0 Negative variable power supply using LM337 regulator IC

 using LM337 regulator Negative variable power supply  jpg

This variable power supply project uses LM337 regulator IC that can supply an output current up to 1.5A maximum at negative 28V.This simple LM337 power supply is the exact opposite pair of   positive regulator that uses lm317 IC. It is very useful in making or designing electronic projects that requires negative variable voltage inputs.

Power supply operation:
1. The transformer steps down the voltage from 220VAC to 26VAC per winding (52VAC in total)
2. The AC voltage is converted to DC by the rectifier diode
3. The DC voltage is filtered by the capacitor to eliminate voltage ripples
4. The LM317 regulates the output voltage and varies it from -1.25V to -30V through potentiometer

The transformer used in this power supply project is rated 220V to 28V with center tap and about 50VA. The diode D1 is 1N5401 or similar while diode D2 is 1N4001. The resistors used are rated 1/2W.The input capacitor (470uF in diagram) must be 3300uF 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


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