LM337 Variable Negative -VE Voltage Regulator IC

The LM337 is the equivalent counterpart of the LM317 Positive Voltage regulator. The IC commonly used in Adjustable Lab Voltage generators in combination with the LM317 IC. It can also be used as Current Regulators and negative voltage protection circuits, refer the datasheet linked below for application circuits.

The IC has three pins, in which the input voltage is supplied to VIN pin then using a pair of resistors (potential divider) we set a voltage at Adjust pin which will decide the output voltage of the IC that is given out at VOUT pin. Now to make it act as a variable voltage regulator we have to set variable voltages which can be done by using a potentiometer in the potential divider (R2 shown below). The below circuit is shown for reference from the LM337 datasheet.

The output voltage thus obtained can be calculated using the below formulae

VOUT = – 1.25 × (1 + (R2/R1))

The actual formulae in the datasheet will also include Iadj (Current through the adjust pin), but for simplification purpose we have assumed Iadj to be 50uA constant which will slightly differ in practical application.

Also note that the output current of the IC will not be 1.5A always, if the difference voltage between the input and output voltage is high the output current will also decrease. Refer to the difference voltage vs Output Current graph from the datasheet for more information.

Applications

• Used for Negative voltage regulations
• Variable power supply
• Current limiting circuits
• Reverse polarity circuits
• Commonly used in Desktop PC, DVD and other consumer products
• Used in motor control circuits