AN-EVALLED-ICL8002G-B2 INFINEON | Alldatasheet
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Phase Cut Dimmable Non-isolated Buck Converter for LED Retrofit Bulb with ICL8002G & CoolMOS™ 600V C6 Application Note Revision 1.1, 2012 -08 -03 Power Management & Multimarket
81726 Munich, Germany
© 2012 Infineon Technologies AG All Rights Reserved. Legal Disclaimer The information given in this document shall in no event be regarded as a guar antee of conditions or characteristics. With respect to any examples or hints given herein, any typical values stated herein and/or any information regarding the application of the device, Infineon Technologies hereby disclaims any and all warranties and liabilities of any kind, including without limitation, warranties of non -infringement of intellectual property rights of any third party. Information For further information on technology, delivery terms and conditions and prices, please contact the nearest Infineon Technologies Office ( www.infineon.com). Warnings Due to technical requirements, components may contain dangerous substances. For information on the types in question, please contact the nearest Infineon Technologies Office. Infineon Technologies components may be used in life-support devices or systems only with the express written approval of Infineon Technologies, if a failure of such components can reasonably be expected to cause the failure of that life-support device or system or to affect the safety or effectiveness of that device or system. Life support devices or systems are intended to be implanted in the human body or to support and/or maintain and sustain and/or protect human life. If they fail, it is reasonable to assume that the health of the user or other persons may be endangered.
Phase Cut Dimmable Non-isolated Buck Converter for LED Retrofit Bulb with ICL8002G & CoolMOS™ 600V C6 ICL8002G Revision History: 2012-08-03, Version 1.1 Previous Version: 1.0 Page Subjects (major changes since last revision)
17 Add “Production Tolerance and Normal Distribution”
Application Note 3 Version 1.1, 2012-08-03
Phase Cut Dimmable Non-isolated Buck Converter for LED Retrofit Bulb with ICL8002G & CoolMOS™ 600V C6 Application Note 4 Version 1.1, 2012-08-03
Phase Cut Dimmable Non-isolated Buck Converter for LED Retrofit Bulb with ICL8002G & CoolMOS™ 600V C6
1 Introduction
ICL8002G is a quasi -resonant PWM controller specially designed for high efficient offline LED driving application. It can be configured for different topologies such as flyback and buck converter. This document illustrates the ICL8002G in dimmable LED bulb application using the non -isolated buck topology. The ICL8002G IC’s quasi-resonant operation mode, precise cycle -by-cycle peak current control, integrated PFC and phase -cut dimming control, and various protections make it an outstanding system solution for dimmable LED bulbs. The ICL8002G non -isolated bulb demo board shows high efficiency and power factor with single stage design. Damping and bleeder circuit blocks were added to achieve high compatibility with wide range of di mmers. The output current is well regulated over a wide input and output voltage range. Its compact form factor makes it easy to fit into many LED lamp shapes and sizes. Other available demo boards for ICL8001G/ICL8002G are designed with isolated flyback topology. If galvanic isolation is not required, a non-isolated buck topology can be used with the following advantages:
- Lower PCBA BOM cost due to less costly power inductor and lower voltage rated MOSFET
- Smaller form factor due to more compact size of the power inductor This demo board can be ordered with the sales code EVALLED-ICL8002G-B2.
2 List of Features
- Smooth dimming curve with high dimmer compatibility
- High efficiency (>86%)
- High power factor (>0.95) with low THD (<20%)
- Small form factor (40mm x 20mm x 25mm)
- Quasi-resonant floating buck operation
- Precise cycle-by-cycle peak current control
- Integrated start-up power cell and built-in digital soft-start
- Comprehensive protection functions
- Low system BOM cost for dimmable bulbs
3 Technical Specification
Table 1 lists the performance specification of the EVALLED-ICL8002G-B2 demo board. Table 1 Design Specification Parameter Value Unit Input voltage 90-132 V Line frequency 50/60 Hz Input power* 12 W Output power* 10 W Output voltage 30-38 V Output current 300 mA Power factor > 0.95 THD < 20% Efficiency 86% *: Actual input and output power depends on the output voltage **: Measured at 120Vac with output of 34.3V/295mA Application Note 5 Version 1.1, 2012-08-03
Phase Cut Dimmable Non-isolated Buck Converter for LED Retrofit Bulb with ICL8002G & CoolMOS™ 600V C6
4 Demo Board
Both top and bottom side of the demo board EVALLED-ICL8002G-B2 are shown in Figure 1. Figure 1 EVALLED-ICL8002G-B2 demo board (Dimension: 40x20x25mm)
5 Schematic
Figure 2 shows the schematic for a 10W non-isolation dimmable LED bulb application designed with ICL8002G. Figure 2 EVALLED-ICL8002G-B2 schematic
6 TRIAC Based Dimmer Compatibility
TRIAC based dimmers work smoothly with resistive loads such as incandescent lamps. However, when connected to non-resistive loads such as switch mode LED drivers flickering issue can happen primarily due to insufficient hold-up current and due to current oscillation especially during TRIAC firing. Therefore, to improve compatibility with TRIAC based di mmers, usually bleeder circuit and damping circuit are implemented in the LED drivers. In this design, the fusible resistor F1 is functioning as a fuse as well as a damping element to reduce oscillation and inrush current. Moreover, both passive bleeder c ircuit (formed by R1 and C1) and active bleeder circuit (formed by R3-R6, C3, C4, ZD1, Q1, and Q2) are incorporated to maintain input current above the hold-up current Application Note 6 Version 1.1, 2012-08-03
Phase Cut Dimmable Non-isolated Buck Converter for LED Retrofit Bulb with ICL8002G & CoolMOS™ 600V C6 threshold of the TRIAC. When the input voltage is low, ZD1 as well as Q2 will not conduct. Q1’s gate is charged by Vcc through R6. When Q1 turns on, the current through R5 helps the TRIAC maintain conduction. As input voltage rises, ZD1 will pass current to trigger Q2. Once Q2 is on, Q1’s gate will discharge, turning off Q1. Meanwhile TRIAC’s current is high enough for it to remain in conduction due to the increased current drawing by the buck converter.
7 Single Stage Power Factor Correction
Single stage power factor correction (PFC) allows for a highly efficient, cost effective and compact LED driver. In this demo board design, PFC is achieved by sensing the input mains voltage (via R8 and R10) and regulating the peak current of the coupled inductor T1’s main winding (Pin 4 to Pin2) during each switching cycle to be proportional to the input voltage. The formula describing the relationship between the peak current and VR pin’s voltage is given by: I p pk (t) VVR (t) VPWM V1(t) Vbe VPWM V1 (t) (1) G PWM R CS G PWM RCS G PWM R CS where Ip-pk(t) is the peak current of the transformer’s primary winding; VVR(t) is the VR pin’s voltage; V1(t) is the input voltage sensing signal at the base of Q3; V be is the transistor Q3’s base to emitter voltage; V PWM is the IC’s internal offset voltage with typical value of 0.7V, which is compensated by Q3’s V be; G PWM is the IC’s PWM gain; and RCS is the current sense resistor. The ICL8002G operates the buck converter in quasi -resonant PWM mod e, that means, the current of the inductor’s main winding is in critical conduction mode. The high frequency sawtooth current in the main winding is filtered by the output capacitor before flowing to the LED load. Meanwhile the high frequency component of the input current is filtered by LC filters formed by L1, L2, C2, and C5. Input voltage and current waveforms in half an AC cycle are illustrated in Figure 3. Rectified input Primary peakcurrent Voltage envelope Inductor current Average input current Figure 3 Voltage and current waveforms in half an AC cycle As can be noted from Figure 3, the averaged input current is shaped to be approximately sinusoidal and thus high power factor is achieved, with input current harmonics fulfilling the requirements of EN 61000 -3-2 and ANSI C82.77-2002 standard. Application Note 7 Version 1.1, 2012-08-03
Phase Cut Dimmable Non-isolated Buck Converter for LED Retrofit Bulb with ICL8002G & CoolMOS™ 600V C6 The average output current mainly depends on the peak current of the main winding. As a rule of thumb, the average output current can be calculated as Io 0.29Ip pk (2) It can be also noted that the switching frequency varies with the in stantaneous line voltage and reaches minimum value when minimum line voltage reaches its peak value. Ignoring the zero crossing detection delay and voltage drop on the MOSFET, shunt resistor, and the freeweeling diode, the minimum frequency is given by: f MIN Vo(Vin_MIN 2 Vo) (3) T on T off L I ( 1 1 ) L p I p pk V in_MIN p pk V p V 2 V in_MIN o o where Ton and Toff are the ON and OFF time of the MOSFET respectively; L p is the inductance value of the inductor main winding; Vin-min is the minimum line voltage as specified in the design specification; and Vo is the output voltage. Considering the system’s form factor, efficiency, and EMI performance, it is recommended to set minimum switching frequency to between 80kHz and 100kHz by choosing proper primary inductance value.
8 Line Regulation
The power factor correction scheme described above also indicates that with higher input voltage, the output current tends to increase due to higher VR pin voltage. Therefore to produce a stable output current (and lumen output) versus mains voltage variations it is necessary to implement some compensation scheme to achieve good line regulation. In this design, the line regulation is achieved by the I C’s integrated foldback correction function as well as the circuitry formed by R9, C10, D4, and R13. IC’s ZCV pin is able to detect the input voltage level through R12 and the Vcc winding (T1’s Pin 7 to Pin8), allowing the IC to vary primary current sense voltage limit according to the input voltage level. This means the primary current will be decreased when the input voltage increases. The extent of the compensation can be adjusted with varying the value of R12. Meanwhile C10, together with D4 and the tr ansformer’s auxiliary winding (Pin1 to Pin8) will produce a negative voltage which is proportional to the rectified input voltage. With a proper value of R9, the peak voltage level at the base of Q3, and thus VR pin’s voltage, will be regulated against lin e voltage variation. The circuit formed by R14, R15 and ZD3 will add a DC offset to the base of Q2 to prevent it from going to a negative voltage. This offset alters the peak level of VR’s voltage and as a result determines the output current. Fine tuning of resistance value of R9 is necessary to provide optimum compensation to the line voltage variation. As a rule of thumb, R9 can be calculated with the following formula: R9 R8 N aux (4) Np where Naux and Np are the number of turns of the coup led inductor T1’s auxiliary winding (Pin1 to Pin8) and main inductor winding (Pin2 to Pin4) respectively. Application Note 8 Version 1.1, 2012-08-03
Phase Cut Dimmable Non-isolated Buck Converter for LED Retrofit Bulb with ICL8002G & CoolMOS™ 600V C6
9 Setup and Results
ATTENTION: LETHAL VOLTAGES ARE PRESENT ON THIS DEMO BOARD. DO NOT OPERATE THE BOARD UNLESS YOU ARE TRAINED TO HANDLE HIGH VOLTAGE CIRCUITS. DO NOT LEAVE THIS BOARD UNATTENDED WHILE IT IS POWERED UP.
9.1 Input / Output
9.1.1 Input
Connect AC line (90V-132V) to the red (Hot) and black (Neutral) wires. For dimming operation the phase cut dimmer shall be connected to the input according to the dimmer’s instructions by its manufacturer.
9.1.2 Output
Connect LED module (30V~38V/300mA) to the yellow (positive) and white (negative) wires from the demo board. Attention: As this is a NON-isolated design, high voltage exists at the output! An isolated AC source at the input is advised to be used during evaluation of this demo board.
9.2 Power Up
The ICL8002G integrates a start-up cell to charge up the Vcc capacitor until it starts up successfully. Figure 4 demonstrates the start-up waveforms from mains voltage switch-on to light output. Figure 4 Start-up waveforms: Rectified mains input voltage (C1, yellow), Controller Vcc (C2, red), output voltage (C3, blue), and output current (C4, green)
9.3 Operation Waveforms
The ICL8002G is a quasi-resonant PWM controller and operates the buck converter in critical conduction mode. Through zero crossing detection via ZCV pin, the ICL8002G turns on MOSFET when its drain voltage drops to the Application Note 9 Version 1.1, 2012-08-03
Phase Cut Dimmable Non-isolated Buck Converter for LED Retrofit Bulb with ICL8002G & CoolMOS™ 600V C6 first valley point. This helps to reduce current spike as well as switching loss and thus improve both efficiency and EMI performance. Figure 5 shows typical switching waveforms. Figure 5 Typical operation waveforms: ZCV pin voltage (C1&Z1, yellow), shunt signal Vcs (C2&Z2, red), drain voltage Vds (C3&Z3, blue) and primary winding’s current (C4&Z4, green) showing quasi-resonant switching
9.4 Output Waveforms
The single stage PFC design inevitably produces double mains frequency ripple at the output. Increasing output capacitance value helps reduce output ripple. However, this is often at the expense of the system’s form factor. In this demo board design, the output capacitor (C9) is sized for an output current ripple wh ich exhibits no visible light modulation. Figure 6 shows the measured waveforms of output voltage and output current. The modulation depth of the current ripple is about 25%. Figure 6 Typical waveforms: Output voltage (C2, blue) and output current (C4, green) Application Note 10 Version 1.1, 2012-08-03
Phase Cut Dimmable Non-isolated Buck Converter for LED Retrofit Bulb with ICL8002G & CoolMOS™ 600V C6
9.5 Input Waveforms
Figure 7 shows the waveforms of input voltage, input current, and the current shunt voltage during normal operation at 120Vac and full load. Figure 7 Input voltage Vin (C2, blue), Input current Iin (C4, green) and shunt voltage Vcs (C2, red)
9.6 Power Factor Correction
The measured power factor and total harmonics distortion (THD) at different input voltages are shown in Figure 8. The power factor is above 0.95 over the whole input voltage range. PF & THD vs. AC input voltage Power Factor THD 1 25% 0.98 20% Output Power 0.96 15% 0.94 10% T H D 0.92 5% 0.9 0% 80 90 100 110 120 130 140 Input Voltage [Vac] Figure 8 Power Factor and THD versus line voltage Application Note 11 Version 1.1, 2012-08-03
Phase Cut Dimmable Non-isolated Buck Converter for LED Retrofit Bulb with ICL8002G & CoolMOS™ 600V C6
9.7 Output current regulation
Figure 9 shows the LED driver system’s output current versus line voltage. The output current is regulated within +/-3% over the whole input voltage range. Iout vs. AC input voltage Output Current [mA] 300 290 280 270 260 250 80 90 100 110 120 130 140 Input Voltage [Vac] Figure 9 Output current vs. input voltage Figure 10 shows the LED driver system’s output current versus output voltage (LED module’ s forward voltage). With the number of LED changes from 11 to 13, which corresponds to forward voltage of 34.2V to 40.4V, the output current is regulated within +/-2%. Iout vs. Vout LED current Tolerance % 310 4% (mA) 305 3% 300 2% current 295 1% 290 0% 285 ‐1% Output 280 ‐2% 275 ‐3% 270 ‐4% 34 36 38 40 Output Voltage Figure 10 Output current vs. output voltage Application Note 12 Version 1.1, 2012-08-03
Phase Cut Dimmable Non-isolated Buck Converter for LED Retrofit Bulb with ICL8002G & CoolMOS™ 600V C6
9.8 Phase Cut Dimming
9.8.1 Test set-up
When evaluating dimming performance, the phase cut dimmer should be connected according to the arrangement as shown in Figure 11. LED Module Offline LED Driver AC Vac Phase cut dimmer Designed with ICL8002G Figure 11 Phase cut dimming arrangement
9.8.2 Waveforms during dimming
Figure 12 shows the waveforms of input voltage, input current, and the LED module’s current when the LED driver is operated with a leading edge phase cut dimmer. Figure 12 Waveforms during dimming operation: Input voltage Vin (C2, blue), Input current Iin (C1, yellow) and LED current (C4, green) Application Note 13 Version 1.1, 2012-08-03
Phase Cut Dimmable Non-isolated Buck Converter for LED Retrofit Bulb with ICL8002G & CoolMOS™ 600V C6
9.8.3 List of compatible TRIAC dimmers
A variety of TRIAC dimmers wer e tested with this demo board. These dimmers were chosen based on recommendations from customers and dimmer manufacturers. The table below lists the dimmers that exhibit no flickering and shimmering when tested with the demo board. Table 2 Compatible dimmers tested at input 120 Vac / 10 W Manufacturer Model Power limit Dimming range Leviton RPI06-1LW 600 W 7 – 100 % Leviton 6684 600 W 6 – 100 % Leviton SureSlide 6633 600 W 5 – 100 % Lutron TT-300H-WH 300W 10 – 100 % Lutron DVCL-153P-WH 600 W 6 – 100 % Lutron SKYLARK S-600-WH 600 W 6 – 100 % Lutron D-600PH-DK 600 W 10 – 100 % Lutron LXLV-600PL-WH 450 W 5 – 100 % Lutron S-603PG-WH 600 W 8 – 100 % Lutron Ariadni/Toggler AY-600P 600 W 8 – 100 % Lutron Vareo V-600 600 W 15 – 100 % Lutron NT-600 600 W 10 – 100 % GE DI61ULM5 600 W 10 – 100 %
9.9 System Efficiency
Figure 13 shows the LED driver system’s efficiency versus line voltage, which exhibits high efficiency (>85%) over the whole input voltage range due to the quasi-resonant operation. Efficiency [%] Efficiency vs. AC input voltage 90.00% 88.00% 86.00% 84.00% 82.00% 80.00% 80 90 100 110 120 130 140 Input Voltage [Vac] Figure 13 LED driver efficiency vs. input voltage Application Note 14 Version 1.1, 2012-08-03
Phase Cut Dimmable Non-isolated Buck Converter for LED Retrofit Bulb with ICL8002G & CoolMOS™ 600V C6
9.10 Protection Functions
The protection functions listed in Table 3 are provided with ICL8002G. Table 3 ICL8002G protection functions VCC Overvoltage Auto Restart Mode VCC Undervoltage Auto Restart Mode Output Overvoltage Latched Off Mode Output Short Circuit Auto Restart Mode Short Winding Latched Off Mode Over temperature Auto Restart Mode
9.10.1 Output Open Circuit Protection
When output is left open (not connecting to LED load) during op eration, the output voltage will rise and accordingly the voltage produced by the auxiliary winding when MOSFET turns off will increase. This voltage is detected by ZCV pin of ICL8002G via R7 and R12 . Output overvoltage protection will be triggered once t his voltage reaches the OVP threshold (Vzcovp = 3.7 V) and IC will go into Latched Off Mode. The power consumption during Latched Off Mode is kept below 0.3W. The output voltage can reach 43V and therefore, it is advised to connect proper LED loads before switching on the power. Figure 14 shows some waveforms when powering up the LED driver with no load connected. Figure 14 Waveforms during start-up without load: Input voltage at HV pin (C1, yellow), Vcc voltage (C2, red), ZCV signal (C3, blue), and output voltage (C4, green)
9.10.2 Output Short-circuit Protection
In the case of an output short circuit, the IC will switch to Auto Restart Mode by means of VCC undervoltage detection. Total input power consump tion under this condition is below 0.7W. Figure 15 shows the waveforms when powering up the LED driver with output short circuited. Application Note 15 Version 1.1, 2012-08-03
Phase Cut Dimmable Non-isolated Buck Converter for LED Retrofit Bulb with ICL8002G & CoolMOS™ 600V C6 Figure 15 Waveforms during start-up with output short-circuited: Input voltage at HV pin (C1, yellow), Vcc voltage (C2, red), MOSFET drain voltage (C3, blue), and output current (C4, green)
9.11 Conducted EMI
The conducted EMI test is performed at 120Vac with full load condition. The EMI’s peak value is plotted against quasi-peak limit of the FCC Class B and EN55015 (CISPR15). There is approximately 6 dB margin observed. Live Neutral Figure 16 Tested at 120Vac with full load. EN55015 Class B limit. Application Note 16 Version 1.1, 2012-08-03
Phase Cut Dimmable Non-isolated Buck Converter for LED Retrofit Bulb with ICL8002G & CoolMOS™ 600V C6
10 Production Tolerance and Normal Distribution
In total 47 demo board samples have been tested and the output current of each board was recorded at the same test condition (line voltage of 120Vac and am bient temperature of 25 oC) to check the production tolerance, which is contributed by both the IC and external components tolerance. Figure 17 shows the distribution data of output current. The result indicted that the output current tolerance is within +3%, and standard deviation is 3.62mA. Figure 17 Production variation of output current (board to board deviation) Application Note 17 Version 1.1, 2012-08-03
Phase Cut Dimmable Non-isolated Buck Converter for LED Retrofit Bulb with ICL8002G & CoolMOS™ 600V C6
11 Board Layout
A single layer PCB with dimension of 40x20mm and thickness of 0.8mm is used for this demo board. The maximum height of the demo board (at C9) is 23.2mm. With its compact form factor, this demo board is able to fit into many different LED lamps such as A19 bulb and Par30. Figure 18 EVALLED-ICL8002G-B2 - Top and Bottom Layer Figure 19 EVALLED-ICL8002G-B2 - Silkscreen Top and Bottom Application Note 18 Version 1.1, 2012-08-03
Phase Cut Dimmable Non-isolated Buck Converter for LED Retrofit Bulb with ICL8002G & CoolMOS™ 600V C6
12 BOM and Power Inductor Spec
12.1 Bill of Material
Number Reference Value Description Package Part Number Manufacturer
1 U1 ICL8002G IC SO8 ICL8002G INFINEON
2 F1 22OHM,2W Fusible Resistor,±10% 4×10 EMC2-22RKI WELWYN
3 Z1 360V VARISTOR,13.5J, 140Vrms 7mm Disc V07E140P LITTELFUSE 4 Q1 600V 0.09A Small Signal Mosfet SOT89 BSS225 INFINEON 5 Q2 45V 0.1A NPN Transistors SOT323 BC847BW INFINEON 6 Q3 45V 0.1A PNP Transistor SOT23 BC857B INFINEON 7 Q5 600V 2.4A MOSFET DPAK IPD60R2K0C6 INFINEON
9 C2 15nF 630V MLCC,X7R 1206 GRM31CR72J153KW03L MURATA
10 C4 50V 1nF MLCC,X7R 0603 GRM188R71H102KA01D MURATA
11 C5 250V 0.22uF Film Cap, 10mm Pitch 12×5.5×10.5 ECQ-E2224JF PANASONIC
12 C6 25V 22uF MLCC,X7R 1210 GRM32ER71E226KE15L MURATA
13 C7 50V 56pF MLCC,COG 0603 GRM1885C1H560JA01D MURATA
14 C8 50V 10nF MLCC,X7R 0603 GRM188R71H103KA01D
15 C9 50V 330UF Electrolytic Cap,Lo=10000H 10×20 50ZLH330MT810X20 RUBYCON
16 C10 50V 4.7uF MLCC,X7R 1206 GRM31CR71H475KA12L MURATA
17 D1 400V 1A Ultrafast Rectifier Diode DO-41 UF4004 VISHAY
18 D2,D4 150V 250mA Switching Diode SOD80C BAV102 NXP
19 D3 600V 1.5A Ultrafast Rectifier Diode SMA BYG20J VISHAY Coupled inductor, 210uH±10%
20 T1 210uH Np:Nvcc:Naux = 70:40:11 EE13 750341383 Würth Elektronik
21 L1,L2 1.5mH 0.19A Filter Choke 7447462152 Würth Elektronik 22 BD1 600V 0.5A Bridge Diode TO-269AA MB6S-E3/80 VISHAY
23 ZD1 11V Zener Diode,500mW SOD123 MMSZ5241B -V-GS08 VISHAY
24 ZD2 4.7V Zener Diode,500mW SOD123 MMSZ4688 -V-GS08 VISHAY
25 ZD3 15V Zener Diode,400mW SOD323 PDZ15B,115 NXP
26 R1 1K 1/2W Metal Film Resistor,5% 1210
27 R2 4K7 Metal Film Resistor,5% 0603
28 R3 1.5M Metal Film Resistor,5% 1206
29 R4 604K Metal Film Resistor,5% 0603
30 R5 3.6K 3/4W Metal Film Resistor,5% 2010
31 R6,R15 121K Metal Film Resistor,1% 0603
32 R7 3.48K Metal Film Resistor,1% 0603
33 R8 576K Metal Film Resistor,1% 0805
34 R9 118K Metal Film Resistor,1% 0603
35 R10 12K7 Metal Film Resistor,1% 0603
36 R11 0R Metal Film Resistor,5% 0603
37 R12 20K Metal Film Resistor,1% 0603
38 R13 10R Metal Film Resistor,5% 0603
39 R14 33K Metal Film Resistor,5% 0603
40 R14A 1R Metal Film Resistor,1% 0805
41 R14B 1R5 Metal Film Resistor,1% 0805
Figure 20 Bill Of Material Application Note 19 Version 1.1, 2012-08-03
Phase Cut Dimmable Non-isolated Buck Converter for LED Retrofit Bulb with ICL8002G & CoolMOS™ 600V C6
12.2 Power Inductor
Figure 21 EVALLED-ICL8002G-B2 Inductor Design Application Note 20 Version 1.1, 2012-08-03
Phase Cut Dimmable Non-isolated Buck Converter for LED Retrofit Bulb with ICL8002G & CoolMOS™ 600V C6
13 Common Questions and Troubleshooting Hints
13.1 Q&A
How does ICL8002G realize dimming control and power factor correction? Both dimming control and PFC are achieved with the input mains voltage sensing with the VR pin. This signal is used to set the peak current of the primary winding and consequently allows both PFC and phase -cut dimming functionality by regulating the cycle energy. Is it possible to test the demo board with different LED modules with big variations in total forward voltages? The operation range of output voltage is specified in Table 1. The demo board will switch into protection mode when tested with LED load with out -of-range forward voltage either due to Vcc overvoltage protection or Vcc undervoltage protection. Modifications on the transformer design are necessary for applications with different output voltage.
13.2 Design and Troubleshooting Hints
Why is there no light output after the LED load is connected and power is on? Please verify the following:
- Connectivity of AC input and LED load
- LED module’s polarity
- Whether LED module’s forward voltage is out of the range specified in Table 1 How to change output current? The easiest way to set the desired output current is to adjust the VR pin’s voltage and shunt resistor. However, care must be taken to ensure that the transformer is not driven into saturation. Moreover, the VR pin’s voltage should be kept below 3.7V for maximum power factor. How to change the open circuit protection to Auto Restart Mode? If Auto Restart Mode is preferred for output open circuit protection, R7 and/or R12 can be adjusted so that Vcc overvoltage threshold (Vvccovp = 25V) is reached first before OVP threshold (Vzcovp = 3.7 V) is re ached. Please note that with changing R12, the voltage foldback correction will be affected and as a result the line regulation will be affected. In this case R9 can be tuned for better line regulation. Why is the LED flickering in my dimming application? How to improve? Flickering can be either caused by IC auto -restart or by dimmer's uneven conduction phase angle. For the auto - restart case, the ICL8002G’s Vcc voltage should be maintained between Vvccovp and Vvccoff over the whole dimming range. This can be achieved by proper transformer turn ratio design and, if necessary, a voltage regulation circuit for the Vcc. For dimmer’s uneven conduction case, it is advised to tune the damping and bleeder circuits. How to improve system efficiency? For applications which require higher efficiency, first of all, an active damper circuit can be used to replace the lossy passive damper circuit. Switching frequency can be reduced so as to minimize the switching loss and this may require bigger inductor size. Low ESR capacitor can be used for the output capacitor to improve efficiency. Using a higher current rated MOSFET for Q5, however, may not necessarily produce higher efficiency as the switching loss may dominate the total power loss of the MOSFET. How to modify the board for non-dimmable LED bulb application? For non -dimmable application, the highlighted damping and bleeder circuits as shown in Figure 2 can be removed for better efficiency and cost reduction. Application Note 21 Version 1.1, 2012-08-03
Phase Cut Dimmable Non-isolated Buck Converter for LED Retrofit Bulb with ICL8002G & CoolMOS™ 600V C6 How to reduce BOM cost? For low cost application, the active bleeder circuit (formed by R3 -R6, C3, C4, ZD 1, Q1, and Q2) can be removed. Please note that dimming performance may be affected. If lightning surge performance requirement is not stringent, a 250V rated MOSFET can be used for Q2 while a 500V rated MOSFET can be used for Q5 for cost reduction.
14 References
ICL8002G Datasheet at www.infineon.com/ledoffline Design Guidelines for ICL8001G/ICLS8082G at www.infineon.com/ledoffline Application Note 22 Version 1.1, 2012-08-03
w w w . i n f i n e o n . c o m Published by Infineon Technologies AG