Problem with a MAX038 -how to test-?

Discussion in 'General Electronics Chat' started by adam555, Dec 12, 2013.

  1. adam555

    Thread Starter Active Member

    Aug 17, 2013
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    Today I bought a MAX038 function generator, but after trying it with 3 different test circuits the IC doesn't seem to work properly.

    For example, I tried it with the circuit below -which is one that comes in the datasheet- and the most I get is only a sort of a sine/saw wave of 200mVpp, offset +0.5V, and at a frequency much higher than what it should.

    I also noticed that it doesn't work when you supply it exactly ±5V; it would only work from ±5.14V to ±5.35V and any tiny difference in supply voltage will have a huge effect on output amplitude and frequency.

    I would appreciate if anyone could advice me on how to test the IC properly to make sure it's not damaged. Thanks.

    [​IMG]
     
  2. adam555

    Thread Starter Active Member

    Aug 17, 2013
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    By the way, what's the meaning of the round symbol on the output (pin 19 center-right of the diagram)
     
  3. Dr.killjoy

    Well-Known Member

    Apr 28, 2013
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    Not to thread jack
    But where did you find that cause thats not a cheap chip????
     
  4. adam555

    Thread Starter Active Member

    Aug 17, 2013
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    On ebay, from China. Could that be why it doesn't seem to work? :(
     
  5. ronv

    AAC Fanatic!

    Nov 12, 2008
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    Data sheet schematics almost always work so check it carefully. The round thing represents coax cable out to a test probe.
    2 supplies - plus and minus 5?
     
  6. adam555

    Thread Starter Active Member

    Aug 17, 2013
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    Thanks, I'm about to give it another try; just trying to figure out where I got it wrong the previous times.

    Yesterday I measured the supply voltages, and they are fine +5V and -5V; as I said, it only seems to output something like a sine/saw wave from ±5.14V to ±5.35V, and the output varies a lot between those 2 voltages. I also measure the REF output from the IC (pin 1), and it also seems fine (2.5V)... but can't get a good output.
     
  7. adam555

    Thread Starter Active Member

    Aug 17, 2013
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    I have to say that I don't have much confidence in the seller. But for $10 I couldn't resist giving it a try.

    Every other IC that I got from China through ebay worked perfectly well.
     
    Last edited: Dec 13, 2013
  8. adam555

    Thread Starter Active Member

    Aug 17, 2013
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    My mistake; I'm an idiot. :D

    It's working.
     
  9. BobTPH

    Active Member

    Jun 5, 2013
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    Care to clue us in on what the mistake was?

    Bob
     
  10. adam555

    Thread Starter Active Member

    Aug 17, 2013
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    Sorry.

    I don't have a dual power supply. So, when I need positive and negative voltages (e.g for op-amps, etc) I use I small splitter circuit (see attach) I made to achieve this from my single power supply.

    Obviously, when you need ±5V, since the total voltage output from the power supply is split in two by this circuit, you need a total of +10V. But since this IC has an absolute maximum limit of ±6V, and I was so careful not to burn it, when I connected it I was looking at the power supply, which stated 5V. I also connected a multimeter to the power supply output, and was also reading the 5.14V and 5.34V mentioned above; thinking that I was supplying it the right voltages. But those voltages are the total before the split; so I was only supplying half of the voltage the IC really needed.

    Resuming, just a silly mistake for not having a real dual supply.
     
    Last edited: Dec 13, 2013
  11. t06afre

    AAC Fanatic!

    May 11, 2009
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    Ouch the splitter approach of yours is just asking for problems. Why not build your self another power supply. And then combine these two then you need a dual supply.
     
  12. adam555

    Thread Starter Active Member

    Aug 17, 2013
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    You're absolutely right: it only works when you need the exact same amount of current for both polarities; the greater the difference in current needed between positive and negative supply, the less reliable it becomes.

    But since I just use it as a quick fix for testing op-amps, comparators and IC function generators, which usually need the same positive and negative current, it does the trick quite well.

    I wouldn't use it for anything else than testing purposes; for example, I'm planning on making for the MAX038 its own dual supply from scratch; as soon as I decide which configuration I'm going to use... suggestions are more than welcome. :)
     
  13. bertus

    Administrator

    Apr 5, 2008
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  14. adam555

    Thread Starter Active Member

    Aug 17, 2013
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    Thanks Bertus,

    I was looking for a circuit like that to install permanently inside my power supply and add the possibility of dual output; rather than changing the whole design or building a new one from scratch.

    The design I posted was quite convenient because I could build it with common components that I had at home; and didn't need to buy anything else. But as I said, it was no good to install permanently because it doesn't work well when the loads on the positive and the negative are different; though it works pretty well with differential amplifiers and function generator ICs.
     
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