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bridge rectifier circuit

Discussion in 'General Electronics Discussion' started by Surjitsinh, Jan 1, 2015.

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  1. Surjitsinh

    Surjitsinh

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    Jan 1, 2015
    I am Trying to design a simple bridge rectifier on Breadboard by connecting negative of source to ground but when i connect Node 1 to 4 Channel Oscilloscope +ve pin with -ve pin GND , i get Half wave , but when i connect +ve pin to Node 1 and -ve pin to Node 2 i get same half wave at output and Input also becomes half wave how to solve this issue please help ??
     

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  2. Laplace

    Laplace

    1,252
    184
    Apr 4, 2010
    Do not ground the AC input, leave it floating. Instead ground Node 1 or Node 2, depending on whether you want positive or negative DC voltage with respect to ground.
     
  3. hevans1944

    hevans1944 Hop - AC8NS

    4,595
    2,149
    Jun 21, 2012
    It looks like your 4 Channel Oscilloscope +ve pin and -ve pin are not true differential inputs. Probably the -ve pin is chassis common and also in common with the "ground" side of V1. You will obtain full-wave rectification between Node 1 and Node 2, but not referenced to "ground". You should "float" the V1 "ground" and its connection between diodes D2 and D3. Then "ground" Node 2 to obtain positive full-wave rectification between Node 1 and the now "grounded" Node 2.

    You didn't specify what the source of V1 is. If it is an audio signal generator then it is likely that the "ground" terminal is internally connected to its chassis. In any case, V1 should be a "floating" source if you need full-wave rectification between Node 1 and Node 2. You can then "ground" either Node 2, for positive output on Node 1 with respect to "ground," or "ground" Node 1 for negative output on Node 2 with respect to "ground." In either case it is important that V1 be a floating source.

    If V1 is a single-ended output that cannot be "floated," you can add a unity-gain inverter to its output to drive and replace the "ground" connection between diode D2 and D3. Ordinarily I would suggest connecting V1 to a small audio transformer with a 1:1 turns ratio to provide an isolated signal to drive the bridge, but 100 Hz may be problematically too low a frequency for an inexpensive transformer. Depending on how much power you want to draw from the bridge, a simple unity-gain op-amp inverter is easier and less expensive than a transformer.

    Why don't you tell us what you are trying to accomplish? Is this a learning experience, or part of a larger project? Where are you obtaining the 100 Hz sine wave? What is the amplitude of V1? How much current will be sourced from V1? What kind of load will be presented across Node 1 to Node 2?
     
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  4. Surjitsinh

    Surjitsinh

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    Jan 1, 2015
    @Laplace : Thank you for your answer , I am using a function generator so i connect -ve to common . But its not working i am doing the same . Yellow signal is output , blue is input
     

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    Last edited: Jan 1, 2015
  5. hevans1944

    hevans1944 Hop - AC8NS

    4,595
    2,149
    Jun 21, 2012
    Is the energy harvester a magnet that moves back and forth within a coil of insulated wire? If so, you should be able to float the two terminals, Connect them to the junction of D1 and D4 and to the junction of D2 and D3. Then "ground" if necessary either Node 1 for negative output from Node 2 with respect to "ground," or "ground" Node 2 for positive output from Node 1 with respect to "ground". Either way, your 'scope should show full-wave rectification with respect to "ground".

    Note: you cannot measure a "floating" input signal without a differential input to your oscilloscope. Sometimes this can be accomplished by using two channels on the oscilloscope. You apply one of the two floating signal wires from your energy harvesting device to each channel. Set one channel to invert its signal, then subtract the two channels. There must be a "ground" return from the energy harvester source for the two channels, easily synthesized by connecting, say, 100 kΩ resistors to each energy harvester output and then connecting the junction of these two resistors to your circuit "ground". The actual value of these two "virtual ground" resistors is not critical, but their series combination does place an additional load on the energy harvester, so use as large a value as practical, depending on the input impedance of the oscilloscope. This input impedance is typically one megohm shunted by a few picofarads of capacitance. The resistors for the "virtual ground" should be about one tenth of this value or less.

    Actually, if you connect the two resistors as described above to create a "virtual ground," you don't need to have the channel differencing method to monitor the output of the energy harvesting device. You can use either channel on the oscilloscope to monitor half of the output.
     
    Last edited: Jan 1, 2015
    Surjitsinh likes this.
  6. Surjitsinh

    Surjitsinh

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    Jan 1, 2015
    Thank you ...since i want to try rectification with function generator first i am facing problem , see yello is output at node 1 and when i connect ground of Oscilloscope to Node 2 , input sine wave ( blue signal ) is also getting affected !!

    I will now try series resistor method explained by you ..
     

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  7. Surjitsinh

    Surjitsinh

    17
    0
    Jan 1, 2015
    You mean like this setting up virtual ground .
     

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  8. Surjitsinh

    Surjitsinh

    17
    0
    Jan 1, 2015


    Thank you sir , i understood the problem , issue was with Oscilloscope ground , and it can be solved with differential measurement .
     
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