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Connecting Linear Regulators

Brian Cavanagh
Intellectual 285 points
Other Parts Discussed in Thread: LP38692

Hi All,

I have a 24VDC input  to my design.  I have one12VDC Linear Regulator to power two 5VDC Linear Regulators.

I'm not certain if I should have any filtering from the 12VDC output and the input to the  5VDC regulators.  I understand capacitors are important, but what about inductors?

Equally important, I have a reverse protection diode at the 24V input.  I do gave a connector on the output of the 5VDC regulator that I can connect to external devices.  Should I have a reverse protection diode on that as well?

Thanks,

B

  • 0
    TI__Guru 55940 points
    Hi Brian,

    The level of filtering and required and reverse current protection requirements are both application specific and specific to the LDO used. In order to better address your question, could you please provide the LDO's part number and a schematic (partial schematic is fine)?

    Very Respectfully,
    Ryan
  • 0 in reply to Ryan Eslinger
    Intellectual 285 points

    Hi Ryan, thanks for responding.  I will use the LM7805 to power the LP38692MP-3.3 linear regulator.   I'm more accustomed to using Flyback topologies however this design will only use linear regulators.  Customers choice.  Thanks, Brian

  • 0 in reply to Brian Cavanagh
    TI__Expert 3920 points
    Hi Brian,
    The LM7805 should not need an output capacitor to be stable since its pass transistor is in the darlington configuration. An output capacitor will help in reducing the amplitude of the output voltage dip during load transients.

    Placing an inductor in between the regulators might cause oscillations due to the tank circuit you will create with the capacitors, so I would not recommend this.

    If you have a diode at the input, then it will block current from flowing backwards, but only at that point. If for example, you have a large cap at the output of the second regulator, then nothing will stop current from flowing from the load and back into that output cap unless you have a diode at the output. So the choice of placing a diode at the output will depend on your load requirement.

    I am not familiar enough with the LP38692, but hope these comments help.

    Tim