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Help calculating resistance values

Discussion in 'Circuit Simulation & PCB Design' started by Pravin Gosavi, Jul 8, 2017.

  1. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    Doesn't look like it:
    gd.png
     
  2. Pravin Gosavi

    Pravin Gosavi Member

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    Thank you so much for all your efforts!

    I just need to replace Q3 with an optocoupler. I have one with having capacity of 50 mA. Will it do? What do you suggest?
     
  3. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    I1 represents the NPN output of an opto-isolator that can source 5mA. One sinking 12mA could be used to replace q3
     
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  4. dave

    Dave New Member

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  5. Pravin Gosavi

    Pravin Gosavi Member

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    Ok. Thanks a lot.
     
  6. Pravin Gosavi

    Pravin Gosavi Member

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    Hello. There is a problem. The resistors are dissipating a lot of heat when in off mode ( low input). Also optocoupler becomes hot. I am using 817. Is there any way to "shutdown" this circuit in "standby" mode?
     
  7. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    Did you not notice that I labeled R1 and R4 as 1W resistors? If the the opto has the original 5mA flowing through it, then it shouldn't get hot.
    The only way of reducing the standby power consumption is to build a driver with active source and active sink. This one charges/discharges the gate capacitance of the IGBT quite fast, but at the expense of power...
     
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  8. Pravin Gosavi

    Pravin Gosavi Member

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    I used 1W resistors. Can you share .asc file so that I can see if I can increase the values of the resistances.
     
  9. Pravin Gosavi

    Pravin Gosavi Member

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    Hello! Waiting for your reply. ☺
     

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