[EE]: Power supply regulators

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[EE]: Power supply regulators

Rodrigo Real

Hi guys

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? I am
worried if the pic could get lost, or something like it. I also
control another board, which is a power system for a dc motor, and it
has a different power supply.

Do you have any other suggestions of regulators?

Best regards,
Rodrigo
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Re: : Power supply regulators

vasile surducan
Linear: LM2940 LDO

About switching, if you coud minimize the spikes less than 30mV,
consider yourself a happy man.

best,
guy Vasile

On 6/9/05, Rodrigo Real <[hidden email]> wrote:

>
> Hi guys
>
> 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? I am
> worried if the pic could get lost, or something like it. I also
> control another board, which is a power system for a dc motor, and it
> has a different power supply.
>
> Do you have any other suggestions of regulators?
>
> Best regards,
> Rodrigo
> --
> http://www.piclist.com PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
>

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Re: Power supply regulators

Olin Lathrop
In reply to this post by Rodrigo Real
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.


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(978) 742-9014, http://www.embedinc.com
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Re: Power supply regulators

vasile surducan
On 6/9/05, Olin Lathrop <[hidden email]> wrote:

> 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.

  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) ?

thx,
Vasile


>
>
> *****************************************************************
> Embed Inc, embedded system specialists in Littleton Massachusetts
> (978) 742-9014, http://www.embedinc.com
> --
> http://www.piclist.com PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
>

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