LED应用中，LED电路的形式，及电阻的计算-----LED applications and circuit calculation method

七、工程中的简易计算方法
1. 由已知电源功率计算LED的数量
(即取所得数据的整数) （7-1）
例：额定输出功率为10W电源，使用额定的正向电流20mA，耗散功率为70mW条件下可配置多少个LED？
依以上公式
(即取所得数据的整数)
2. 对于恒压驱动方式：由已知的输出电源电压计算每支路串联LED数量及并联支路数
（1）计算每条支路的LED个数 公式： (最大值)
（2）计算并联支路数 公式:
注：VLED值依不同发光颜色各有不同，用稳压电源驱动LED时，为了控制电流，通常需要串联电阻器。
例：一个额定输出电压为DC 24V,功率为10W电源，使用额定正向电流20mA，耗散功率为70mW额定的正向电压为1.8V。可配置多少个LED呢？
依以上公式可以得出
(即取所得数据的整数)
即可以带10组支路，每支路14个LED串联构成的电路，共140个LED。
3. 对于恒流驱动方式：由已知的电源输出电流及LED的电流值计算出并联支路数及每支路数量
（1）计算并联的支路数公式： (最小值)
（2）计算支路串接LED个数:
注：其中n按（7-1）计算
例：一个额定输出电流为DC 0.35A，额定功率为10W电源，驱动耗散功率为70mW，正向电流为0.02A的LED，可怎样配置？
依以上公式可以得出
并联支数路：
(即取所得数据的整数)
每支路串接数：个数
即可以带17组，每组8个LED串接，共136个LED。
4. 线路损耗及线路压降的计算
P电线=I R V电线=IR
R电线=σ （备注：L为电线长度；S为电线横截面积；σ为电线电导率）也可以查电工手册。
例：用长度为10米（正、负极电线各5米），24AWG的铜芯电线，通过电流为2A，其损耗的功率及线路压降为多少?
查电工手册可知：R电线 = 0.737W
V电线 = 2×0.737 =1.474V
P电线 = 2 ×0.737 = 2.948W
从以上计算可以看出，线路电流较大时，要注意选择合适的导线截面，否则线路损耗及线路压降是相当大的。
我们只有完全了解LED和LED电源的基本特性，才能正确设计和使用LED光源。

GOOGLE TRANSLATE

Introduction of LED light source applications:
LED lighting industry is an emerging industry, it is by the people for its unique advantages of all ages. Today in the optical engineering to improve lighting efficiency, energy saving and high reliability has become a common pursuit of purpose. We are in discussions and use of LED light source, will think of LED's long life, energy saving, high brightness characteristics. Is precisely because of this LED light source was popular. Despite these advantages LED light source, but not as it says it is magic. Only to its coupled with appropriate, efficient LED power supply, reasonable circuit design, improved anti-static measures, proper installation and use of technology to give full play to advantages of LED light source above. Here I LED light source applications in the works of some common sense to do a brief introduction for your reference.
2, LED life understanding
LED life is generally believed that under ideal conditions, 10 million hours. Actually in the course of its intensity with the use of the gradual decay over time, that the efficiency of light energy into electrical energy decreases. We can really use the effective range of light intensity should be in its decay to the initial light intensity of 70% or more, life is defined as the luminous efficiency can be gradually reduced to 70% of the time. There is no clear national standards to measure. LED chip life and its quality and packaging technology, process is directly related to LED packaging factory, according to a test data under some chips 20mA continuous light, after 4000 hours the brightness of its light attenuation reached 50%. But with the technology, process improvement, light failure time is slow, that is, the longer life expectancy.
3, LED energy-saving and reliability
LED is a current control element, by the current flowing through directly to electrical energy into light energy, it also called electron converter. Does not exist because of friction losses and mechanical losses, so energy saving light source than the average efficiency, but the LED light source and not as an ordinary light source can be directly used as grid voltage, it must configure a voltage converter to provide meet rated voltage, current, to the normal use, the LED Power Supply. However, a variety of LED power conversion efficiency of its performance and different, so choose a suitable and efficient LED dedicated power supply, can only truly efficient LED light source characteristics. Because of the low efficiency of LED power supply itself consumes a lot of power, with LED's used in the process of not simply reflect the high efficiency LED power-saving features. And the LED power supply must also be highly reliable power supply, can the long-life LED light source system.

4, LED's basic features and use precautions
1. Optical characteristics:
LED in its current limits within the parameters of the current flowing through LED larger, the higher its brightness. The LED's brightness is proportional to the current through the LED. But the green and blue and white situation in the high current saturation phenomenon occurs not only significant reduction in luminous efficiency, and life will become shorter.
2. Optical properties
LED divided by the color red, orange, yellow, green, blue, purple, white and other colors. Brightness divided by general light, bright, super bright, etc., the same kind of chips in different packages, it is not the same brightness. By human vision can be divided into visible and invisible light. According to the number of luminous color can be divided into monochrome, color, colorful and many other types. The purity of color vary widely different prices, the current pure white LED at a price you. At the same time emitting different perspectives, have different optical effects, especially should pay attention when using.
3. Common parameters of the electrical properties of LED
(1) LED forward voltage
Different colors of LED forward current at rated conditions, with their different forward voltage drop value, red, yellow: 1.8 ~ 2.5V, between green and blue: 2.7 ~ 4.0V between. For the same color LED, the forward voltage drop and the light intensity is not entirely consistent. The following table:
LED type: 5 4HCA
Color Appearance Color LED wavelength λD (nm) Forward Voltage VF intensity Iv (mcd)
IF = 20mA
Min. Max.
Red water transparency 1.8 2.2 500 620 ~ 645 ~ 10000
Transparent yellow-green water, 570 ~ 575 1.8 2.2 500 ~ 3000
Transparent yellow water 1.8 2.2 500 585 ~ 595 ~ 10000
Transparent Blue Water 475 3.0 3.4 455 ~ 500 ~ 10000
Transparent green water 515 ~ 535 3.0 3.4 2000 ~ 20000
Transparent blue-green water, 490 ~ 515 3.0 3.4 2000 ~ 20000
White water transparency 3.0 3.4 3000 ~ 25000
In the same circuit should make full use of the forward voltage drop under rated current value of the same intensity range of small LED. The only way to ensure consistent LED glow. Its specific electrical properties we can also provide various packaging factory packaging products for each spectral parameter tag value. (Some companies are inconsistent with each batch of separation)
(2) LED's rated current
The rated current of LED vary the LED current is usually normal 20mA, high-power LED current is typically 40 mA or 350 mA range. According to the packaging factory to provide the specific current parameter values.
General LED in the reverse voltage: VR = 5V conditions, the reverse current: IR ≤ 10μA.
(3) LED power
The size of LED power is also different, with 70mW, 100mW, 1W, 2W, 3W, 5W, etc.
Must be chosen according to the LED, designed to use and configure the appropriate LED circuit the number of LED power supply to fully meet the ratings, if the circuit design so that each LED would be too high voltage or current-sharing seriously affect the LED's life or even burning LED, if the share of low voltage or current excitation of the LED light intensity is not enough, we can not give full play to the effect of LED should not reach our expectations purpose.
4. Temperature characteristics
(1) LED soldering temperature should be below 250 ℃, welding time control between the 3 ~ 5S. LED temperature is too high to be taken to avoid damage to the chip.
(2) LED's light output with temperature is inversely proportional to the temperature not only affects the LED's brightness, but also affect its life. To minimize the use of the circuit, fever, and do some heat treatment.
5. Anti-static properties
LED assembly process must strengthen the anti-static measures, and the human body because the operation will have a static, two-electrode of the LED for the most vulnerable to static reverse breakdown, which seriously affect the service life of LED and even make it completely scrapped.
Such as anti-static environment is not very well, can give the user increased anti-static wrist strap LED, set a good anti-static grounding system, ion blower and other equipment.

5, LED connection circuit of the common forms of
1. Series: This circuit requires a higher voltage power supply.
V total = the sum of the LED's VF = VF1 + VF2 + VF 3 + VF 4 ------+ VF N
I total = the value of single LED's IF
2. Parallel: This circuit requires a power supply can provide higher current.
V = total value of single LED of the VF
I total = sum of all LED's IF = IF1 + IF2 + IF3 + IF4 ------ + IFN
3. Series / parallel combinations
a, in practice, the load is often used by the formation of series-parallel LED array;
b, the LED connected in series / parallel combinations of forms, can be significantly reduced due to a small number of LED's VF inconsistent impact;
c, the number of changes in array form, or LED, current limiting resistor should be changed accordingly.
d, series / parallel combination will form the output current with input voltage and ambient temperature changes and other factors more significant;
4. In order to effectively control the circuit current in the circuit configuration to be the appropriate current limiting resistor.
R = (V input voltage-VLED total voltage) / I (flow through the current limiting resistor)
The main function of the current limiting resistor to control LED current, the voltage is more smooth, and to the parallel branch is more uniform brightness. Limiting resistor big is better, but the values of the current limiting resistor can not be too much, otherwise it will increase the power loss and component temperature.

6, the power of the classification and characteristics
1, by driving mode can be divided into two main categories:
(1) Constant Current:
a, constant current drive circuit output current is constant, while the output DC voltage is different as the size of the load resistance varies within a certain range, the load resistance is small, the output voltage is low, the greater the load resistance, output the higher voltage;
b, constant fear load short circuit, but the non-load fully open.
c, constant current drive circuits to drive the LED is ideal, but relatively higher prices.
d, should be noted that the use of the maximum withstand current and voltage, it limits the number of LED's use;
(2) Regulators type:
a, when the regulator to determine the parameters of the circuit after the output voltage is fixed, while the output current but increase or decrease with load change;
b, open circuit voltage regulator circuits are not afraid of the load, but completely short-circuit the load is strictly prohibited.
c, regulator drive circuit to drive LED, each with an appropriate resistor string needs to be the average brightness of each string of LED display;
d, the brightness will come by the rectifier voltage change.
2, the circuit structure by way of classification
(1) resistor, capacitor step-down way: through the capacitor step-down, when used in the flashing, because the role of charge and discharge, the instantaneous current through the LED extremely easy to damage the chip. Vulnerable to grid voltage fluctuations, power efficiency is low, low reliability. (See Figure 1)
(2) resistance step-down way: through the resistance of blood pressure, interference by the larger power grid voltage, regulated power supply is not easily made, step-down resistor to consume very much energy, so this power supply power supply efficiency is low, and the reliability of the systems are also low. (See Figure 2)
(3) conventional transformer step-down approach: power small, too much weight, power efficiency is very low, only 45% to 60%, so seldom used, reliability is not high.
(4) Electronic transformer step-down approach: power efficiency in low voltage range is not wide, generally 180 ~ 240V, wave interference of.
(5) RCC buck mode switching power supply: voltage range is wide, more efficient power supplies in general can do 70% to 80%, applications are wider. As the oscillation frequency of this control method is not continuous, the switch frequency is not easy to control, the load voltage ripple coefficient is relatively large, abnormal loads and less adaptable.
(6) PWM control mode power supply: mainly composed of four parts, input rectifier filter section, some of the output rectifier, PWM regulator control part, switching power conversion section. PWM switching regulator is the basic working principle of the input voltage, the internal parameters and external load changes, the control circuit is controlled by the difference between signal and reference signal for closed-loop feedback, adjust the primary circuit switching devices turn the pulse width, makes the switching power supply's output voltage or current stable (ie the corresponding power supply or a constant current power supply). High power efficiency, the general can do 80% to 90%, the output voltage and current stability. This circuit has a good general protection measures, is a highly reliable power supply.
As can be seen from the above description is designed PWM control mode LED power supply LED power supply is ideal. Currently Zhuhai South Yuxing Electronics Company production of "King Xing" brand is the LED switching power supply switching power supply PWM control techniques, such LED power by users to reflect good results.

7, the simplified calculation method works
1. By a known amount of power supply LED power calculation
(Ie take the data of the integers) (7-1)
Example: Rated output power 10W power supply, use the rated forward current of 20mA, 70mW power dissipation can be configured under the conditions of the number of LED?
According to the formula above
(That is, the data obtained integer)
2. For the constant drive mode: from the known output voltage LED calculating the number of each road series and parallel circuit number
(1) calculation formula for each branch of the LED Number: (max.)
(2) The formula for calculating the number of parallel branch:
Note: VLED values according to different colors in different light, LED driver with regulated power supply, in order to control the current, usually in series resistor.
Example: a rated output voltage of DC 24V, 10W power supply, use the rated forward current of 20mA, 70mW power dissipation rating of the forward voltage of 1.8V. How many LED can be configured to do?
According to the above formula can be drawn
(That is, the data obtained integer)
10 groups that can take the slip road, each road 14 LED series circuit consisting of a total of 140 LED.
3. For the constant current drive mode: from the known power supply output current and the LED's current value and the number of parallel branch number of each road
(1) formula for calculating the number of parallel branch: (minimum)
(2) calculating the number of slip cascading LED:
Note: where n according to (7-1) calculated
Example: A rated output current of DC 0.35A, 10W rated power, drive power dissipation of 70mW, forward current of 0.02A of the LED, can be how to configure?
According to the above formula can be drawn
Road parallel count:
(That is, the data obtained integer)
Each road series with a few: the number of
That can bring 17 groups of eight LED connected in series, a total of 136 LED.
4. Line loss and line pressure drop calculation
P wire = I R V = IR wire
R cable = σ (Note: L for the cable length; S was wire cross-sectional area; σ over electrical conductivity) can also check electrical manual.
Example: with a length of 10 meters (positive and negative wires each 5 meters), 24AWG the copper wires, through the current of 2A, the loss of power and line pressure drop as much?
Charles Electrical Manual known: R wire = 0.737W
V wire = 2 × 0.737 = 1.474V
P wires = 2 × 0.737 = 2.948W
As can be seen from the above calculation, the line current is high, pay attention to choose the right wire section, or line loss and line voltage drop is considerable.
Only when we fully understand the power LED and LED's basic characteristics, to properly design and use of LED light sources.