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I built a RF circuit powered by a 12v 500mA wall outlet. The RF circuit draws currently around 100mA. I would like use this power supply to also power the microcontroller that will ultimately control this RF circuit (rather than running two different wall warts to the project). Here is my problem...I'm struggling to figure out the proper way of connecting the microcontroller to the circuit, while not pushing too much current through the RF circuit.

I'm using a LM7805 regular to regulate the 12v down to a manageable 5v for the microcontroller. Where do I add this to the circuit without pushing too much current through either the MC or the RF circuit?

Here are some examples of ways i thought would work...

Option 1 enter image description here

Option 2 enter image description here

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  • \$\begingroup\$ How will the microcontroller control the RF circuit? Will it turn it on/off, or something else? \$\endgroup\$
    – FMarazzi
    Commented Jan 12, 2016 at 15:36
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    \$\begingroup\$ In parallel (your option #1) not in series (your option #2). In the latter case the voltage across the '12V' circuit would be no more than about 6V if the microcontroller was getting 5V and there would be no guarantee of that. You waste power in the 7805 depending on the microcontroller power- if it's more than 100mA or so you might want to consider a switching regulator. \$\endgroup\$
    – Spehro 'speff' Pefhany
    Commented Jan 12, 2016 at 15:52

2 Answers 2

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I would suggest option 1.

Why not Option 2: If you connect as per option 2, the current flow throught the 12V circuit PCB's track will be more.

Why option 1: µC Board is directly fed from 12V. And it wont disturbed by RF circuit

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  • \$\begingroup\$ i am unable to find the reason behing why its downvoted !! \$\endgroup\$
    – Photon001
    Commented Jan 13, 2016 at 3:25
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Option 1 will have two different current paths for the microcontroller and the 12V circuit, so it will work fine.

I honestly don't understand Option 2: the 12v circuit doesn't have a GND? What's coming out of it that you connected to the 12v IN?

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  • \$\begingroup\$ It shoulld have ground,Prrobably he might missed to add gnd line in drawing. \$\endgroup\$
    – Photon001
    Commented Jan 12, 2016 at 15:54

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