With the advent of high-power LED, general fluorescent or incandescent 5 to 7 times its luminous efficiency, energy-saving effect is very significant. Thus, the high-power LED has broad application prospects. Currently, a single high-power LED has 1W, 3W, 5W and 10W, has been heavily used 1W and 3W high power LEDs, multiple high-power LED series and parallel, the the combination output power reached 70W ~~ 100W.

High-power LED with high luminous efficiency and energy-saving advantages, but inconsistent pipe pressure drop is the need to overcome the shortcomings. Second, poor temperature characteristics of the high-power LED. Tube current and luminous efficiency varies greatly with the junction temperature and ambient temperature changes, which bring inconvenience to use.

High power LED above shortcomings, people use more than two drive options: 1. Constant voltage source driver. That is, using a plurality of LED in parallel with a constant voltage source driver. Thus, since the tube voltage drop of the LED is inconsistent, so that the diode current is inconsistent, so that the luminous efficiency is also quite different. This program is seldom used in high-power LED. 2 constant current source driver. Inconsistent pipe pressure drop of the high-power LED, LED by their junction temperature and ambient temperature influence, so the number of LED series and driven with a constant current source can effectively overcome these shortcomings.

The main features of the high-power LED

Operating wavelength
The operating wavelength of the high-power LED with its glowing colors. For example, cold white LED operating wavelength of 525 angstroms to 600 angstroms, while warm white LED operating wavelength between 525 angstroms to 675 angstroms.

Forward voltage drop
High power LED's forward voltage for each change of 0.1V, the current change of about 100mA.

The relationship of the working current and luminous intensity
The high power LED luminous intensity of its junction temperature and ambient temperature. This is mainly due to temperature increases, the operating current is also reduced correspondingly, Similarly, LED's luminous intensity and its current relationship is approximately linear, and its working current each reduction 100mA for 1W and 3W LED, the light emitting intensity is reduced about 15%.

High power LED series constant current

The principle of the source drive
Currently appearing on the market of high power LED series drive has its limitations, typically three to six LEDs in series, and the number to be sure, can not be any coection. In this paper, an arbitrary (1 to 20) LED constant current source driver program series, shown in Figure 1, the following works:

1W LED, for example, the rated current of 350mA. For some reason, the LED current is reduced, the constant current source circuit of the acquisition to the current value of the change (decrease) after having amplified by U1 transmission to the control circuit. Inversion processing in the control circuit of the sampling signal, the output pulse width is increased. Power tube D5 conversion stage of the driving power of the output pulse width increases, so that the secondary output voltage increases. In this way, the voltage across the LED in series also increases, therefore, the current flowing through the LED is also increased, which maintain a constant LED current. Similarly, if for some reason, so that the LED current is increased, contrary to the control process. Advantages that: The constant current source drives regardless of the LED voltage drop difference Junction ambient temperature changes cause changes in diode current much, can be accessed through the rapid adjustment of the high-speed constant-current source circuit to Maintain constant current LED.

High power LED constant current source
To pay attention to the design of the drive

The design of high-power LED constant current source drives should pay attention to the following points:
1. To select the control of the control chip of the circuit in accordance with the number of the LED series. Because of the number of LED chips required output power is different. Figure 1 ICE 2A165, also choose other similar switching power supply control chip.

2. Switching power supply transformer leakage induction is as small as possible, otherwise the drive will reduce the reliability. Because the leakage inductance of the transformer, switch off instantly produces very high reverse voltage spikes, severe cases may exceed the breakdown voltage of the control switch, leaving the LED chip breakdown, causing the reliability of the drive is greatly reduced. Switching power supply transformer T1 is the key parts of the product, it is necessary to the production of the professional manufacturers.

3. The operating speed of the constant-current source circuit to be fast, so that can make the LED safer. In this paper, series of LED drive any number (1 to 20) of the series, this would require the change of the output voltage of the switching power supply faster to adjust slowly, and may cause damage to the LED's.
Practice has proved that this paper, high-power LED constant current source drives the program is feasible, and compared with other drives, lower cost, which has broad application prospects.

Zhejiang Intel Optoelectronics Technology Co., Ltd. in the Changfeng Garden Hotel held a grand press conference grand release SMD3535 light source new products. Shanghai Sansi Electronic Engineering Co., Ltd., Shenzhen City the Xiang Hui Keguang electric Science and Technology Co., Ltd., Shenzhen, as Kaiwei Optoelectronics Co., Ltd., Shenzhen Ralink Technology Co., Ltd., Shenzhen the Corrente Science and Technology Co., Ltd., Shenzhen Lan Pu Technology Co., Ltd and other well-known brand manufacturers are invited to participate in the event.

Intel to photovoltaic research and development center director, Mr. Li Gesheng introduced to the guests the LED display market trends, and Intel to SMD3535 characteristics lnteled SMD3535 new “cook” Italy and lnteled of SMD3535 overall solution done a detailed explanation .

The face of growing demand of the market for high-definition display status of traditional plug-in oval LED clearly does not meet customer needs. Outdoor full color SMD LED has wide viewing angle, light distribution and light mixing good, high contrast and easily automated production advantage, becoming the next screen mainstream light emitting devices. As a professional LED packaging manufacturers, lnteled Optoelectronic this release SMD3535 products lnteled latest first outdoor LED HD display special products production has a domestic first episode. The product has two the lnteled patented moisture-proof, moisture level; possess super anti-UV, anti-sulfide capacity, long used outdoors; with a high-definition, high-resolution, very suitable outdoor high density screen; and brightness Up to 1600mcd.

For the SMD lamp beads used for outdoor display, the industry has been the existence of two doubts: only heightening the height of the lamp body will be able to crack the SMD moisture-proof problem? The SMD moisture resistant plug-in LED can transcend it? To this end, lnteled Optoelectronic released SMD lamp beads for outdoor display humidity the Thermal Shock destructive experimental standard, to test SMD lamp beads suitable for outdoor display. (SMD lamp beads First on the -40 ° C cold red box cold red 30 minutes, and then immediately placed into a 100 ° C boiling water and cook for 30 minutes, remove and lit test and record to do 100 times this reincaation. ) after the experiment, we leaed that no one lights died the 100 lnteled SMD3535 after 100 full humidity of hot and cold shock destructive testing, the dead lights rate of 0, a well-known foreign brands SMD3535 rate of 2 dead lights %, SMD5050 dead lights rate of 83%, the 546 dead average lamp was 40%; 100% rate of a well-known domestic brands SMD3535 dead lights, its the SMD5050 dead lights rate of 34%. So bad under the experimental conditions, lnteled SMD3535 dead lights, what the environment can not adapt to it! Lnteled SMD3535 outdoor high-definition display partners!

In today’s competitive market, as a professional LED packaging manufacturers in order to help clients improve their competitiveness, Intel , need to understand customer needs, close to good customer service, so that a SMD3535 the play to the best performance, and provide customers with one-stop solutions, enabling customers to do “to that war, the war will be won. On this basis, Ge Li Sheng, director for the optical, thermal, SMD3535 highest use of the relationship between temperature and the brightness of the screen, the SMD3528 the largest screen brightness LED dot pitch, LED display cabinet design several ways to do a comprehensive and detailed analysis. Cabinet design (PCB drawings, schematic drawings, structural drawings, BOM list of module test report can refer to physical PH10 sample box, reference suite PH10 3535 suite), free for partners available.

The switching regulated power supply volume is small, light weight, high efficiency, the Regulator a wide range of safe and reliable, to be used in many electronic devices. However, like other circuits also exist some problems, such as the control circuit complexity, higher operating frequency be TV, radio, electromagnetic radiation interference to radio noise appears, TV noise points, even feedback interfere with other electronic devices work properly.

1 super audio interference oscillation problems

The operating frequency switching regulated power supply is more than for 20-100kHz, is a super audio range. To a frequency corresponding to work as a switching regulator of the power supply device transistor or field effect transistor in the conduction and cutoff state, the oscillatory waveform approximates a square wave (overshoot), and can be decomposed according to the Fourier analysis method, i.e. to obtain the DC component, the fundamental and higher harmonics of the fundamental energy, followed by three, five, seven ...... and so on.

Radio and electromagnetic interference

As we all know, radio modulation method to disseminate information. The audio signal in the high frequency load uses amplitude modulation (AM) and frequency modulation (FM) method, and then modulated wave through the transmission antea will be radiated out in the form of electromagnetic Phi radio receiving device via the receiving antea receiver down s and then The frequency selection, frequency conversion, amplification, and demodulation, restore an audio signal, and finally through the low-frequency amplifier, the sound emitted by the loudspeaker. If only a modulation signal of the high frequency carrier without audio range, then its energy is again large, the radio receiving apparatus is also not be restored through a speaker any audio information. It can be thought, just super audio side Phi the presence of interference (the lower limit frequency of the audio oscillator 15k! Carpet, already outside of the audible range of the human ear), generating a higher harmonic does not become through Xin, the radio interference signal to the audio range, fact such interference sometimes very serious, may in the medium wave, short wave range are strongly noise, then the interference from where? there is audio switching regulated power supply scope of the interference signal, and modulation of each harmonic oscillation super audio, similar to the way radio interference with radios and other equipment, is an important source of interference.

3. Direct rectifier capacitor filter circuit characteristics

Directly to AC power rectifier filter high-frequency switching power supply, AC input voltage of 220V, 50Hz, generally use a bridge rectifier circuit, and then becomes 100Hz jagged pulsating DC voltage electrolytic capacitor filter, to the switching regulated power supply.

Can be seen from the figure, the role of the AC power supply is the energy of each Wms to the electrolytic capacitor charge time, to complement consumption by the switching circuit, a sawtooth-shaped voltage waveform from the point of view, but is pulsed current waveform from the point of view shaped, they are non-sinusoidal periodic volume contains rich harmonics, and the vast majority in the audio range (20-20000Hz) which l00Hz composition is likely to produce an important source of audio interference.

Similarly, according to the Fourier analysis, the non-sinusoidal periodic function can be decomposed into the fundamental wave and higher harmonics, its energy is concentrated in the vicinity of the fundamental and higher harmonics little energy. Because of its peak-to-peak value is small (only a few volts to a few card volts), if in the form of electromagnetic waves emitted by certain circuit elements (such as the LC network, etc.), the interference on the radio, etc. Element radio receiving apparatus is small. The the 1000kHz frequency in the medium wave band (531-1611kHz), for example, 1 ∞ Hz pulse-shaped current of 1 kHz harmonic before whom resonant frequency energy is almost zero, unless the radio is close to the place it , it is impossible for interference. But in fact many of the radio in the far distance of the switching regulator power position can still appear interference, because what is it? Can conclude the following analysis.

A low frequency signal to modulate the amplitude of the high frequency carrier so that a high-frequency carrier the same as the overall envelope and the variation of the low-frequency signal, which is an AM the corresponding modulated wave is amplitude modulated wave. If the low frequency signal is a single frequency sine wave, the high frequency carrier is a single frequency sine wave, both obtained by modulating role amplitude modulated wave, according to the principle of amplitude modulation, the amplitude of the amplitude of the low frequency signal with the high frequency carrier signal is less than 1: 3 cases, the carrier envelope is substantially similar to the low-frequency signal. If the low frequency signal is a plurality of frequencies, the amplitude modulation wave spectrum is the carrier and the two upper and lower sidebands. The switching regulator power supply of the low-frequency pulse amplitude is smaller the larger the amplitude of the high frequency of the switching pulses in the switching regulator power supply inteal AM role is bound to occur, and therefore the electromagnetic radiation generated by the power supply is amplitude modulated interference wave, since Both contain a wealth of fundamental and harmonic. The result of cross-modulation makes interference throughout the the super audio over a wide frequency range, Xin strong interference sound in the medium and short wave range, and this interference almost throughout the entire band.

To further verify the presence of the aforementioned problems, instead of AC power directly to the switching power supply with a DC power supply, test results, as anticipated, as that since there is no 100Hz charging pulse, tu the radio on which are Xin less than the noise emitted by the radio.

According to the above test can get the following conclusion: switching power supply for the yuan radio broadcast interference from 100Hz low frequency charging pulse harmonic modulation high frequency square wave form complex amplitude modulation wave. As the intensity of high-frequency switching square wave, not easily suppressed, it should not be reimbursing to strengthen the capacity of the high-frequency filter capacitor.

Thus think of the Electronic Ballast pollution problem of the electromagnetic environment, Electronic Ballast also do the test, fluorescent lamp can be lit, but the attendant problems in the fluorescent light is almost impossible to use The Radio received Xin broadcast, the radio signal is drowned in the noise, but also due to the load of the electronic ballast is exposed to the space and the size large fluorescent interference by its radiation intensity of electromagnetic waves, the noise is very serious.

Anti-jamming measures

In summary, the switching regulator power electromagnetic radiation interference from the low-frequency the 100Hz charge pulse and its harmonics amplitude modulation, super audio oscillator square wave and its harmonics weakened mainly by the following:

(1) using the appropriate filtering capacity electrolytic capacitor. Mainly from two aspects of anti-interference and cost performance should be considered.
(2) In the case of the possible, using appropriate methods to reduce overshoot and ringing super audio oscillation square waveform. The purpose of doing so is to reduce the super audio oscillation high harmonic energy, which can reduce the level of radio interference.
(3) the perfect calendar filter network, weaken the interference of switching regulated power supply to the AC mains reinfusion. The filter network in the form of a lot, according to the specific power supply manufacturer and the load to comprehensively consider the selection circuit forms.
(4) reasonable design of printed circuit board, a large area of ground measures, while strengthening the shield. This can effectively reduce the intensity of electromagnetic radiation caused by the distributed capacitance, and is also able to improve the reliability of the power supply.