The LM337 (a negative complement to the LM317) regulates voltages below, rather than above, the reference. It was designed by Robert “Bob” Pease (1940 – 2011).
LM317 VOLTAGE REGULATOR IN PAKISTAN:
The LM317 has three pins: INput, OUTput, and ADJustment. The device is conceptually an op amp with a relatively high output current capacity. The inverting input of the amp is the adjustment pin, while the non-inverting input is set by an internal bandgap voltage reference which produces a stable reference voltage of 1.25 V.
A resistive voltage divider between the output and ground configures the op amp as a non-inverting amplifier so that the voltage of the output pin is continuously adjusted to be a fixed amount, the reference voltage, above that of the adjustment pin. Ideally, this makes the output voltage:
Vout = Vref (1 + RL/RH)
Note that Vref is the difference in voltage between the OUT pin and the ADJ pin.Vref is typically 1.25 V during normal operation.
Because some quiescent current flows from the adjustment pin of the device, an error term is added:
Vout = Vref (1 + RL/RH) + IQRL
To make the output more stable, the device is designed to keep the quiescent current at or below 100µA, making it possible to ignore the error term in nearly all practical cases.