[SI-LIST] Re: LDO power supply vs DC-DC switching supply
- From: Rick Collins <gnuarm.2006@xxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Fri, 02 Aug 2013 12:55:15 -0400
LDO (or more correctly, linear) regulators act as high pass filters
with a lower pass frequency around the 100 kHz ballpark The noise
rejection not too far above 100 kHz can approach just -10 dB. Some
units have poor line regulation in the higher end of the audio
region. Switching regulators have most of their noise at high
frequencies. "High" depends on the unit with some switching around
50 kHz up to several MHz. There is a lot of harmonic content at
frequencies higher than the switching rate and there can be some
content at lower frequencies if the units "hunt" or "motorboat" as
they regulate (this is not generally considered correct operation,
but is sometimes tolerated).
To damn switching regulators because they emit noise can be overly
broad depending on your application. If you are designing an HF
radio receiver, then you likely don't want any switchers you don't
have to have. For many other applications swtichers will work just
fine if you pay careful attention to the details of noise
mitigation. It mostly depends on the frequency range your design is
sensitive to. Switchers are normally used when the power dissipation
of a linear regulator would be too high.
Rick
At 12:32 PM 8/2/2013, steve weir wrote:
>In general the answer is yes. A switching power supply in very
>simplistic terms: the switching superimposes a carrier on top of the
>normal regulator output that then requires filtering to remove. Hard
>switching converters are simple and cheap, and tend to be the worst
>offenders. However, there are switchers that are very quiet whether by
>brute force filtering and/or that use soft switching. It shouldn't be
>surprising to learn that the latter cost more money.
>
>Steve
>On 8/2/2013 8:50 AM, Faraydon Pakbaz wrote:
> > Greetings SI experts;
> >
> > Is LDO (Low drop out) power supply, less nosier than DC-DC switching power
> > supply type?
> > Are there application trade-offs between these two types of supply? Thanks
> > in advance for
> > your advise and comments.
> >
> > Regards;
> >
> > Don Pakbaz
> >
> >
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>--
>Steve Weir
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