The circuit shown above is of a practical LDO regulator circuit using IC LM2941 from National semiconductors. LM2941 is an integrated LDO voltage regulator IC whose output can be adjusted. The IC has many good features like thermal shutdown, transient protection, short circuit protection etc. The reverse polarity protection feature makes this IC very applicable in automotive applications. The output voltage can be adjusted from 5V to 20V and the dropout voltage is 0.5V at 1A output current.
In the circuit the voltage divider network comprising of R1 and R2 sets the output voltage. Capacitor C2 is the input filter which is very essential if the regulator circuitry is situated away from the rectifier+filter module. Capacitor C1 is the output filter while S1 is the ON/OFF switch. Resistor R3 is used to ensure the necessary 300mA pull up current which is necessary for proper shutdown when the switch S1 is made open.
Notes.
The circuit must be assembled on a good quality PCB.
A heat sink is required for application above few hundred milli amps.
Vout = 1.275 ((R1 + R2)/R1)
During calculation select R1=1K and solve for R2.
Selecting R1 = 1K will make the input bias current error of the adj pin negligible.
Reducing the value of C1 below 22uF will induce instabilities and also this capacitor must be placed as close as possible to the IC on the PCB.
Read more: http://www.circuitstoday.com/ldo-regulator#ixzz1PYuKlUfp
