Battery Vs Direct Power Issue

Discussion in 'Wireless & RF Design' started by saikumar.elab, Jan 6, 2018.

  1. saikumar.elab

    Thread Starter New Member

    Jan 6, 2018
    Thanks for the solution dendad. Let me try this LM2596 instead LM1117 since LM2596 has low switching frequency. i'll try that and let you know. meanwhile i need some knowledge on adding decoupling capacitors and ferrite beads.

    how to choose the ferrite bead for this module and where the decoupling capacitors has to be added in the circuit. it could be helpful, if you guide me on this.

  2. saikumar.elab

    Thread Starter New Member

    Jan 6, 2018
    Hi bug,

    Thanks for your reply. I just need your guidance in adding the decoupling caps on board.

  3. bug13

    Senior Member

    Feb 13, 2012
    For the MCU, just add some 100n caps for every pair of VCC and GND, as close to the chip as possible, generally within 2mm.

    If you are using ADC, do this:
    Page 313, Datasheet is your friend:

    For the RF module, you need to actually confirm your power source (battery) can not supply enough current is the problem, before trying to fix it.
    • Have you confirmed this is the cause of your problem yet?
    • What battery are you using? Mainly what chemistry of your battery?
  4. BobaMosfet

    Senior Member

    Jul 1, 2009
    Just going off of your original statement above, this is really simple.

    An LM1117 (5VDC version) requires at least 6.2VDC input at 1A in order for it to be able to output 5VDC @ up to 800mA (max). The only way you can power your PCB with an external power-supply (PSU) at 5VDC @ 1A, is if you bypass (go around) the LM1117.

    If you power the LM1117 via a 7.4VDC 3.xAh battery, the LM1117 still limits you to 800mA on the output.

    This is why it's failing.

    Powering directly with a 5VDC @ 1A PSU is giving your tranceiver enough juice. The battery isn't because the regulator only puts out 800mA, which apparently is not enough for your tranceiver.

    Why don't you put an ammeter on the output of your PSU into your tranceiver and find out how much current it actually takes, and then choose an appropriate regulator (like an LM7805), which can deliver 1-1.5A.
  5. Safdar khan

    New Member

    The main things is that's your Rf module tuned at 5volt, if you change RF module power supply voltage, your RF module tuned to another frequency, RF Module is still working but it's frequency you don't find it. If you want to run RF Module to 7.4 volt, you tell it's frequency and working purpose. I will help you.
  6. dendad

    Active Member

    Feb 20, 2016
    The RF module frequency will not be affected by the voltage. It will be crystal locked. Otherwise if would be largely unusable.