The LM337L is an adjustable 3-pin negative voltage regulator capable of supplying 100 mA over a –1.2-V to –37-V output range. The LM337L is easy to use and requires only two external resistors to set the output voltage. Both line and load regulation are better than standard fixed regulators. The LM337L is packaged in a standard, easy-to-use TO-92 transistor package.
In addition to higher performance than fixed regulators, the LM337L offers full overload protection. Included on the chip are current limit, thermal overload protection, and safe area protection. All overload protection circuitry remains fully functional even if the adjustment pin is disconnected.
Normally, only a single 1-µF solid tantalum output capacitor is required unless the device is situated more than 6 inches from the input filter capacitors, in which case an input bypass is required. A larger output capacitor can be added to improve transient response. The adjustment pin can be bypassed to achieve very high ripple rejection ratios, which are difficult to achieve with standard 3-pin regulators.
Besides replacing fixed regulators, the LM337L is useful in a wide variety of other applications. Because the regulator is floating and monitors only the input-to-output differential voltage, supplies of several hundred volts can be regulated as long as the maximum input-to-output differential is not exceeded.
The LM337L makes a simple adjustable switching regulator, a programmable output regulator, or by connecting a fixed resistor between the adjustment and output, the LM337L can be used as a precision current regulator. Supplies with electronic shutdown can be achieved by clamping the adjustment pin to ground, which programs the output to 1.2 V, where most loads draw little current.
The LM337L is available in a standard TO-92 transistor package and a standard SO-8 surface mount package. The LM337L is rated for operation over a –25°C to 125°C range.
For applications requiring output current in excess of 0.5 A and 1.5 A, The LM137 series may be suitable. For the positive complement, the LM117 and LM317L series are options.