The LM117 series of adjustable 3-terminal positive voltage
regulators is capable of supplying in excess of 1.5A over a
1.2V to 37V output range. They are exceptionally easy to use
and require only two external resistors to set the output voltage. Further, both line and load regulation are better than
standard fixed regulators. Also, the LM117 is packaged in
standard transistor packages which are easily mounted and
In addition to higher performance than fixed regulators, the
LM117 series offers full overload protection available only in
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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 terminal is disconnected.
Normally, no capacitors are needed unless the device is situated more than 6 inches from the input filter capacitors in
which case an input bypass is needed. An optional output capacitor can be added to improve transient response. The
adjustment terminal can be bypassed to achieve very high
ripple rejection ratios which are difficult to achieve with standard 3-terminal regulators.
Besides replacing fixed regulators, the LM117 is useful in a
wide variety of other applications. Since the regulator is floating” and sees 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, i.e.,
avoid short-circuiting the output.
Also, it makes an especially simple adjustable switching regulator, a programmable output regulator, or by connecting a
fixed resistor between the adjustment pin and output, the
LM117 can be used as a precision current regulator. Supplies
with electronic shutdown can be achieved by clamping the
adjustment terminal to ground which programs the output to
1.2V where most loads draw little current.
For applications requiring greater output current, see LM150
series (3A) and LM138 series (5A)...
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