasheet of the LM336 and it says it is like a 2.5V Zener diode.But how do you get the 5V over a 2.5V Zener diode?

author: MikeK
author_rank: Super Contributor
timestamp: June 22, 2022, 02:06:32 pm
content: It's an LM336-5.0

author: alpha_rolf
author_rank: Newbie
timestamp: June 22, 2022, 02:29:57 pm
content: Yes, you are right. Sorry
Lm339 gain adjustment  - Page 1
Forum section: electronics / beginners

author: vis5254
author_rank: Contributor
timestamp: May 08, 2019, 04:15:55 pm
content: i use a comparator lm339 . one of the input given at inverting terminal is below 5v , mostly 3.5v (obtained after full bridge rectifiying12v ac and reducing down 14v dc to 3.5 scale using voltage dividers - 8k2 , 2k2 , 10k2 .i use a variable resistor to drop 5v into some 3.3v across non inverting terminal . when i kept a resistor 2k2 , diode and 10k as a feedback to inverting terminal , i found output of comparator went high to 4.8V across output .how exactly did that output voltage got regulated to that range ?

author: golden_labels
author_rank: Super Contributor
timestamp: May 08, 2019, 05:43:02 pm
content: LM339 is a comparator, not a general purpose op-amp. It has no gain¹. Under conditions for which they are specified, comparators have only two stable outputs: high and low. LM339 has an open-collector output. Its “low” is around its negative rail (typically 500mV, depending on the current sinked). “High” simply means that the output is not sinking current at all — it may be treated as an open switch.In that particular circuit:“High” is determned by the network formed of R4, D6, R5, R1 and R2.“Low” is around 0V — the exact value depends on how much current it has to sink.One could drive the comparator so it never stabilizes, but this is not what they’re designed for. In particular open-collector output can’t source current. So while it may fall into oscillation, I doubt it can reliably produce nice, predictable results. But, if you really want to try: TI’s LM339 has amplification of at least 50000, typically 200000.For the stable “high” and “low” states, see the attachment.____¹ Not in the meaning used for op-amps. Technically the output stage must have some gain, but this is the same meaning of the word as in a logic inverter. As it happens, LM339 has a logic inverter as its output stage.
LM339 - Page 1
Forum section: electronics / beginners

author: MAD MACRO
author_rank: Regular Contributor
timestamp: June 20, 2016, 01:32:24 am
content: I was reading this very interesting blog of how to work with comparator lm339:http://www.ermicro.com/blog/?p=1578When using the feedback from the output, he has two equations to get the VLT and the VUT.VUT = (R2 / (R2 + R1||R3)) x VccVLT = (R2||R3 / (R2||R3 + R1)) x Vccnow, i'm using this exact scheme to blink LED, and it's doing just that, it's working just fine.My question is this:from where did he get that number "0.694" ?I've tried to use those two equations of VLT and VUT and none of the results came close to 0.694.

author: MAD MACRO
author_rank: Regular Contributor
timestamp: June 20, 2016, 07:26:46 am
content: got the answer from :http://bitsavers.informatik.uni-stuttgart.de/pdf/national/_appNotes/AN-0074.pdfln(0.5) = 0.6931
LM3409 - Page 1
Forum section: electronics / beginners

author: LameHd
author_rank: Newbie
timestamp: April 16, 2019, 09:24:28 pm
content: Hi,I have a question regarding weebench. How I can use this tools with LM3409?Can I use this driver to drive 8 leds in parallel with Vf=3,4 and I_led=466mA I_tot = 3,73AVin 12V to 24Vthanks
LM35 "PIC" of the bunch - Page 1
Forum section: electronics / beginners

author: PerranOak
author_rank: Frequent Contributor
timestamp: May 05, 2018, 01:20:48 pm
content: I am having a go at designing a temperature logger using and LM35 and a PIC ... 16F probably.I have to get the analogue part right first or the digital part will never work; I realise that.So, the LM35 goes up to 0.35V at 35degC so I amplified it with an op amp so that I would get a better FSD and so more significant figures. I used a very simple non-inverting circuit.Problem is that the gain on the op amp seems to vary wildly with the input from the LM35.I set it at 25degC and then cooled it to 20degC and the op amp output suggested a temp that was a whole degree different.This can only mean that the gain changed!Is this normal?

author: David Hess
author_rank: Super Contributor
timestamp: May 06, 2018, 08:32:56 pm
content: Is the supply voltage to the LM35 +4 volts or higher? I am not sure what the LM35 does with a supply voltage of +3.0 or +3.5 volts.You might need an RC filter at the non-inverting input to the operational amplifier. A feedback capacitor between the output and inverting input would not hurt either.

author: PerranOak
author_rank: Frequent Contributor
timestamp: May 08, 2018, 07:44:10 pm
content: Cheers David.Yes, the supply is at 4.9V and the LM35 measures accurately. It's only the output from the op amp that varies.I'll try your suggestions, thank you.PSAh. I've just noted what the problem is. I had tried to offset the LM35 because the output goes negative below 0degC and this is no good for the uC. However, I did this by placing a resistor between ground (i.e. battery negative) and the ground pin of the LM35. It did offset the output but interferes with the op amp gain!PPSDurr. I've just realised why. I am amplifying the resistor offset too! Sorry for sharing the thought process!
LM35 series resistor - Page 1
Forum section: electronics / beginners

author: PerranOak
author_rank: Frequent Contributor
timestamp: July 29, 2018, 02:39:25 pm
content: I have seen circuits with a 1k resistor between the output of an LM35 and the pin (for ADC) of a microcontroller.I get that with the input impedance of the uC the current is low and so the resistor will not materially affect the reading but for what purpose is the resistor? I mean, what good does it do?Cheers.

author: David Hess
author_rank: Super Contributor
timestamp: July 29, 2018, 03:04:27 pm
content: Sometimes a series resistor is used in combination with a capacitor to filter out noise and provide a low AC impedance to the ADC. Just a series resistor might be used to limit fault current but that seems unlikely unless the LM35 and ADC are separately powered. Or if the series resistor is located at the LM35, it might be to prevent instability when driving a long line.

author: rstofer
author_rank: Super Contributor
timestamp: July 29, 2018, 06:15:56 pm
content: A real schematic might help. Links to datasheets...FWIW, Figure 12 of the LM35 datasheet shows a 2k series resistor for use when driving a capacitive load > 50 pf. Most ADCs are capacitive due to the sample and hold circuit but I don't know that they have that much capacitance.The LPC1768 ADC has an input capacitance of 15 pf.

author: PerranOak
author_rank: Frequent Contributor
timestamp: August 02, 2018, 01:23:46 pm
content: Thanks both.Sorry, I hadn't a particular circuit in mind it just that my circuit doesn't have a series resistor. I put one in and nothing seemed to change so I wondered what was up.I though that it would confuse things as the voltage drop across the resistor surely reduces the voltage "seen" by the ADC but it didn't seem to!

author: rstofer
author_rank: Super Contributor
timestamp: August 02, 2018, 05:23:10 pm
content: Quote from: PerranOak on August 02, 2018, 01:23:46 pmSure, it reduces the voltage, WHEN the current is flowing. The idea behind a sample-and-hold ADC is to charge a capacitor through the resistor during the sample period and then analyze it during the hold period. The sample circuit is designed to limit current flow such that a given driving impedance (check the datasheet) won't affect the reading. Some ADCs want < 10k Ohms driving impedance, others want somewhat less. It is important to check the datasheet.

author: atmfjstc
author_rank: Regular Contributor
timestamp: August 02, 2018, 07:10:31 pm
content: It could be there for safety. Some microcontrollers such as ATMEGAs allow you to switch the direction of pins such that an ADC input pin becomes a digital output. While all pins start off as inputs by default, it is possible to accidentally switch them to outputs if a crash or a bug occurs. Nothing good will happen if the LM35 and the ATMEGA try to drive the same wire to different voltage levels without any resistor there to limit the current.

author: PerranOak
author_rank: Frequent Contributor
timestamp: August 03, 2018, 10:04:18 am
content: Cheers, thank you both.
LM358 alternative suggestion (better slew rate)? - Page 1
Forum section: electronics / beginners

author: s3c
author_rank: Contributor
timestamp: July 13, 2011, 12:32:53 pm
content: Hi guys, I'm looking for an alternative to the LM358. I need a single supply op amp (10V min) with input and outputs that can reach fairly close to ground. The LM358 works but the slew rate is probably going to be a problem as it's only 0.6V/uS, it takes about 10uS for full swing which I'd like to get down to below 1uS. I'm a bit overwhelmed by the thousands of components available and was hoping someone here had some experience with a part that would do the trick.

author: Zero999
author_rank: Super Contributor
timestamp: July 13, 2011, 04:34:18 pm
content: There may be other things to consider, please post a schematic.
LM358 amplifier circuit - Page 1
Forum section: electronics / beginners

author: cosminnci
author_rank: Regular Contributor
timestamp: September 30, 2014, 10:31:17 am
content: Hello,I want to make an ir barrier used indoors with a tv set close by.I tought of a tsop but there might be conflicts with the tv remote, so I tought of making it with sfh300 phototransistor.the distance between ir led and receiver should be 1m.I found a schematic the one attached, but it does not give the range.I generate a 1khz pulse with an arduino and at about 10cm it starts to narrow the pulse then rounds the falling edge and the signal dissapears.what could I do to improve the sensitivity?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 30, 2014, 07:53:50 pm
content: IC1 inputs are reversed.Tim
LM358 PWM circuit - Page 1
Forum section: electronics / beginners

author: oliver602
author_rank: Regular Contributor
timestamp: May 15, 2023, 12:02:56 am
content: Can someone explain this circuit for me?V1_AO is the input between 0V and 5V and V1 is a PWM output to a solenoid valve. The output frequency varies with duty cycle and seams to have supply voltage compensation.

author: m k
author_rank: Super Contributor
timestamp: May 19, 2023, 12:36:38 pm
content: U1A is an adapter.U1B is an integrator.If components are difficult to understand try redrawing the circuit.Turn Q2 around and it's just a PNP regulator, so just a driver.One side of C4 is R11-D1-R8 and other Q2-R3-R1.But since D3 is low D1 must be so also.So actually R8 is for U1B5 what R6 is for U1B6.

author: jwet
author_rank: Frequent Contributor
timestamp: May 22, 2023, 01:02:00 pm
content: I'll try- it is drawn badly-Starting at Q1, it is just a buffer for the output transistor, it looks more exotic but its just a buffer that takes the the opamp output and drives the base of the output Q hard.The top op-amp circuit is just a follower that takes the 0-5 input, scales its it by 1/2, low pass filters it to make it analog and passes it aloong. I suspect this input is actually a uP a PWM signal ironically that he converting to an analog voltage- why not use the PWM? After scaling and filtering a 0-2.5v DC level goes to stage 2. Don't know why the designer didn't just use this PWM output to drive the load through some transistors?This second circuit is a sort of a single supply integrator/oscillator. A standard integrator is inverting but that often requires dual supplies- this is single supply. The 10k and two diodes is a 0V reference! It makes a .7v drop with the first diode and then subtracts .7 with the second diode pinning the bottom of the range of the OPAMP V+ to 0V minimum- weird. The circuit below that forces the circuit to oscillate with feedback from the output transistor. The 1N4007 diodes are inductive load protection- done in an odd way.The designer of this circuit only had two op-amps and a single supply apparently. This isn't a very good circuit. There are elegant single supply integrators- the deBoo circuit is one, This is a bit of kluge. I think if you look around the web, you'll find better. A 555 timer can make a decent PWM, look for those.I assume you've built it and it works and if it suits your needs, use it. Its just sort of a unconventional mess of a circuit. If you want more insight, you might try simulating in Falstad or Spice.

author: m k
author_rank: Super Contributor
timestamp: May 22, 2023, 06:42:19 pm
content: D1/D3 can be a protection against illegal common mode voltage range.But D2 and C2 are missing so maybe original situation was different.
lm358 rail current - Page 1
Forum section: electronics / beginners

author: LaserTazerPhaser
author_rank: Regular Contributor
timestamp: August 28, 2019, 04:06:39 pm
content: According to lm358 datasheet supply current is 5mA for DC and 50mA bipolar rails.For a DC output of 4mA will the lm358 draw an additional 4mA of input current at the rails raising it to 9mA?Its unlikely for an 28mA output the rails will remain at the stated 5mA constant rather rail current will surpass the output current but Im not sure about how the lm358 draws current at its rails.

author: magic
author_rank: Super Contributor
timestamp: August 28, 2019, 04:33:02 pm
content: Supply current of LM358 is rated less than 1mA typically, 2mA max.This is idle state consumption. Any output current of course needs to be added to it, it doesn't just come from nowhere.Well, actually, the first 50µA ofsinkingcurrent is for free due to the way it's output stage works. But that's not very much of current.
LM358 scaling and offset a signal - Page 1
Forum section: electronics / beginners

author: joegtp
author_rank: Contributor
timestamp: May 08, 2013, 01:46:03 pm
content: I'm trying to scale and offset a 10Vpp (-5V to 5V) signal using an LM358. I would like the output of the signal to be compatible with an Arduino's ADC (5Vpp at 0-5V).The attached image of the circuit is what I tested. I used a -12V and 12V power supply for the op-amp and the offset adjustment.I was able to get a 1kHz signal to scale and offset correctly and the output looked great (see the attachment below).But when I upped the signal to 10kHz I started to see some noise (Is noise the correct term to use here?). At 40kHz the signal was unreadable.Any thoughts on what might be causing this? The LM358 says it can handle a 1.1MHz signal. I also tried substituting in a LM6181 and I didn't see this issue all the way up to >10MHz.

author: grumpydoc
author_rank: Super Contributor
timestamp: May 08, 2013, 03:06:14 pm
content: QuoteNot with a 5V p-p swing it can't. 1.1Mhz is only for small signals, the slew rate is only 0.6V/µs typical (0.3 V/µs worst case) which limits you for larger swings. According to the data sheet the bandwidth is 10kHz for 10Vp-p and about 25kHz for 5Vp-p.Not sure that's your problem thoughI'm trying to get my head around what your circuit actually does (all but the simplest op-amp circuits make me scratch my head) but it looks wrong.Edit: Oh, Ok it's just wired as a diff amp, don't know why I didn't see it at first, except that I would use the summing amp configuration as a level shifter.

author: kizzap
author_rank: Unknown
timestamp: May 09, 2013, 12:46:59 am
content: Maybe try something like a popular audio op amp like a TL072 or something?

author: w2aew
author_rank: Super Contributor
timestamp: May 09, 2013, 12:54:57 am
content: That's actually a fairly common phenomenon with low power op amp output stages like the LM358 has. It is a distortion that happens when the output stage is driven close to its slew rate limit and the output devices in the totem-pole output are driven with a large/fast signal.

author: kg4arn
author_rank: Unknown
timestamp: May 09, 2013, 02:12:08 am
content: Just a thought,Try changing the 1Meg load resistor to 4.7K. This will properly bias the output stage of the 358.
LM358N opamp variations? - Page 1
Forum section: electronics / beginners

author: mikeinfodoc
author_rank: Regular Contributor
timestamp: November 05, 2017, 11:53:40 pm
content: I was going to multi sim a LM358N, but I am uncertain what the U1A, U2A, etc stuff/syntax is all about?I did not see U1A listed in the datasheethttp://www.ti.com/lit/ds/symlink/lm358-n.pdfI assume it has something to do with 1 or 2 amp capability, but I am not sure what the U stands for. I assume that means "Unity" gain, but this is just a guess.Can someone help me understand the syntax/variations and what they mean?

author: tooki
author_rank: Super Contributor
timestamp: November 06, 2017, 12:19:50 am
content: I've never used Multisim, but I assume it follows common convention:"U" is a component prefix for ICs in a schematic. (Like how R is the prefix for resistors, L for inductors, Q for transistors, etc. e.g. R3, L23, Q2.) So U1 means "IC 1".The A/B suffix means the specific functional block within a chip that has more than one. The LM358 is a dual op-amp. So U1A means the first op-amp, and U1B means the second op-amp,within the same chip.None of this is specific to the LM358, which is why it's not on the datasheet.

author: Audioguru
author_rank: Super Contributor
timestamp: November 06, 2017, 02:14:02 am
content: The voltage gain of an opamp is how you connect its negative feedback. Its gain could be less than unity, unity or more than unity. An opamp can even invert a signal.A simulation of an opamp will show nothing until you learn how to connect an opamp.The LM358 and its sister the LM324 quad opamp are two of the worst old opamps. They are noisy, produce crossover distortion and perform poorly above 2kHz at high output levels.

author: tooki
author_rank: Super Contributor
timestamp: November 06, 2017, 11:21:16 am
content: Oh, one more thing about schematics: most ICs are drawn as blocks with just numbered pins. However, some types of chips are exceptions, and tend to be drawn as their functional blocks instead. Op-amps are arguably the most common example of this, as you saw. So adding a dual op-amp chip like your LM358, instead of adding one rectangle to your schematic, adds two amplifier functional blocks (triangles) instead.Logic gates are the other ICs that are drawn using functional blocks instead of just the IC as a whole.In contrast, discrete components are normally drawn using a symbol specific to the component type. The package of the component is not normally reflected in the schematic.https://learn.sparkfun.com/tutorials/how-to-read-a-schematichas a nice overview of these for beginners.Hope this helps!
LM380-8...ok, now what? - Page 1
Forum section: electronics / beginners

author: roach969
author_rank: Newbie
timestamp: October 21, 2013, 11:23:43 pm
content: So, I acquired a LM380-8 amplifier IC and have no idea what to do with it(I guess I lost A LOT of what I had learned). I've recently built a couple of LM386 amplifiers but those are only 1/2 watt. So I found this one in the hopes of building something a little louder but can't seem to find any good schematics. On that note, if this can be used for anything other than audio amplification it would be nice to know. If anyone could point me in the right direction with this little IC I'd greatly appreciate it. Thanks and I look forward to any and all replies.

author: david77
author_rank: Frequent Contributor
timestamp: October 21, 2013, 11:32:22 pm
content: Your first stop should be the datasheet.http://pdf.datasheetcatalog.com/datasheet2/a/0aor7xsk92te983lieo67ewd8eky.pdf

author: rsjsouza
author_rank: Super Contributor
timestamp: October 22, 2013, 02:42:01 am
content: A more modern datasheet (possibly) ishereThe LM380N-8 is the 8-pin PDIP version of the traditional LM380, and it not able to dissipate as much (you need to be more careful not to melt it).
LM385-ADJ  Minimum Operating Voltage / Drop - Page 1
Forum section: electronics / beginners

author: hgg
author_rank: Frequent Contributor
timestamp: December 07, 2016, 09:39:49 am
content: Hi guys,I would like to use a voltage reference of 3.2V with a VCC supply of +5V and I am thinkingof the LM385-ADJ. It is adjustable from 1.24V up to 5.30VMy question is, do you know if it will be able to produce the steady 3.2V from a 4.5 to 5V supply?http://www.ti.com/lit/ds/snvs741f/snvs741f.pdfThanks.

author: Gyro
author_rank: Super Contributor
timestamp: December 07, 2016, 09:52:26 am
content: The LM385 is an adjustable voltage reference. Think of it as an adjustable zener diode with very good characteristics, so doesn't have a minimum voltage drop like a series reference. To use it you need a series resistor from the supply (see the application diagrams in the datasheet you linked). It can be used as a shunt regulator for low currents, but is really intetended to provide a reference voltage.You haven't included enough information about what you're trying to do to be able to advise whether it would be suitable or not.Chris

author: hgg
author_rank: Frequent Contributor
timestamp: December 07, 2016, 09:58:09 am
content: Hello Chris,I want to use it in a NiMH solar charger to control the upper charging cutoff voltage.Thanks.

author: Gyro
author_rank: Super Contributor
timestamp: December 07, 2016, 10:04:45 am
content: It would be fine to use it as the reference element of a charging regulator - either series pass or shunt, but I doubt if you would be able to use it as a charging shunt regulator on its own (unless it's a really small solar cell) because its maximum operating current is only 20mA.

author: hgg
author_rank: Frequent Contributor
timestamp: December 07, 2016, 10:08:50 am
content: No, it will only provide the reference voltage, no loading.It will be part of the comparator that will terminate the charging.

author: Gyro
author_rank: Super Contributor
timestamp: December 07, 2016, 10:22:30 am
content: You should be fine then - just size the series resistor so that the LM385 current is somewhere in the 100uA - 1mA range across the possible battery voltage range to minimise wasted current. The LM385 has dynamic resistance of about 1 ohm so it is quite insensitive to changes in operating current.

author: hgg
author_rank: Frequent Contributor
timestamp: December 07, 2016, 10:23:36 am
content: Great!Thank you very much.
LM385 Differential Configuration - Page 1
Forum section: electronics / beginners

author: kaykan
author_rank: Newbie
timestamp: March 29, 2014, 02:53:59 pm
content: I have a problem with the circuit attached, in the schematics you found the voltage values expected and real.I tried with another op-amp (LM6462) and this work as expected, the problem is that this op-amp work up to 15V and I would like to use VCC=VDD=30V at the end (LM385 is up to 32V), in any case I don't understand how to select the good op-amp for the application.From the real.png, seems that the op-amp don't work for low difference V+ - V-, my first design have VDD=VCC=19V so I think that the issue is that on the V+ I get a value too near with op-amp VDD of the unity gain, but now there are over 5V, but still not working..Have any suggestion? What's are the most important op-amp characteristics?

author: Andreas
author_rank: Super Contributor
timestamp: March 29, 2014, 06:34:11 pm
content: Quote from: kaykan on March 29, 2014, 02:53:59 pmIt´s simply the wrong circuit and the wrong part(s).The tolerances of the resistors are eating up precision.And the OP-Amp cannot deliver current when pulling output near negative rail.(You would have to use a negative supply).Have a look at the inner circuit of the LTC6102 datasheet.http://cds.linear.com/docs/en/datasheet/6102fd.pdfIf you don´t want to use the LTC6102 you can replace the OP-Amp by a TL061 .. TL081 and the P-Channel FET by a small signal FET like the BSS84P. (The TL061 has a common mode range of typical to the positive rail so that the supply does not need to be higher than the 13.65V).The ratio of the 2 resistors ROUT/RIN gives the amplification.With best regardsAndreas

author: kaykan
author_rank: Newbie
timestamp: March 30, 2014, 11:38:42 am
content: Hi Andreas,the resistors are 18K 0.1%, the tollerance is too low?Probably the issue is for the proximity to the negative rail, I will try with a negative rail at -3V.Thank you Andreas!

author: Andreas
author_rank: Super Contributor
timestamp: March 30, 2014, 01:53:49 pm
content: Quote from: kaykan on March 30, 2014, 11:38:42 am4 resistors = 4 times 0.1% in worst case.And this is only at room temperature directly after production.There are up to 1 or 2 % soldering or ageing drift if using cheap resistors.at 14 V * 0.4% = up to 56 mV error only due to common mode voltage supression error.With 100mV measurement range there is not much precision left of your 0.1%There is a reason why the LTC6102 does not use the simple differential amplifier circuit.with best regardsAndreas
lm386 amp on a breadboard - oscillation - Page 1
Forum section: electronics / beginners

author: icon
author_rank: Regular Contributor
timestamp: February 02, 2014, 10:20:56 pm
content: HiIs it even possible to make an amp on a breadboard that doesn't oscillate? I had an LM386 kicking around, so I thought it would be amusing to wire it up, listen to some music while I play. I made the 'minimum parts count' layout from the data sheet, which has a 250uF cap in series with the speaker, and a 50nF cap/10R resistor in series to ground (from the output).It buzzed horribly to start with, but I twisted the speaker wires together and put a 100uF cap in parallel with a 10nF cap directly across the power supply pins. Now no buzz, but it oscillates at 690kHz. Sounds kind of OK, and doesn't draw a huge amount of current (20-30mA), but it would be nice if it didn't oscillate!Any ideas how I can tame it?Many thanksJohn

author: Rerouter
author_rank: Super Contributor
timestamp: February 03, 2014, 03:23:16 am
content: 10nF cap between inverting feedback pin and output pin,

author: icon
author_rank: Regular Contributor
timestamp: February 03, 2014, 08:21:25 am
content: Thanks, I'll give that a go.John

author: blackdog
author_rank: Frequent Contributor
timestamp: February 03, 2014, 11:50:57 am
content: Hi Icon, :-)Do not forget to use a capacitor from pin7 to ground, say 10uF (Bypass).And the zobel network on the output, 10-Ohm and 47nF on pin-5 (output)It is all in the datasheet, firtst page.Minimum components circuits is asking for troublesKind regarts,Blackdog

author: icon
author_rank: Regular Contributor
timestamp: February 03, 2014, 08:56:54 pm
content: The bypass capacitor on pin 7 seems to have mostly done it - still a very slight wobble at ~700KHz, but there's too many wires trailing around...ThanksJohn
lm386 m-82 output value? - Page 1
Forum section: electronics / beginners

author: d4n13l
author_rank: Regular Contributor
timestamp: May 06, 2017, 10:49:44 pm
content: Hi guys,I want to try the lm386 N-4 which has 1W output however were I live I can only find the lm386 m-82 which does appear on the datasheet.. I can find this version online but not its datasheet, does anyone knows its output or its equivalent (N-1, N-3, N-4)?

author: Zero999
author_rank: Super Contributor
timestamp: May 06, 2017, 11:00:02 pm
content: I don't know. An educated guess would be it's the same as the LM386N-1What power supply voltage are you intending to use? The LM386N-4 can only drive a higher powered load because it has a higher maximum power supply voltage rating. Given the same voltage the LM386N-4 can't output any more power than the LM386N-1.If you want more power, then there are better, more modern amplifier ICs.

author: d4n13l
author_rank: Regular Contributor
timestamp: May 06, 2017, 11:12:10 pm
content: I'm not worry much about the input voltage right now, I'm just starting to experiment with audio amplifiers and want to see how loud could the volume get with this IC... could you recommend some of these better ones?

author: Zero999
author_rank: Super Contributor
timestamp: May 06, 2017, 11:26:00 pm
content: Quote from: d4n13l on May 06, 2017, 11:12:10 pmThe maximum output power is proportional to the square of the input voltage. The theoretical maximum RMS output power, when outputting a sinewave, is given by the following formula:P = V2/(2R)In real life, it's lower, thanks to the voltage drop in the output transistors.There are lots of audio amplifier ICs. So many that I can't recommend one to you, without knowing what your requirements.

author: Audioguru
author_rank: Super Contributor
timestamp: May 06, 2017, 11:40:59 pm
content: With a 9V supply, an LM386 can produce a maximum of 0.45W into an 8 ohm speaker with low distortion. 0.45W is not loud.Some audio amp ICs can drive 4 ohm speakers for double the output power. Driving a 4 ohm speaker an LM386 simply produces more heat, not more output power.Some audio amp ICs are bridged with two amplifiers that effectively almost double the output voltage swing resulting in about 3.5 times the power of an ordinary LM386 amp.

author: danadak
author_rank: Super Contributor
timestamp: May 07, 2017, 12:37:54 am
content: http://www.ti.com/lit/ds/symlink/lm386.pdfhttp://amplifiercircuit.net/low-voltage-bridge-audio-amplifier.html

author: Audioguru
author_rank: Super Contributor
timestamp: May 07, 2017, 01:36:23 am
content: No. The website ampifiercircuit.net did not read the datasheet for the LM386 and do the calculations so they claimed 3.5W!The datasheet for the LM386 amplifier does not show it bridged with a 12V supply and a 4 ohm speaker because it calculates to an output power of only 0.76W with high distortion (0.6W with low distortion) and 1.25W of heat (the maximum allowed heating) in each LM386.
LM393 comparator or op-amp question - Page 1
Forum section: electronics / beginners

author: lordvader88
author_rank: Frequent Contributor
timestamp: August 05, 2018, 10:27:54 pm
content: I mapped out a fan controller circuit that uses an LM393 comparator, and I'm trying to calculate what it's doing.If I used basic ideal rules, a certain transistor would not be on at all due to the infinite input impedance of the LM393. (it's emitter resistor terminates at the inv. input, until the LM393 output goes low creating a 2nd path)When I simulate it with circuit wizard, they say about 4uA @4V, 6uA @6V into the inputs.For op-amps in general, where in the datasheet can find or figure out the current into them, with any confidence ? I see nanoAmpsWhats a rule of thumb ?

author: Audioguru
author_rank: Super Contributor
timestamp: August 05, 2018, 11:49:28 pm
content: The LM393 has PNP input transistors. Their positive bias current (you must provide an input path to 0V for it) is shown as400nA max.There is no rule of thumb, instead there is a datasheet with the specs of every part number.

author: JS
author_rank: Frequent Contributor
timestamp: August 06, 2018, 12:25:51 am
content: Bias current or input vias current or input current (look also at current offset, drift and noise while dealing with any kind of precission)JS

author: Zero999
author_rank: Super Contributor
timestamp: August 06, 2018, 08:10:00 am
content: Dave did a video about this awhile ago.https://www.eevblog.com/2013/06/07/eevblog-479-opamp-input-bias-current/The LM393 has a PNP input stage so will source a tiny current out of its inputs, to whatever impedance is between them and 0V. The voltage generated by this current, will simply be the current, multiplied by the resistance. The datasheet lists a worst case of 400nA, for the LM393.http://www.ti.com/lit/ds/symlink/lm393-n.pdfThe bias current will have a negative temperature coefficient, because it's inversely proportional to the Hfe, which increases with temperature.As Dave mentioned in the video, it's possible to minimise the effects of bias currents by keeping the input impedances the same, but this can be difficult in a comparator application.The simulation software you're using probably uses a generic model for the LM393. No doubt there are more accurate simulator packages than Circuit Wizard, but they most likely have a steeper learning curve. I use LTSpice, but it isn't interactive, like the simulators aimed at the educational market.

author: lordvader88
author_rank: Frequent Contributor
timestamp: August 06, 2018, 10:11:55 am
content: Ok thank's so it's not something I could easily calculate or would be expected to know.I'll try some emitter currents and work back to see if the voltages I'm wondering about make sense. I'm just using the basic transistor model.

author: Zero999
author_rank: Super Contributor
timestamp: August 06, 2018, 12:28:29 pm
content: Quote from: lordvader88 on August 06, 2018, 10:11:55 amIt can be calculated, if you know the exact bias current, which can be measured. In reality, it's only worth doing calculations, to work out the typical and worst case scenarios.
Lm393N bad how do we know? - Page 1
Forum section: electronics / beginners

author: Savetheday
author_rank: Regular Contributor
timestamp: September 21, 2021, 02:21:34 pm
content: Hi everyoneI would like to know a bad LM393N How can I do that?There is 70 Ω between GND (4) and VCC (And If I supply a 4.5V power and check the legs (4-8) 3.8V, (1-4) 1.8V, (2-4) 2.0V and (3-4)1.7V.Thanks.

author: james_s
author_rank: Super Contributor
timestamp: September 21, 2021, 05:30:49 pm
content: Is that in or out of circuit? If you see 70 ohms between Vcc and GND out of circuit then that's a pretty good clue that it's bad.

author: Savetheday
author_rank: Regular Contributor
timestamp: September 21, 2021, 09:49:17 pm
content: Quote from: james_s on September 21, 2021, 05:30:49 pmYes out of circuit.How do can we test it if it's general IC bad?

author: Ian.M
author_rank: Super Contributor
timestamp: September 21, 2021, 10:29:59 pm
content: Quote from: james_s on September 21, 2021, 05:30:49 pmThe qualifier to that is "... between Vcc and GND,with Vcc positive,out of circuit ...". Many ICs have structures that will look like one or more diode junctions if supply polarity is reversed.

author: james_s
author_rank: Super Contributor
timestamp: September 22, 2021, 01:47:00 am
content: Testing an IC involves having a bit of knowledge about how the IC is supposed to work. I would plug it into a breadboard and wire it up to a current limited bench supply and slowly turn up the voltage while watching the current draw. Then hook up a very simple circuit, many datasheets include a test circuit.

author: perieanuo
author_rank: Frequent Contributor
timestamp: September 22, 2021, 05:12:21 am
content: hi,usually it doesn't work this wayic's like lm393n can be tested on output side with diode tester, they usually have shorted output transistor, and in his datasheet in the simplified schematic you see some npn or pnp transistor as output transistor. for the input side, it's not the same, as the inputs are more 'complicated' schematics.so what we can do? for AC, use the scope and see if ac waveform is amplified as it should be, for DC we can verify if he 'triggers' in the right direction. that means we understand very well how opamp works.that 'shorted output' diagnose works from my experience in maybe less than 50% situations, usually when the designer left the possibility of opamp output to be overloaded on output side (like not protecting him from oscillations, short circuits - i found opamps with short-circuit protection included to be shorted!, bad layout on output side etcaetera). inputs can suffer the same and you got the input protection diodes or input transistors shorted or smoked, in that case you won't see the short with your diode tester.finally, as @james_s pointed, the test schematic from datasheet is finally the 100% reliable test, but anyway often enough we find that one implemented with +- modifications on our defective board

author: james_s
author_rank: Super Contributor
timestamp: September 22, 2021, 09:14:13 pm
content: Another option is to simply try replacing it with a known good new part and see if that behaves differently.