Opto-Coupler Idea ?

Discussion in 'Embedded Systems and Microcontrollers' started by Chef, Aug 22, 2013.

  1. Chef

    Thread Starter New Member

    Jun 20, 2013
    9
    0
    I had used the PWM outputs of micro to connect with AND Gates and another input of AND Gates for all are the same, which is apply manually. These 6 PWM signal use to drive 2 level, 3 phase inverter. The AND gates are always collapsed.:mad: I think that inside the IGBT drives might not have a separated signal part as Opto coupler. Moreover, the DC link - and the GND of Digital are the same. However, the using DC link voltage for IGBT is just 30 V.


    1. Is it the correct reason because without separated GND?

    2. If I am going to add the opto-coupler circuit, could you please recommend the opto coupler number? The voltage input and output must be 5 V the same for the logic gate.

    I prefer to have DIP package, which is easy to do the PCB.
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,515
    2,369
    There should be no reason why you cannot use the Opto for just Voltage transition rather that total isolation, (separate commons).
    Opto's are not usually rated for a certain voltage as you tailor the LED and Output current with suitable resistor accord to the respective supplies either side of the Opto.
    The 4N35 may suit if fast enough for you?
    HCPL4503M alternative.
    Max.
     
    Last edited: Aug 22, 2013
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  3. Papabravo

    Expert

    Feb 24, 2006
    10,137
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    Several parts of your post make absolutely no sense at all to me.

    The AND gates are always collapsed. Does this mean that the gates are failing. If that is the case you should try to identify the root cause. Speculating that opto isolators will solve your problem is unwise.

    I think that inside the IGBT drives might not have a separated signal part as Opto coupler. This is a meaningless statement as written.

    Moreover, the DC link - and the GND of Digital are the same. However, the using DC link voltage for IGBT is just 30 V.So what!!??

    We really need a schematic diagram to help us understand the problem.
     
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  4. Chef

    Thread Starter New Member

    Jun 20, 2013
    9
    0
    3 microsec, it is not fast for my application. Would you please give me other numbers?
     
  5. Chef

    Thread Starter New Member

    Jun 20, 2013
    9
    0
    - I meant that the gates are broken, do not work anymore e.g. have an offset value as output.

    - For all schematic, I do not have at the moment. I just draw it roughly as attached. All inputs for AND gates are from the micro-controller. The IGBT part needs +5V and +15V as inputs. The DC Link Voltage is provided by an external DC power supply directly. Using big C to charge for the system, while driving.

    hopefully, this information will help.
     
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    Last edited: Aug 22, 2013
  6. Papabravo

    Expert

    Feb 24, 2006
    10,137
    1,786
    I'm sorry you don't have the capability to draw a complete schematic. It is difficult to impossible to identify the source of your problem from the information that you have provided.

    When you say the AND gates have an offset value, what does this mean? Is it a constant value between Vcc and GND that you can see with an oscilloscope, or is it a value that you measured with a DC multimeter, that is oscillating between VCC and GND with a duty cycle that averages to the "offset value"? If the input to one of your gates is not connected to a driving source it will oscillate, at a frequency inversely proportional to the delay time of the gate.
     
    Last edited: Aug 23, 2013
  7. techristian

    New Member

    Aug 27, 2013
    26
    2
    I'm using the 4N28 for my purposes. They work and are cheap.

    Dan
     
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