This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LM358: Overheating

Part Number: LM358

Hi Experts,

A customer is using LM358P as a comparator and they encounter an issue that is heating up the device and the lifetime average is roughly 48 hours.

The connections are described below:

Supply voltage: Ground/+12-13V DC
IN1-: connected to 700 Ohm
In2+: connected to 1kOhm potentiometer (Ground/+12V)
Out1: connected to a Power Mosfet Transistor
In2- and In2+: connected to Ground
Out2: no connection

Can you help? Thank you in advance



  • Hello Marvin,

    What about other side of 700 ohm resistor?

    IN2+ is center tap of pot?

    Is there any series resistance from output to FET? Is it FET gate?

    Don't ground both inputs. A lesser mistake is to ground neither 

    Does the top feel hot? Do this happen on every board?

    Measure the voltage on every pin and report it back to me.

  • Hi Marvin,

    a MOSFET can show a huge gate source capacitance. This would mean a high capacitive load at the output of OPAmp which can destabilize the OPAmp and make it oscillate. And wHen oscillating an OPAmp can dratamically heat up. One cure is to mount an isolation resistor in front of the MOSFET's gate. (Ron has already asked about the presence of such an isolation resistor in your circuit.)

    From your description it's not quite clear how your circuit looks like. Can you show a schematic?


  • Hi Ron and Kai

    Thanks for the response. Here is the response from the customer:

    In1- / Capacitor 47 Mikrofarad (to ground) / Zener Diode 4,7V (to ground) / series resistance 700 Ohm / Signal 0 .... 19V
    In2+ / pot is at a lower position. In2+ see 1,8V.
    Out 1 / series resistor 1 kOhm/ FET gate

    Pin Measurements:

    Pin 1: 12V
    Pin 2: 0...4,7V
    Pin 3: 1,8V
    Pin 4: 0V
    Pin 5: 0V
    Pin 6: 0V
    Pin 7: 0V
    Pin 8: 12V

    I will provide the schematic once the customer sends a copy.



  • Marvin,

    It looks like pin 1 is shorted to 12V for two reasons. With pin 2 changing, so should the output. 

    LM358 output high should be close to 10.7V 

    Are the voltages from a device that already became damaged?

  • Hi Ron,

    Thank you for waiting.

    Yes, the measurements were from the damaged device. Now the customer changed the layout and added 20k to all inputs. The + Pin was added by 440 Ohms. Now seems that the device is working properly and no abnormal heating can be detected.

    Can you agree with this design? or can you suggest a better approach?



  • Hi Marvin,

    a schematic would be helpful to answer your question.