Part of voltage divider?

Discussion in 'General Electronics Chat' started by WineJ, Aug 23, 2015.

  1. WineJ

    Thread Starter New Member

    Aug 23, 2015
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    Can someone explain to me what is the purpose of R8 resistor? While R1 and R2 (in yellow) form a voltage divider to furnish voltage to the pot on the bottom, I cannot figure out, what R8 does. It is connected between the ground bus (in green) and the positive side of rectifier (in red).
    It cannot be part of divider, but having it connected in parallel with a rectifier also doesn't make sense to me.
    Any ideas.
    The pot provide voltage for voltage controlling section, by the way.
     
  2. tcmtech

    Well-Known Member

    Nov 4, 2013
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    It's the bleed off resistor for the main power capacitor.
     
  3. MaxHeadRoom

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    Jul 18, 2013
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    I have seen it often used in circuits that don't really need it, If the DC power is disconnected at power off then it can be implemented for safety reasons, but if there is circuitry still connected to the bridge, it will often bleed off this way.
    i.e. the AC power-in switched for e.g.
    Max.
     
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  4. MikeML

    AAC Fanatic!

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    It is impossible to tell without seeing the rest of the schematic.
     
  5. #12

    Expert

    Nov 30, 2010
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    The size of the filter capacitors seems to be very important.

    "Anybody that designs a product containing large storage or filter capacitors that doesn't provide "bleeder" resistor(s) to discharge the capacitors when the device is turned off is an idiot, and should be sued for gross negligence...."
     
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  6. MaxHeadRoom

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    Who is quoted there, Einstein?:)
    Max.
     
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  7. MaxHeadRoom

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    Unless the load is rather large, I would expect the capacitor value to be fairly trivial in the posted .png as it is full wave 3phase rectifier so the ripple will be 360hz and <5%.
    Max.
     
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  8. WineJ

    Thread Starter New Member

    Aug 23, 2015
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  9. WineJ

    Thread Starter New Member

    Aug 23, 2015
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    I believe both C1 and C4 are filter capacitors. C4 connected between ground bus and Point 3 (which is positive side of +28 VDC bus for transistors and IC1, IC2. + 28 comes via those two relay contacts on top right of the sketch). And C1 filters out AC component from the cable-drop section, I think.

    The second post says: :It's the bleed off resistor for the main power capacitor"?
     
    Last edited: Aug 23, 2015
  10. #12

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    Pretty close. It was MikeML.
     
  11. tracecom

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    Did Max call you Einstein?
     
  12. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Not even...
     
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