LM358P from Aliexpress Issues

Hi all!

I purchased a set of LM358Ps from aliexpress to learn and experiment with Op Amps (link
here).

As for the pinout, I referred to the TI datasheet here. The pinout image is attached below.

The first thing I tried out was a simple non-inverting circuit (kindly refer to attachments for the schematic). Vcc and GND were connected to a 5V power supply and V+ was connected to one cell of a LiPo battery at 3.83V. The grounds were tied together.

However, Vout was constantly at the same voltage as the V+ voltage (3.83V in my case) although I was expecting an amplification of 2x as I used 10k resistors for both R1 and R2.

Having tried out all the chips in the set and getting the same result all the time, I’m inclined to think that there could be a systematic error in the way in which I am wiring up the Op Amp. However, could it be possible that all the boards are defective?

I’ve attached a photograph of my breadboard setup if that helps in identifying the issue.
Any help would be greatly appreciated!

Cheers,
RCPilot1604

Pinout.PNG

Dear all,

The breadboard image failed to attach to the original post so I’ll post it here.

Cheers,
RCPilot1604

Firstly you can't get a higher voltage out from a chip than the supply voltage (switched-capacitor chips are an exception).

Secondly the LM358 isn't rail-to-rail so you won't ever get more than about 3.5V from the output pin when powered from 5V.

Thirdly if you bought it from AliExpress its not necessarily upto spec anyway. Then again the LM358 is about the worst performing opamp out there, so its unlikely to be worse!

There is a spec called Vo (Voltage output swing from rail). Depending on conditions you can only get within about 1.5V from the power supply (about 3.5V max with a 5V power supply). It also won’t go down to the negative supply voltage either (ground =0V in your case).

There are “rail-to-rail” op-amps that can go a lot closer to the power supplies.

The LM358 does take the output down to the negative rail, just not to the positive one. And all rail-to-rail outputs can only get close to the rail (10mV perhaps) anyway if loaded at all (which they always are due to the feedback network).

Wire up a basic voltage follower and see if the device(s) function. Use a pot as a variable voltage source, anything in the 1 to 100k range will work fine for the application. If they function at all, you’ll see per the earlier comments that the LM358 output can never reach the supply voltage. Do watch out for loose connections with those 1/4 watt resistors on a breadboard, the leads aren’t large enough in diameter to connect reliably.

Stuff from China can be absolute junk. Quite literally stuff pulled from the bin and remarked. You do get what you pay for.

The LM358 is an ancient device and has plenty of gotchas for newbies, consider using something modern like the TLV2462 or similar as they are rail-to-rail on input and output.

For conducting such experiments, you could also consider the Ltspice simulation software. It is free and, after watching a couple of introductory videos, very easy to use, at least for static DC circuits for example the schematic in the OP.
In some cases, models from the Analog Devices product range are available only, so maybe you’ll have to select an Analog Devices rail to rail opamp.

Hi everyone, thanks for the speedy replies!

MarkT:
Firstly you can't get a higher voltage out from a chip than the supply voltage (switched-capacitor chips are an exception).

Ah, I see that was a silly mistake on my part x_x
Does that also mean you cannot get an output voltage lower than the supply voltage? So if I were to use the op amp in an inverting circuit, I will need to supply a negative voltage on V- to get a negative output voltage?

WattsThat:
The LM358 is an ancient device and has plenty of gotchas for newbies, consider using something modern like the TLV2462 or similar as they are rail-to-rail on input and output.

Thanks for the advice I will try out the TLV2462.

Once again thanks to everyone for your help!

Cheers,
RCPilot1604

RCPilot1604:
Does that also mean you cannot get an output voltage lower than the supply voltage? So if I were to use the op amp in an inverting circuit, I will need to supply a negative voltage on V- to get a negative output voltage?

Exactly. You can't go above or below the supply voltage. As a rule of thumb, no circuit will ever get you higher or lower voltages than the supply voltage, unless it's designed to do exactly that (such as a boost converter).

The results as you post sound perfectly normal for the LM358 indeed.

Another fine general purpose rail to rail OpAmp is the MCP6002, and there are dozens more. With a rail/rail OpAmp you can expect an output of very close to your supply voltage (which you say is 5V, but which in reality is very likely a bit more or less than that).

opamps are magical but not as magical as to make voltage out of thin air. :slight_smile:

Just to demonstrate LTspice with an old "741 like" op amp (non rail to rail) :

The horizontal (X) axis is the voltage at the "+" input of the op amp and the vertical (Y) axis is the output voltage :