Safety Question

Discussion in 'The Projects Forum' started by dixie_normous, Jun 29, 2013.

  1. dixie_normous

    Thread Starter New Member

    Jun 29, 2013
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    Hey guys. I have an idea and I would like your input. I have already been able to do everything on prototype. I have a load which I control via pulse width modulation and I high power MOSFET. The load consumes 2A. My source is rated 4.5A. This device will be running for a long time. Since I am getting my MOSFET DC bias with PWM (instead of pure DC), is that dangerous for the source? The source must cycle between 0 and 2A continuously. Is this harmful for the source? Keep in mind that the source itself is not turning on and off like my load. In my mind I think this will be fine. Thank you.
     
  2. wayneh

    Expert

    Sep 9, 2010
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    What kind of source is it? It would be zero issue for a battery or a traditional wall wart+filter. It MIGHT be an issue for modern SMPS.
     
  3. dixie_normous

    Thread Starter New Member

    Jun 29, 2013
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  4. wayneh

    Expert

    Sep 9, 2010
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    What's the frequency and duty cycle of your PWM signal? Is the 2A load only when the load is 100% on, or is that the time-weighted average? [oh, I see you answered that in #1]

    I think the manufacturer of that SMPS would be the best source for an answer but assuming you cannot get an answer, I think I'd use some kind of a low-pass filter in between the supply and the load. Or, just give it a try and see what happens!

    Maybe somebody here has better advice. I just think that if your PWM is much slower or much faster than the operating frequency of that SMPS, you'll have no problems. But if the PWM frequency is similar, the SMPS will have a hard time regulating.
     
  5. dixie_normous

    Thread Starter New Member

    Jun 29, 2013
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    wow. I just called the company (Mean Well) to ask the question in #1. And the applications group won't talk to me unless I am with a company.
     
  6. crutschow

    Expert

    Mar 14, 2008
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    It's unlikely to harm the power supply, although as noted, it could have a problem with proper regulation, depending upon the PWM frequency, which you haven't stated.
     
  7. Metalmann

    Active Member

    Dec 8, 2012
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    A lot of companies are getting like that. If you do not spend enough....they don't have time to converse.
     
  8. wayneh

    Expert

    Sep 9, 2010
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    I think it's more about liability than crass economics, although that's a factor too.
     
  9. dixie_normous

    Thread Starter New Member

    Jun 29, 2013
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    Thanks everybody. I ordered it anyway because they are the only manufacturer that makes power supplies anything near what I want. Almost a monopoly. I can make the PWM frequency anything between 10Hz and 12 Mega Hz. I have no digital to analog at my disposal so I have to rely on PWM, although I have read that PWM can be converted to dc using a second order low pass filter. I will do this but I have no oscilloscope to verify.
     
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