Led Panel Light Is A Soft Light (Sep 18, 2011)
Led Tube is a soft light that is effective and popular in all of the world .It can use in not only many different place ,such as room , shops , offices ,schools ,super markets ,cinemas but also can be used in the Light box , metro station , subway , night markets etc . Anyway it will be used in anywhere where needed .It is not so ideal of the traditional fluorecsent power utilization:The power of extra ballast is too high , need high voltage when start , the mercury that built in the fluorescent lamp cant deal when it stop working and becomes to hazards of environmental pollution . Phosphor fluorescent tube fluorescent tube in the filling into the process, contain higher amounts of mercury (mercury), so the breakdown of fluorescent tubes, mercury vapor came out great harm to human body. Authoritative sources: mercury vapor up from 0.04 to 3 mg when will people in 2 to 3 months of chronic poisoning, up from 1.2 to 8.5 mg will induce acute mercury poisoning, should the the amount of 20 mg, will directly lead to animal death.As the fourth and new light source The Led panel light sources is used in many different area when it start.The leds quantity in every different LED panel light are not the same ,it is about 840-1200 leds depend on the different power and lumen .and the color also not the same cause the different color temperature and the different color light ,for example ,white ,warm white etc ..Energy saving is the most special point of the Led panel light. Foe example , one T8 traditiona fluorescent tube ,the standard power is 36W ,and the extballast power is 8W , so total power is 44W when its working and the lumen is 420lm ,the serve life is 30,000 hours .But if you use a same features led panel light , the working power is only 16W and the lumen is 815W and the serve life is even more than 50,000 hours .PWM LED panel light driver PT4107There many different solution of the led panel light driver. The current program because of its high efficiency non-isolated and the mainstream though, and with PWM LED panel light driver controller to do another drive power LED fluorescent is majority.PT4107 Is a typical PWM LED driver controller, its internal topology shown in Figure 1.PT4107 is a high voltage step-down type PWM LED led panel light-driven controller, through the external resistor and the internal zener diode that can be rectified 110V or 220V AC voltage clamp at 20V. When the voltage Vin on over-voltage lockout threshold of 18V, the chips began to work, in accordance with the peak current control mode to drive the external MOSFET. The external MOSFET's source and to the current sampling resistor indirectly, the resistor voltage directly to the PT4107 chip CS side. When the CS terminal voltage exceeds the internal threshold voltage the current sample, GATE-side drive signal termination of the external MOSFET off. Threshold voltage can be internally set, or by applying a voltage to control the LD side. If the required soft-start, end in LD parallel capacitor voltage needs to be increased speed and increased speed and consistent LED current.PT4107 main technical characteristics: from 18V to 450V wide voltage input range, constant current output; Frequency jitter to reduce electromagnetic interference, use of random source to modulate the oscillation frequency, it can extend the audio power spectrum, the energy spectrum can be expanded effectively reduce small band of electromagnetic interference, reducing system-level design difficulty; available linear and PWM dimming to support hundreds of 0.06W LED driving applications, operating frequency of 25kHz-300kHz, can be set by external resistors.PT4107 package shown in Figure 2, the pin function as follows:1. Chip ground terminal GND;2. CS LED peak current input sample;3. LD linear dimming access terminal;4. RI Rosc access terminal;5. ROTP over-temperature protection setting end;6. PWMD PWM dimming input and enable the chip internal 100K pull-up resistors;7. VIN-chip power supply terminal;8. GATE drive external MOSFET gate;Design full voltage 20W Led panel light switch current sourceTo AC 85V ~ 245V wide voltage input, for example, with PT4107 PWM LED panel light drive controller to do Led panel light-driven power of the main chip, the design of a better program application circuit (Figure 3). The program consists of the whole circuit by the anti-surge protection, EMC filter, full-bridge rectifier, passive power factor correction (PFC), buck regulators, PWM LED panel light-driven controller, extended flow constant current circuit.Click philosophy, designed to switch the entire voltage 20W fluorescent lamp power constant current source schematic diagram shown in Figure 4. From the look into AC 220V, AC power entry has had 1A fuse FS1 and anti-surge of negative temperature coefficient thermistor NTC, EMI filter followed by the L1, L2, and CX1 composition. BD1 is a full-bridge rectifier, the internal pressure is four silicon diode. C1, C2, R1, D1 ~ D3 composition of passive power factor correction circuit. PT4107 chip from the T1, D4, C4, R2 ~ R4 formed after the power supply step-down regulator electronic filter, the filter input impedance is high, the output impedance is very small, close to 300V DC high voltage after rectification by the step-down to the transistor PT4107 Vin of about 18 ~ 20V voltage, to ensure that chip in the whole voltage range in stability.Unlike the previous program that the resistance of the circuit step-down circuit as energy and hot. PWM control chip U1 (PT4107) and the power MOS tube Q1, ballast power inductor L3, diode D5 form continued buck regulator circuit, U1 collect current sampling resistor R6 ~ R9 on the peak current, the internal logic in a single cycle GATE pin control signal pulse duty cycle for constant current control. Output constant current and D5, L3 of the continued flow of the circuit to the LED light source combined constant current power supply, change the resistance of resistor R6 ~ R9 can change the circuit's output current, but the D5, L3 changes have followed. R5 is a part of chip oscillator, the oscillation frequency can be adjusted to change it. Potentiometer RT in this circuit is not used for dimming, but to fine-tune the current source of current design of the circuit to power. As the dispersion device, a power board for each batch when the output current will be slightly different from the production line can use this potentiometer to adjust the power board for each block of the output current. To ensure good power plate modulated stability, we must use turbine vortex rod trimmer potentiometer, and after moving, Solid Epoxy sealed.The circuit parameters are 22 per string 0.06W LED, a total of 15 series and parallel, driving 330 load of 60 mW of white light LED design, each string of the current is 17.8 mA, the design output 36-80V/25OmA. If you change the LED number, you need to amend R6 ~ R9 parameters.PCB board arrangement is the key to good products, so the alignment of PCB board according to the design of power electronic specifications. The circuit also can be used for T10, T8 fluorescent tubes, space for two different, two different PCB board width will need to reduce the height of all the parts, in order to put T10, T8 lamp. Figure 5 is a constant current source plate T10-kind photos, 33 components installed in the 235 25 0.8 mm epoxy PCB, on one side.Key design and considerations1. Anti-surge of the NTC.Anti-surge of the NTC thermistor used 300/0.3A, such as changing the output of this program, such as increased current, the NTC must also select a large number of current, so as not to over flow from the heat.2. EMC filterAC power input, the general need to increase the inductance by the conjugate, X and Y capacitor filter capacitor formed to increase the resistance to the circuit effects of EMI, filter out interference signal conduction and radiation noise. The circuit inductance plus conjugate simple way X capacitors, mainly because of the overall cost considerations, the spirit of good-enough design principles. X capacitor should be marked with the safety certification mark and voltage AC275V words, the real DC voltage at 2,000 V or more, look more orange or blue. Conjugate is around the inductance on the same core of two identical inductance inductance is mainly used to suppress common mode noise, inductance in the range of 10 ~ 30mH selection. To reduce the volume and improve the filtering effect, preferred ceramic materials with high permeability core of products, higher inductance values should be selected. Using two identical inductance inductance replace a conjugate is also a way to reduce costs.3. Full-bridge rectifierFull-bridge rectifier BD1 mainly for AC / DC conversion, and therefore require a 1.5 factor of safety margin, suggested the use of 600V/1A.4. Passive PFCOrdinary bridge rectifier output current is rectified pulsating DC current is not continuous, large harmonic distortion, power factor is low, so need to increase the low-cost passive power factor compensation circuit, shown in Figure 6. This circuit is called the balance of half-bridge compensation circuit, C1 and D1 form half-bridge of the arm, C2 and D2 form the other half-bridge arm, D3, and R channels composed of charge to connect using the principle of compensation to the valley. Filter capacitors C1 and C2 in series, the maximum charge voltage on the capacitor to the input voltage of the half, once the line voltage down to less than half the input voltage, diodes D1 and D2 will be forward biased, C1 and C2 begin to discharge in parallel. This is a half weeks of input current conduction angle from the original 75 ~ 105 up to 30 ~ 150 ; negative half cycle of the input current conduction angle from the original 255 ~ 285 up to 210 ~ 330 ( Figure 7). And D3 series resistance R help smoothing the input current peak, but also by limiting the inflow of capacitors C1 and C2 of current to improve power factor. Using this circuit, the system's power factor from 0.6 to 0.89. R a surge buffer and limiting, it should not be omitted.5. Buck regulator circuitPower supply circuit to the PT4107 is the times of capacitive ripple filter (Figure 8), with capacitance multiplier-type low-pass filter and the dual role of regulator Series regulator. In the emitter of the base to the ground after another capacitor C4, as base current only emitter current of 1 / (1 + ), equivalent to the emitter access a content value of (1 + ) C4 large capacitor, which is the capacitance of the principle of double-type filter. If the base to the ground and then connected between a Zener diode is a simple series regulator, the circuit can effectively eliminate the high frequency switching ripple of. Please note, T1 should choice bipolar transistors Vbceo500V, Ic = 100mA. Zener diode D4 to use 20V, 1/4W any type of small power regulator.6. Ballast Power InductorsBallast power inductors L3 and Q1 MOS pipe, and R6, R7, R8, R9 parallel current sampling resistor, constant current output of this circuit the three key components. Power Inductors L3 requirements ballast high Q value, saturation current, low resistance. Nominal 3.9mH inductor, in the 40kHz ~ 100kHz frequency range in Q value should be greater than 90. Designed to use saturation current is 2 times the normal operating current power inductors. The circuit output current 250mA, so the election 500mA. Use power inductor winding resistance should be less than 2, the Curie temperature greater than 400 oC quality power inductors. Once the inductor saturation occurs, MOS tube, LED panel light source, PWM control chip will be instantly destroyed. Recommend the use of ceramic materials with high permeability the power inductor, which can ensure long-term safe and reliable current source to work.L3 inductor to use EE13 closed magnetic circuit core inductors, or high low point EPC13 core (Figure 9). Most are now LED fluorescent lamp using a half aluminum half-PV plastic tubes, LED light to help heat dissipation. H magnetic core inductor is open when using the core characters inductor power driver board into the semi-aluminum semi-PV plastic tube, because aluminum can change its magnetic circuit, often will have good power driver board debug output current decreases.7. Freewheeling diodeFreewheeling diode D5 will surely opt for fast recovery diode, which MOS tube to keep the switching cycle. If the use of 1N4007, then the work will be burned. In addition, the current through the freewheeling diode LED panel light source should be the load current of 1.5 to 2 times, to use the circuit 1A of the fast recovery diode.8. PT4107 switching frequencyPT4107 switching frequency determine the level of power inductors L3 and input filter capacitor C1, C2, C3 size. If the switch frequency is high, you can use a smaller inductor and capacitor size, but the Q1 MOSFET switching losses tube will increase, resulting in reduced efficiency. Therefore, the power input is AC 220V, 50kHz ~ 100kHz is more appropriate. PT4107 switching frequency setting resistor R5 formula is as follows. When F = 50kHz when, R5 = 500K.9. The choice of MOSFET,MOSFET, Q1 is the output of the key components of this circuit. First of all, it's RDS (ON) to be small, so that it work on a small power itself. In addition, its pressure must be high, so high voltage surges encountered in the work can not easily be puncture.Every switch in the MOSFET process, the sampling resistor R6 ~ R9 current spikes will inevitably occur. To avoid this, set the 400ns chip sampling delay time. Therefore, the traditional RC filter can be omitted. During this delay, the comparator will no longer work, can not control the GATE pin of the output.10. Current sampling resistorResistors R6, R7, R8, R9 in parallel as a sampling resistor, this can reduce the accuracy and temperature resistance of the output current, and can easily change one or more of the resistance, to modify the current purpose. Suggested the use of one-thousandth of accuracy, temperature coefficient of 50ppm of SMD (1206) 1/4W resistor. Current sampling resistor R6 ~ R9 to set the total resistance and power use, according to the circuit based on LED light source to calculate the load current.R (6-9) = 0.275/ILEDPR (6-9) = ILED2 x R (6-9)11. Electrolytic capacitorLED panel light source is a long-life light sources, theoretical life of up to 50,000 hours, but unreasonable application of circuit design, improper selection of the circuit components, LED light source heat is not good, will affect its life. Especially in the drive power supply circuit, as AC / DC rectifier bridge output filter electrolytic capacitor, it's life at 5,000 hours less, and this became the manufacture of long-life LED lighting technology stumbling block. The circuit design uses the C1, C2, C4, C5, C7 and more satellites aluminum electrolytic capacitors. Life expectancy of aluminum electrolytic capacitors with temperature has a lot to use the environment to speed up the loss of electrolyte temperature, ambient temperature each increased 6 oC, electrolytic capacitor life will be reduced by half. LED fluorescent tube temperature is not easy because of the air flow, such as power-driven board design is unreasonable, tube temperature will be higher, thus greatly reduced the life of electrolytic capacitors. Use solid electrolytic capacitor, may be a good way to extend the life of one, but led to higher costs.Applications can be designed to more satellites PT4107 0.06W WLED light series and parallel to the load, input voltage AC 110V or AC 220V to T10, T8, T5 fluorescent lamps in the LED program, and similar applications in the ceiling, sky full of stars lights, outdoor lighting work light, bulb lights, also designed the high brightness 1W WLED light series LED garden lights for the load, LED lamps, LED tunnel lights.Early 2009, the Japanese government to reduce carbon emissions from public lighting, the implementation of mandatory carbon reduction company policy, Japan is gradually heating up the office needs of energy-efficient lighting, and vigorously promote the LED panel light, to promote the production of Chinese LEDpanel light. Therefore, optimal design with reference to the design of circuits for the LED panel light AC110V circuit has been widely used in the production.
