lm358L vs LM358A

hi

I installed on breadboard a lm358 unitygain circuit last week. The purpose of the circuit is to increase the input impedance and not disrupt the input signal. The signal is an 8kHz ramp wave which includes 0.7v low and 5v high values. Opamp has 12V single supply and v- terminal connected to common ground. Also there is a bypass cap (100nF) connected between V+ and V- terminals.
As I said, I installed the circuit last week on the breadboard and the LM358L (from UNISONIC TECHNOLOGIES CO., LTD) worked exactly as I wanted on the circuit.
I made a printed circuit yesterday and this time I used the LM358A (OnSemi), which is a soic-8 package. But I saw a constant value of only 3v at its output. Then I changed the integration 2 times to solve the problem, but the problem was not solved. As a last resort, when I reduced the ramp frequency to 345Hz with the external element, I observed that the opamp was working with an oscilloscope.
I examined the datasheet of both opamps, but I did not see any significant difference. I also shared the diagram of the circuit below. Does anyone know what this issue might be causing?

What are you doing with the other channel of the op-amp?

The LM358A seems to share some bias circuitry between both amplifiers, but the LM358L doesn't.

You should ground the inputs that are not used. However, that is only a suggestion and I am not sure if that is the problem,

Diver300 said:

What are you doing with the other channel of the op-amp?

The LM358A seems to share some bias circuitry between both amplifiers, but the LM358L doesn't.

You should ground the inputs that are not used. However, that is only a suggestion and I am not sure if that is the problem,

Click to expand...

hi. thanks.

the other pair of opamp is amplifying of first pair. About 2 times with non inverting amplifier . So it makes the output of the signal about 10v high pk and 2v low pk voltages.

I don't know what is happening. The gain of the op-amp reduces when the frequency increases but it shouldn't be a problem with small gains and 8 kHz

Can you obtain an LM358L in the SOP-8 package? It will be the same dimensions as the LM358A SOIC-8.

Diver300 said:

I don't know what is happening. The gain of the op-amp reduces when the frequency increases but it shouldn't be a problem with small gains and 8 kHz

Can you obtain an LM358L in the SOP-8 package? It will be the same dimensions as the LM358A SOIC-8.

Click to expand...

Ordering the LM358L takes me time. I can do it as a last cure. There is a local electronics store near where I live, and the LM358DR and lm358G are sold. I don't know which of these can solve my problem.

Can you get an A in DIP to try in your breadboard? It could be a problem unrelated to the chip - solder bridge etc.

Mike.

Since the - input of the first opamp is grounded then it is NOT a unity-gain buffer. Your opamp is operating "open-loop" with no negative feedback. Depending on the amount and polarity of its input bias current then the output could be high (about +10.8V with no load and a 12V supply) all the time.
A unity-gain buffer has the - input connected to the opamp output, then its voltage gain is 1 like a buffer.

audioguru said:

Since the - input of the first opamp is grounded then it is NOT a unity-gain buffer. Your opamp is operating "open-loop" with no negative feedback. Depending on the amount and polarity of its input bias current then the output could be high (about +10.8V with no load and a 12V supply) all the time.
A unity-gain buffer has the - input connected to the opamp output, then its voltage gain is 1 like a buffer.

Click to expand...

I didnt mean to inverting pin of opamp when i say " v- " . Its supply voltage pin. Generaly it calls VEE.

Pommie said:

Can you get an A in DIP to try in your breadboard? It could be a problem unrelated to the chip - solder bridge etc.

Mike.

Click to expand...

out of stock in the local market. I will have to order.

As far as I understand from your discourses, there is no difference between the two chips, right?
But although I checked it many times, I did not find any short circuits or dust particles. I also checked the pcb paths.
Also, if there was a malfunction in the pcb paths, when I dropped the frequency with the external element, I should not see the same input signal at its output. However, when I look with the oscilloscope, I can see the output (at lower frequency).
This is really interesting and I can't find why !

Thank you.

1) You said that you "shared the diagram of the circuit below" but your schematic was not posted. Please post it.
2) You buy electronic parts in "a local market" (ebay, Alibaba or Amazon?) instead of at a real electronic parts distributor.