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Basic Knowledge about LEDs
Jul 10,2014
Classification of LED lights:
Fluorescent lights, panel lights, downlights, ceiling lights, spotlights, track lights, etc. (There are many classifications, just like people's names. You can search online, but you will find that the search results are generally incomplete. We can check the indexed directory on Alibaba; all kinds of lights are listed there, so get familiar with it.)
Classification of common light beads:
1. The specifications for direct plug-in small power types include: hat/helmet, round head, concave, oval, tombstone type (2*3*4) bullet head, flat head, (3/5/flat head/bread type) piranha, etc.
2. SMD chips are generally divided into (3020/3528/5050, which are front-emitting) / 1016/1024, etc., which are side-emitting light sources. The naming is based on the specifications of the chip, such as 3020, which refers to a specification of 30mm*20mm.
3. High-power LEDs cannot be classified into the chip series; their power and current usage are different, and their optical and electrical parameters vary significantly. A single high-power LED light source, if not equipped with a heat sink (usually a hexagonal aluminum base), looks similar to ordinary chips. High-power LED light sources are round, and the packaging method is basically the same as SMD chips, but there are essential differences in usage conditions/environment/effects.
Single bead voltage: The voltage of ordinary beads is 2.8-3.6vf, and when calculating in series and parallel, the average value of 3.3vf is taken.
Power supply classification:
Divided by output characteristics: constant voltage series (CV), constant current series (CC) (constant voltage means constant voltage output, constant current means constant current output; there is also a complementary power supply that is constant voltage + constant current).
Divided by input characteristics: ordinary series, high power factor series (high power factor mainly refers to power factor, which will be detailed later).
Divided by purpose: waterproof series, non-waterproof series (this doesn't need explanation, everyone understands).
Divided by circuit structure: isolated series, non-isolated series (the difference between isolation and non-isolation mainly lies in whether there is a transformer. As we know, household voltage is 220V AC. The design idea of isolated power supplies is to step down the voltage through a transformer before rectification, which can separate high and low voltage areas. This design has advantages over non-transformer power supplies, such as our LED power supply outputting a safe DC voltage that can be directly touched by people (except for high-power supplies). Even if the low-voltage part fails, it won't leak electricity, but non-isolated ones can easily lead to electric shock).
Divided by control method: dimmable series, non-dimmable series (dimming parameters will be detailed later).
Series and parallel:
First, confirm the total forward voltage of each series of LEDs, then add about 2V for the constant current driver voltage drop.
Each series LED working voltage = 3.5V X 12 beads = 42V.
Driver circuit voltage = 42V + 2V = 44V.
LED current = 0.7A X 4 series in parallel = 2.8A.
Driver circuit wattage = 44V X 2.8A = 123.2W.
The wattage/voltage selection of the LED power supply should be greater than and closest to the required wattage/voltage.
First, select the LED power supply based on 150W/48V, then confirm whether the actual wattage of the driver circuit meets the PF>0.9 load requirement (123.2W /150W = 82.13%>75%).
For example, this question can choose the CLG-150A-48 model and adjust the output voltage to 44V or apply it directly without adjusting the output voltage.
Note: Generally, the Vf voltage of the same batch of LEDs may be within a range (e.g., 3.4~3.6V), and each LED has differences, so this difference must be considered in power supply selection.
PWM dimming:
The dimming methods for MW dimming power supplies mainly include controlling signals (resistor/voltage/PWM) to adjust current dimming and thyristor AC (phase-shifting) to adjust voltage dimming.
1. Products with control signal dimming include ELN, LPF-XD, HLN-XB, HLP, HLG-XB, HVG(S)-XB, etc. Their adjustment range is 5/15%～100/103% of the rated current. There are three options for control signals as follows.
a). Potentiometer (100kΩ/1～2kΩ variable resistor, adjusts the current through the LED by changing the potentiometer resistance value).
b). 1～10V DC voltage, adjusts the current through the LED by changing the control voltage.
c). PWM signal (pulse width 10V, f:100～3000Hz, duty cycle: 0～100%). Adjusts the average current through the LED by changing the duty cycle, and this control method can maintain the color temperature of the LED.
Some specifications also have timing control functions (e.g., HLG/HVG-D).
The electromagnetic compatibility (EMS) of dimming power supplies with control signal dimming is good, with a wide and smooth dimming range.
2. Thyristor AC (phase-shifting) voltage dimming products include the PCD series. (The matching thyristor dimmer has specified models; other models cannot guarantee dimming effects). Thyristor voltage dimming power supplies have poorer performance and are generally used in old system renovations and low-cost applications.
Power supply input voltage:
For example: 88-264V/AC, as long as the voltage used in various countries is within this range, it is fine. However, it is worth noting the frequency; our country uses 50Hz, while other countries may differ, so this should be noted.
Power supply output voltage/current/power:
Output is generally also a range. If the voltage required by the user is within this output range, it is acceptable. Of course, the output power must also be sufficient.
Power supply power factor:
The cosine of the phase difference (Φ) between voltage and current is called the power factor. Conceptual things can be really troublesome; if a liberal arts person looks at it, they would probably feel overwhelmed and confused. Let me put it this way: to do work, there must be voltage. Just having voltage is not enough; there must also be current. Because the voltage delivered by the power plant is slightly slower than the current, it leads to some complex concepts. However, we are not here to study this, so we just need to know that the power factor is roughly an efficiency measure, and the closer its value is to 1, the better the effect. There is also a parameter called PFC, which is used to improve the power factor, as you will see in the subsequent parameters.
Surge:
Surge voltage/current: 1. The input surge current refers to the large surge current in the input circuit of the power supply due to its capacitive characteristics during cold start, generally ranging from 20 to 60A, lasting no more than 20mS. The surge current in the power supply under hot conditions is slightly smaller, and frequent power cycling should be avoided to reduce the impact of large currents on the power supply and distribution system. 2. The surge withstand capability of the power supply refers to the surge voltage tolerance at the input end (L to N or GND), with a typical surge voltage tolerance of 300Vac/5S for 220V level power supplies.
Current accuracy
Current harmonics
Output ripple:
Ripple voltage: The ripple voltage of a switching power supply contains two components: one is the double frequency component of the input power supply, which has a larger amplitude, and the other is the switching frequency component, which has a higher frequency (up to several kHz) and a smaller amplitude (sometimes referred to as noise signal). The impact of these two components varies with different loads; usually, only the more significant component is considered, and it is uncommon for both components to have a significant impact on the load simultaneously.
Safety regulations:
Safety regulations are standards established to prevent six types of hazards (these six hazards are: 1) electric shock; 2) energy hazards; 3) fire hazards; 4) mechanical and thermal injuries; 5) radiation; 6) chemical injuries) caused by poor materials, design errors, or misuse of components.
Safety regulations include two major product certification directions: American and IEC.
The American system is represented by UL and CSA (UL/CSA60950-1-03),
The European IEC system (EN/IEC60950-1,
China's GB4943-2001 is equivalent to IEC60950-1999) is guided by CB,
The most famous and influential is the CE certification of the European Union. Common safety certifications include CB, CE, UL, FC, TUV, IEC, CAS, CCC, etc.
UL and VDE safety standards have essential differences; UL specifications focus more on preventing fire hazards, while VDE specifications focus more on the safety of operators. For power supplies, VDE is the strictest electrical safety standard.
EMC:
EMC refers to the electromagnetic compatibility requirements of products. EMC = EMI + EMS, where EMI refers to the electromagnetic interference limit requirements of the product, and EMS refers to the product's resistance to electromagnetic interference. These two requirements ensure that products can coexist with surrounding products without interfering with each other in terms of electromagnetic interference. EMC's assessment of a product's electromagnetic impact mainly focuses on EMS's resistance to electromagnetic interference, including electrostatic discharge, electrostatic fields, radio radiation, pulse radiation, lightning, radio conduction, power frequency electromagnetic fields, and power supply transient withstand. It also includes EMI's interference limit assessment, such as radio emission/conduction, voltage flicker, harmonics, and other interference limits.
PFC
PFC (Power Factor Correction) is mainly for improving the ratio of effective power to apparent power at the input of the power supply. Generally, models without PFC circuits have a power factor of only 0.4 to 0.6, while those with active PFC circuits can reach above 0.95, as shown in the following formulas:
Apparent power = Input voltage x Input current (VA)
Effective power = Input voltage x Input current x Power factor (W)
From an environmental perspective: Power companies must generate electrical energy greater than apparent power for their generators to stably supply market energy demand, while the actual use of electrical energy is effective power. If the power factor is 0.5, it means the generator must output more than 2VA of power to safely supply 1W of demand, which is inefficient. Conversely, if the power factor is improved to 0.95, the power company only needs to output more than 1.06VA of power to meet the 1W demand, resulting in better energy efficiency.
MTBF:
Mean Time Between Failure (MTBF) and Life Cycle are both important indicators of product reliability. MTBF (Mean Time Between Failure) is the expected value of reliability estimation, referring to the average time after which the reliability of a product drops to 36.8% after continuous operation for a period. Mean Well's MTBF currently uses the MIL-HDBK-217F standard, estimating the expected reliability of the product using the parts count method (excluding fans), indicating that the product has a 36.8% probability of functioning normally after reaching the counted time. If the product is used for twice the counted MTBF time, the probability of it functioning normally drops to 13.5%.
Life Cycle refers specifically to the temperature rise of the product's electrolytic capacitor under full load conditions, calculating the reference value for the lifespan of the electrolytic capacitor. For example, for the product SP-750-12, MTBF=769.3K hours, and capacitor C108 Life Cycle=202.2K hours (Ta=45°C).
Aging:
This is equivalent to testing whether the product can work normally after it is released. This test is not just a simple check to see if it is okay; it involves long-term testing to see if the product is stable, and it may even require testing in an environment with abnormal temperatures. As for how long to test, it seems to be at least four hours, depending on the situation.
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