Supply isolation cct

Discussion in 'General Electronics Chat' started by Dritech, Nov 27, 2013.

  1. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
    756
    5
    Hi all,

    I did the attached schematic to isolate the circuit supply (5V) from the motor supply (12V). This is to eliminate any noise of ground voltage leak from interfering with voltage reference points and ADCs.

    Basically the circuit works like this:

    The 12V supply is connected directly to the H-bridge (BTS7960). Since the H-bridge use a common ground (internally in the IC) for the power and the logic, a DC/DC converter isolator (DCR010505P) is used. This way if noise in the ground line is present, it will not effect the voltage references since it is totally isolated. To operate the H-bridge a 5V signal is sent to the opto isolator.

    Will this circuit work? Is it designed well?
    Any help will be appreciated before I buy any components and start implementing the circuit.

    Thanks in advance.
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,532
    2,369
    If the ground plane is design properly you do not have to isolate one circuit from the other.
    Also noise can be transferred both inductively and capacitively from one circuit to the other.
    Max.
     
  3. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,797
    1,103
    I don't see how Q1 can drive the opamp unless they share a common reference point (ground). If you are concerned about high currents causing ground line bounce, then can't you just use a star-ground system with a single earthing point for the control signal ground and power ground lines? Is the converter even necessary?
     
  4. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
    756
    5
    Hi, Q1 and the NOT gate will share the same ground. The convertor/isolator is used to isolate the PIC and other ICs ground from the motor power ground.

    So the schematic is not practical?
     
  5. zeppelinator

    New Member

    Nov 25, 2013
    4
    1
  6. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
    756
    5
    Hi again, I came across the below paragraph in the datasheet so I decided to eliminate all the external components:

    I have another question regarding the slew rate. Quoting from the datasheet:

    Since I will be using PWM to control the motor, shell I keep the slew rate as low as possible?
     
  7. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,797
    1,103
    If the slew rate is lower, RF emission is lower but the MOSFETs run hotter.
     
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