Application Note 1070 Design Guideline and Application Notes of AP1681 System Solution Prepared by Wang Zhao Kun System Engineering Dept. 1. Introduction • The AP1681 is a powerful high performance AC/DC power supply controller for dimmable LED lighting applications. The device uses Pulse Frequency Modulation (PFM) technology to regulate output current according to the wall dimmer conduct angle without opto-coupler and secondary CV/CC control circuitry. • • • • • • • • • The AP1681 achieves wide dimming range without visible flicker and is compatible with diverse dimmers. The AP1681 features low start-up current, low operation current and high efficiency. It also has rich protection functions including over voltage, short circuit, over current and over temperature protections. 3. Pin Configuration and Description The AP1681 is available in SOIC-8 package. 2. Product Features • • • • Primary Side Control for Output Current Regulation Without Opto-coupler and Secondary CV/CC Control Circuitry Eliminates Control Loop Compensation Circuitry Adjustable Full Brightness and Full Dimming Setting Wide Dimming Range From 100% to 1%, Down to Pin Number Sep. 2011 DIM 2 RD 3 RI 4 CS 5 FB 6 GND DIM 1 8 VCC RD 2 7 OUT RI 3 6 GND FB 4 5 CS Figure 1. Pin Configuration of AP1681 Pin Name 1 Full Darkness Adjustable Dimming Curve for Human Eye Sensitivity No Visible Flicker Connectivity with Analog / Digital / Hybrid Dimming Mode Built-in Acceleration Start Adjustable Soft-start Timing CV Open-load Regulation and Reload Detection Over Voltage and Short Circuit Protection Over Temperature Protection Over Current Protection Maximum Switch On-time Protection Function This pin is dim signal sensing pin. It senses the dimming signal and then controls output current. Output current will at maximum when DIM voltage reaches 3.5V. Usually a second order RC filter is connected between rectified AC voltage and DIM pin. This pin is the IC internal bias pin. There is a 1.5V reference voltage at the pin. The 1.5V voltage divide RD pin resistor will determine a bias current for the IC. Usually a 51k resistor is connected at this pin to GND. This pin will generate a current according to DIM pin voltage. Change the RI pin resistor will change output current dimming curve gradient. Usually a 100k to 120k resistor is connected at this pin to GND. The current sensing pin. The primary switch maximum current sensing threshold is 0.51V. This pin captures the feedback voltage from the auxiliary winding. When secondary N V AUX = AUX × (VO + Vd ) NS , Where side diode turns on, the auxiliary voltage is given by: the Vd is the output rectify diode forward drop voltage. FB voltage is used to control no load output voltage and determine acceleration stop point at start up phase. Ground. Current return for gate driver and control circuits of the IC. The power ground and signal ground should be connected by one node. The ground of transformer must be separated from the ground of IC in order to pass ESD test. Rev. 1. 0 BCD Semiconductor Manufacturing Limited 1 Application Note 1070 Pin Number Pin Name Function 7 OUT Gate driver output pin. AP1681 is designed to drive MOSFET. A series resistor between this pin and the power switch gate can reduce high frequency noise. 8 VCC Supply pin of gate driver and control circuit of the IC. VCC 8 8V FB_OVP COMP SHORT_OCP VCC_OVP FB_OVP OTP 1.75V FB 4 COMP 0.1V 5 Tons Constant Current Control CC_CTRL CV_CTRL COMP 4V Reference VCC_OVP Tonsec Detector CC_CTRL CS pro Demag COMP 4V Protection & Latch FB_ACC UVLO CC_ON pro SHORT_OCP COMP Regulator & Bias pfm R CC_ON Driver 7 OUT Q 0.5V S PEAK_CTRL COMP 6 S DIM 1 Dimming Control 2 Q GND CC_CTRL R 3 RD RI Figure 2. Functional Block Diagram of AP1681 4. Operation Guideline Principle and AP1681 is a Primary Side Regulation (PSR) LED driver IC with dimming function for narrow range application. According to different requirements, the AP1681 can be applied to three types of circuit structure as Table 1. Design 4.1 Circuit Structure Introduction of AP1681 Application Table 1. AP1681 Application Architecture Types Structure Types Single Stage Single Stage with Valley-Fill Circuit Two Stages with Boost Input Voltage Range 90-132VAC or 220-264VAC 90-132VAC or 220-264VAC 90-132VAC or 220-264VAC PF No Low High THD Very bad Bad Very good Cost Very Low Low Very high Sep. 2011 Rev. 1. 0 BCD Semiconductor Manufacturing Limited 2 Application Note 1070 Figure 3. Block of Two Stages THD and good dimmable function. This document is based on a two stage design with AP1662 boost converter and AP1681dimmable LED driver. The document contents focus on AP1681 design guideline and application notes, the detailed design information of AP1662 refers to the BCD relative document. For low cost application, the simple single stage structure with AP1681 is the better solution to realize dimmable LED driver. Combined with valley-fill circuit, the single stage structure can not only improve PF performance to meet basic PFC requirement, but also keep the lower cost benefit. It is noticed that a bleeding circuit is required to maintain the conduction current of dimmer switch when the conduction angle is too small. As to high end application which needs the higher PF and very low THD, it is recommended to select two stages structure with boost converter and AP1681 PSR LED driver. The AP1662 controller from BCD is a cost efficient choice for boost converter. The combined solution with AP1662 and AP1681 is a best solution for wall dimmer application to achieve the better performance: the higher PF, the lower 4.2 Introduction of PSR LED Driver with AP1681 Compare to Secondary Side Regulation (SSR) solution on LED driver application, PSR is very simple and low cost solution without secondary side CC control circuit, opto-coupler and even external loop compensation circuit. Figure 4 shows a common used flyback schematic with AP1681 PSR controller, which can realize output constant current function with very simple circuit. T1 VBUS R1 + D2 C2 R2 + VO D1 R5 C1 R6 VCC FB AP1681 R3 Q1 R7 OUT GND CS R4 Figure 4. Simple Schematic of PSR time of secondary side “ON”, TSW is the switching period. primary peak current IPK is The AP1681 uses PFM control strategy and keeps the flyback converter operating at Discontinuous Current Mode (DCM). Figure 5 shows the basic operation waveform. The output current IO is Io = Tons ⋅ I pks 2 ⋅ Tsw I pk = I pks = N t ⋅ I pk ⋅η tr (1) (2) (3) VCS is the primary current sense voltage on CS pin, RCS is the primary current sense resistor, Nt is the primary to Here IPKS is the peak current of secondary side, TONS is the Sep. 2011 Vcs Rcs Rev. 1. 0 BCD Semiconductor Manufacturing Limited 3 Application Note 1070 threshold on CS pin is a constant value at non-dimming mode. Therefore, by means of parameter design of Nt, TONS/TSW and RCS, it can be realized output constant current control with PSR structure. Furthermore, FB pin senses the auxiliary winding voltage of the transformer, which reflects the secondary side output voltage, to carry out Constant Voltage (CV) mode control. The CV mode control can keeps output voltage below the rating voltage at no load condition. secondary winding turns ratio of transformer and ηtr is the transformer conversion ratio considering the transformer power loss and VCC winding output power loss. From above equations, the output current IO could be Io = N t ⋅ Tons ⋅ Vcs ⋅η tr 2 ⋅ Tsw ⋅ Rcs (4) As to AP1681 control scheme, the turn off voltage Figure 5. Basic Operation Waveform proportional to the voltage of DIM pin flows out the CS pin which will cause a voltage across the RCS_EXT (in Figure 6). Then the primary peak current will change with the voltage on DIM pin because the voltage threshold on CS pin is constant. The internal algorithm for TONS/TSW and VCS realizes exponential dimming curve which is compatible with human eye perception. 4.3 Dimming Principle The AP1681 regulates the output current according to the DIM pin voltage. From formula (4), IO can be adjusted accordingly by changing TONS/TSW if the turn ratio Nt and RCS are fixed. In AP1681, the TONS/TSW is positively proportional to the voltage on DIM pin whose limited voltage is 3.5V. Furthermore, there is micro-current which is inversely RCS_EXT CS C1 RCS Figure 6. Peripheral Component of CS Pin Sep. 2011 Figure 7. Dimming Curve for AP1681 Rev. 1. 0 BCD Semiconductor Manufacturing Limited 4 Application Note 1070 voltage will be charged by external source. Because of the external capacitor, DIM pin and the output current are increased gradually to the settle value. The soft start time is determined by DIM pin outside capacitor and external source. 4.4 Acceleration Start For LED lighting application, quickly start-up is necessary. In order to reduce start-up time, an acceleration start-up function is embedded in AP1681. At start-up, after VCC voltage is higher than turn on threshold, DIM pin voltage is pulled to zero by internal switch to realize soft start function for next phase. When FB pin voltage keeps below 1.75V, AP1681 system will neglect the dimming function, which means TONS/TSW keeping the maximum value and CS pin sourcing current keeping zero. Then the switch operates at the maximum IPK mode to provide more energy to secondary side. The acceleration start phase will stop when the FB pin voltage reaches soft start threshold 1.75V, and the DIM pin voltage will start increasing from zero. When open load, the system works in CV mode and output voltage is clamped to a higher level. DIM pin is pulled to zero by internal switch. At reloading situation, sensed FB pin voltage drops to below 4V, then DIM pin internal switch is open and DIM pin voltage will be charged by external source. The output current is increased gradually to the settle value. This procedure is called soft reloading stage. This effect will help for safe reloading and prevent output capacitor high discharge current when reloading. 4.5 Soft Start and Soft Reloading After acceleration start phase, AP1681 will enter soft start phase. The DIM pin internal switch is open and DIM pin 4.6 FB Pin Voltage Region Figure 8. Diagram for the FB Function higher power pulse push output voltage rising and power system entering CV mode again. It is recommended to add dummy load at output side to balance the transferred power from primary side at CV mode. If abnormal condition happened, such as fault connection or excess auxiliary winding turns, FB pin voltage reaches to 8V, and then AP1681 will enter FB OVP latch mode protection state. Figure 8 shows the FB pin working regions diagram. The FB pin has several voltage thresholds to realize the different function. When FB pin voltage is below 1.75V, the AP1681 system works in acceleration start phase. The acceleration start phase stop when FB pin sensed voltage reach 1.75V. From 1.75V to 4V, the system works in Constant Current (CC) region, the LED driver normal operation situation. When FB pin voltage is higher than 4V, the system will work in Constant Voltage (CV) state. AP1681 will output 7kHz switching frequency pulse and source the maximum current to CS pin resistor so that the power converter operates with the minimum peak current and very low switching frequency. Generally the transferred power at CV mode is lower than the required power which maintains the power system working at standby mode. With the output voltage decreasing, the FB pin voltage may drop to below 4V, then there will be the Sep. 2011 4.7 CS Pin As for CS block, AP1681 includes two comparator functions: the comparator for primary peak current control and OCP. The CS pin turn off voltage threshold is 0.5V for current loop control. The OCP threshold is 4V. When OCP happened, AP1681 will enter latch mode and switch stops working. The latch mode will be reset when input power off. Rev. 1. 0 BCD Semiconductor Manufacturing Limited 5 Application Note 1070 The primary peak current depends on the CS pin resistor RCS_EXT when the voltage on DIM pin is changing because there is a micro-current flowing out the CS pin. Under the condition of same DIM pin voltage, the larger value of RCS_EXT, the lower primary peak current. Figure 9 shows the relation curve of primary peak current with DIM pin voltage VDIM and RCS_EXT Value. From the curve it can be seen that the higher RCS_EXT value, the lower primary peak current. The lower IPEAK means the LED driver achieve the lower output current, and then the lower darkness LED lighting performance. Usually it is recommended to use 5.1k value CS resistor. 4.8 RD and RI Pin IPEAK (A) RD and RI pin feature to set the dimming curve of output current with external resistor. The RD pin resistor RRD, usually recommended as 51k, is used to generate reference bias current for internal dimming function circuit. RCS_EXT=1K RCS_EXT=2.2K RCS_EXT=3.3K RCS_EXT=3.9K RCS_EXT=5.1K VDIM (V) Figure 10. Resistor for RD Pin and RI Pin IOUT (A) Figure 9. Curve of IPEAK and VDIM VDIM (V) Figure 11. Curve of VDIM and IOUT The RI pin resistor (RRI) is used to set the dimming curve of output current. Figure 11 is the curve of output current with DIM pin voltage under the different RI resistor. From the curves it can be seen that the LED brightness changes faster with the smaller RRI. The designer can select suitable resistor according to this dimming curve to achieve the required dimming characteristics. Sep. 2011 4.9 Max TONP Protection When primary side switch turns on, the current will increase because of input voltage and flyback primary inductor. If the sensed CS pin voltage doesn’t reach 0.5V over 16.5µs, maximum TONP protection happens, the switch will be turned off immediately. Rev. 1. 0 BCD Semiconductor Manufacturing Limited 6 Application Note 1070 The output voltage of boost circuit is a constant DC voltage, so the flyback system could be designed to operate on quasi resonant mode to improve efficiency, and the quasi resonant mode could be reached by adjusting fSW, turn ratio and VBUS. Usually fSW and VBUS are determined firstly and the turn ratio is adjusted to realize the quasi resonant mode. (For designing method, please refer to designing file by BCD). Figure 12 shows the working waveform of flyback MOSFET drain voltage and current sensing resistor voltage VCS waveform. The MOSFET works at quasi resonant mode. 4.10 Over Temperature Protection (OTP) For LED application, the LED driver usually works in high ambient temperature. Over temperature protection (OTP) is necessary to avoid improper installation and protect LED lifetime. If AP1681 junction temperature reaches 140°C, OTP happens. The AP1681 system will be shut down. 20°C hysteresis is provided for robust operation. The OTP will be relieved after the IC junction temperature drops below 120°C. 5. Operation Parameter Design and Components Selection for Two Stages 5.3 Calculate Current Sensed Resistor Usually, Boost + PSR flyback topology is suggested for triac dimming LED driver application because of excellent dimming compatibility, no flickering operation, high power factor, low THD and extremely low output current ripple. The boost PFC stage output voltage is constant. So this makes easy for flyback system design. Below is the design procedure only for PSR with AP1681 (please refer to the application of AP1662 for design of boost circuit). The voltage threshold on CS pin is 0.5V. The primary current sense resistor can be calculated according to equation Rcs = In order to guarantee flyback operating at DCM, the maximum turn ratio Nt_max is 0.978 ⋅ Vbus Vo + Vd (8) ηtr is the efficiency of transformer, usually about 0.9. A RC filter is recommended to be added between the CS pin and sampling resistor and the maximum value of resistor is recommended for 5.1kΩ for dimming consideration. 5.1 Calculate the Maximum Turn Ratio of XFMR N t _ max = 0.127 ⋅ N t ⋅η tr Io 5.4 Calculation of the Inductance of Primary Side---LP (7) The primary peak current is Firstly the designer should determine the turns ratio and then calculate the other design parameter. I pk = 5.2 Determine Full Load Working Frequency fSW and Turn Ratio I pks N t ⋅ η tr = 3.952 ⋅ I o N t ⋅ η tr (9) According to the rule of conservation of energy, we can get The switch working frequency of AP1681 is relative to system efficiency and transformer size. Usually 50kHz to 75kHz is recommended to balance the efficiency and size. P 1 2 ⋅ f sw = o L p ⋅ I pk 2 ηp (10) Here, ηp is the total power conversion efficiency. So, the primary inductance can be calculated by: 0.128 ⋅ Po ⋅ N t ⋅ η tr2 I o2 ⋅ f sw ⋅ η p 2 Lp = (11) 5.5 Calculate the Turns of Primary, Secondary and Auxiliary Sides The primary winding turns is Np = L p ⋅ I pk Ae ⋅ Bmax (12) Figure 12. Flyback MOSFET Q2 Drain Voltage and VCS Waveform at Full Load Sep. 2011 Rev. 1. 0 BCD Semiconductor Manufacturing Limited 7 Application Note 1070 The turn of secondary winding is Ns = The maximum drain to source current (RMS value) is Np I d _ max = I pk ⋅ (13) Nt (16) The maximum voltage on secondary diode is The turn of auxiliary winding is Na = T D = I pk ⋅ onp 3 3Tsw N s ⋅ Vccmax Vo _ max + Vd (14) Vd _ max = Vbus + Vo _ max + Vd Nt (17) Here, VCCmax can be set a typical value of 23V, Bmax is usually selected between 0.25T and 0.3T. The maximum average current of secondary diode is output current. 5.6 Primary MOSFET and Secondary Diode Selection 5.7 Output Capacitor Selection Output capacitor is key factor for output current ripple. Because of Boost PFC stage, there is no line frequency ripple at output side. But there is still the switching frequency output voltage and current ripple since of output capacitor ESR. In order to achieve the lower output ripple performance, it’s preferred to select low ESR capacitor. The below table shows the recommended value of output capacitance. The maximum voltage on primary MOSFET is Vds _ max = Vbus + N t ⋅ (Vo + Vd ) + Vspike (15) Where VSPIKE is the spike voltage which is result from the leakage inductance and depends on the primary peak current value and leakage inductance value, it is approximately about 100V to 200V. Output Power 1W to 10W 10W to 20W 20W to 30W Output Capacitor 82µF to 120µF 120µF to 180µF 180µF to 250µF 5.8 DIM Pin Elements Selection turns on. The function of DIM pin is to control output current by sensing input AC voltage. Usually a second order filter is connected between rectified AC voltage and DIM pin. The voltage on DIM pin could be set between 3.5V and 4V at typical input voltage and full load. The second order filter which is 100kΩ and 1 micro Farad is recommended to get a small ripple of output current. 6.2 Iron Powder core is suggested for EMI filter because of high saturation flux density. When Triac dimmer turns on, high inrush current will flow into the filter. Iron Powder core inductor can effectively limit the peak inrush and makes the system works stable. 6.3 Quick response of PFC control loop is needed. The designed PFC output feedback capacitor is small to give fast response when dimming. 5.9 FB Pin Elements Selection The system will operate at CV mode if the voltage on FB pin reaches 4V. So the voltage on FB pin is recommended to be set at 3.5V at full load. 6.4 Be careful for the AP1661 and AP1681 VCC supply. The PFC is controlled by AP1661 and flyback is controlled by AP1681. The two IC VCC supply comes from the same auxiliary winding of flyback. But the two ICs have different VCC operation range. Usually, a linear regulator is needed for AP1661 power supply. 6. Dimming Consideration Though PFC circuit makes the whole system act as resistive load for dimmer in theory, improper components value design can still cause flickering when dimming. Here is some design tips for no flickering dimming. 7. Layout Consideration 6.1 Design EMI filter capacitor as small as possible. Filter The PCB layout rules are highlighted as following: capacitor is necessary to pass EMI standard, but big filter capacitor may cause Triac dimming oscillation when Triac 7.1 The boost converter and flyback converter loop area Sep. 2011 Rev. 1. 0 BCD Semiconductor Manufacturing Limited 8 Application Note 1070 8. Design example should be minimized for better EMI performance. Here is a design example of dimmable LED driver. The specification is: AC mains RMS voltage: VIN_RMS=85V to 150V DC output regulated voltage: VO=21V Rated output current: IO=0.5A Flyback full load switching frequency: fSW = 65kHz Expected efficiency: η> 80% Figure 13 shows the designed electrical schematic. 7.2 The RCD clamp snubber and output rectifier loop areas should be minimized to achieve good EMI performance. 7.3 The power ground and signal ground should be connected by one node. Common connection of GND will introduce disturbances to small signals. The ground of transformer must be separated from the ground of IC in order to pass ESD test. 7.4 C1 should be placed as close as possible to Pin VCC of the AP1681 respectively. L F1 R2 AC Input D7 L2 R38 BD1 L3 R1 R8 R5 U1 AP1661 VR1 C1 N L1 C2 C3 R6 R39 GD MULT R7 CS R12 R11 R37 C6 R15 R16 C5 Q1 + R10 VCC COMP INV C4 D2 C16 R9 D1 ZCD GND R13 R14 T1 R24 ZD1 R29 C17 R19 C13 R32 D6 D8 R17 R25 C14 R20 D4 8-VCC U2 AP1681 4-FB D5 6-GND R21 C8 1-DIM 7-OUT 2-RD 3-RI 5-CS R18 R22 R23 C15 R33 OUT R35 C10 C9 + + Q3 D3 C7 C11 R26 R34 R27 C12 R31 CY Q2 R30 R28 Figure 13. Typical Application Schematic of AP1681 Solution BOM Item Sep. 2011 Description QTY C1 68nF/400V, capacitor CL21 1 C2 100nF/400V, capacitor CL21 1 C3 33nF/400V, capacitor CL21 1 C4 1nF/25V, 0603, ceramic capacitor 1 Rev. 1. 0 BCD Semiconductor Manufacturing Limited 9 Application Note 1070 Item QTY C5 100nF/25V, 0603, ceramic capacitor 1 C6 470nF/50V, 1206, ceramic capacitor 1 C7 1µF/25V, 0603, ceramic capacitor 1 C8 1µF/25V, 0603, ceramic capacitor 1 C9,C10 1µF/50V, 1206, ceramic capacitor 2 C11 10µF/400V, 105°C, 10mm*11mm electrolytic capacitor low ESR(R<3.5Ω) 1 C12 10pF/25V, 0603, ceramic capacitor 1 C13 1nF/100V, 0805, ceramic capacitor 1 120µF/50V, 105°C, 8mm*11mm electrolytic capacitor low ESR(R<0.15Ω) 2 C16 2.2nF/275V, Y safety capacitor 1 C17 1nF/500V, 1206, ceramic capacitor 1 Diode, 1N4148, SOD323 2 STTH2L06A, 2A/600V, SMA, ultrafast diode, 60ns 1 BAV21WS, 250V, 200mA, SOD323 2 D6 3A/100V, Schottky Diode, SMA, SS310 1 D7 1A/600V, SMA, US1J 1 D8 1A/1000V, SMA, 1N4007 1 L1 4.5mH, Differential-Mode Inductor, EF16, 250Ts 1 L2 6.8mH, Inductor,6mm*8mm 1 L3 3mH, Inductor, EE16 1 F1 Fuse, 1A/250V 1 VR1 Varistor 07D471K 1 BD1 Bridge diode, 0.5A/600V, TO-269AA, MB6S 1 R1 to R4 1kΩ, 5%, 1206, resistor 4 R5 1MΩ, 5%,1206, resistor 1 R6 1.5MΩ, 5%,1206, resistor 1 R7 15kΩ, 5%, 0603, resistor 1 R8 82kΩ, 5%,0603, resistor 1 R9 27Ω, 5%, 0603, resistor 1 R10 330Ω, 5%, 0603, resistor 1 C14,C15 D1,D5 D2 D3,D4 Sep. 2011 Description Rev. 1. 0 BCD Semiconductor Manufacturing Limited 10 Application Note 1070 Item R11 Description 100kΩ, 5%,0603 , resistor 1 4.7Ω, 5%,1206 , resistor 2 R14 2.2MΩ, 5%,1206 , resistor 1 R15 82kΩ, 5%,1206, resistor 1 R16 18kΩ, 5%,0603, resistor 1 R17 10kΩ, 5%, 0603, resistor 1 R18 39kΩ, 5%, 0603, resistor 1 R19,R20 470kΩ, 5%,1206, resistor 2 R21 100kΩ, 5%,0603, resistor 1 R22 51kΩ, 1%,0603, resistor 1 R23 120kΩ, 1%,0603, resistor 1 R24, R25 510kΩ, 5%, 1206, resistor 2 R26 100Ω, 5%,1206, resistor 1 R27 2.2Ω, 1%,1206, resistor 1 R28 2.4Ω, 1%,1206, resistor 1 R29 10MΩ, 5%, 1206, resistor 1 R30 8.2kΩ, 5%,0603, resistor 1 R31 51kΩ, 5%, 1206, resistor 1 R32 47Ω, 5%, 1206, resistor 1 R33 18kΩ, 5%, 1206, resistor 1 R34 5.1kΩ, 5%, 0603, resistor 1 R35 10Ω, 5%, 1206, resistor 1 R37 220kΩ,5%, 0603, resistor 1 R38, R39 10kΩ,5%, 1206, resistor 2 T1 EE19 10 pin 1.8mH, 5%, Transformer 1 U1 AP1661AMTR-G1, SOIC-8, BCD’s IC 1 U2 AP1681MTR-G1, SOIC-8, BCD’s IC 1 Q1 MOSFET, Fairchild, SSR4N60B, TO252 1 Q2 MOSFET, ST, P4NK60Z, TO220 1 Q3 Transistor, NPN, BC847,SOT-23 1 Z1 Zener 15V, SOD-80 1 R12，R13 The Flyback transformer use EE19 bobbin and core, Sep. 2011 QTY LP=1.8mH, NP=140T, NS=32T, Na=34T. Rev. 1. 0 BCD Semiconductor Manufacturing Limited 11 Application Note 1070 Figure 14. Demo Board PCB and Component Layout (Top View, Real Size 55mm×45mm ) Figure 15. Demo Board PCB and Component Layout (Bottom View, Real Size 55mm×45mm) Sep. 2011 Rev. 1. 0 BCD Semiconductor Manufacturing Limited 12 Application Note 1070 The tested IO Vs. dimmer conduct angle has exponential relation which is compatible with human eye perception. 500 IO (mA) 400 300 200 100 0 0 20 40 60 80 100 120 140 160 180 Dimmer Conductor Angle Figure 16. IO vs. Dimmer Conduct Angle The input current is in shape with input ac voltage and there is very low inrush current when dimmer begins to conduct. Leading edge and trailing edge type dimmers are both tested. The input voltage and input current are shown below. Test condition is VIN=120Vac. Figure 17. ө=150o(leading), IPEAK=147mA Sep. 2011 Figure 18. ө=135o(leading), IPEAK=192mA Rev. 1. 0 BCD Semiconductor Manufacturing Limited 13 Application Note 1070 Figure 19. ө=90o(leading), IPEAK=370mA Figure 20. ө=30o(leading), IPEAK=160mA Figure 21. ө=140o(trailing), IPEAK=169mA Figure 22. ө=115o(trailing), IPEAK=150mA Figure 23. ө=90o(trailing), IPEAK=119mA Sep. 2011 Figure 24. ө=45o(trailing), IPEAK=106mA Rev. 1. 0 BCD Semiconductor Manufacturing Limited 14