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Heat problem in AD811ANZ

Hello all,

    I am using AD811 in my amplifier circuit.In this circuit ,I am giving 1V sine ,triangular and square wave signal at 10Hz to2MHz  to the input of amplifier.If I  use this IC ,over a  long period of time ,it produce the heat on the surface of the IC.Eventhough I got a good  output response form this IC .If  I use this IC continuously  the heat problem completely affect the IC of  functionality and it will lead to IC dead.

Hereby, I attached the my amplifer circuit for your reference.

Please suggest the good solution for this problem.

Thanks with Regards,

Newengg

  • Hi-

    I moved this question about the AD811 to the Operational Amplifier Community.  Someone here should be able to assist you.

    Regards,

    AndyR

    EngineerZone Community Manager

  • Hello Newengg,


    It would be helpful to know the load on the amplifier as well as a description of the layout, particularly the trace length and impedance.  Also, are the signal voltages you indicate in your schematic in Vp-p?

    Best regards.

    --Jonathan

  • Newengg,

      Your feedback resistor is way too high.  I would suspect it is oscillating.  Put a scope on the output.

    Also, you need a cap, say 10uF, on the wiper of R1.  If there is no noise on the -15V, but 2mV on the

    +15V, and the pot is centered, you will have 1mV noise on the wiper which goes directly into your

    signal path.  The LM324 will have drift with temperature, so you probably can eliminate the op amp

    entirely.  If you don't need a large adjustment range, make R6 ten times larger.

    Harry

  • Newengg,

      With 30V across the part, and 16 mA, max, you have 0.48 Watts, so it will get hot.....

    Harry

  • Thanks for your reply...The output voltage is 2 to 20 Vp-p only.

    Then I tested the amplifier output response  in the aspect of adding  the resistive load and capacitive load  at the output terminal of the IC.Eventhough the heat problem is not solved.

    Please suggest in which way have to test the IC...

    Regards,

    Newengg

  • Thanks for your reply,

    I didn't get the oscillating output response throughout the whole testing process ;Please explain the matter of LM324.I didn't get your point regarding of LM324.

    Is it necessary to add the 10uF with +/- 15 V of LM324?

    Should the LM 324 eliminate  from the amplifier circuit?

    Regards,

    Newengg

  • Newengg,

      Yes, I think you can eliminate the LM324 buffer.  It only adds more error/noise.

    As I mentioned earlier, noise on the +15V or on the -15V will affect the voltage on

    the wiper of the pot, so it will get into your signal path.  That is why you need a

    cap on the wiper to ground.

    Harry

  • Harry,

       In your another reply mentioned the power disipation on IC  0.48 Watts so,it gets hot.

    Now how  to reduce the power disipation problem.

  • newengg,

      You could consider switching to the ADA4948-1 or the AD829, both have lower supply current.

    Harry

  • The Lm324 is not needed unless you are trying to set the output offset voltage to a particular value. If you are concerned about eliminating output offset consider using a composite amplifier (with the AD811 inside the feedback loop of the 1st amplifier) configuration with the 1st amplifier having extremely low offset voltage which will maintain the overall offset at the 1st amplifier specification. The overall gain will be the sum of amp1 gain and AD811 gain.

    Also the AD811 is recommended to be used with a heat sink at +/- 15v supply voltages.  

    The optimal feedback resistor for the AD811 is 909 to 1000 ohms. Higher values will roll off the high end response.