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PICList Thread
'Power supply regulators'
2005\06\09@074644 by olin piclist

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Rodrigo Real wrote:
> I've been working for some time using the 78XX series as regulators,
> but I was never very satisfied, specially because of the heat
> generation and poor quality of the regulated voltage.
> I am now testing the LM2575/76 series, which seems to performance
> better. It is switched and uses an internal frequency of 50KHz, we can
> see in the output voltage some spikes (the ouput voltage varies in
> +-10%) in this frequency. I reduced the spikes using an
> inductor/capacitor filter, but I could never eliminate it when I
> have load.
> So, my question is, considering that I will power a PIC and some other
> circuits (mostly discrete) should I be worried with those spikes?

Probably not.  Unless you've got a truly horrible circuit, the PIC Vdd
should still stay within the min/max limits for your PIC and oscillator
frequency.  While the PIC will probably run fine, spikes can cause serious
trouble to analog circuitry.  If everything is digital and you're guaranteed
always within 4.75 to 5.25V than you'll be fine.

Lately I've been using a 5.5V switcher followed by an LDO to make clean
5.0V.  The Microchip MCP1700 is a nice LDO for that purpose.  It can deliver
1/4 A if I remember right, and with only 1/2 V drop you can use the tiny
SOT-23 package without running into heat problems.  The output of the
MCP1700 is very clean.

Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014,

2005\06\09@111541 by vasile surducan

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On 6/9/05, Olin Lathrop <> wrote:
{Quote hidden}

 Hi Olin,

 How clean compared with the switcher output (I'm interested only
about the switching ripple component and LDO output ripple using a
pure resistive load, if you measured) ?


> *****************************************************************
> Embed Inc, embedded system specialists in Littleton Massachusetts
> (978) 742-9014,
> --

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