LM317
The LM317 is an integrated linear series regulator developed by Robert Dobkin at National Semiconductor in 1976 . It was one of the first commercially successful series regulators for positive supply voltages in the field of electronic circuits . Due to its long availability on the market of over 40 years and its widespread use, it is one of the best-known linear DC voltage regulators. In contrast to the linear regulators such as the LM109, which have been available since 1969 and have a fixed output voltage, the LM317 can be changed in the output voltage using two external resistors .
The adjustable linear DC voltage regulator LM337, which is designed for negative supply voltages, is complementary to the LM317, has a similar structure and was developed in the 1970s by Robert Allen Pease , also at National Semiconductor.
construction
The first LM317 and LM337 were implemented with bipolar transistors with a structure size of 7 µm. They have three connections: one each for the input voltage and one for the output voltage, and the third connection is used to set the regulated output voltage. This can be selected between 1.25 V and 37 V at maximum input voltage using two external resistors in the form of a voltage divider . The maximum direct current that can be supplied by the series regulator depends on the thermal load capacity, which is determined, among other things, by the chip housing used. In larger metal housings such as the TO-3 , an output current of 1.5 A can be achieved.
To stabilize the output voltage, a band gap reference is used internally , which was developed in 1971 by Robert Widlar at National Semiconductor. This means that the output voltage can be kept within a narrow tolerance range even with different load conditions and different operating temperatures.
Compared to fixed voltage regulators
In comparison with fixed voltage regulators such as the LM78XX regulator series for positive voltages and LM79XX for negative voltages - XX stands for the fixed output voltage such as LM7805 with 5 V - the LM317 and LM337 have a cross-current at their control input that is largely independent of the input voltage and load current. In the case of fixed voltage regulators, the cross-current is more dependent on the level of the input voltage, which means that its third reference pin should be permanently connected to ground potential and not be available for setting the output voltage.
Web links
Individual evidence
- ↑ Ashok Bindra: A look back: Three-terminal linear regulator Evolution continues unabated. IEEE Power Electronics Magazine, 2014, accessed July 24, 2016 .
- ↑ Datasheet: LM317 3-Terminal Adjustable Regulator. Retrieved July 26, 2016 .
- ↑ Datasheet: LMx37 3-Terminal Adjustable Regulator. Retrieved July 26, 2016 .
- ^ Theodore P. Pavlic: Bandgap Voltage Reference Example: LM317. Retrieved July 27, 2016 .