In the event we need to build a variable DC power supply that output of 1A and can adjust up to about 30V.
Most people will use LM317 because of high-efficiency, easy to apply and cheaper
It has an adjustable 3-terminal positive voltage regulator designed to supply more than 1.5 A of load current with an output voltage adjustable over a 1.2V to 37V range.
It has an internal current limiting, temperature detects shutdown and safe area compensation.
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Figure 1: LM317 pinout on TO-220
LM317T on TO-220: output 1.5A
LM317L on TO-92: output 100mA
LM317K on TO-3: output 1.5A
LM317 on DPARK: output 1.5A
-Output current in excess of 1.5A
-Output-Adjustable between 1.2V and 37V
-Internal Short-Circuit Current Limiting or Output is short-circuit protected
-Internal Thermal Overload Protection or Current limit constant with temperature
-Output-Transistor Safe Operating Area Compensation
-TO-220 Package like 2SC1061 transistors.
-There are 1% output voltage Durability
-There are max. 0.01%/V line regulation(LM317), and 0.3% load regulation (LM117)
-There are 80 dB ripple rejection
Figure 2 the basic circuit diagram
Basic circuit diagram
If power supply filter has distance from IC-regulator too much, should insert Ci to lower noise before IC-input. Next in figure circuit, Co is not needs if you do not high-efficiency, but we put it better, it is use for lower a output ripple.
As Iadj is controlled to less than 100uA, the little error Unimportant in most applications.
The input voltage to the LM317 must be at least 1.5v greater than the output voltage.
This calculator will work for most DC Voltage Regulators with a reference voltage (VREF) of 1.25. Typically, the program resistor (R1) is 240 ohms for the LM117, LM317, LM138, and LM150.
LM317 heat sink calculator
What is the size of heat sink enough?
While The LM317 is running. It is so hot. Though it has over temperature cut-out. But we do not need it hot. We always install the heat sink.
Someone ask me. How much should you use the smallest heat sink? LM317 has a maximum temperature of 50 °C/W without a heat sink.
I found this site it good with LM317 heat sink calculator.
For example LM317 circuit
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