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'[EE] AC to DC Conversion = PIC problem?'
2008\06\17@011344 by Estevan

picon face
I have a strange problem here. I have an AC to DC converter circuit that is powering a PIC16F873A that is connected to a 2x16 LCD. When the unit is connected to the AC line (US 60Hz) the PIC does not begin it's program (LCD has nothing but bars). The +5V regulator has a solid +5V, but as soon as I unplug the AC cord the program begins to run (large filter cap) until the filter cap discharges (LCD displays prompt). Could this be from the 60Hz noise causing problems or ... ? Any ideas, recommendations or "magic" pointers out there?
Thanks ahead of time!


2008\06\17@023608 by Vasile Surducan

face picon face
As long your PIC is really floated (there is no leackage current to
the earth) it must run perfectly even the hot wire of the AC line is
connected directly with any PIC input or PIC supply.
How looks your AC to DC converter ?
SMPS, transformer, capacitor based ?
What means in your language "solid +5V". Have you measured the +5V
ripple with a floated scope ? Maybe is swamp there.


On 6/17/08, Estevan <> wrote:
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> -

2008\06\17@032701 by Picbits Sales

Do you have good decoupling capacitors very close to the PIC ? Try a 100nF
capacitor directly across the PIC power pins.

{Original Message removed}

2008\06\17@035043 by Jinx

face picon face
Do you have a delay on /mclr so that Vcc comes up first ? Might be
that the unplugging of the mains causes a pulse that gets through to
/mclr and that's what starts the program

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