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Heating operational amplifier OP284FSZ-REEL7

Discussion in 'Troubleshooting and Repair' started by Glebiys, Feb 1, 2020.

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  1. Glebiys

    Glebiys

    1
    0
    Feb 1, 2020
    Hello,

    Task: to make a square wave with a frequency of 1 kHz in the voltage range (-12V - +12V), using a PWM signal with voltage (0V-5V).

    Circuit:
    [​IMG]

    Originally LM258WYDT (ST) was used as an operational amplifier, it did not heat up, but since it was not from the Rail-to-Rail series, there was a 1.5V drop at the output, which did not allow us to give out a voltage close to 12V. So I decided to switch to Rail-to-Rail, for these purposes I found OP284FSZ-REEL7 (AnalogDevices). After replacing with this amplifier, the value of the output voltage became close to 12V (+-11.85 V), but the operational amplifier began to heat up (after 5 minutes its temperature was about 45-60 degrees).
    I did not find a short circuit, but noticed that at the output of the voltage divider (R1, R2), instead of 2.5V, the voltage became 4.5V. On the LM258WYDT, this voltage was 2.5V. Perhaps there are elements on this input of the operational amplifier that should lift it?

    Unfortunately, at the moment I do not have an oscilloscope and I can not see the output signal.

    My suspicions:
    1. The amplifier is not designed for such a load or, conversely, it is not enough for it, and it begins to oscillate.
    2. Is this an accurate amplifier, perhaps additional elements are needed for its operation?
    3. The amplifier is damaged.
    Parameters of currents from datasheets:
    LM258WYDT
    1. Input current: 5mA (DC)
    2. Source output current (Isource): 20-60mA
    3. Output sink current (Isink): 10-20mA
    OP284FSZ-REEL7
    1. Supply current: 2.25mA
    2. Output current: 10mA

    Question: What could be the reason?
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    10,025
    2,138
    Nov 17, 2011
    The op284 can drive up to +- 10 mA, this should not be an issue here.
    Oscillations may be an issue, especially as you provide no feedback to the opamp.
    Connect the "+" input to gnd instead of the mcu output. connect a multimeter in AC mode to the output of the opamp using a coupling capacitor. If the opamp oscillates, you should read am ac voltage.
    Not necessarily. Although it is not good practice to use an opamp as comparator. And if you do, you should provide positive feedback to set it up as a Schmitt-Trigger.
    A possibility easily to be checked by using another chip.

    What did you do with the 2nd opamp in the package (the types you name are dual opamps)?
    Tie its inputs to a well defined potential, e.g. gnd, to prevent it from oscillating or doing any other fun stuff.
     
  3. bertus

    bertus Moderator

    665
    227
    Nov 8, 2019
    Hello,

    As posted on the other forum you asked the question:

    op184_284_484_Absolute_max_ratings.png

    Bertus
     
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