LM358: Using LM358 as a replacement to LMV324D

Hi Mohamat,

Can you please try attaching the schematics again? 

Thank you,

Tim Claycomb

The Net Port 57 is going to the positive power supply of the Op Amps while the Net Port 129 is connected to a 24 V power supply.

If the voltage drop over Z2 is 2.5 V, then I'd have to conclude that Z2 is not a 15 V Zener.

Does the same happen if you remove the LM358 chip?

Clemens Ladisch That was my initial diagnosis but after I removed the Z2, the input to the LM328 was still 2.5V but when I remove the LM328 from the circuit the output from the Z2 is 15V.

Is the LM358 pinout correct?

Can you check with another LM358 chip?

 Yes the pinout is correct and we have 15 replicas of these. And the Z2 is MMSZ5245BT1G. We measured the current going into the supply pin of the LM358 to be around 32 mA.

I am suspecting the Z2 works fine when we take out the lm358 as there is not as much current drawn through the Z2 compared to when it's connected to LM358. Is there an explanation or information for this?

Hi Mohamat,

The LM358 should only draw about 600uA total. It is possible the device has been damaged. I suggest replacing the device with a new one to see if that solves the issue.

Thank you,

Tim Claycomb

Hello Tim,

Sorry for the delay in the reply. We ordered a new batch of LM358D to use as a replacement as you suggested. We currently did the same test and unfortunately, the op amp is still draining about 30mA of current.

Just a recap: When we remove the 15V Zener Diode, the voltage going into supply pin of op amp is close to 24 V and works fine.
When we remove the op amp, the zener diode is dropping the 24V correctly to 15V.
But the problem occurs when we have both of them in the circuit.
Ideal operation will be 24V dropped to 15V by the Zener Diode before supplying it into the op amp's supply pin but it seems like there isn't enough current flowing into it, as most of the current is flowing into the op amp's supply pin instead causing the zener diode not to be able to reach the reverse breakdown region causing a low voltage supply instead (2.5V).

Please correct me if any of my assumptions are wrong and appreciate any help guidance. 

Thanks,
Mohamat.

Hi Mohamat,

Are you testing the LM358, LMV324, or LM324? These are all different devices. Your schematic shows LMV324 which is a quad channel low voltage device. But you have mentioned using the LM358 which is a dual channel high voltage device. 

What device is your PCB designed for? The LM358, LMV324, or LM324?

Thank you,

Tim Claycomb

Hello Tim.

We are using the LM358. The LM328 was a typo I made, sorry about that. As for the LMV324, that was the original op amp used in a different version of our pcb design which worked fine. We just ported that design into a new pcb design we are making now. 

Thanks,
Mohamat.

Hi Mohamat,

Can you please send the new design schematic showing the LM358?

Thank you,

Tim Claycomb

So this is the schematic. One more thing to mention, the purpose of this circuitry is to amplify a PWM signal ( 0- 3.3 V) to a PWM signal (0 - 15 V). Btw the the op amp is LM358(labelled wrongly as LT1013) and the Zener Diode, D1 is supposed to be MMSZ5245BT1G. 

Thanks,
Mohamat.

Hi Mohamat,

I would like to see the schematic used to create your PCB, similar to the one you showed in a previous post. This appears to be a simulation schematic. The LM358 should not draw 30mA of current so something is wrong.

Thank you,

Tim Claycomb

As the input into the LM358 is a PWM at 0 - 3.3 V at frequency 0.5 Hz. Does this cause a saturation affect on the op amp or something when we have shunting done to produce the 15 V going into the op-amp? We removed the PWM feeding into the Op-Amp, and the supply voltage into OP Amp was successfully at 15 V.

The LM358 appears to be configured as a comparator since I do not see negative feedback. As the PWM changes from 0V to 3.3V this will cause the output to change from 0V to 15V and the op amp will have to drive whatever load is connected to the output. When at 15V it is possible the op amp outputs 30mA of current which would explain the current into the supply pin. All output current must come from the power supply.

Also, I recommend using the LM358B. This is a newer version of the old LM358.