DC Power Supply 11

Regulator Transistor
In the simplest case emitter follower is used, the base of the control transistor is directly related to the reference voltage:

 
Stabilizer uses the power source, having voltage UIN may vary from time to time. It delivers Uout voltage constant. Output load RL can also vary from time to time. For such a device to work properly, the input voltage must be greater than the output voltage and voltage drop must not exceed the limit of transistor used.
Stabilizer output voltage is equal to the UZ - Ube Ube which is about 0.7 V and depends on the load current. If the output voltage drops below the limit, this increases the voltage difference between the base and emitter (Ube), opening the transistor and delivering more current. Delivering more current through the same output resistor RL increase voltage again. When the output voltage increases, because the base-emitter voltage is reduced BJT will run less and regulations will be maintained.

Rv values ​​limit the maximum output current Iout, which have upper limits. Rv (a rough estimate) should not be greater than (UIN - UZ) / IB, where IB is the maximum Iout current ratio dividing the transistor amplification.
 
Regulator with operational amplifier
 
Stability of the output voltage can be increased significantly by using operational amplifiers:

 
In this case, the operational amplifier drives the transistor with more current if the voltage at the inverting input drops below the output voltage at the input reference is not inverted. Using a voltage divider (R1, R2 and R3) allows choice of arbitrary output voltage between Uz and UIN.  

LM317

Attribute	Value
Vout range	1.25 V – 37 V
Vin – Vout difference	3 V – 40 V
Operation ambient temperature	0℃ – 125℃
Output Imax	less than 1.5 A (assuming factory-suggested heat sinking)
Minimum Load Currentmax	10 mA

operation
LM317 is a linear voltage regulator is used in a DC to DC converter applications. Overall function similar LM317 regulators LM78xx series. While the 78XX series regulators have set the output voltage (eg 7805 has an output 5V), LM317 can be adjusted to any voltage (within limits).