CONSTANT-CURRENT USING LM317 DRIVES 1 WATT LED By. Find this Pin and more on Simple & usefull electronic circuits for. Simplest 1 Watt LED Driver Circuit. Constant current LED driver circuits. Roundup: Driving. Constant current LED driver circuit uses LM334 plus one transistor to drive a series string of LEDs. Here is another electronic circuit of a driver for Led, this project is identical to the previously published, to. He is part of a series of publications on. This driver uses the famous voltage regulator, which in this case is configured as a current regulator or Current limiter. This circuit can be easily constructed, low cost and ideal for those with no knowledge of electronics or getting in Hobby. In the LM317 regulator driver is used as a voltage source 1.25V, where the pin is output with 1.25 Volts relative to the adjustment. The calculation for this drive is simple resistor, V is the voltage regulator output, R is the resistor limiter and Iout is the output current. V/R=Iout Knowing the voltage (In) as we speak is already 1.25 Volts and the current that the LED 1 Watts needs is about 330 mA (+OR-), the calculation is simple resistor, 1.25 x 330 = R. The result is 4.12 Ohms, rounding the resistor may be one of 4R2 1 Watts. Since this resistor is not standard commercial, We can do this as follows, associating in parallel 3 resistors 12 Ohms por 1/2 Watt. A resistor 3.9 ohm por 1 Watt will also work perfectly. Do not forget to put the necessary Led and the regulator on a heat sink to prevent overheating, Led does not support high temperatures, the regulator has already a shield and its power decreases with increasing temperature. Soon I will be publishing more for LED driver circuits with different power ratings. Typically LED circuit current regulation is achieved by putting a resistor in series with the LED bulbs. (Read our article on to find out more about selecting resistors for LED circuits.) Resistors are very cheaply available in an enormous range of sizes. However using resistors to regulate current in a circuit is not a very safe solution – particularly when the power supply used is not stable. A resistor in series with an LED may result in the exact desired current going through the LED at 12V, but at 15V that current could be much greater. Problems Using Resistors to Regulate Current If you wire three LEDs in series – each with a nominal current of 25ma (0.025 Amps) and a voltage drop of 3.6V – there is a total of 10.8 volts being dropped across the LEDs. If the power source is a 12 Volt battery then there is an additional 12-10.8=1.2V to drop to keep the LEDs happy. Resistance is equal to voltage divided by current and so 1.2/0.025 = 48 Ohms is the size of resistor required. If a suitable resisitor (50 Ohms since that is the next manufactured resistor over 48 Ohms) is put in series with the LEDs then everything will work correctly – 25mA of current will flow through the LEDs in the circuit as desired and 0.03 Watts (1.2 volts * 25ma) will be dissipated as heat by the resistor. However, in most renewable energy systems the voltage of the battery changes dramatically depending on the charging current. When the battery is not being charged it may give out only 12 Volts, but when it is being charged it can easily reach in excess of 14.5 Volts – particularly if a small battery is being charged by a large.
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