9 Dual Variable Power supply Project by LM317 and LM337 regulator IC


This variable power supply project is made out from two complementary regulator IC, the positive LM317 regulator IC and negative LM337 regulator IC. This is a combination of variable power supply using LM317 and negative variable power supply using LM337. Unlike other dual power supply project that has a minimum voltage of plus and minus 1.2V to 1.5V, this power supply is designed that to have an output of 0V to 28V and 0V to -28 DC, which a great help specially when designing circuits that requires less than 1V.

 schematic of Dual Variable Power supply Project by LM317 and LM337 regulator IC


Power supply operation

This power supply uses LM317 for the positive regulation that can supply an output of 0V to 28V dc at a maximum current of 1.5A (with heatsink or cooling fan). The output voltage of the positive regulator is given by the formula:
Vout = 1.25(1 + 5K/240) + (100uA) (5K) - 1.4V
Where,
240 is the resistance from adjust and output terminal of LM317
5K is the resistance of the potentiometer connected to adjust terminal
-1.4V is the forward voltage of the two diode connection

Similar to LM317 operation, LM337 control the negative regulation of output voltage to ensure its output to 0V to -28V of a maximum current of -1.5A (of course wit heatsink). The variable negative output is given by the formula:
Vout = -1.25(1 + 5K/240) – (100uA) (5K) + 1.4V
Where,
240 is the resistance from adjust and output terminal of LM337
5K is the resistance of the potentiometer connected to adjust terminal
1.4V is the forward voltage of the two diode connection

 
Power supply materials

D is 1N4001 diode or any of the same maximum current capacity. Fuse must be 0.5A, 250V or much lower amperage rating. Transformer is 220VAC to 26V -0 -26V, 2A  or 120V to 26V -0 – 26V rating of 60VA or higher, bridge diode must be rated 3A or higher for good circuit operation. The resistors used are rated 1/2W.The input capacitor must be  4700uF or larger for better regulation and stability. The output capacitor Cout is 10uF.



Note: This power supply project is powered through 220V main and can cause electrocution

9 comments:

  1. I would like to know how to convert this power supply to 0 to 12v and 0 to -12v.

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  2. Richard good day!
    Since you ask about a +12V,0V,-12V version of the power supply, i design a very simple circuit for you.just follow the link.
    dual 12V supply

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  3. Q: What are the 5.6K resistors from (+) (-) Diode Bridge to the four 1N4004 Diodes labeled D?
    What is their function and why the four Diodes?

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  4. Q: What are the 5.6K resistors from (+) (-) Diode Bridge to the four 1N4004 Diodes labeled D?
    What is their function and why the four Diodes?


    LM317 and LM337 are has a minimum output voltage of 1.2V and -1.2V and not equal to zero.
    By adding 5.6K with 2 diodes in series in each regulator, it ensures that the output of both regulator is zero since
    new min output = (1.2V -2VD) where VD is the forward voltage of the diode and 1.2V is the original minimum voltage of the regulators.
    As we know diode drop is around 0.6V to 0.7V, meaning the new minimum output voltage is zero and not 1.2V

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  5. I QUIT ELECTRONICS THIS THING IS DIFFICULT TO UNDERSTAND HEY

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  6. where is the filter in this ckt?

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  7. the 10uf cap will act as the filter(voltage regulation).
    You can increase its value..The larger the value of capacitor the better. But larger means bigger and more expensive

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  8. how can filter capacitor act as regulator? for that we have reg ic right? filter should be before regulator..4470uf cap ?

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