Explain this section.....

Discussion in 'General Electronics Chat' started by onlyvinod56, Nov 25, 2010.

  1. onlyvinod56

    Thread Starter Active Member

    Oct 14, 2008
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    Hello,
    Im attaching a 150W inverter ckt. Check it. Explain, how the overload section works.
     
  2. GetDeviceInfo

    Senior Member

    Jun 7, 2009
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    I'm guessing that the feedback amp IC9, negates the current source T3, and causes missing pulses out the IC7 flip flop.
     
  3. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Part of it is a comparator measuring input current across R20, a sense resistor of 0.001Ω pretty much in the center of the schematic. R20 is probably a wide trace on the circuit board, or a something that looks like a thick wire jumper.
     
  4. onlyvinod56

    Thread Starter Active Member

    Oct 14, 2008
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    If it is a comparator, see, the inverting terminal is grounded. and the non-inverting is connected to your so called sense resistor. The R20 is placed in the DC side of the transformer (12V side). So, the current passing through it and hence the voltage across it will be a DC.

    If this type of constant DC is given to a comp..., whose inverting is grounded, the output will be always high. Am i correct? So, how it is protecting from overloads.??
     
  5. GetDeviceInfo

    Senior Member

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    R20 is indeed a sense resistor. The transformer mirrors current in the secondary via the primary, be it at some ratio.
     
  6. onlyvinod56

    Thread Starter Active Member

    Oct 14, 2008
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    ok. but how the opamp decides the over load situation???
     
  7. GetDeviceInfo

    Senior Member

    Jun 7, 2009
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    well, when the T3 / IC9 combination make or break the logic levels of IC7, then I would say you do in fact have a comparator of sorts, going back to what thatoneguy suggested.
     
  8. onlyvinod56

    Thread Starter Active Member

    Oct 14, 2008
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    Same question in detail....

    see the schematic... a voltage waveform is shown. V1 be the voltage across the Rsense (=0.001) for safe limit of the battery current. And V2 be the overload situation.

    What will be the signal at output? See the second schematic...
     
    Last edited: Nov 26, 2010
  9. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Looking at it again, it appears that the TL081 is being run as an op amp rather than a comparator, I missed the feedback.

    So the output of the TL081 is a voltage that increases with the current increase. The actual overload action appears to happen with the 4013-II flip flop. Once the voltage on the output of the comparator is at what the FF considers "Logic High", it will shut down the inverter by !Q going low on the input of 4093-I schmitt trigger AND gate, closing the path from the oscillator to the output MOSFETs.
     
    Last edited: Nov 26, 2010
  10. onlyvinod56

    Thread Starter Active Member

    Oct 14, 2008
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    ThanQ thatoneguy. Thats what i want. one morething.
    in the same schematic, what if the R33 (0.1 ohm, 17w) is removed....???? Assume that the 6v winding of the transformer withstand for the load current..
     
  11. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    If R33, a 0.1Ω current sense resistor is missing, the automatic enable will not work.

    The schematic indicates this is an optional add on/upgrade. The detection for load circuit is the entire lower right side of schematic. If the resistor is missing, the manual override switch on the lower middle right edge of schematic would be needed to trigger the relay and start the inverter. As it is, it is labeled to automatically start when a device draws more than ~50mA (10VA) is drawn from the outlet.

    The auto turn on feature allows an extension cord to be used with the inverter, and it won't draw full current from the battery until a device is plugged in and turned on. This allows the inverter to be placed where better airflow or cooling is available, usually losing the ability to easily physically turn it on or off.
     
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