TL431 Regulator Adjustable Explanation and circuit

This be simple Adjustable voltage regulator power supply circuit, at use integrated number circuit TL431. By from the circuit can fine volt 3V – 30V, depend on feed volt supply input and change the value R2 , R1. It follow a formula calculates Vout = (1+R1/R2) , Vref = 3V-30V , but this circuit gives current get not tall 100mA only. It just if want to enhance current , must use the transistor helps to enlarge current, such as 2N3055, TIP41 numbers or the other.

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Adjustable Voltage Current Power Supply Circuit Using IC L200

1.  IC2 is connected as a differential amplifier and compares the signals at its two inputs.
2. Referring to the circuit diagram: the input comprises a mains switch, fuse, transformer, bridge rectifier and smoothing capacitor (C2).
3. The difference between the inputs is the voltage drop across current’ sensor R4. This IC feeds the current sensing input (pin 2) of the L200.
4. P1 in the feedback loop of the 741 is used to vary the output current of the circuit. IC1 must be mounted on a suitable heat sink as it dissipates nearly all the power of the circuit.
5. The reference level output from I pin 4 of IC1 goes to the voltage divider made up of R5 and P2 (this pot sets the value of the output voltage).
6. The power supply can quite easily be built into a case and a voltmeter and ammeter mounted on the front panel. ln view of the accuracy of the circuit these should ideally be digital meters, but virtually any type will do.
7. If you compare the expense and the rating of this power supply you will get a surprise, because the output voltage and current are fully adjustable between O. . . 18 V and 0 . . . 1.8 A respectively and costs have still been kept very reasonable.
8. Diode D5 and capacitor C1 produce a negative auxiliary voltage, which is stabilized by zener diode D6 and capacitor C4.
9. All this is necessary to enable the output voltage to be adjusted down to zero volts. During the construction of this part of the circuit bear in mind that the positive lead of electrolytic capacitor C4 is connected to earth! Regulation is provided by IC1 and IC2. Capacitor C3 suppresses any residual transients at the input of lC1 and it should therefore be connected as closely as possible to IC1 similarly C4 and IC2).
10. The negative voltage provides the negative supply for the two ICs. 

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3 30V 3A Adjustable Regulated DC Power Supply circuit and explanation

This power supply is meant as an auxiliary or as a permanent power supply for all common circuits based on a stabilized DC voltage between 3 and 30V provided that the consumption does not exceed 3A. Of course this power supply unit can also be used for other purposes. Be replacing the trimmer by a potentiometer, it may even be used as an adjustable power supply unit. A good quality heatsink must be used.
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Parts list:
R1 = 8.2K
R2 = 2.2K
R3 = 680R
R4 = 1K
R5 = 82K
R6 = 0.18R/5W
C1 = 470p
C2 = 100nF-63V
C3 = 100nF-63V
C4 = 100uF-63V
C5 = 10KuF-60V
D1-D6 = 6.6A
Q1 = MJ3001 (Darligton)
IC1 = UA723D

Specifications:
* Overload protected
* Sshort-circuit stable
* Output current: max. 3A
* Output ripple voltage: 0.5mV
* Output voltage: adjustable from 3 to 30V, stabilized
* Input voltage: 9 to 30V AC (depending on the desired output voltage)

Source: http://www.extremecircuits.net/2010/02/3-30v-3a-adjustable-regulated-dc-power.html

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