Why cant a function generator output 100mA?

Discussion in 'General Electronics Chat' started by Bakez, Sep 13, 2013.

  1. Bakez

    Thread Starter New Member

    Aug 21, 2012
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    If its outputting 5V and has 50ohm output impedence then surely its outputting 100mA also?
     
  2. MrChips

    Moderator

    Oct 2, 2009
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    Depends.
    What is the make and model number?
     
  3. Bakez

    Thread Starter New Member

    Aug 21, 2012
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  4. studiot

    AAC Fanatic!

    Nov 9, 2007
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    Looking at the specs it says 10v pk to peak into 50 ohms, which comes out at 70 milliamps max.
     
  5. Bakez

    Thread Starter New Member

    Aug 21, 2012
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    How did u get 70milli amps? Im looking at pulse data

    I dont understand why it cant output 100ma although my gut instinct says it wont

    PULSE
    Frequency Range: 500 µHz to 12.5MHz (TG2511 - 500 µHz to 6.25MHz)
    Resolution: 1µHz , 14 digits
    Output Level: 10mVp-p to 10Vp-p into 50 Ω
    Overshoot: <5%
    Jitter: 300ps + 0.01% of period
    Rise/Fall Times: Rise and Fall times can be independently varied or can be varied
    together simultaneously.
    Edge Range: <8ns to 40µs (TG2511 - <13ns to 40µs)
    Edge Resolution: 0.1ns for rise/fall time ≤100ns; 1ns for rise/fall >100ns and ≤2µs;
    10ns for rise/fall >2µs and ≤40µs
    Width Range: 20ns to 2000s (20ns minimum for period ≤40s; 200 ns minimum for
    period >40s and ≤400s; 2µs minimum for period >400s)
    Width Resolution: 10ns for period ≤40s; 100ns for period >40s and ≤400s;
    1µs for period >400s
    Delay Range: 0ns to 2000s
    Delay Resolution: 10ns for period ≤40s; 100ns for period >40s and ≤400s;
    1µs for period >400s
     
  6. studiot

    AAC Fanatic!

    Nov 9, 2007
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    I did the calculations, that anyone contemplating such an instrument should be able to do.

    This is a function generator and to output a sine wave:

    10V pk-pk = 5 volts peak = 5/√2 volts rms.

    5/√2 volts into 50 ohms gives 5/√2*50 amps rms.
     
  7. Bakez

    Thread Starter New Member

    Aug 21, 2012
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    Yes that is for a sine wave

    For a 5V pulse, it should be able to do 100mA, if I just use the same calculation you have?
     
  8. hexreader

    Active Member

    Apr 16, 2011
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    I set my function generator to square wave 0.1 Hz 10V p-p

    A multimeter directly across the output reads 93 mA for 5 seconds, then -87 mA for 5 seconds.

    Seems pretty close to 100 mA to me.

    Of course, the average DC current is close to 0 mA.

    10V p-p sine wave (3.5v RMS) 50Hz gives 63mA RMS AC, which sounds about right to me.

    I see no inconsistency in my experiments.

    I agree that a 5V pulse should (and probably does) give 100mA for the time the pulse is at 5V, but average current will be much less if you count the off time.

    How are you measuring current? Most multi-meters expect pure DC on the DC range, then 50 or 60 Hz sine wave on the AC range. Anything else, and a cheap multimeter is likely to give false readings.
     
    Last edited: Sep 13, 2013
  9. wmodavis

    Well-Known Member

    Oct 23, 2010
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    Your figuring seems to be amiss.
    Output current is not only determined by the device output impedance but the load impedance. If you shorted the output is may put out 100mA.
     
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