circuit protection schematic design (OrCAD)

Discussion in 'General Electronics Chat' started by Skyland, Jul 21, 2014.

  1. Skyland

    Thread Starter New Member

    Jul 1, 2014
    28
    0
    I have designed a protection circuit for my pcb and I would appreciate having some feedback before starting the PCB design.

    The circuit is broken down as follow;

    -ESD protection provided by a one channel IC

    -low pass filter to suppress noise above 4.5Khz

    -pmos to protect against reverse polarity

    -crowbar for overvoltage protection

    -current sensor which is connected to a uC ( ideally I would like the op amp to work with the PSU IN in the range 3.3v to 16v)

    The maximum voltage is 16V and the minimum votlage is 3.3V.
     
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,804
    1,105
    R8 shorts out the V4 supply.
     
  3. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,999
    745
    R8 is across the 3V supply, connect the op amp similar to this sense circuit where R1 is your R8
     
  4. shakilabanu

    Member

    Jul 8, 2014
    44
    2
    If you have the possibility you should either replace the output Opamp to a rail-to-rail opamp or increase the power supply voltage to the Opamp, because with a OP471 and a single 5V supply you have very little useful range to work with.

    Having said that it depends on the current, sense resistor and the gain you want...etc
     
  5. shakilabanu

    Member

    Jul 8, 2014
    44
    2
    Also if you are going to operating at 3.3V to 16V, you might want to consider a logic level FET...not sure the one you have is a logic level FET, going by the drop across the FET.
     
  6. RichardO

    Well-Known Member

    May 4, 2013
    1,238
    384
    Although Q2 protects most of the circuit from reverse voltages, it does not prevent negative voltages on C3 and C5. Remember to make sure that C3 and C5 are non-polarized caps such as X5R or X7R ceramic.
     
  7. Skyland

    Thread Starter New Member

    Jul 1, 2014
    28
    0
    The current monitored is in the range of 0 - 1A . ADC is from 0 - 3.3V

    The actual models used have been implemented in the schematic for clarity.

    The supply voltage range is from 3.3V to 16V

    The low pass filter has been replaced by a ferrite bead

    Differential Op amp is used for current monitoring with 165K for R load to provide the adequate gain (0 to 3.3V input to the ADC).
     
  8. RichardO

    Well-Known Member

    May 4, 2013
    1,238
    384
    When you replaced the inductor and caps with the bead you removed all power supply bypassing. You need to add a 0.1 uF ceramic cap from the Vin+ pin of U1 to ground. I would also add a larger capacitor such as a 4.7 uf in parallel with the 0.1 uF to help remove large power supply transients.
     
    Skyland likes this.
Loading...