Negative rail workhorse — what the LM337KC delivers
The LM337KC is a three-terminal negative adjustable voltage regulator from the LM337 family, delivering up to 1.5 A output current with an adjustable output range from -1.2 V down to -37 V. It provides 77 dB of power supply rejection at 120 Hz, attenuating ripple from a full-wave rectified mains supply. The TO-220-3 through-hole package allows direct mounting to a heatsink with a single screw, and the tab is the output pin — keep that in mind when designing the thermal interface and the PCB layout.
Setting the output voltage — the two-resistor divider
Like the standard LM337, the KC variant uses an external resistor divider between the output and adjust pins to set the negative output voltage. The minimum output is -1.2 V, the maximum is -37 V, limited by the -40 V maximum input rating. The single regulator channel means one negative rail per device — for dual-polarity supplies you pair it with a positive regulator.
Built-in over-temperature shutdown and short-circuit protection are included — the regulator survives an output short indefinitely at room temperature, but thermal cycling from repeated faults can stress the die attach in the TO-220 package.
Sourcing an obsolete part — what to expect
For a drop-in replacement, look for any TO-220-3 negative adjustable regulator with the same pinout (adj, output, input from left to right with the tab as output) and matching -1.2 V to -37 V range at 1.5 A — several second-source manufacturers still produce the LM337 in this package.