<P> In electronics, an LED circuit or LED driver is an electrical circuit used to power a light - emitting diode (LED). The circuit must provide sufficient current to light the LED at the required brightness, but must limit the current to prevent damaging the LED . The voltage drop across an LED is approximately constant over a wide range of operating current; therefore, a small increase in applied voltage greatly increases the current . Very simple circuits are used for low - power indicator LEDs . More complex, current source circuits are required when driving high - power LEDs for illumination to achieve correct current regulation . </P> <P> The simplest circuit to drive an LED consists of a voltage source and two components connected in series: a current limiting resistor, sometimes called the ballast resistor, and an LED . Optionally, a switch may be introduced to open and close the circuit . Although simple, this circuit is not the most energy efficient circuit to drive an LED, since energy is lost in the resistor . More complicated circuits improve the energy efficiency . </P> <P> An LED has a voltage drop specified at the intended operating current . Ohm's law and Kirchhoff's circuit laws are used to calculate the appropriate resistor value to obtain the desired current . The value is computed by subtracting the LED voltage drop from the supply voltage and dividing by the desired operating current . If the supply voltage is equal to the LED's voltage drop, no resistor is needed . </P>

How does an led work in a circuit
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