Non-inverting amplifier - LM358N

Status
Not open for further replies.
B

boylesg

Advanced Member level 4
Joined
Jul 15, 2012
Messages
1,023
Helped
5
Reputation
10
Reaction score
6
Trophy points
1,318
Location
Epping, Victoria, Australia
Activity points
11,697
Frustrating!

What have I done wrong with this circuit and why is the postive phase of the input signal bering clipped?

Is this what will happen if I wire this circuit up as is or is this clipping some bizzare artefact of this software?
 

Just simple modification...Use this...

Regards
Udhay
 

Attachments

  • LM358.png
    14.7 KB · Views: 134

Hello plz refer to the data sheet of this op_amp, I also attached it to you
as it is very clear to see that this op-amp is designed to work with single supply not dual supply (only positive Vdd and ground )
second thing even through the single supply you see the output range from the data sheet is (0 to Vcc-1.5) so you will get clipping in the positive side if you exceed this level while the negative side is down to ground. therefore to avoid the clipping, you must keep in your mind the the maximum output is (vcc-1-0)/2

- - - Updated - - -

here is the attachment i forgot it
 

Attachments

  • lm358.pdf
    289.1 KB · Views: 98

udhay_cit said:
Just simple modification...Use this...

Regards
Udhay
Click to expand...

Power Supply Voltages Vdc
Single Supply VCC 32 26
Split Supplies VCC, VEE ±16 ±13
Input Differential Voltage
Range (Note 1)
VIDR ±32 ±26 Vdc

You can use either a single or dual supply according to the datasheet I have.

And I figured it out finally - you need a capacitor on the resistor to ground.

Very few websites seem to bother specifying this in their non-inverting amplifier shematics and I guess it is assumed people will know to add it. Very frustrating for the likes of me however.
 
Last edited:

rightm here is the updated datasheet, but still the output range is the same and he has to work with the condition I stated in my previous post.

regarding the capacitors, I it will not effect the D.C operation of the circuit like the output swing and clipping so it doesnt matter if you put it or not .


- - - Updated - - -

again I forgot the attachement
 

Attachments

  • datasheet.pdf
    318.8 KB · Views: 96


Well then apparently this clipping is an nuissance artefact of multisim 11 & 12.

Because this software will simply not simulate the circuit correctly unless you put that capacitor in.
 

if the capacitor has an effect on the output behavioural (which I dont believe) then it must has the same effect on the negative side of the signal not only the positive

take it easy, I have mentioned that the positive range is up to vcc-1.5 Volt, so if you cross it the signal will clip while the negative is not clipping because it can be down to zero. that is all.

if you look at his input of 1Vp and the gain is (1+100/10 = 11)
so Vo = Av.vin = 11*1= 11V
the maximum output is VCC-1.5 = 12-1.5 =10.5V
since 11V > 10.5 then the output is clipping at 10.5V........ here we finished


boylesg said:
Well then apparently this clipping is an nuissance artefact of multisim 11 & 12.

Because this software will simply not simulate the circuit correctly unless you put that capacitor in.
Click to expand...
 

Multisim is bloody useless for simulating opamp circuits.

I mean look at this:



According to everything I have read this should amplify the signal with no clipping.

So clearly you have to do something bizarre in multisim to make it work properly that you don't have to do in real life electronics......which makes multisim utterly useless.
 

Ltspice is always best... The results are more realistic compare to the practical hardware output...
 

boylesg said:
Multisim is bloody useless for simulating opamp circuits.

I mean look at this....
Click to expand...
Don't blame Multisim - that circuit won't work in real life either. The problem is you have no DC connection to the non-inverting input of the opamp.

You can fix it as Udhay showed in post 2 or, more simply, by just connecting a 10K resistor from the non-inverting input of the opamp to ground.
 

If you are using a capacitor in series you may loss your DC bias of OPAMP input...
Multisim is very simple to use but i dont impressed with the performance...

You can use Ltspice for analog simulations(Transistor & OPAMP)& the result will very closer to practical hardware...
Ltspice is simple to use if you understand it fully, but it is a bit difficult to draw schematic...

If you want to use the Ltspice, the most useful study material available in internet is here....
https://www.scribd.com/doc/51765014/LTspice-4-e2
 

hahahahahaha

so for two days we are discussing the problem and he forgot to connect the ground

connect it man
 

Junus2012 said:
so for two days we are discussing the problem and he forgot to connect the ground

connect it man
Click to expand...

Why hahaha? He connected the ground before the 1uF capacitor. Really you have to notice this... For my circuit(post #2) is equivalent to his schematic. even if you are using the capacitor you will experience the same problem...
 

udhay_cit said:
Why hahaha? He connected the ground before the 1uF capacitor. Really you have to notice this... For my circuit(post #2) is equivalent to his schematic. even if you are using the capacitor you will experience the same problem...
Click to expand...

Well didn't some body mentioned that the capacitor was not essential in a real life circuit? Probably why none of the example circuit I have looked at previously specified it in the schamatics.
 

I haven't seen a complete schematic of the discussed circuit yet, so I can just guess what's exactly going on.

I agree with godfreyl that Multisim has no problems to simulate trivial OP circuits like the present one apparently is.
 

ALERTLINKS said:
**broken link removed**
Click to expand...

So I am missing the 10k resistor from the output pin to GND?

OK well I just tried a 10k resistor from the output to ground as in the datasheet above and multisim clips the positive signal again.

If move that resistor to the non-inverting input to GND then the positive signal doesn't clip, but that connection is not specified in the datasheet.

So who do I believe? The datasheet or multsim? I am confused!

It is actually an ST device: View attachment OpAmplifierLM358N.pdf

I will follow
Figure 21. AC coupled non-inverting amplifier
Click to expand...
to the letter and see what multisim does.
 
Last edited:

So I am missing the 10k resistor from the output pin to GND?
Click to expand...
No. LM358 has a push-pull output stage and can both source and sink current. In some situations, a pull-down resistor will help to reduce the minimal output voltage in single supply operation, but that's not the point with your circuit.

It would be reall helpful to see a schematic that shows all components of your circuit without wires leading to nowhere.

P.S.: As already mentioned by others, a resistor to bias the non-inverting input is clearly missing. The circuit can't work as shown.
 
Reactions: tpetar

    tpetar

    Points: 2
    Helpful Answer Positive Rating
FvM said:
P.S.: As already mentioned by others, a resistor to bias the non-inverting input is clearly missing. The circuit can't work as shown.
Click to expand...

I have been following the vast number of examples of non-inverting amplifier in google: https://www.google.com.au/search?q=...yICwAw&sqi=2&ved=0CAQQ_AUoAA&biw=1366&bih=536

And they seem fairly consistant on how you set it up in its most basic form.

FvM said:
It would be reall helpful to see a schematic that shows all components of your circuit without wires leading to nowhere.
Click to expand...

DONE!

This is what I have at present:



- - - Updated - - -

Here is what I did before and as you can see the output signal no longer clips. However I have not seen any example circuits where there is such a connection.

So same problem. Who do I believe? Multisim or the thousands of example circuits?
 

Status
Not open for further replies.

Similar threads

Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…