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  1. #1
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    Using AD831 in parallel

    Hello every one,

    I am software guy. Some how trying to use ad831 as a mixer connecting in parallel as seen on attached file. +5V and -5V are supplied to both of the mixers from the same source. The problem I faced is here. While measuring the supplied -5V at each mixer it shows ~ -1.2V. what could be the problem?
    Click image for larger version. 

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  2. #2
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    Re: Using AD831 in parallel

    Hi,

    * bad DVM
    * bad -5V power supply
    * too high current

    Klaus
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    Re: Using AD831 in parallel

    Quote Originally Posted by KlausST View Post
    Hi,

    * bad DVM
    * bad -5V power supply
    * too high current

    Klaus

    Dear Klaus,

    Thank you very much for your help.

    I have been using my digital multimeter(DVM) for some other circuit and working properly. The -5V supply source is also working perfectly while applying for other circuits. As you mentioned, there is high current measured. That could be a problem. how I may resolve that one?

    Thank you once again.



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  4. #4
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    Re: Using AD831 in parallel

    Hi,

    First you need to determine:
    * How much current can your supply deliver
    * How much current do you expect your circuit to draw
    * Measure how much your circuit really draws

    We don't know how to debug your circuit, because you didn't show.
    Are the ICs socketed? Breadboard, PCB, is something getting hot....do you have coolant spray? Soldering skills...

    Btw: some brand (negative) voltage regulators suffer from not properly starting up when negative voltage is applied.
    In one application we also had +5V and -5V regulators, but the negative did not start up because the positive was faster..causing some positive glitch at the negative VR's output. This was a cheap 7905 .... we solved this problem by using a high quality brand VR.

    Klaus
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    Re: Using AD831 in parallel

    Quote Originally Posted by KlausST View Post
    Hi,

    First you need to determine:
    * How much current can your supply deliver
    * How much current do you expect your circuit to draw
    * Measure how much your circuit really draws

    We don't know how to debug your circuit, because you didn't show.
    Are the ICs socketed? Breadboard, PCB, is something getting hot....do you have coolant spray? Soldering skills...

    Btw: some brand (negative) voltage regulators suffer from not properly starting up when negative voltage is applied.
    In one application we also had +5V and -5V regulators, but the negative did not start up because the positive was faster..causing some positive glitch at the negative VR's output. This was a cheap 7905 .... we solved this problem by using a high quality brand VR.

    Klaus
    Dear Klaus,

    The -5V voltage regulator I am using is NJM7905A which can supply up to 1A. I expect my circuit to draw around 0.65A approximately. But, what it actually draws is 1.2A. The PCB is getting very hot for which I disn't use coolant spray. I will try to use standard VR as you suggested. would you suggest me one to use?

    If you have any more suggestions depend on the information I am writing now, I would love to say thank you in advance.


    Thank you a lot.



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    Re: Using AD831 in parallel

    Hi,

    The PCB is getting very hot for which I disn't use coolant spray.
    I doubt the PCB is getting hot. Usually the electronic parts getting hot. .. and only some of them.

    To detect which one is getting hot:
    * power off and let all get down to room temperature
    * use coolant spray in a way that everything gets white / icy surface.
    * then switch power ON and watch the parts which ones first melt the icy surface.

    Klaus
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  7. #7
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    Re: Using AD831 in parallel

    Hello every one,

    I have solved the problem mentioned above by using standard voltage regulator.

    I stack again due to some other problems. A local oscillator oscillates 59MHz where as input RF is 60MHz. An output IF is supposed to be 1MHz, I guess. But, it is 60MHz instead. What could be the reason? would you help me in solving this problem?

    Its schematic is attached above in the beginning.

    Thank you a lot .



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    Re: Using AD831 in parallel

    For correct double balanced mixer operation (e.g. achieving the specified LO to IF isolation), RF and LO inputs must be DC free. According to your schmematic, this is at least not the case for LO.



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    Re: Using AD831 in parallel

    Quote Originally Posted by FvM View Post
    For correct double balanced mixer operation (e.g. achieving the specified LO to IF isolation), RF and LO inputs must be DC free. According to your schmematic, this is at least not the case for LO.

    FvM,

    Thank you a lot for your help.

    I am sorry, i couldn't get your explanation fully(take in to consideration that I am just a beginner to circuit design). As to my understanding, there is no any DC supply to these RF and LO inputs. how could that happen? would you brief it more?

    Thank you once again.



  10. #10
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    Re: Using AD831 in parallel

    Crystal oscillator output has DC bias of Vcc/2, RF in bias is unknown. Where is it connected to?

    Use capacitor to clock oscillator DC bias. It's also unclear if the oscillator can drive 2x50 ohm load you may want to increase the resistor value.



  11. #11
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    Re: Using AD831 in parallel

    Quote Originally Posted by FvM View Post
    Crystal oscillator output has DC bias of Vcc/2, RF in bias is unknown. Where is it connected to?

    Use capacitor to clock oscillator DC bias. It's also unclear if the oscillator can drive 2x50 ohm load you may want to increase the resistor value.


    FvM,

    Thank very much.

    Actually the RF is from signal generator with 50 ohms output and transmission line impedance. does that matter?



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  12. #12
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    Re: Using AD831 in parallel

    RF should be ok then.



  13. #13
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    Re: Using AD831 in parallel

    Quote Originally Posted by FvM View Post
    Crystal oscillator output has DC bias of Vcc/2, RF in bias is unknown. Where is it connected to?

    Use capacitor to clock oscillator DC bias. It's also unclear if the oscillator can drive 2x50 ohm load you may want to increase the resistor value.

    FvM,

    Very sorry, I am back again. I have two questions here:

    1. "Use capacitor to clock oscillator DC bias" mean using capacitor instead of supplied Vcc? if yes, how I may make its circuit?
    2. "you may want to increase the resistor value", I need to increase the resistors value you mean?

    I would like to extend many thanks for your huge help.



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