Overview

The LM337 (LM337T) is a 3-terminal adjustable negative linear voltage regulator manufactured by Texas Instruments, ON Semiconductor, and STMicroelectronics. Capable of supplying continuous load currents up to $1.5\text{ Amps}$ over an adjustable output voltage range of $-1.25\text{V}$ to $-37\text{V}$, it is the negative-voltage complement to the famous LM317 positive regulator.

Widely used in dual symmetrical bench power supplies ($\pm 15\text{V}$, $\pm 12\text{V}$), op-amp rail supplies, audio preamplifiers, and analog active crossover networks, the LM337 requires only two external resistors to program the output voltage.

Quick reference

Pinout (TO-220AB Package — LM337T)

Looking at the front labeled face of the TO-220 package with leads pointing down:

        ┌─────────────┐
        │   O   [TAB] │  (Metal Mounting Tab = INPUT V_IN)
        ├─────────────┤
        │   LM337T    │  (Front Package Face)
        └─┬───┬───┬───┘
          1   2   3
         ADJ  IN OUT

Output Voltage Formula

The output voltage is set by resistor $R_1$ (typically $120\ \Omega$ to $240\ \Omega$) between OUT and ADJ, and resistor $R_2$ between ADJ and Ground:

$V_{OUT} = -1.25\text{V} \times \left(1 + \frac{R_2}{R_1}\right) + (I_{ADJ} \times R_2)$

For $R_1 = 120\ \Omega$ and $R_2 = 1.3\text{ k}\Omega \implies V_{OUT} \approx -15.0\text{ Volts}$.

Common mistakes

• Reversing LM337 and LM317 pinouts: Swapping LM337 and LM317 into identical footprint slots causes wrong connections on Pins 2 and 3.
• Shorting metal tab to ground: The metal tab of the TO-220 package is internally connected to INPUT (negative supply rail), NOT ground. When mounting both LM317 (tab is OUT) and LM337 (tab is IN) onto a shared metal heatsink, isolate both tabs with mica washers.
• Omitting tantalum output capacitor: Tantalum or low-ESR ceramic capacitors ($1.0\ \mu\text{F}$ on output, $10\ \mu\text{F}$ on $V_{IN}$) are required to prevent high-frequency oscillation.

Notes

• LM337 vs LM7915: LM337 is an adjustable negative regulator; LM7915 is a fixed $-15\text{V}$ negative regulator. LM337 provides higher ripple rejection ($77\text{ dB}$) when an adjustment bypass capacitor is used.