Analyze circuit to determine output:

Discussion in 'General Electronics Chat' started by mbxs3, Aug 27, 2011.

  1. mbxs3

    Thread Starter Active Member

    Oct 14, 2009
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    Can someone please analyze this circuit and determine what the output voltage will be?
     
    Last edited: Aug 27, 2011
  2. Kermit2

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    That seems to be a 3 volt zener, right?

    What happens when you make it a 5 volt, or a 10 volt zener?

    Believe it or not, those are hints at what the output will be.
     
  3. SgtWookie

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    The primary intent is for the circuit to be a ~5 second delay. Once C1 charges to ~1,7v, the output is turned on.

    You should see somewhere around 23.1v-23.5v depending on the output load; load shouldn't draw more than about 25mA without causing problems.

    BTW, that's a 4.7v 1W Zener.
     
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  4. Kermit2

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    [​IMG]
     
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  5. SgtWookie

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    Thanks, Kermit2 - I realized that in my state of exhaustion yesterday evening (lots of yard work in humid 100°F weather) that I'd transposed the 1N4372A to 1N4732A; the latter of which is in fact a 4.7v 1 Watt Zener.

    That DOES change the output voltage, but I'll need to throw a model for that Zener into my simulator to make sure.

    [eta]
    Couldn't find a model for that particular diode in a short period of time; but the output should now be approximately 25v, give or take some, depending on the load.
     
    Last edited: Aug 28, 2011
  6. Kermit2

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    We all make mistakes, and I seem to make more than my fair share most days.

    :)
     
  7. mbxs3

    Thread Starter Active Member

    Oct 14, 2009
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    Thanks for breaking it down for me guys.

    The output load is a 26vdc relay that is PCB mounted. I don't know the current requirements of the relay.

    I guess that when the signal at power source #2 is high, the output of the circuit is capable of energizing the relay, when the signal at power source #2 goes low, the relay is de-energized.
     
  8. SgtWookie

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    What is the part number of the relay? I could see if it would simulate OK or not, but I'd need to know the resistance of the coil.

    If the relay does not have a built-in diode, or if the diode is burned open, it would take out (fry) the Zener and Q6 rather quickly
     
  9. mbxs3

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    Oct 14, 2009
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    Relay part number is W260-A1A-004L1.
     
  10. SgtWookie

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    Leach Int'l
    Interesting, those are mil-spec parts.
    http://www.leachintl2.com/english/english1/vol0/properties/00028.html
    The coil has 700 Ohms resistance, so ~35.7mA current.

    I'm seeing about 24.5v with that much of a load on it, and it takes an extra second for the voltage to reach that point.

    Note that there is no reverse-EMF suppression diode in these relays. This circuit really needs a reverse-EMF diode added, or Q6 is going to be blasted.

    What's this circuit in? A vintage military aircraft? We used extremely similar relays in F-4 Phantoms.
     
  11. mbxs3

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    Yeah, P-3's.
     
  12. SgtWookie

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    Cool. It's amazing that they're still flying those birds; they were old when I was on active duty.

    I added some more test points so that you can get an idea of the voltages over time. If you need anything else, holler. ;)
     
  13. mbxs3

    Thread Starter Active Member

    Oct 14, 2009
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    Thanks Sgt. They are some oldies. As always, I appreciate the info you provide.
     
  14. SgtWookie

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    You're welcome - anything to keep NAVAIR up there. ;)
     
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