LDO vs Buck converter

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Hi friends!!


we all know about buck converter as well as LDO.....is there any specific reason???in any circuit we have to use buck instead of LDO and vice versa...i want to know..where we are using LDO??? where we are using buck converters?? is there any criteria for using both?


if anyone knows please reply me as soon as possible.thank u......

 

[shaiko]

Buck is a switching regulator - it'll be much more efficient (80% and up...)
LDO is a linear regulator - the efficiency depends on the actual load but it's much lower than Bucks.

LDOs are "quiter" (very low ripple) than switching regulators - therefore they tend to be used in applications that require that - FPGA core voltage supply for example. LDOs are also simpler in design making them cheaper devices - and somewhat more reliable when the power is low...

Because of the low efficiency, LDO's are almost never used in high power applications - the generated heat becomes impractical to dissipate - dictating the use of switching regulators.
There're Buck regulators with VERY high efficiencies (~95%).

 

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thank you for your reply.........if we connect heavy load i.e,500mA instead of 100mA to LDO what will happen? is it manage???how can manage?

 

[jmsattard]

You have to check the datasheet of your LDO if it can handle 500mA. Altough if you are going to pass 500mA it is better to have the regulator rated for a bit more. Also you have to see what the power loss in your regulator will be. LDO will have a voltage drop across then multiplied by the current will give power lost in the regulator. This power loss is turned into heat. If the LDO package isn't suited for good heat dissipation then you may have to add a heatsink.

 

[shaiko]

You can find an LDO that can manage 500mA with no problem - you'll still have to dissipate the heat though...
Just choosing an LDO that is 500mA capable isn't enough.

What is the input voltage to your system?

 

[dick_freebird]

Divide Vout/Vin and if it's > 85%, select a LDO and
call it a day. LDOs have simplicity and (lack of) noise
and low BOM cost on their side. Beware also the nuances
of the efficiency vs load curves, and the "use model"
profile of current, because even a 90% efficient buck
can look more like 50% at low load (you need Iload
to be > 9X I(noLoad) to hit that 90%-ish number as
you come up from the low end).

 

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thanks for your help...i want to know what is the process going on inside the LDO when i connect a load with 500mA instead of 100mA...operation of LDO if load varies....is it clear??? how the voltage is stable eventhough i vary the load??? what is happening.....

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[dick_freebird]

It's just feedback nulling against a reference voltage.
Same process as a buck converter, there. Difference
is in whether you modulate output conductance in a
dissipative element (pass device) or whether you
modulate duty cycle and then filter it to DC with
reactive components (lossless, ideally; minor loss,
practically).