Currents of 2 mA, 10 mA and 20 mA are common. Miniature indicator LEDs are normally driven from low voltage DC via a current-limiting resistor. Series resistors are a simple way to stabilize the LED current, but energy is wasted in the resistor. In 2008, they were used for controlling the solid-state lighting in the Beijing National Aquatics Center during the 2008 Summer Olympics. These MOSFET-based Supertex IC chips are the most common LED drivers for solid-state lighting with LED lamps. Power integrated circuit (IC) chips such as the Supertex HV9910B are widely used to drive the MOSFETs directly, without the need for additional circuitry. Power MOSFETs are typically used for switching LED drivers, which is an efficient solution to drive high-brightness LEDs. Switched-mode power supplies or buck converters are used in LED flashlights and household LED lamps. Low drop-out (LDO) constant current regulators also allow the total LED voltage to be a higher fraction of the power supply voltage. Active constant current is typically regulated using a depletion-mode MOSFET (metal–oxide–semiconductor field-effect transistor), which is the simplest current limiter. Household LED light bulb with its internal LED elements and driver circuitry exposed.Īn active constant current source is commonly used for high power LEDs, stabilizing light output over a wide range of input voltages which might increase the useful life of batteries. This can encourage the current to increase. CC drivers are used when the electrical load of the LED circuit is either unknown or fluctuates, for example, a lighting circuit where a variable number of LED lamp fixtures may be installed.Īs an LED heats up, its voltage drop decreases (band gap decrease ). In CC drivers, the voltage changes while the current stays the same. Drivers may be constant current (CC) or constant voltage (CV). LED drivers are designed to handle fluctuation load, providing enough current to achieve the required brightness while not allowing damaging levels of current to flow. If the voltage is too high, the current will exceed the maximum rating, overheating and potentially destroying the LED. If the voltage is below or equal to the threshold no current flows and the result is an unlit LED. Current is approximately an exponential function of voltage according to the Shockley diode equation, and a small voltage change may result in a large change in current. The voltage versus current characteristics of an LED is similar to any diode. If the supply voltage is close or equal to the LED forward voltage, then no reasonable value for the resistor can be calculated, so some other method of current limiting is used. With a sufficiently high supply voltage, multiple LEDs in series can be powered with one resistor. Ohm's law and Kirchhoff's circuit laws are used to calculate the appropriate resistor value, by subtracting the LED voltage drop from the supply voltage and dividing by the desired operating current. However, this circuit is not energy-efficient, because energy is dissipated in the resistor as heat.Īn LED has a voltage drop specified at the intended operating current. It is commonly used for indicators and digital displays in many consumer appliances. The simplest circuit to drive an LED is through a series resistor. More complex, current source circuits are required when driving high-power LEDs for illumination to achieve correct current regulation. ![]() Very simple circuits are used for low-power indicator LEDs. 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. The circuit must provide sufficient current to light the LED at the required brightness, but must limit the current to prevent damaging the LED. In electronics, an LED circuit or LED driver is an electrical circuit used to power a light-emitting diode (LED). Simple LED (Light Emitting Diode) circuit diagram
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