Negative rail regulator — why the LM337T exists
The LM337T is a three-terminal adjustable negative voltage regulator from STMicroelectronics, the complement to the ubiquitous LM317 positive regulator. It delivers up to 1.5A output current with an adjustable output range from -1.2V down to -37V, making it the go-to part for generating a clean negative rail from a negative input supply as low as -40V. A single external resistor divider sets the output voltage, and the 77dB PSRR at 120Hz provides meaningful ripple rejection for analog supplies feeding op-amps, ADCs, or audio circuits that need a quiet negative rail.
Output current and voltage — sizing the rail
Rated for 1.5A continuous output, the LM337T handles moderate loads like a small analog front-end or a local negative rail for a sensor signal chain. The minimum output voltage is -1.2V (the internal reference), and the maximum is -37V, set by the input voltage ceiling of -40V. The TO-220-3 package with a metal tab can dissipate several watts with a heatsink attached — the tab is the output pin, so the heatsink carries the output potential and must be electrically isolated or the system ground scheme accounted for.
Protection and temperature range
Built-in over-temperature shutdown and short-circuit current limiting protect the regulator and the load from fault conditions, reducing the need for external protection diodes in many designs.
For new designs, a pin-compatible negative adjustable regulator from another manufacturer (such as the LM337 series from TI, ON Semiconductor, or Microchip) should be evaluated for form-fit-function replacement.