Basic Adjustable Regulator
VOUT = VREF * ( 1 + R2/R1) + IADJ * R2
Basic Fixed Regulator
Fig.2 Basic Adjustable Regulator
Consider Figure 2. The resistance R1 generates a constant
current flow, normally the specified load current of 10mA.
This current will go through the resistance R2 to set the
overall output voltage. The current IADJ is very small and
constant. Therefore its contribution to the overall output
voltage is very small and can generally be ignored.
Parasitic line resistance can degrade load regulation. In order
not to affect the behavior of the regulator, it is best to connect
directly the R1 resistance from the resistor divider to the case,
and not to the load. For the same reason, it is best to connect
the resistor R2 to the Negative side of the load.
The fixed voltage LDO voltage regulators are simple to use
regulators since the VOUT is preset to the specifications. It is
important however, to provide the proper output capacitance
for stability and improvement. For most operating conditions
a capacitance of 22uF tantalum or 100uF electrolytic will
ensure stability and prevent oscillation.
RP Parasitic Line
Connect R1 to
Case of Regulator
Connect R2to Load
Fig.3 Basic Adjustable Regulator
Alpha Semiconductor Inc. 1031Serpentine Lane. Pleasanton, CA 94566 Tel: (925) 417-1391 Fax: (925) 417-1390
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