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.
Basic circuit
[
edit
]
The simplest circuit to drive an LED is through a series resistor. It is commonly used for indicators and digital displays in many consumer appliances. However, this circuit is not energy-efficient, because energy is dissipated in the resistor as heat.
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, by subtracting the LED voltage drop from the supply voltage and dividing by the desired operating current. With a sufficiently high supply voltage, multiple LEDs in series can be powered with one resistor.
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.
Power source considerations
[
edit
]
The voltage versus current characteristics of an LED is similar to any diode. 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. If the voltage is below or equal to the threshold no current flows and the result is an unlit LED. If the voltage is too high, the current will exceed the maximum rating, overheating and potentially destroying the LED.
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. Drivers may be constant current (CC) or constant voltage (CV). In CC drivers, the voltage changes while the current stays the same. 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.
As an LED heats up, its voltage drop decreases (band gap decrease[1]). This can encourage the current to increase.
MOSFET drivers
[
edit
]
Household LED light bulb with its internal LED elements and driver circuitry exposed.An 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. Active constant current is typically regulated using a depletion-mode MOSFET (metal–oxide–semiconductor field-effect transistor), which is the simplest current limiter.[2] Low drop-out (LDO) constant current regulators also allow the total LED voltage to be a higher fraction of the power supply voltage.
Switched-mode power supplies (e.g. buck, boost, and buck-boost converters) are used in LED flashlights and household LED lamps. Power MOSFETs are typically used for switching LED drivers, which is an efficient solution to drive high-brightness LEDs. Power integrated circuit (IC) chips are widely used to drive the MOSFETs directly, without the need for additional circuitry.[2]
Series resistor
[
edit
]
Series resistors are a simple way to stabilize the LED current, but energy is wasted in the resistor.
Miniature indicator LEDs are normally driven from low voltage DC via a current-limiting resistor. Currents of 2 mA, 10 mA and 20 mA are common. Sub-mA indicators may be made by driving ultrabright LEDs at very low current. Efficiency tends to reduce at low currents,[3] but indicators running on 100 μA are still practical.
In coin cell powered keyring-type LED lights, the resistance of the cell itself is usually the only current limiting device.
LEDs with built-in series resistors are available. These may save printed circuit board space, and are especially useful when building prototypes or populating a PCB in a way other than its designers intended. However, the resistor value is set at the time of manufacture, removing one of the key methods of setting the LED's intensity.
The value for the series resistance may be obtained from Ohm's law, considering that the supply voltage is offset by the voltage drop across the diode, which varies little over the range of useful currents:
R = V p o w e r − V l e d − V s w i t c h I l e d {\displaystyle R={V_{power}-V_{led}-V_{switch} \over I_{led}}}
or
I l e d = V p o w e r − V l e d − V s w i t c h R {\displaystyle I_{led}}={V_{power}-V_{led}-V_{switch} \over R}
where:
R {\displaystyle R}
ohms, typically rounded up to the next higher resistor value.V p o w e r {\displaystyle V_{power}}
volts, e.g. 9-volt battery.V l e d {\displaystyle V_{led}}
V f {\displaystyle V_{f}}
band gap, a blue LED may drop around 3 to 3.3 volts. Light-emitting diode physics § Materials has a list of colors with their voltage drop ranges.V s w i t c h {\displaystyle V_{switch}}
BJT transistor, useV C E ( s a t ) {\displaystyle V_{CE(sat)}}
I l e d {\displaystyle I_{led}}
amps. The maximum continuous-on current is shown on LED datasheets, for example 20 mA (0.020A) is common for most small LEDs. Many circuits operate LEDs at less than the specified maximum current to save power, or to reduce brightness, or to use a common resistor value. For indoor use, tiny surface mount high-efficiency LEDs can easily light up with 1 mA (0.001A) or more current, which most digital logic outputs can easily source or sink.Using the algebraic formula (above) and assuming V s w i t c h {\displaystyle V_{switch}} is 0 (to simplify examples), the resistance is calculated as follows:
V p o w e r {\displaystyle V_{power}}
V l e d {\displaystyle V_{led}}
I l e d {\displaystyle I_{led}}
R {\displaystyle R}
common resistor values).V p o w e r {\displaystyle V_{power}}
V l e d {\displaystyle V_{led}}
R {\displaystyle R}
I l e d {\displaystyle I_{led}}
LED arrays
[
edit
]
Schematic of LEDs in seriesSchematic of LEDs in parallelStrings of multiple LEDs are normally connected in series. In one configuration, the source voltage must be greater than or equal to the sum of the individual LED voltages; typically the LED voltages add up to around two-thirds of the supply voltage. A single current-limiting resistor may be used for each string.
Parallel operation is also possible but can be more problematic. Parallel LEDs must have closely matched forward voltages (Vf) in order to have similar branch currents and, therefore, similar light output. Variations in the manufacturing process can make it difficult to obtain satisfactory operation when connecting some types of LEDs in parallel.[4]
LED display
[
edit
]
LEDs are often arranged in ways such that each LED (or each string of LEDs) can be individually turned on and off.
Direct drive is the simplest-to-understand approach—it uses many independent single-LED (or single-string) circuits. For example, a person could design a digital clock such that when the clock displays "12:34" on a seven-segment display, the clock would turn on the appropriate segments directly and leave them on until something else needs to be displayed.
However, multiplexed display techniques are more often used than direct drive, because they have lower net hardware costs. For example, most people who design digital clocks design them such that when the clock displays "12:34" on a seven-segment display, at any one instant the clock turns on the appropriate segments of one of the digits—all the other digits are dark. The clock scans through the digits rapidly enough that it gives the illusion that it is "constantly" displaying "12:34" for an entire minute. However, each "on" segment is actually being rapidly pulsed on and off many times a second.
An extension of this technique is Charlieplexing where the ability of some microcontrollers to tri-state their output pins means larger numbers of LEDs can be driven, without using latches. For N pins, it is possible to drive n2-n LEDs.
The use of integrated circuit technology to drive LEDs dates back to the late 1960s. In 1969, Hewlett-Packard introduced the HP Model 5082-7000 Numeric Indicator, an early LED display and the first LED device to use integrated circuit technology. Its development was led by Howard C. Borden and Gerald P. Pighini at HP Associates and HP Labs, who had engaged in research and development (R&D) on practical LEDs between 1962 and 1968.[5] It was the first intelligent LED display, making it a revolution in digital display technology, replacing the Nixie tube and becoming the basis for later LED displays.[6]
Polarity
[
edit
]
Unlike incandescent light bulbs, which illuminate regardless of the electrical polarity, LEDs will only light with the correct electrical polarity. When the voltage across the p-n junction is in the correct direction, a significant current flows and the device is said to be forward-biased. If the voltage is of the wrong polarity, the device is said to be reverse biased, very little current flows, and no light is emitted. LEDs can be operated with alternating current, but they will only light on the half of the AC cycle where the LED is forward-biased. This causes the LED to turn on and off at the frequency of the AC supply.
Most LEDs have relatively low reverse breakdown voltage ratings compared to standard diodes, so it may be easier than expected to enter this mode and cause damage to the LED due to overcurrent. However, the cut-in voltage is always less than the breakdown voltage, so no special reverse protections are necessary when driving an LED directly from an AC supply when properly current-limited for forward-biased operation.
The manufacturer will normally advise how to determine the polarity of the LED in the product datasheet. However, there is no standardization of polarity markings for surface mount devices.[7][8]
Pulsed operation
[
edit
]
Many systems pulse LEDs on and off, by applying power periodically or intermittently. So long as the flicker rate is greater than the human flicker fusion threshold, and the LED is stationary relative to the eye, the LED will appear to be continuously lit. Varying the on/off ratio of the pulses is known as pulse-width modulation (PWM). In some cases, PWM-based drivers are more efficient than constant current or constant voltage drivers.[3][9]
Most LED data sheets specify a maximum DC current that is safe for continuous operation. Often they specify some higher maximum pulsed current that is safe for brief pulses, as long as the LED controller keeps the pulse short enough and then turns off the power to the LED long enough for the LED to cool off.
LED as a light sensor
[
edit
]
Mobile phone IrDAIn addition to emission, an LED can be used as a photodiode in light detection. This capability may be used in a variety of applications including ambient light detection and bidirectional communications.[10][11][12]
As a photodiode, an LED is sensitive to wavelengths equal to or shorter than the predominant wavelength it emits. For example, a green LED is sensitive to blue light and some green light, but not to yellow or red light.
This implementation of LEDs may be added to designs with only minor modifications in circuitry.[10] An LED can be multiplexed in such a circuit, such that it can be used for both light emission and sensing at different times.[10][12]
See also
[
edit
]
References
[
edit
]
When it comes to installing LED light strips, one crucial consideration is choosing the right connectors. Proper connectors ensure secure connections and reliable performance. In this article, we will guide you through the process of selecting the most suitable LED light strip connectors for your specific needs.
Table of Contents:
Connectors serve as the link between different sections of LED light strips or between the strips and their power source. They provide electrical continuity and ensure a secure connection, allowing the flow of current without any interruption and create a seamless installation.
LED light strip connectors come in various types and designs, each serving specific purposes. The right connector choice depends on factors such as the type of LED light strip, the intended application, and the installation requirements.
The best type of connection and connector will always be soldering gauge wires (DC wires) directly onto the LED strips. This is the strongest, most stable, and more permanent approach in connecting the lights and the driver. However, using connectors saves you time, the hassle of bringing extra tools, challenges of hooking up your tools, and even the required experience to solder correctly.
When choosing LED light strip connectors, several factors should be taken into account. By considering these factors, you can ensure compatibility, ease of installation, and optimal performance. Here are the key factors to consider:
LED light strips are available in different variations, including single-color, RGB (Red, Green, Blue), and RGBW (Red, Green, Blue, White). Each type requires a specific type of connector due to variations in the number and arrangement of contacts. It is crucial to choose connectors that are compatible with your specific LED light strip type.
Single-Color LED strips works with 2-Pin connectors
RGB or Multi-color LED strips works okay with 4-Pin connectors
RGBW LED strips will need 5-Pin connectors
LED light strip connectors are available in various types, such as:
Snap-on connectors, also known as quick connectors, are popular due to their ease of use. They feature a simple snap-on mechanism that allows you to connect and disconnect LED light strips effortlessly. These connectors are ideal for applications that require frequent reconfiguration or temporary installations.
Solderless connectors provide a reliable and secure connection without the need for soldering. They are designed with clamps or screws that hold the strip in place, ensuring a strong electrical connection. These connectors are suitable for both temporary and permanent installations.
Waterproof connectors are essential when installing LED light strips in outdoor or damp environments. They provide a protective seal that prevents moisture from entering the connection points, ensuring safe and reliable performance. If your installation requires outdoor or moisture-resistant lighting, be sure to choose connectors specifically designed for waterproofing.
The size and shape of the LED light strip connectors should be considered to ensure proper fit and compatibility. Connectors come in various sizes, ranging from compact designs for thin strips to larger connectors for high-density LED light strips. Measure the dimensions of your LED light strips and select connectors that match the size requirements.
When choosing LED light strip connectors, it's crucial to match the connector size with the width of your LED light strip to ensure a proper fit and reliable electrical connection.
When choosing LED light strip connectors, it's essential to consider both the width and density of your LED strip to ensure compatibility and proper functionality.
Standard Density Connectors: Standard density LED strips typically have fewer LEDs per meter compared to high-density strips. The connectors for standard density strips are compatible with the spacing and arrangement of LEDs in such strips.
High-Density Connectors: High-density LED strips have a higher number of LEDs per meter, resulting in brighter and more vibrant lighting. The connectors for high-density strips are designed to accommodate the closer spacing and increased number of LEDs on these strips.
L-connectors are similar to corner connectors but provide more flexibility in terms of angles. They are designed to create connections at both corners and other angles that are not necessarily 90 degrees. L-connectors allow you to customize the shape and layout of your LED light strip installation, making it easier to fit the strips around obstacles or create unique patterns.
T-connectors are designed to create connections in the shape of a "T." They are useful when you need to branch off or split your LED light strip installation into two separate paths. With T-connectors, you can extend the lighting in different directions or create multiple lighting branches from a single power source.
4-way connectors are designed to create connections in four different directions, allowing you to expand your LED light strip installation in multiple paths. These connectors enable you to split the LED strip into four separate paths, creating a more complex and versatile lighting layout. 4-way connectors are particularly useful when you want to create cross-like or grid-like patterns with your LED light strips.
LED light strip connectors utilize different connection methods, including:
Push-to-connect connectors feature a push-in mechanism that allows for quick and good connections. These connectors are user-friendly and require no additional tools for installation. However, the connection at times loses its grip.
Screw terminal connectors use screws to secure the wires in place. They offer a more reliable connection and are suitable for heavy-duty applications or installations that require extra stability. However, these connectors fit more on installations where the focus is more on stable connections.
Ensure that the LED light strip connectors are rated for the voltage and current requirements of your lighting system. Exceeding the connector's rating may result in overheating, poor performance, or even damage to the LED light strips and may even be a safety concern. Always check the capacity of the accessories like the LED connectors. Often, the rating is around 3 Amps, 5 Amps, 10 Amps, and so on.
Here at HitLights, we have several options that you can choose from depending on your project. One of the versatile connectors will be the 5-inches-any-angle connectors that we have for single-color LED strips.
Choosing the right LED light strip connectors is vital for a successful and reliable installation. By considering factors such as the type of LED light strip, connector type, size, shape, and density, connection method, and voltage/current rating, you can ensure compatibility and optimal performance. Take the time to research and select connectors that meet your specific needs, and enjoy the benefits of well-connected and beautifully illuminated LED light strips in your space.
If you need further assistance, feel free to reach out to us at customerservice@hitlights.com or give us a call at 1 (855) 768-4135. Our team of expert engineers and electricians are here to assist you every step of the way! If you are a professional installer, an integrator, or a business owner and you want to save more to do more projects, you can join our professional partnership program risk-free, no contracts, no hassle process.