LM317T Voltage Regulator with Pass Transistor

LED power driver on the basis of LM317 chipLEDs have become very popular lately. They are used to light up pretty much everything.However, LED is quite a fragile component. It can break when affected by voltage drops, continuous operation in peak modes, and incorrect connection. It is important to know that LED's main longevity parameter is not its power supply voltage but the current which flows through it.I'd like to show you a simplest current regulator which is quite reliable at the same time. It can be easily used in various feed circuits of LEDs.The circuit of such regulator is quite simple. To stabilize voltage "ajust" terminal is usually connected to earth, through a resistor or without it. In this case it is connected with a regulator output.So you can see that you need only one resistor to transform LM317 chip into LED power driver!Rated value of the resistor can be calculated with this simple formula. So we'll have 62 Ohms of rated resistance for an LED with a 20mA current. The chip's maximum input voltage equals 37V. That means you should use the regulator for voltage up to 37V.The only condition that you have to follow is that you must select the number of LEDs in such a way so that the regulator has as little voltage left as possible - but no less than 1.3V. This is necessary for reducing dissipated power on the regulator itself. It is especially important for large currents.And do not forget to install a chip onto the radiator at 350 mA currents or above.



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