low drop out regulator

[aman]

When I am looking at voltage regulator I come across a term "low drop
out regulator". Can somebody tell me how it is different from a "linear
voltage regulator".

 

[John Fields]

On 28 Feb 2005 14:27:28 -0800, "aman" <aman.bindra@gmail.com> wrote:

When I am looking at voltage regulator I come across a term "low drop
out regulator". Can somebody tell me how it is different from a "linear
voltage regulator".

---
It _is_ a linear voltage regulator, the difference being that an "LDO"
regulator uses a PNP or a PNP-like pass transistor in order to
minimize the input-to output differential with low input voltages.

--
John Fields

 

[aman]

That answers my question. Thanks John.


John Fields wrote:

On 28 Feb 2005 14:27:28 -0800, "aman" <aman.bindra@gmail.com> wrote:

When I am looking at voltage regulator I come across a term "low
drop
out regulator". Can somebody tell me how it is different from a
"linear
voltage regulator".

---
It _is_ a linear voltage regulator, the difference being that an
"LDO"
regulator uses a PNP or a PNP-like pass transistor in order to
minimize the input-to output differential with low input voltages.

--
John Fields

 

[Peter Bennett]

On 28 Feb 2005 14:27:28 -0800, "aman" <aman.bindra@gmail.com> wrote:

When I am looking at voltage regulator I come across a term "low drop
out regulator". Can somebody tell me how it is different from a "linear
voltage regulator".

With "normal" three-terminal voltage regulators, you need the input
voltage to be 2 volts or more above the regulated voltage - otherwise
the regulator doesn't have room to work correctly, and the output
voltage will drop.

A low dropout regulator will continue to operate with as little as 0.5
volts (or so) difference between input and output.


--
Peter Bennett VE7CEI
email: peterbb4 (at) interchange.ubc.ca
GPS and NMEA info and programs: http://vancouver-webpages.com/peter/index.html
Newsgroup new user info: http://vancouver-webpages.com/nnq

 

[John Popelish]

aman wrote:

When I am looking at voltage regulator I come across a term "low drop
out regulator". Can somebody tell me how it is different from a "linear
voltage regulator".

Low drop out regulators are a variant of linear regulators. Most
linears are based on an emitter follower output stage, and usually an
emitter follower driving a bigger emitter follower. This implies a
significant voltage across the regulator to make it function (usually
1.5 to 2 volts). If the pass transistor is connected as a common
emitter (output on the collector) the device may operate below one
diode drop (less than .6 volts) across the regulator. This
configuration is harder to stabilize against oscillations under varied
conditions than the emitter follower configuration is. The base
current for the pass transistor must also go through the reference pin
of the regulator, which makes the current in that pin related to the
load current. The follower configuration has a more stable reference
pin current, making it easier to connect that kind of regulator in an
adjustable output voltage arrangement.

--
John Popelish