Categories: Regulated Power Supply

Single Output Power Supply +1.25 V to 28 V / 1A Based on LM317

This Single output power supply is based on the LM317 voltage regulator, a little more efficient in terms of noise and ripple rejection of 50 Hz, and can provide power for analog or digital circuits with low energy consumption (less than 1 A).It is capable of providing a voltage between 1.25 V and 28 V at 1 A maximum intensity (or 1.5 A, depending on the LM317 manufacturer).

Power
The voltage regulator used here (LM317) theoretically can provide 1A maximum current. Its heating depends on two factors: the potential difference between its input and output, and the current passing through it (which is what the charge will apply). If the potential difference is important, you can not make out much power to the controller. At the same time, the controller must have its input voltage of at least 3 volts higher than the output voltage (for 12V regulated output, the input voltage must be at least 15V). Knowing that the regulator accepts a voltage as high as 37V input, you will find what is reasonable between these two limits, depending on the desired current output. In summary, avoid using an input voltage too high for a low output voltage if you really do charge to 1A power supply, limit yourself to 5V or 6V differential. In order to to work the regulator in the power range for which it is said, it is imperative to provide a sufficiently large cooling radiator.

Selecting the output voltage
The output voltage is determined by the value of two resistors R1 and R2, using the following formula:

Vout (output voltage) = 1.25 * (1 + (R2 / R1))

In the diagram above, the values given are for components to an output voltage of 12 V. For an output voltage other than 12V, you must use the values given in the following table. The values in parentheses are the values for R2 standard routine.

Desired Output voltage(Vout)	Transformer secondary voltage. TR1	R1(1% or 5%)	R2(1% or 5%)	R3(0,5W – 10%)
1.25V	6V	No resistance	0 ( short-circuit )	1
1.5V	6V	220	44 (22 + 22)	10
3.0V	6V	220	308 (309)	100
3.3V	6V	220	361 (180 + 180)	120
4.5V	6V	220	572 (470 + 100)	220
5.0V	9V	220	660 (330 + 330)	270
6.0V	9V	220	836 (820 + 15)	390
7.2V	9V	220	1047 (1K + 47)	510
9.0V	12V	220	1364 (680 + 680)	680
12.0V	12V	220	1892 (1800 + 91)	1K
13.5V	15V	220	2156 (1800 + 360 ou 2000 + 150)	1K2
13.75V	15V	220	2200	1K2
14.0V	15V	220	2244 (2200 + 47)	1K2
15.0V	15V	220	2420 (2200 + 220)	1K2
18.0V	18V	220	2948 (1500 + 1500)	1K5
24.0V	24V	220	4004 (2000 + 2000)	2K2
28.0V	24V	220	4708 (4700 + 10)	2K7

Note : It is possible to use a potentiometer (adjustable or table) of 2K2 or 4K7 in place of R2 to set the output voltage, but in this case, choose a very high quality potentiometer. You can also put in series resistance and potentiometer adjustable to limit the range of possible variation of the output voltage, which makes possible amore precise adjustment, even with an ordinary single-turn potentiometer with carbon track. As an example resistance 1.8 ohm and 220 ohm potentiometer adjusted to regulated outputs voltage between 11.5 V and 12.7 V.

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