LM317 Voltage Regulator

Posted on Feb 7, 2014

The LM317T is an extremely common positive voltage regulator - many laboratory supplies and other equipment are based on it. It can produce any amount between 1. 25V and up to 35V by adjusting the resistance (opposition to current) between its adjustment pin and ground. Secondly, and this is IMPORTANT, the LM317T is a linear regulator. This means t

LM317 Voltage Regulator
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hat it dissipates the excess voltage as heat, with more heat produced as the voltage is set lower and lower. You MUST have a heatsink mounted on the regulator that is capable of dissipating the heat produced. Most fans give their total output in watts - if they give it in amps, multiply that by 12. Your heatsink MUST be capable of dissipating the total wattage of all fans on the regulator safely. Heatsinks can get BIG at the upper wattages. (Be careful with published heatsink ratings; most sinks will say they dissipate 5W, but will heat up to 20 or 30 degrees above ambient at that wattage. ) Here`s one last thing to keep in mind; fans pull more amperage when they`re run at a lower voltage, on account of having less torque. For example, a Panaflo 120mm H1A pulls 0. 6 A at full 12V. However, at 6V, it pulls closer to 0. 85 A. You need to account for the highest possible current draw (usually occurs at 6V) from each fan connected to the regulator, and make sure you keep under the 1. 5A limit. If you need more than 1. 5A of current, and have a heatsink large enough to handle the wattage (old stereos and amplifiers are great for finding massive heatsinks, btw), you can use an LM350, which is rated up to 3 A and is identical to the LM317 in all other respects. The LM338 is also compatible, and is rated up to 5 A. The regulator itself. LM317/350/338s come in a variety of packaging; I suggest using the TO-220 package, it`s the most...

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