[SI-LIST] Re: LDO power supply vs DC-DC switching supply
- From: Rajesh Kumar <msrajesheee@xxxxxxxxx>
- To: pakbazf@xxxxxxxxxx
- Date: Sat, 3 Aug 2013 00:06:28 +0530
Hi Don,
Right, LDO's Dissipates power as heat Iout equals Iin (assuming very low
bias current) but switching regulator output current follows the efficiency
curve, efficiency = Pout/ Pin . In switching regulators VOUT/VIN ratio
decides the output current. LDO's are preferable only when VIN is twice
VOUT, above this limit efficiency is poor and heat is high.
Thanks,
Rajesh
On Fri, Aug 2, 2013 at 11:20 PM, Faraydon Pakbaz <pakbazf@xxxxxxxxxx> wrote:
> Hi Rick;
>
> First many thanks for taking time and explaining the difference. It seems
> the trade-off comes down to
> power consumption and heat. Do I get that correctly?
> For example if one try to route crystal Oscillator at the board level with
> number of buffering stages
> and branches at the board level and use LDO then it is possible that excess
> heat, efficiency maybe
> an issue?!
>
> Regards;
>
> Don Pakbaz
>
>
>
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> |Rick Collins <gnuarm.2006@xxxxxxxxx>
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> |08/02/2013 01:10 PM
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> | Subject: |
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> |[SI-LIST] Re: LDO power supply vs DC-DC switching supply
> |
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> | Sent by: |
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>
>
>
>
> 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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