Calculating the supply voltage of an LED is a necessary step for any electric lighting project, and fortunately it's easy to do. Such measurements are necessary to calculate the power of the LEDs, since you need to know its current and voltage. The power of an LED is calculated by multiplying the current by the voltage. In this case, you need to be extremely careful when working with electrical circuits, even when measuring small quantities. In the article, we will consider in detail the question of how to find out the voltage in order to ensure the correct operation of the LED elements.
LED operation
LEDs exist in different colors, there are two and three colors, flashing and changing color. In order for the user to program the sequence of operation of the lamp, various solutions are used that directly depend on the supply voltage of the LED. To illuminate the LED, a minimum voltage (threshold) is required, while the brightness will be proportional to the current. Voltage onLED increases slightly with current because there is internal resistance. When the current is too high, the diode heats up and burns out. Therefore, the current is limited to a safe value.
The resistor is placed in series because the diode grid needs a much higher voltage. If U is reversed, no current flows, but for a high U (e.g. 20V) an internal spark (breakdown) occurs which destroys the diode.
As with all diodes, current flows through the anode and exits through the cathode. On round diodes, the cathode has a shorter wire and the body has a cathode side plate.
Dependence of voltage on the type of lamp
With the proliferation of high-brightness LEDs designed to provide replacement lamps for commercial and indoor lighting, there is an equal, if not more, proliferation of power solutions. With hundreds of models from dozens of manufacturers, it becomes difficult to understand all the permutations of LED input/output voltages and output current/power values, not to mention the mechanical dimensions and many other features for dimming, remote control and circuit protection.
There are many different LEDs on the market. Their difference is determined by many factors in the production of LEDs. Semiconductor makeup is a factor, but fabrication technology and encapsulation also play a major role in determining LED performance. The first LEDs were roundas models C (diameter 5 mm) and F (diameter 3 mm). Then, rectangular diodes and blocks that combine several LEDs (networks) came into implementation.
The hemispherical shape is a bit like a magnifying glass that determines the shape of the light beam. The color of the emitting element improves diffusion and contrast. The most common designations and form of LED:
- A: red diameter 3mm in holder for CI.
- B: 5mm red diameter used in front panel.
- C: purple 5mm.
- D: bicolor yellow and green.
- E: rectangular.
- F: yellow 3mm.
- G: white high brightness 5mm.
- H: red 3mm.
- K- anode: cathode, indicated by a flat surface in the flange.
- F: 4/100mm anode connecting wire.
- C: Reflective cup.
- L: A curved shape that acts like a magnifying glass.
Device specification
A summary of the various LED parameters and supply voltage is in the seller's specifications. When choosing LEDs for specific applications, it is important to understand their difference. There are many different LED specifications, each of which will influence the choice of a particular type. LED specifications are based on color, U, and current. LEDS tend to provide one color.
The color emitted by an LED is defined in terms of its maximum wavelength (lpk), which is the wavelength that has the maximum light output. Typically, process variations give peak wavelength changes of up to ±10 nm. When choosing colors in the LED specification, it is worth remembering that the human eye is most sensitive to hues or color variations around the yellow/orange region of the spectrum - from 560 to 600 nm. This may affect the choice of color or position of the LEDs, which is directly related to electrical parameters.
LED current and voltage
During operation, LEDs have a given U drop, which depends on the material used. The supply voltage of the LEDs in the lamp also depends on the current level. LEDs are current controlled devices and the light level is a function of the current, increasing it increases the light output. It is necessary to ensure that the operation of the device is such that the maximum current does not exceed the allowable limit, which can lead to excessive heat dissipation within the chip itself, reducing the luminous flux and shortening the service life. Most LEDs require an external current limiting resistor.
Some LEDs may include a series resistor, so what voltage to supply the LEDs is required. LEDs do not allow large inverse U. It should never exceed its stated maximum value, which is usually quite small. If there is a possibility of a reverse U on the LED, then it is better to build protection into the circuit to prevent damage. These can usually be simple diode circuits that will provide adequate protection for any LED. You don't have to be a pro to get it.
Power supply for LEDs
Lighting LEDs are current-powered, and their luminous flux is proportional to the current flowing through them. The current is related to the supply voltage of the LEDs in the lamp. Several diodes connected in series have equal current flowing through them. If they are connected in parallel, each LED receives the same U but different current flows through them due to the dispersion effect on the current-voltage characteristic. As a result, each diode emits a different light output.
Therefore, when selecting elements, you need to know what voltage the LEDs have. Each requires approximately 3 volts at its terminals to operate. For example, a 5-diode series requires approximately 15 volts across the terminals. In order to supply a regulated current with sufficient U, the LEC uses an electronic module called a driver.
There are two solutions:
- External driver installed outside the luminaire, with safety extra-low voltage power supply.
- Internal built into the flashlight, i.e. sub-unit with an electronic module that regulates the current.
This driver can be powered by 230V (Class I or Class II) or Safety Extra Low U (Class III), such as 24V..
Advantages of LED voltage selection
Proper calculation of the supply voltage of the LEDs in the lamp has 5 key advantages:
- Safe ultra-low U, possibly regardless ofnumber of LEDs. The LEDs must be installed in series to guarantee the same level of current in each of them from the same source. As a result, the more LEDs, the higher the voltage at the LED terminals. If it is an external driver device, then the oversensitive safety voltage should be much higher.
- The integration of the driver inside the lanterns allows for a complete system installation with safety extra low voltage (SELV), regardless of the number of light sources.
- More reliable installation in the wiring standard for LED lamps connected in parallel. Drivers provide additional protection, especially against temperature rise, which guarantees a longer service life while respecting the supply voltage of LEDs for different types and currents. Safer commissioning.
- Integrating LED power into the driver avoids mishandling in the field and improves their ability to withstand hot plugging. If the user only connects the LED light to an external driver that is already on, it may cause the LEDs to overvoltage when they are connected and therefore destroy them.
- Easy maintenance. Any technical problems are more easily visible in LED lamps with a voltage source.
Power and heat dissipation
When the U drop across a resistance is important, you need to choose the right resistor capable of dissipating the required power. Consumption20 mA may seem low, but the calculated power suggests otherwise. So, for example, for a voltage drop of 30 V, the resistor must dissipate 1400 ohms. Power dissipation calculation P=(Ures x Ures) / R, where:
- P - value of power dissipated by the resistor, which limits the current in the LED, W;
- U - voltage across the resistor (in volts);
- R - resistor value, Ohm.
P=(28 x 28) / 1400=0.56 W.
A 1W LED power supply would not withstand overheating for a long time, and 2W would also fail too quickly. For this case, two 2700Ω/0.5W resistors (or two 690Ω/0.5W resistors in series) must be connected in parallel to evenly distribute heat dissipation.
Heat control
Finding the optimal wattage for your system will help you learn more about the heat control required for reliable LED operation, as LEDs generate heat that can be very damaging to the device. Too much heat will cause the LEDs to produce less light and also shorten the lifespan. For a 1 watt LED, it is recommended to look for a 3 square inch heatsink for each watt of LED.
Currently, the LED industry is growing at a fairly rapid pace and it is important to know the difference in LEDs. This is a general question as products can range from very cheap to expensive. You need to be careful when buying cheap LEDs, as they can work.excellent, but, as a rule, do not work for a long time and burn quickly due to poor parameters. In the manufacture of LEDs, the manufacturer indicates in the passports the characteristics with average values. For this reason, buyers do not always know the exact characteristics of LEDs in terms of lumen output, color and forward voltage.
Forward voltage determination
Before you know the LED supply voltage, set the appropriate multimeter settings: current and U. Before testing, set the resistance to the highest value to avoid LED burnout. This can be done simply: clamp the multimeter leads, adjust the resistance until the current reaches 20 mA and fix the voltage and current. In order to measure the forward voltage of the LEDs you will need:
- LEDs to test.
- Source U LED with parameters higher than constant voltage LED.
- Multimeter.
- Alligator clamps to hold the LED on the test leads to determine the supply voltage of LEDs in fixtures.
- Wires.
- 500 or 1000 ohm variable resistor.
The blue LED's primary current was 3.356V at 19.5mA. If a voltage of 3.6V is used, the value of the resistor to use is calculated by the formula R=(3.6V-3.356V) / 0.0195A)=12.5 ohms. To measure high power LEDs, follow the same procedure and set the current by quickly holding the value on the multimeter.
Measuring the supply voltage of smd LEDs high> 350 mA direct current power can be a little tricky because when they heat up quickly, U drops drastically. This means that the current will be higher for a given U. If the user does not have time, he will have to cool the LED to room temperature before measuring again. You can use 500 ohm or 1k ohm. To achieve coarse and fine tuning, or to connect a higher and lower range variable resistor in series.
Alternative definition of voltage
The first step to calculate the power consumption of LEDs is to determine the voltage of the LED. If there is no multimeter at hand, you can study the manufacturer's data and find the passport U of the LED block. Alternatively, you can estimate U based on the color of the LEDs, for example, the supply voltage of a white LED is 3.5V.
After the LED voltage is measured, the current is determined. It can be measured directly with a multimeter. The manufacturer's data gives a rough estimate of the current. After that, you can very quickly and easily calculate the power consumption of the LEDs. To calculate the power consumption of an LED, simply multiply the U of the LED (in volts) by the LED current (in amps).
The result, measured in watts, is the power the LEDs use. For example, if an LED has a U of 3.6 and a current of 20 milliamps, it will use 72 milliwatts of energy. Depending on the size and scale of the project, voltage and current readings may be measured in smaller or larger units than base current or watts. Unit conversions may be required. When doing these calculations, remember that 1000 milliwatts equals one watt, and 1000 milliamps equals one ampere.
LED test with multimeter
To test the LED and find out if it works and what color to choose - a multimeter is used. It must have a diode test function, which is indicated by the diode symbol. Then, for testing, fix the measuring cords of the multimeter on the legs of the LED:
- Connect the black cord on the cathode (-) and the red cord on the anode (+), if the user makes a mistake, the LED does not light up.
- They supply a small current to the sensors and if you can see that the LED is glowing slightly, then it is working.
- When checking the multimeter, you need to consider the color of the LED. For example, yellow (amber) LED test - LED threshold voltage is 1636mV or 1.636V. If white LED or blue LED is tested, the threshold voltage is higher than 2.5V or 3V.
To test a diode, the indicator on the display must be between 400 and 800 mV in one direction and not show in the opposite direction. Normal LEDs have threshold U as described in the table below, but for the same color can have significant differences. The maximum current is 50 mA, but it is recommended not to exceed 20 mA. At 1-2 mA, the diodes already glow well. Threshold LED U
| LED type | V up to 2 mA | V up to 20 mA |
| Infrared | 1, 05 | 1.2 |
| Red LED supply voltage | 1, 8 | 2, 0 |
| Yellow | 1, 9 | 2, 1 |
| Green | 1, 8 | 2, 4 |
| White | 2, 7 | 3, 2 |
| Blue | 2, 8 | 3, 5 |
When the battery is fully charged, the current is only 0.7mA at 3.8V. In recent years, LEDs have made significant progress. There are hundreds of models, with a diameter of 3 mm and 5 mm. There are more powerful diodes with a diameter of 10 mm or in special cases, as well as diodes for mounting on a printed circuit board up to 1 mm long.
Starting LEDs from AC power
LEDs are generally considered DC devices, operating on a few volts of DC. In low power applications with few LEDs this is a perfectly acceptable approach, such as mobile phones powered by a DC battery, but other applications such as a linear strip lighting system extending 100m around a building cannot function with this arrangement.
The DC drive suffers from distance losses, requiring higher drive U from the start, andadditional regulators that lose power. AC makes it easier to use transformers to step down U to 240 V AC or 120 V AC from kilovolts used in power lines, which is much more problematic for DC. Starting any type of LED with mains voltage (e.g. 120V AC) requires electronics between the power supply and the devices themselves to provide a constant U (e.g. 12V DC). The ability to drive multiple LEDs is important.
Lynk Labs has developed a technology that allows you to power the LED from AC voltage. A new approach is to develop AC LEDs that can operate directly from an AC power source. Many standalone LED fixtures simply have a transformer between the wall outlet and fixture to provide the required constant U.
A number of companies have developed LED light bulbs that screw directly into standard sockets, but they invariably also contain miniature circuits that convert AC to DC before being fed to the LEDs.
A standard red or orange LED has a threshold U of 1.6 to 2.1 V, for yellow or green LEDs the voltage is from 2.0 to 2.4 V, and for blue, pink or white, this voltage is approximately 3.0 to 3.6 V. The table below lists some typical voltages. Values in brackets correspond to the closest normalizedvalues in series E24.
The power supply voltage specifications for LEDs are shown in the table below.
Symbols:
- STD - standard LED;
- HL - high brightness LED;
- FC - low consumption.
This data is enough for the user to independently determine the necessary device parameters for the lighting project.
