Function Generator Current

Discussion in 'General Electronics Chat' started by bilalbajwa, May 6, 2011.

  1. bilalbajwa

    Thread Starter Member

    Feb 21, 2007
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    Guys, i have a function generator with 50 OHMS output impedance that means the max current i can draw at 10Vpp is about 200mA Vpp. I was wondering what will happen if i try to run a small dc motor directly using the function generator. I want to ask wise men around before i burn something.
     
  2. Jaguarjoe

    Active Member

    Apr 7, 2010
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    Why would you want to run a DC motor from an AC source? It's just gonna act rotationally challenged (trying to be PC).
    A DC motor draws lots of current when it starts up.
     
  3. bilalbajwa

    Thread Starter Member

    Feb 21, 2007
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    Have you heard about PWM (Pulse Width Modulation)?

    What happens when the motor will draw a lot of current from Function Generator? Will it burn something?:confused:
     
  4. Jaguarjoe

    Active Member

    Apr 7, 2010
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    Why take the chance of damaging your function generator's internal circuitry when you can put a $0.79 MOSFET between the two and be safe?
    What function generator does PWM?
     
  5. bilalbajwa

    Thread Starter Member

    Feb 21, 2007
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    Rigol DS1022. If you have a square wave and you can change its duty cycle. Then the VOltage Avg changes w.r.t to the duty cycle. As you said, function generator are not built for this; however, theoretically its possible given enough current.
     
  6. Wendy

    Moderator

    Mar 24, 2008
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    Why not build a simple circuit that will produce the desired waveforms? This is not rocked science, just electronics, and function generators are expensive.

    You tell us what kind of waveform, amplitude you need and we can point to cheap circuits. You blow one of these circuits you are out the cost of cheap parts, blow a function generator and you may not be able to replace or repair it.
     
  7. Adjuster

    Well-Known Member

    Dec 26, 2010
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    Using a function generator to produce a low-level PWM test signal is acceptable, if it has the relevant waveform capability. I have used power converter test setups that are driven that way, using calibrated generators that can be set to deliver accurate duty cycles.

    Risking ruining your function generator by connecting it to a load which it was not designed for is a very bad idea.
     
  8. bilalbajwa

    Thread Starter Member

    Feb 21, 2007
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    Last edited: May 7, 2011
  9. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    In what frequency range do you want the amplifier to work?
    You could take a look at some audio power amplifiers like the LM1875 or LM3875 (datasheets attached).

    Bertus
     
  10. Jaguarjoe

    Active Member

    Apr 7, 2010
    770
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    I was thinking one of these:

    http://www.national.com/mpf/LM/LM675.html#Overview

    If you are only doing PWM then that MOSFET is all you need. Something like an IRL530 if your motor is under 10 amps.

    That TS200 modulated PS looks nice but I'm sure it is very expensive, much, much more than a transistor or an IC. They do have demo units though. That might be the freebie way to go.

    Could an LM317 be modulated like that?
     
  11. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    I was under the understanding from another thread (that I can't find now) that a square wave from a function generator was not able to have duty cycle changed, only the sine and triangle/sawtooth was able to change?
     
  12. Jaguarjoe

    Active Member

    Apr 7, 2010
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    A Rigol DS1022 is an obsolete 25MHz digital scope that, as far as I can tell, does not have a function generator in it.
     
  13. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    I think he meant - Rigol DG1022
     
  14. Jaguarjoe

    Active Member

    Apr 7, 2010
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    That's a nice piece of equipment. It would be a shame to break it.
    Why don't you give these people your motor specs and get an answer straight from the horse's mouth:

    http://www.rigolna.com/tech-support/
     
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