LED模块开关电源设计原理

Power Logics Co., Ltd.High PF/AC Direct LED DriverLID-PC-R101BFeatures⏹ Wide input range : maximum AC 300V⏹ LED protection by constant current driving and power compensation⏹ Drive max. 40W @ 220V, max. 30W @ 110V in 25mm x 30mm x 1.6mmmetal PCB condition⏹ Adjustable efficiency and power factor by LED array and group configuration⏹ Tap switching structure to implement high power factor⏹ 83% typical efficiency, minimum power factor 0.95 using 1tap⏹ No EMI issue⏹ Small package MLF 20pin, 7mm x 7mm⏹ Implementation of light and slim lighting fixture by minimizing necessary components Applications.⏹ Various kind of LED lighting⏹ Small size LED lighting – Down light, Bulb, etcGeneral DescriptionPC-R101B includes circuits which provide load with constant current and adjust LED power so as to be less sensitive to change of input voltage and protect LED from overloads. Also it helps to achieve high power factor by internal switching circuits and LED group separation scheme. Consequently, PC-R101B is a LED driver guarantees effective use of LEDs which are sensitive to the change of voltage and current.LED drivers generally used such as SMPS or AC/DC converter include switching component and inductors, capacitors of large capacity. These cause complex circuit and problems of noise and life of lighting apparatus. On the contrary, this driver is designed as AC direct concept without complicated circuit and huge inductors, capacitors. Therefore it helps to prolong the life of lighting apparatus and make it free from difficulties of design and debugging. Especially, using properly designed tap structure supported by this driver, it ensures over 0.99 power factor. Total three LED groups are able to be set up connecting with two tap point (TP1, TP2) and power factor will be improved by applying this tap structure interlocked with LED groups. In addition, itPower Logics Co., Ltd.has function not only to protect LED and circuit from overload even in 30% of overvoltage situation from line input but also to reduce the deviation of intensity of illumination by internal power compensation circuit. It can drive up to 40W LED power for nominal line input 220~230V and 30W LED power for nominal line input 100~120V, applying metal PCB and adequate heat sink. It also ensures minimum 83% of efficiency in using two tap.Block DiagramPower Logics Co., Ltd.Pin Description<Fig 2. Pin Connections>Power Logics Co., Ltd.<Table 1. Pin Description>※ LED grouping is to improve power factor, it’s generally recommended to separate each groups into total number of LEDs/3, when all taps are used. In the view of efficiency, you can design your circuit without use of tap and LED grouping.Power Logics Co., Ltd.Typical Application Circuits<Fig 3. Typical Application><Table 2. External Component Value (LED power 15W, 2Tap used, total 81EA LED chips)>Power Logics Co., Ltd.Absolute Maximum RatingsElectrical Characteristics(Ta=25℃, AC input=220V, LED consumed power=15W, 2Tap and 81EA LED chips used)Power Logics Co., Ltd.Application InformationLine Input Rectification BlockThis driver is recommended to run with rectified line input through an external bridge diode without filtering by large bulk capacitor on the output of bride diode. This means that it will be synchronized with 120Hz rectified waveform if line input has 60Hz. This is to accomplish high power factor.Constant Current Driver BlockThe constant current circuit is included in PC-R101B in order to supply stable current into LED group against external circumstance change such as line input fluctuation. The R8 resistance producing current reference should be set larger than that of R4 to ensure sufficient current to drive LED. These resistors adjust LED power consumption. i.e. the smaller R4 on the condition of fixed R8, the higher current flows into LED and larger R4 will make lower current flow into LED. On the other hand, the smaller R8 on the condition of fixed R4, the lower current flows into LED and larger R8 will make higher current flow into LED.Power Logics Co., Ltd.LED Grouping and Switching BlockBecause the PC-R101B designed as AC-direct type LED driver, enough number of LEDs in serially connected considering nominal line input voltage and power loss of driver are needed. The total number of LEDs of a LED string or array should be designed so that the necessary total forward voltage does not exceed the peak voltage of nominal line input. Necessary total number of LEDs can be roughly extracted from below equation.N=P D_TOT_LED / P D_LEDWhere, PD_TOT_LED is required total power consumption, PD_LED is power consumption of a LED.For example, total 15W power consumption is required for VF 3.0V, 20mA/LED chip, total 0.18W/LED package (3-in-1 LED package) and 220V nominal input condition, about 84 LED chips is needed. That means 28 LED packages of 3-in-1 type package. The increase of the number of LED packages for the same line input will achieve better efficiency by reducing power loss consumed in driver. However, this should be selected within rated range that can sufficiently drive LEDs.As one of important benefit of this driver, tap switching structure provides improvement of power factor. This improvement is accomplished by changing input current waveform shape from a discontinuous square wave brought by discontinuous turn-on/off characteristic of LED into step wave similar to sine wave. The shape of the waveform is determined from the number of LED in a group and resistor R4, R8, R6 and R11. In current dimension, the horizontal gap of each step is controlled by corresponding number of LED group and vertical height of each step is controlled by R4, R8, R6 and R11. Also THD will be improved because the result waveform is more similar to sine wave which has single frequency than square waveform. the other hand, there will be power loss by internal switching component, so the consideration of trade-off between power factor and efficiency is required if tap switching is used. For instance, to maximize the efficiency, current waveform should be close to square wave. Therefore the number of each LED group should be arranged that LED group1 > LED group2 > LED group3 and R6, R11 should be selected relatively large.T1, T2, TP1 and TP2 can be left open if this optional tap structure is not necessary. And only one tap can be used according to the requirement of power factor. Even if there are many variations of tap structure application as mentioned, it is recommended that the number of LEDs in each groups is identically allocated based on the below equation.N=(Total number of LED package or chips) / (the number of used tap+1)As a result of tuning resistors, R6 and R11, the height of LED group switching in current dimension isPower Logics Co., Ltd.changed and power factor is also tuned. The larger R3 and R4 makes the lower switching point of current and the smaller makes the higher switching point. To minimize the difference of the intensity of illumination among LED groups inherently happened by this mechanism, it is more effective that LED chips included in a group are decentralized than these are locally concentrated in the lighting apparatus. For example, when 28EA of 3-in-1 package LEDs are applied to design, if all of threechips of a package are allocated in different three groups, not same group, even though there is the difference of intensity of illumination in package level, it is not sensible by eyes or measurement because the difference is scattered equally in whole lighting apparatus.<Fig 4. Relationship between switching control resistors, number of LEDs in a LED group and the current waveform >Power Logics Co., Ltd.Power Compensation BlockThe compensation level can be controlled by R14 in Fig 5. The purpose of power compensation is the protection of LED and driver from overstress in certain range of line input, especially when higher input than rated voltage is applied. The power compensation circuit is designed to bypass the driving current of internal LED driver circuit when the input voltage is higher than we want. If more current should be bypass through this circuit, R14 should be adjusted to smaller value. On the other hand, if R14 has larger value, the load current will be higher. The line input range performed the power compensation can be adjusted by combination of R14 and R13. The waveform of fig. 5 depicts changes of peak LED current for each line input level. We can have constant LED power using this function in some range of input.<LED group and compensation circuit><Output current shape according to input voltage variation> <Fig 5. Power compensation circuit and current waveform according to different input voltages>Power Logics Co., Ltd.Reference Generation BlockThis is to provide the reference to internal and external bias. It supplies not only the bias of T1, T2 thru T_REF but also the bias of load driving and power compensation circuit. It has typical 11.7V generated from V1 and V2 input.Package Dimension (MLF 20 pin)<Fig 6. Package Dimension>Power Logics Co., Ltd.Solder Pad Recommendation< LAND PATTEN DIMENSION > < THERMAL PAD HOLD DIMENSION ><Fig 7. Solder Pad Recommendation>。