DN05051/D 120 VAC, Dimmable, Linear 3‐stage, Parallel‐to‐Series LED Lighting Circuit http://onsemi.com DESIGN NOTE Table 1. DEVICE DETAILS Device Application Topology Efficiency Input Power Power Factor THD NSIC2030JB, NSIC2050JB AC LED Lighting Linear 82% 7.8 W 0.99 13.6% Overview an additional CCR to increase LED current at high voltages to improve PF and THD. This circuit uses inventive techniques to provide a cost-efficient and effective AC LED lighting solution for 120 VAC mains power. Its primary features are its high efficiency, dimmability, high light output, high power factor, and low THD. The circuit is designed for use with input voltages between 110 VAC and 130 VAC. The circuit uses a parallel-to-series topology that dynamically adjusts LED forward voltage (Vf) to match the bridge output voltage for high efficiency. The circuit employs ON Semiconductor Constant Current Regulators (CCRs) to regulate LED current and protect LEDs from over-voltage conditions. The circuit also utilizes F1 D1 D3 D2 D4 Key Circuit Features • Functional with Wide Range of Standard Phase-Cut • • • • • • TRIAC Dimmers Low-Cost PF = 0.99 Efficiency > 80% Over Voltage Range THD < 15% Adjustable for Different LED Voltages Adjustable for Different Currents/Power Levels Vin MOV1 Q6 R6 CCR2 CCR1 R7 R9 LED1 Q4 C1 LED2 R4 Q9 D5 R11 R15 R12 LED3 Q2 D6 Q1 Q10 Q3 Q8 C2 R2 R14 R10 Q7 LED4 R5 Q11 D7 Q5 C3 R16 R8 R3 R13 R1 Figure 1. 3-stage Parallel-to-Series LED Lighting Circuit © Semiconductor Components Industries, LLC, 2014 June, 2014 − Rev. 2 1 Publication Order Number: DN05051/D DN05051/D Circuit Description Using the values VSWITCH(Q1) = 72 V. The circuit consists of a full-wave bridge rectifier (D1–D4), parallel-to-series switching circuitry (R1–R5, R9–R16, C1–C3, Q1–Q5, Q7–Q11), CCR turn-on circuitry (R6–R8, Q6), CCRs (CCR1–CCR2), LED routing diodes (D5–D7), and LEDs (LED1–LED4). R2 = 9.53 kW, †† Similar to the VSWITCH(Q1) relationship, Q11 is triggered on by the R15/R16 resistor divider. Also an ON Semiconductor MMBT3904L, the expected VBE(sat) of Q11 is roughly 0.68 V, and by the following equation: ǒ Circuit Operation Ǔ V SWITCH(Q11) + V BE(sat) @ R15 ) R16 R16 The bridge rectifier outputs a half-wave sine peaking at about 170 V (for 120 VAC). This bridge output is referenced between the cathodes of D3 and D4 to the anodes of D1 and D2. The circuit dynamically adjusts the LED Vf to closely resemble the rectified half-sine output of the full-wave bridge. As seen in the “Representational Circuit Diagrams” section, the LEDs change between three configurations with varying bridge output. The first configuration, when the bridge output is between 0 V and 72 V†, is a “parallel” stage, when all LEDs are in parallel with each other. CCR2 is on, as well as all the Q3 through Q5 and Q7 through Q9 transistors. The D5, D6, and D7 diodes are all reverse-biased. CCR current (when above the LED Vf turn-on voltage of 36 V) is split down the four strings of LEDs. The second configuration, when the bridge output is between 72 V and 145 V††, shifts the LEDs into two parallel strings. Q1 initiates the transition into the second stage switching on at 72 V due to the R1/R2 voltage divider. When Q1 turns on, Q2’s VBE is shorted, eliminating base current for transistors Q3, Q4, Q8, and Q9. As these turn off, the D5 and D7 diodes are forward biased, connecting LED1 to LED2, and LED3 to LED4. D6 is still reverse-biased. The third stage, when the bridge output is above 145 V, puts all the LEDs in one series string. Q11 turns on by the R15/R16 voltage divider and initiates this transition. Q11 turns off Q10, which then deprives Q5 and Q7 of base current, turning them off as well. D6 becomes forward-biased, and all the LEDs pass CCR2’s current. After the LEDs are all in series, CCR1 is set to turn on to provide additional current at high voltages. This matches the total current waveform to the input voltage waveform, achieving better power factor and THD performance. With about an extra 7 V over the device, CCR1 is in full regulation at about 152 V bridge output. Using the values VSWITCH(Q11) = 145 V. R15 = 1 MW, R16 = 4.7 kW, Design Modifications Special modifications for this circuit might include LED string forward voltage (Vf) and CCR1 current value. For optimal performance, it is recommended that LED strings of Vf between 15 V and 40 V are used. Generally, the higher the LED Vf, the greater the efficiency, though the benefits of PF/THD-improving CCR1 are reduced. The lower the Vf, the lower the efficiency and the earlier the LEDs will turn on. Note that changing LED Vf will require R2 and R16 to be changed to adjust switching points. If a higher CCR1 value is desired, a darlington-connected PNP pair or PFET is recommended in place of Q6 to reduce base current and increase gain. Multiple CCRs may be used in parallel with CCR2 to no adverse effect, only ensure that R4, R11, and R12 allow sufficient base current. Circuit Performance Data Table 2. ELECTRICAL CHARACTERISTICS FOR THE CIRCUIT SHOWN IN FIGURE 1 110 VAC 120 VAC 130 VAC IRMS(IN) (mA) 64.39 65.49 66.06 PF 0.9886 0.9907 0.9921 THD (IRMS, %) 14.86 13.56 12.35 PIN (W) 6.93 7.75 8.44 Efficiency (%) 80.4 82.2 81.0 Product parametric performance is indicated in the Electrical Characteristics for the listed test conditions, unless otherwise noted. Product performance may not be indicated by the Electrical Characteristics if operated under different conditions. Dimmers Tested † This switching voltage is determined by the R1/R2 resistor divider and the VBE(sat) of the transistor used − in this case, an ON Semiconductor MMBT3904L NPN BJT. A typical value for VBE(sat) at 25°C is roughly 0.68 V. The switching voltage may be found using the following equation: ǒ R1 = 1 MW, Table 3. THE CIRCUIT WAS FULLY FUNCTIONAL WITH EACH DIMMER TESTED Ǔ V SWITCH(Q1) + V BE(sat) @ R1 ) R2 R2 http://onsemi.com 2 Manufacturer Serial Number Leviton 600W−1D4102 Leviton 600W−1B4105 Lutron Skylark CTCL−153PDH Lutron TG−600P−AC DN05051/D Representational Circuit Diagrams LED1 Q4 D5 Q7 Q9 LED2 LED1 LED2 LED3 LED4 D6 LED3 Q3 Q5 D7 Q8 LED4 Figure 2. Stage 1/Parallel configuration of LEDs, showing behavior of switching circuitry. D5−D7 are open circuits, whereas all the transistors Q3–Q5 and Q7–Q9 are on. The LEDs are then in parallel below the CCR. The driver is in this state at bridge voltages below 72 V LED1 Q4 D5 Q7 Q9 LED2 LED1 LED3 LED2 LED4 D6 LED3 Q3 Q5 D7 Q8 LED4 Figure 3. Stage 2/Parallel-Series configuration of LEDs. Transistors Q3–Q4 and Q8–Q9 are open, and current flows through the routing diodes D5 and D7. Simplified schematic containing only the LEDs is shown to the right. The driver is in this state between 72 V and 145 V http://onsemi.com 3 DN05051/D LED1 Q4 D5 Q7 LED1 Q9 LED2 LED2 D6 LED3 LED3 Q3 Q5 LED4 D7 Q8 LED4 Figure 4. Stage 3/Series configuration of the LEDs and switching circuitry shown. All transistors Q3–Q5 and Q7–Q9 are off at high bridge voltages, and current passes through the routing diodes D5–D7. The driver is in this stage at bridge voltages above 145 V http://onsemi.com 4 DN05051/D Waveforms Figure 5. The total input current follows the voltage waveform very closely, yielding high power factor and outstanding THD performance Figure 6. LED current through each of the LEDs. Note the current waveforms are nearly identical, as well as the three distinct levels of current, coinciding with the three LED configurations http://onsemi.com 5 DN05051/D Figure 7. The LED forward voltage is identical for all LEDs. When the LED voltage is not 0 V, the LEDs are on. Given an LED Vf of 32 V, the LEDs are on about 92% of the time Figure 8. The CCR2 Vak demonstrates the different stages of the LED configurations. Q3 blocks CCR1 from conducting only until the highest bridge voltages. Q3 and CCR1 are in parallel with CCR2 http://onsemi.com 6 DN05051/D Figure 9. The circuit receives no input current when the TRIAC is off, and the current is normal when the TRIAC is on Figure 10. LED1’s voltage and current waveforms, unaffected by TRIAC dimming. The voltage on the LEDs is due to the non-zero voltage out of the dimmer during the “off” state http://onsemi.com 7 DN05051/D Evaluation Board The evaluation board CCR230PS3AGEVB (driver circuitry, pictured below) may be altered from its original design for 230 VAC to replicate the performance of this circuit at 120 VAC. Figure 11. CCR230PS3AGEVB Evaluation Board with Changes Marked for DN05051/D A list of modifications appears below, along with data taken using the metal-clad board. Overall circuit performance is greatly improved when using metal-clad boards. Table 4. LIST OF MODIFICATIONS CCR230PS3AGEVB Reference Recommended Modification Alternative Modification R3 Replace with 9.53 kW Desired Rset1 Value R2 R10 Replace with 4.7 kW Desired Rset2 Value R16 R15 Replace with 255 W Parallel with 309 W R6 R16 Replace with 24.9 kW Parallel with 28 kW R7 R17 Replace with 24.9 kW Parallel with 28.7kW R8 CCR1 Replace with NSIC2030JBT3G − − Circuit Data for switching resistors R2 and R16 is also given, as a function of LED string voltage. Of course, optimizing the system may require some experimentation, but the plot is provided as a ballpark design tool. With this design, four strings between 15 Vf and 40 Vf are recommended, for a total of 60 to 160 Vf total of LEDs. Table 5. USING REFITTED EVALUATION BOARD 110 VAC 120 VAC 130 VAC IRMS(IN) (mA) 61.05 65.03 67.86 PF 0.9864 0.9890 0.9907 THD (IRMS, %) 16.5 14.42 13.02 PIN (W) 6.64 7.75 8.76 Efficiency (%) 84.1 83.3 80.1 DN05051/D Designator Design Modifications If the user wishes to connect their own LEDs to the evaluation board, it should be noted that the off-board connections (in keeping with the design note’s designators) will be as shown in Figure 12. It should also be noted that different LED voltages will require you to adjust switchpoints for best performance. A reference plot (Figure 13) showing recommended values Figure 12. Off-board Connections, from Driver Board to LEDs http://onsemi.com 8 DN05051/D Switching Resistor (R2) Value vs. LED String Vf For Parallel-to-Series Applications given R1 = 1 MW, and MMBT3904L (0.68 V VBEon) Rswitch Resistor Value (kW) 20 18 Rswitch, Stage1-to-2 16 Rswitch, Stage2-to-3 14 12 10 8 6 4 2 0 15 20 25 30 35 40 LED String Voltage (V) Figure 13. Plot showing recommended values for the Rswitch resistor values to determine the driver’s switchpoints. The second-to-third stage trigger resistor is roughly half the value of the first-to-second stage trigger resistor http://onsemi.com 9 DN05051/D Bill of Materials Table 6. BILL OF MATERIALS FOR CIRCUIT SHOWN IN FIGURE 1 Designator Qty Description Value Tolerance Manufacturer Part Number CCR1 1 Constant Current Regulator 120 V, 30 mA ±15% ON Semiconductor NSIC2030JB CCR2 1 Constant Current Regulator 120 V, 50 mA ±15% ON Semiconductor NSIC2050JB F1 1 Fuse 250 V, 1 A − Any − MOV1 1 Varistor 150 VAC − Any − D1−D4 4 Diode 400 V, 1 A − ON Semiconductor MRA4004 D5, D7 2 Diode 75 V, 200 mA − ON Semiconductor BAS16H D6 1 Diode 250 V, 200 mA − ON Semiconductor BAS21L C1 1 Capacitor 2.2 nF, 500 V − Any − C2−C3 2 Capacitor 1 nF, 10 V − Any − Q1, Q11 2 NPN Transistor 40 V, 200 mA − ON Semiconductor MMBT3904L Q2, Q10 2 NPN Transistor 350 V, 100 mA − ON Semiconductor MMBT6517L Q3, Q5, Q8 3 NPN Transistor 140 V, 600 mA − ON Semiconductor MMBT5550L Q4, Q6, Q7, Q9 4 PNP Transistor 150 V, 500 mA − ON Semiconductor MMBT5401L R1, R15 2 Resistor 1 MW, 1/8 W ±1% Any − R2 1 Resistor 9.53 kW, 1/8 W ±1% Any − R3, R14 2 Resistor 300 kW, 1/8 W ±1% Any − R4 1 Resistor 30 kW, 1/8 W ±1% Any − R5, R9 2 Resistor 1 kW, 1/8 W ±1% Any − R6 1 Resistor 255 W, 1/8 W ±1% Any − R7−R8 2 Resistor 24.9 kW, 1/8 W ±1% Any − R10, R13 2 Resistor 2.2 kW, 1/8 W ±1% Any − R11−R12 2 Resistor 15 kW, 1/8 W ±1% Any − R16 1 Resistor 4.7 kW, 1/8 W ±1% Any − LED1−LED4 4 LEDs 36 V, 480 mA − Any − Further Reference • Design Note – DN05047/D: 230 VAC, Low-Cost, For a similar design (3-stage, Parallel-to-Series) adapted to 230 VAC, please refer to design note DN05047. 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