Further, it employs internal current limiting, thermal shutdown and safe. This voltage regulator is exceptionally easy to use and requires only two external resistors to set the output voltage. The LM317 is an adjustable 3terminal positive voltage regulator capable of supplying in excess of 1.5 A over an output voltage range of 1.2 V to 37 V.
Samacsys Manufacturer: STMicroelectronics. The differences between linear and switched mode regulators is explained well by a Linear Technology application note (1).Standard Regulator 1.2V to 37V 1.5A STMicroelectronics LM317T, Single Linear Voltage Regulator, 1.5A Adjustable 1.2 37 V, 3-Pin TO-220. There are different classes of voltage regulator IC, but they are commonly grouped as being either linear voltage regulator or a switched mode voltage regulator. The wide availability of IC's designed as voltage regulators greatly simplifies the problem.
They are designed to supply more than 1.5 A of load current with an output voltage adjustable over a 1.2 to 37 V range. Input-Output Voltage Differential-Min: 3 V.voltage regulators. Input-Output Voltage Differential-Max: 40 V.
Lm317T Voltage Regulator Datasheet Series Fixed Voltage
Excellent choice for a DIY circuit where opportunity for the "magic smoke" to leak out abound). The current limiting and thermal overload shutdown make the LM317 a very tolerant part (i.e. This voltage regulator is exceptionally easy to use and requires only two external resistors to set the output voltage.Standard Regulator 1.2V to 37V 1.5A STMicroelectronics LM317T, Single Linear Voltage Regulator, 1.5A Adjustable 1.2 37 V, 3-Pin TO-220 Voltage regulator,LM317BT 37V ON Semiconductor LM317BTG, Single Linear Voltage Regulator, 1.5A Adjustable 1.2 37 V, 3-Pin TO-220 Samacsys ManufacturerWhile there are numerous linear voltage regulator IC's available, and the LM317 is now an over 30 year old design, this well know component has a wide background literature, is an adjustable analogue to the popular 78xx series fixed voltage regulators, and is easily/cheaply available (in the range of cents/item even for small quantities when sourced from ebay).The LM317 datasheet lists other features of the component, notably thermal and current overload protection with a 1.2V to 37V output range at 1.5A (depending upon heat sinking). While a switched mode power supply can be (is generally?) more efficient than a linear supply, if the un-regulated input voltage is well matched to the desired regulated output voltage (e.g., 13.8V input with a 10V output) the "efficiency" of the linear supply is already very acceptable, and the low parts count/circuit simplicity is an advantage.LM317/D LM317, NCV317 Voltage Regulator - Adjustable Output, Positive 1.5 A The LM317 is an adjustable 3&239 terminal positive voltage regulator capable of supplying in excess of 1.5 A over an output voltage range of 1.2 V to 37 V. TO-220 TO-220FP DPAK Table 1.DDEESSCCRRIIPPTTIIOONN The LM317 are adjustable 3-terminal positive-voltage regulators capable of supplying 1.5A over a differential voltage range of 3V to.Linear voltage regulator IC's are very easy to use and only require generally a couple of capacitors and two feedback resistors in the case of the variable regulators.
The lab notes from this reference (3) provide what I consider is a good compromise, and since internet references can often be ephemeral, the following excerpts/paraphasing is reproduced.Linear Voltage Regulator Operation The LM317 internals can be simplified as comprising the following "block" components in terms of considering voltage regulation.A 1.25V reference voltage (from the zener diode) is input into the non-inverting input of the op-amp. Nevertheless, some knowledge of the device is required to enable appropriate incorporation into the desired circuit. However, for the typical DIY scenario, the LM317 can be largely considered a "black box" that converts an input voltage to a regulated output voltage. Such detail/knowledge is likely of importance to assess the exact interaction of the LM317 with external circuitry.
Therefore, using 220ohm for R1 (which seems to be widely recommended) gives a current of 5.7mA, well within the minimum current requirements for the LM317 and appears to be a good compromise.Taking a value of 220ohm for R1, and taking into account the datasheet specifies a maximum input voltage differential of 40V, this then limits the useful range for R2 (using the equation for Vout given above) to ~6800ohm (hence the usual value of 5K ohm for the potentiometer in the standard LM317 schematics). The lower the value of R1 the more current is wasted, while the higher the value of R1 the more the regulator becomes sensitive to oscillation (and noise). With a minimum current of 10mA, the value of R1 is 125ohm. The remaining circuit the LM317 is supplying) will be greater than this minimum, R1 can also act as a dummy load to ensure operation of the LM317 (ie voltage regulation) even if the real load is not connected.Since the LM317 will "ensure" 1.25V across R1 (see above operation section) with a 3.5mA typical minimum current, this calculates to a required value of 357ohm for R1. While it can be usually expected that the load (i.e. This is discussed in the following sections.From the LM317 datasheet, the IC requires a minimum load current to operate, which is stated to be typically 3.5mA (max 10mA).
If values of output voltage less than 25V are used with a 10uF value for C3, no protection diode is required (otherwise, should be included).The dropout voltage is the minimum difference between the input and output voltages that must be maintained in order for the regulator to perform the voltage regulation. The datasheet advises a 10uF value is sufficient generally. This bypass capacitor prevents ripple from being amplified as the output voltage is increased. The device is more sensitive to the absence of input bypassing when adjustment or output capacitors are used but the above values will eliminate the possibility of problems".Again from the datasheet, the inclusion of C2 is optional, but improves transient response (i.e., protecting against sudden changes in mains or load conditions e.g., surges), with values in the range of 1uF to 1000uF of aluminium or tantalum electrolytic being commonly used (for output capacitors of 25uF or less, there is no need for a protection diode).The following circuit shows the addition of capacitor C3. A 0.1μF disc or 1μF solid tantalum on the input is suitable input bypassing for almost all applications. Calculated Vout of LM317 with R1, R2 combinationsFrom the datasheet, "An input bypass capacitor (C1) is recommended.
See the Testing/Experimental Results section for practical examples.From the testing done (refer to the graphs in the Testing/Experimental Results section), heat sinking of the LM317T is very important in enabling a regulated voltage at higher load current. From the LM317 datasheet, the minimum dropout voltage is approximately 2V, and obviously this should be "de-rated" to give some margin.Another consequence of the input voltage needing to be greater than the output voltage (and allowing for the dropout voltage) is that the greated the difference between the input and output voltage (assuming the same load current), the more power that will need to be dissipated by the LM317 and therefore the hotter it will get. The dropout voltage varies both the load current and temperature.
The thermal equivalent of an electronic circuit has an analogous relationship with Ohm's Law which are explained by these sites, which also include online calculators (4), (5). A thermal evaluation of a circuit, particularly when dealing with increased current, should be done to check if components will remain within thermal tolerances stated on datasheets. The datasheet advises under all possible operating conditions, the junction temperature of the LM317 must be within the range 0 oC to 125 oC.
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