LM317 Based 0 to 3V Adjustable Power Supply

Description:

This is an LM317 based adjustable voltage regulator with a maximum output of 3V and 1.5A.  The output voltage depends on the V_IN, R1 and R2 values, so the circuit can be modified to use with a maximum output of greater than 3V. The maximum current output is also independent of the circuit design, it is related to the package options.In this circuit, LM317T, which is capable of transferring up to 1.5A, is used.

Since the internal reference voltage of the LM317 regulator is 1.25V, the output voltage can be also minimally 1.25V. One way to overcome this problem is using a reference voltage source built on two diodes. But this approach is mostly suitable for 1.5V to 15V regulators since the sensitivity becomes poor for the low voltage outputs less than 1.5 . On the other hand, diodes have temperature dependent forward voltages.

Another way is using LM185 or AD589 adjustable voltage references. But they are expensive and in this application they require both zero adjustment and matching.

In this circuit, the key idea is solving the problem with an inexpensive and easy way by using a temperature stabilized constant current source.  The current source value is calculated by the equation;

2-7V / 6-8A Power Supply by 723 and 7812

Description: 

In this 2-7V power supply circuit, for our purpose, we chose IC 723 instead of a three pin voltage regulator for-why we find it protean and more advantageous in technical details.

Notes: 

Heatsinks of Tr2 and Tr3 transistors must be sufficiently large.

To archive R4,R5 and R6 values, we used some suitable resistors in parallel. For R4 and R5 two parallel connected 0.3ohm/5W resistors for each are used. To take 6A output, we connected two 0.22ohm/5W resistors in parallel, and to take 8A output we connected three 0.33ohm/5W resistors in parallel instead of R6 resistor. 

If you change the marked component values properly you can get up to 14V output. For this situation you must disconnect R1,R2,C5,C6,C1,C2,D1,D2  components and connect the positive terminal of D3 directly to the rectified and stabilized supply....