Looking for some advice for my circuit

Discussion in 'The Projects Forum' started by theanih, Jan 25, 2013.

  1. theanih

    Thread Starter New Member

    Oct 3, 2010
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    I attached the circuit in question. My main concern here is about the voltage regulator U1. I build a prototype using 7809 as a substitute for 7815 and 6V relays for S2 and S3.

    The problem here is whenever I connect the voltage regulator with a 24V adapter, something always goes wrong. But when I connect them to a regulated power supply, there is rarely a problem arise. I had capacitor blown up, 7809 blown up, and smoked capacitors. Does anyone know how to find the optimal value for C1 and C2? Or do I need to use a different configuration for the voltage regulator?
     
  2. Audioguru

    New Member

    Dec 20, 2007
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    If you use the parts shown then the circuit should work perfectly.
    But you used a 7809 regulator then you should have reduced the input voltage to about 13V.
    The input is supposed to be DC. Did you use AC?
     
  3. theanih

    Thread Starter New Member

    Oct 3, 2010
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    I used a 24 DC for the input. It was a test run and all I had at the moment is some 7809s. I thought a 7809 would act no differently than a 7815. Well then maybe I should stick with the original configuration. Do you know how to derive an optimal value for C1 and C2 for this circuit? The ones that I used in the circuit isn't derived using a particular formula so I would like to know if there is a formula of some sort to obtain these values.
     
  4. wayneh

    Expert

    Sep 9, 2010
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    That could be your problem. They do act similar but the 7809 has to drop 6 more volts and therefore dissipates a lot more heat. Perhaps too much for it.
     
  5. John P

    AAC Fanatic!

    Oct 14, 2008
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    Your diagram doesn't show pin numbers, but the voltage regulator is marked In-Adj-Out. That's what I'd expect to see for an LM317 adjustable regulator, which has a different pinout from the 78x regulators. Get the pinout wrong, and just about anything could happen! Have you got it installed with In-Gnd-Out on pins 1-2-3?
     
  6. Audioguru

    New Member

    Dec 20, 2007
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    If your input DC voltage is well filtered then your regulator should use capacitor values that are shown on its datasheet. Ceramic capacitors should be used because they are good at high frequencies where an electrolytic capacitor is lousy. Without using high frequency ceramic capacitors then the regulator can oscillate at a high frequency which is bad. The circuit you copied is bad.
    The input capacitor should be 0.33uF and the output capacitor should be 0.1uF.
     
  7. bertus

    Administrator

    Apr 5, 2008
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  8. sheldons

    Active Member

    Oct 26, 2011
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    one other change i would do is add a transistor to drive each relay from your 555 outputs as shown here...
     
  9. Audioguru

    New Member

    Dec 20, 2007
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    D2 does nothing and is not needed.
     
  10. theanih

    Thread Starter New Member

    Oct 3, 2010
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    Okay, thanks for all the suggestions. I will make sure to change them later.
     
  11. theanih

    Thread Starter New Member

    Oct 3, 2010
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    Does this mean I can also delete D4?
     
  12. Audioguru

    New Member

    Dec 20, 2007
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    You are very confusing.
    Your last schematic has a transistor and does not have D4.
    But your first schematic has 555 ICs with no transistors and has D4.
    Why didn't you keep the original identification numbers??

    D2 on your last schematic does nothing and can be removed. But D4 on your first schematic is shown on some datasheets for the 555.
     
  13. theanih

    Thread Starter New Member

    Oct 3, 2010
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    The relay becomes fuzzy when it is switched off without D2 so I might have to hold on to it.

    I am confused.
    What do you mean when you mentioned my last and first schematic? I only attached one schematic.
     
  14. Audioguru

    New Member

    Dec 20, 2007
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    sorry.
    I saw Sheldon's completely different wrong circuit.

    Some datasheets for a 555 use a diode like your D4. Use it.
     
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