Application Note AN-1074 A new Circuit for Low-Cost Electronic Ballast Passive Valley Fill with additional Control Circuits for Low Total Harmonic Distortion and Low Crest Factor By Cecilia Contenti, Peter Green and Tom Ribarich Table of Contents Page Passive Valley Fill Test Results ......................................................................1 Passive Valley Fill Test Results with 36W/T8 ballast section PIN =36.5W,VAC = 230V, load: 36W/T8 ........................................................................................4 Passive Valley Fill Test Results with 36W/T8 ballast section PIN =36.5W,VAC = 230V, load: 36W/T8 and additional circuit to modulate the frequency ............11 Passive Valley Fill Test Results with 58W/T8 ballast section PIN =63W,VAC = 230V, load: 58W/T8 ........................................................................................20 The goal of this design is to implement a low-cost linear ballast with good PFC, acceptable THD and low current-crest factor. The ballast will use Passive Valley Fill configuration to reduce costs compared to standard PFC. To overcome the disadvantage of the very high current crest factor, additional circuit has been used to modulate the Half Bridge frequency versus the bus voltage. The system will work at a minimum frequency when the bus voltage is low and increase the frequency while the bus voltage increases. This will stabilize the lamp power versus the AC line changes, improve the current crest factor and improve EMI because the operating frequency varies in a frequency range. The solution has been implemented for 2 different lamps: 36W and 58W T8. AN-1074 International Rectifier • 233 Kansas Street, El Segundo, CA 90245 z USA A new Circuit for Low-Cost Electronic Ballast Passive Valley Fill with additional Control Circuits for Low Total Harmonic Distortion and Low Crest Factor by Cecilia Contenti, Peter Green & Tom Ribarich Abstract: The goal of this design is to implement a low-cost linear ballast with good PFC, acceptable THD and low current-crest factor. The ballast will use Passive Valley Fill configuration to reduce costs compared to standard PFC. To overcome the disadvantage of the very high current crest factor, additional circuit has been used to modulate the Half Bridge frequency versus the bus voltage. The system will work at a minimum frequency when the bus voltage is low and increase the frequency while the bus voltage increases. This will stabilize the lamp power versus the AC line changes, improve the current crest factor and improve EMI because the operating frequency varies in a frequency range. The solution has been implemented for 2 different lamps: 36W and 58W T8. Passive Valley Fill Test Results Schematics tested: F1 F1 L L1 N DBR1 L DBR4 C4 DBR2 DBR1 L1 C1 D3 DBR3 DBR4 C4 C1 N DBR2 D3 DBR3 D2 D2 C2 C2 D1 D1 R1 R1 C5 C5 C3 These circuits produced the same result. Test with resistive load (1.5K) to provide 36W load at 230VAC in. DBR1, DBR2, DBR3, DBR4, D1, D2, D3: 10DF6 diode C1 = 0.33uF, 275VAC L1 = 1X10mH 0.7Apk, Common mode EMI inductor C2, C3 (fig. 1) = 100nF, 275V, C2 (fig. 2) = 100nF, 400V C4, C5 = 47uF www.irf.com 1 AN-1074 R1 effects: Higher R1, lower harmonics but lower minimum bus Voltage. The best trade-off is 1.2K: the harmonics are within the Class C limits of EN61000-3-2, the PF is 0.964 and the minimum bus is 110V Harmonics Results AH2 AH3 AH5 AH7 AH9 AH11 AH13 AH15 AH17 AH19 AH21 AH23 AH25 AH27 AH29 AH31 AH33 AH35 AH37 AH39 0 10.8 9.9 4.4 2.5 2.2 2.9 2 0.4 0.8 1.1 1.4 0.8 1.3 0.7 0.3 0.9 1.2 2 1.5 Class C Limits 2 30 10 7 5 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 With a lower value of R1, the harmonics are above the limits. For example, with 1K we have AH13 = 3.3. 2 www.irf.com AN-1074 Figure 1 shows the bus voltage and input current in this situation (R1=1.2K, VAC = 230V, PIN = 36W, Rload = 1.5K). Figure 1: Bus voltage and input current with R1=1.2K, VAC = 230V, PIN = 36W, Rload = 1.5K. www.irf.com 3 AN-1074 Passive Valley Fill Test Results with 36W/T8 ballast section PIN =36.5W, VAC = 230V, load: 36W/T8 Figure 2 shows the circuit with fixed frequency. RSUPPLY F1 L DBR1 L1 N DBR4 DBOOT C1 RDC DCP2 C4 LRES DBR2 DBR3 1 NC VB 14 2 VCC HO 13 3 VDC VS 12 4 RT LO 11 CBOOT D3 CDC RHO CVCC2 CVCC1 D2 RT R1 5 RPH RLO MLS CSNUB RLIM1 CS 10 6 CT SD 9 7 CPH COM 8 CRES D1 IR2156 RPH MHS C2 DCP1 R3 CPH C5 IC BALLAST CT CCS RCS Note: Thick traces represent high-frequency, high-current paths. Lead lengths should be minimized to avoid high-frequency noise problems Figure 2: Passive Valley Fill circuit with fixed frequency. 4 www.irf.com AN-1074 Results with fixed frequency, R1= 1.2K: www.irf.com PF = 0.938 Harmonics Results AH2 AH3 AH5 AH7 AH9 AH11 AH13 AH15 AH17 AH19 AH21 AH23 AH25 AH27 AH29 AH31 AH33 AH35 AH37 AH39 0 6.8 11.7 12.1 8.8 1.7 6.3 5.8 2.4 1.1 1.9 2.5 2.5 0.8 2.3 1.7 1.4 2 4.1 2.9 Class C Limits 2 30 10 7 5 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 5 AN-1074 Figure 3 shows the bus voltage, the lamp voltage and lamp current in this situation (R1=1.2K). Figure 3: Bus voltage (yellow), lamp voltage (green) and lamp current (blue) with R1=1.2K and fixed frequency. As you can see, the lamp current goes too low when the bus voltage goes to the minimum. The lamp re-strikes every half cycle. 6 www.irf.com AN-1074 Figure 4 shows the bus voltage, the lamp voltage and the input current in this situation (R1=1.2K) Figure 4. Bus voltage (yellow), the lamp voltage (green) and the input current (blue) with R1 = 1.2K and fixed frequency. As you can see, we have a peak in the lamp current that we do not have with a resistive load, this has as a result high harmonic distortion. To solve the problem of the multiple ignitions of the lamp, we needed to increase the minimum bus reducing the value of R1 to 200 Ohm. www.irf.com 7 AN-1074 Results Fixed frequency, R1= 200ohm: 8 PF = 0.938 Harmonics Results AH2 AH3 AH5 AH7 AH9 AH11 AH13 AH15 AH17 AH19 AH21 AH23 AH25 AH27 AH29 AH31 AH33 AH35 AH37 AH39 0 7.8 11.4 14.2 4.9 8.7 7.5 2.5 2.6 4.3 1.9 2.3 3 2.9 0.7 3.4 3.1 0.5 1.8 1.8 Class C Limits 2 30 10 7 5 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 www.irf.com AN-1074 Figure 5 shows the bus voltage (yellow), the lamp voltage (green) and lamp current (blue) in this situation (R1= 200 Ohm). Figure 5: bus voltage (yellow), lamp voltage (green) and lamp current (blue) with R1= 200 Ohm. As you can see, the lamp current varies too much also with a minimum bus of 160V. www.irf.com 9 AN-1074 Figure 6 shows the bus voltage, the lamp voltage and the input current in this situation (R1=200 Ohm). Figure 6: bus voltage (yellow), lamp voltage (green) and input current (blue) with R1=200 Ohm. As you can see, the peak in the input current does not improve, causing very high harmonics. To improve the crest factor and reduce the variation of the lamp current during the line voltage half cycle, we have added a circuit, which modulates the working frequency of the ballast according on the bus voltage. The ballast is tuned to work at the minimum bus voltage at a fixed frequency (fmin). When the bus voltage increases, the frequency is also increased to compensate by reducing the lamp current and hence keeping the lamp power as constant as possible. 10 www.irf.com AN-1074 Passive Valley Fill Test Results with 36W/T8 ballast section PIN =36.5W, VAC = 230V, load: 36W/T8 and additional circuit to modulate the frequency. Figure 7 shows the circuit with frequency modulation. R2 RSUPPLY F1 L L1 N DBR1 DBR4 DBOOT C1 RDC DCP2 C4 LRES DBR2 DBR3 1 NC VB 14 2 VCC HO 13 3 VDC VS 12 4 RT LO 11 D3 CBOOT CDC RHO CVCC2 CVCC1 D2 T1 RT R1 5 RPH RLO MLS CSNUB RLIM1 CS 10 6 CT SD 9 7 CPH COM 8 CRES D1 IR2156 RPH MHS C2 R3 DCP1 R6 CPH C5 IC BALLAST CT CCS RCS Note: Thick traces represent high-frequency, high-current paths. Lead lengths should be minimized to avoid high-frequency noise problems Figure 7: Passive Valley Fill circuit with frequency modulation. The amount of modulation (frequency range) can be adjusted by varying R6. The collector of T1 is connected to RT, so that it has not effect on the dead-time. The dead-time is constant when the frequency changes, avoiding hard-switching. www.irf.com 11 AN-1074 Results with frequency modulation, R1= 1.2K: 12 PF = 0.915 Harmonics Results AH2 AH3 AH5 AH7 AH9 AH11 AH13 AH15 AH17 AH19 AH21 AH23 AH25 AH27 AH29 AH31 AH33 AH35 AH37 AH39 0 16.5 9.5 13.5 13.8 5.7 4.1 8.1 7.7 4.3 2.8 5.1 5.3 1.4 2 2.2 2.9 0.6 2.9 2.8 Class C Limits 2 30 10 7 5 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 www.irf.com AN-1074 Figure 8 shows the bus voltage, the lamp voltage and lamp current in this situation (R1=1.2K and frequency modulation). Figure 8: bus voltage (yellow), lamp voltage (green) and lamp current (blue) with R1=1.2K and frequency modulation. As you can see, even with frequency modulation, the lamp current still goes too low when the bus voltage goes to the minimum (110V). The lamp partially re-strikes every half cycle. www.irf.com 13 AN-1074 Figure 9 shows the bus voltage, the lamp voltage and the input current in this situation (R1=1.2K and frequency modulation). Figure 9: bus voltage (yellow), lamp voltage (green) and input current (blue) with R1=1.2K and frequency modulation. As you can see, we cannot solve the problem of the current going too low with the frequency modulation. We needed to increase the minimum bus by reducing the value of R1 to 200 Ohm. 14 www.irf.com AN-1074 Results with frequency modulation, R1= 200ohm: PF = 0.938 www.irf.com Harmonics Results AH2 AH3 AH5 AH7 AH9 AH11 AH13 AH15 AH17 AH19 AH21 AH23 AH25 AH27 AH29 AH31 AH33 AH35 AH37 AH39 0 5 9.9 16.1 8.2 8.4 10 3.9 3.4 5.7 3.9 1.7 4.5 3.9 1.6 4.8 4.2 1 2.1 2.0 Class C Limits 2 30 10 7 5 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 15 AN-1074 Figure 10 shows the bus voltage, the lamp voltage and the lamp current in this situation (R1= 200 Ohm and frequency modulation) Figure 10: bus voltage (yellow), lamp voltage (green) and lamp current (blue) with R1= 200 Ohm and frequency modulation. As you can see, with frequency modulation and minimum bus of 160V, the lamp current does not vary too much. 16 www.irf.com AN-1074 Figure 11 shows the bus voltage, the lamp voltage and the input current in this situation (R1=200 Ohm and frequency modulation) Figure 11: bus voltage (yellow), amp voltage (green) and input current (blue) with R1=200 Ohm and frequency modulation. As you can see, the peak in the input current does not improve and the harmonics are still too high. www.irf.com 17 AN-1074 Figure 12 shows the frequencies at the minimum of the bus and at the maximum VBUS = 150V, frequency 53KHz 18 www.irf.com AN-1074 VBUS = 320V, frequency 64KHz Figure 12: VS pin and frequencies at the minimum of the bus and at the maximum. www.irf.com 19 AN-1074 Passive Valley Fill Test Results with 58W/T8 ballast section PIN =63W, VAC = 230V, load: 58W/T8 Frequency modulation, R1= 100 Ohm: PF = 0.943 20 Harmonics Results AH2 AH3 AH5 AH7 AH9 AH11 AH13 AH15 AH17 AH19 AH21 AH23 AH25 AH27 AH29 AH31 AH33 AH35 AH37 AH39 0 7.8 9.2 18.9 9 9.2 10 4.1 3 6.7 5.8 3 5.6 4.4 2.2 4.3 4.4 1.3 3.3 3 Class C Limits 2 30 10 7 5 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 www.irf.com AN-1074 Figure 13 shows the bus voltage, the lamp voltage and lamp current with R1 = 100 ohm and frequency modulation. Figure 13: bus voltage (yellow), lamp voltage (green) and lamp current (blue) with R1 = 100 ohm and frequency modulation. The results are very similar to what we saw for the 36W/T8: the lamp current is reduced when the bus voltage goes to the minimum. The crest factor is acceptable. www.irf.com 21 AN-1074 Figure 14 shows the bus voltage, the lamp voltage and the input current with R1 = 100 ohm and frequency modulation. Figure 14: bus voltage (yellow), lamp voltage (green) and input current (blue) with R1 = 100 ohm and frequency modulation. The results are very similar to what we saw for the 36W/T8: we have the same peak in the lamp current, causing high harmonic distortion. 22 www.irf.com AN-1074 Figure 15 shows the frequencies at the minimum of the bus and at the maximum. VBUS = 150V, frequency 58.6 KHz www.irf.com 23 AN-1074 VBUS = 320V, frequency 73.5 KHz Figure 15: VS pin and frequencies at the minimum of the bus and at the maximum. 24 www.irf.com AN-1074 BOM 36W/T8, Passive Valley fill, 220/240 VAC Item # Qt 1 8 Manufacturer 2 3 1 1 Roederstein 4 5 6 7 8 1 1 2 1 1 WIMA WIMA 9 10 11 1 1 1 12 13 14 15 2 1 2 2 16 17 18 1 1 1 19 20 21 22 23 24 25 26 27 28 29 30 31 Total 1 1 1 1 1 1 1 1 1 1 1 1 1 42 Panasonic Panasonic International Rectifier Panasonic Part Number Description Reference 10DF6 Rectifier, 1A 600V DBR1, DBR2, DBR3, DBR4, D1, D2, D3, DBOOT F1772433-2200 ELF-15N007A MKP10 MKP10 Capacitor, 0.33uF, 275VAC EMI Inductor, 1X10mH 0.7Apk C1 L1 Capacitor, 0.1uF, 400VDC Capacitor, 0.22uF, 400VDC Capacitor, 47uF, 250V Resistor, 42K Resistor, 430K CDC C2 C4, C5 R61 R2 Resistor, 20K Resistor, 200ohm, 1W Resistor, 1K ohm, SMT1206 R3 R1 RLIM1 Capacitor, 0.1uF SMT1206 Capacitor, 2.2uF 50VDC Transistor, MOSFET Resistor, 22 ohm SMT 1206 CVCC1, CBOOT CVCC2 MLS, MHS RLO, RHO Transistor NPN Resistor, 28K Ohm Resistor, 43K Ohm T1 2 RT RPH3 Capacitor, 560pF, SMT1206 Capacitor, 0.47uF, SMT1206 Resistor, 0.43 Ohm 1/2W Capacitor, 470pF SMT1206 Diode, 1N4148 SMT DL35 18V Zener Diode Capacitor, 1.5nF 1.6KV, 1812 Capacitor, 15nF 1600V IC, Ballast Driver w/PFC Inductor, 0.8mH 3Apk Resistor, 147K ohm Resistor, 100K ohm Fuse, 0.5 ohm, ½ W CT CPH RCS CCS DCP2 DCP1 CSNUB CRES IC BALLAST LRES RSUPPLY RDC F1 ECE-A1HGE02R2 IRF830 ERJ-8GEYJ22 PN2222A Diodes LL4148DICT-ND International Rectifier IR2156 JCT, JRT are in CY and RV1 not mounted USE POT USE POT 3 USE POT 1 2 www.irf.com 25 AN-1074 BOM 58W/T8, Passive Valley fill, 220/240 VAC Item # Qt 1 8 Manufacturer Part Number 2 1 Roederstein F1772433-2200 Capacitor, 0.33uF, 275VAC C1 3 4 1 2 Panasonic WIMA ELF-15N007A MKP10 EMI Inductor, 1X10mH 0.7Apk Capacitor, 0.22uF, 400VDC L1 CDC, C2 5 6 2 1 Capacitor, 100uF, 250V Resistor, 46K ohm C4, C5 R61 7 1 Resistor, 430K R2 8 1 Resistor, 20K R3 9 1 Resistor, 100ohm, 1W R1 10 2 Capacitor, 0.1uF SMT1206 CVCC1, CBOOT 11 1 Panasonic ECE-A1HGE02R2 Capacitor, 2.2uF 50VDC CVCC2 12 2 International Rectifier IRF840 Transistor, MOSFET MLS, MHS 13 14 2 1 Panasonic ERJ-8GEYJ22 PN2222A Resistor, 22 ohm SMT 1206 Transistor NPN RLO, RHO T1 15 16 1 1 Resistor, 22K Ohm Resistor, 18K Ohm RT2 RPH3 10DF6 Description Rectifier, 1A 600V Reference DBR1, DBR2, DBR3, DBR4, D1, D2, D3, DBOOT 17 1 Resistor, 1K ohm, SMT1206 RLIM1 18 19 1 1 Capacitor, 560pF, SMT1206 Capacitor, 0.39uF, SMT1206 CT CPH 20 1 Resistor, 0.22 Ohm 1/2W RCS 21 22 1 1 Capacitor, 470pF SMT1206 Diode, 1N4148 SMT DL35 CCS DCP2 23 24 1 1 18V Zener Diode Capacitor, 1.5nF 1.6KV, 1812 DCP1 CSNUB Capacitor, 22nF 1600V CRES IC, Ballast Driver w/PFC Inductor, 0.4mH 3Apk IC BALLAST LRES Diodes LL4148DICT-ND 25 1 26 27 1 1 28 29 1 1 Resistor, 147K ohm 1/2W Resistor, 100K ohm RSUPPLY RDC 30 1 Fuse, 0.5 ohm, ½ W F1 Total 42 International Rectifier IR2156 JCT, JRT are in CY and RV1 not mounted USE POT USE POT 6 USE POT 4 5 26 www.irf.com AN-1074 L N F1 L1 C1 DBR1 DBR2 DBR4 DBR3 D1 D2 C4 D3 R1 C5 R3 R2 T1 R6 JRT JCT DCP2 CVCC2 RT CT RSUPPLY CVCC1 RPH DBOOT 1 VCC NC VS HO VB 12 13 14 IR2156 2 VDC 11 3 LO RT 10 4 SD CT RPH CS 5 8 9 COM IC BALLAST CPH 6 7 CPH Note: Thick traces represent high-frequency, high-current paths. Lead lengths should be minimized to avoid high-frequency noise problems RHO CBOOT RLO RLIM1 CCS MHS MLS RCS LRES CSNUB DCP1 RDC CDC ce switches ON for freq. Modulation enabled 27 www.irf.com C2 Schematic WORLD HEADQUARTERS: 233 Kansas St., El Segundo, California 90245 Tel: (310) 252-7105 http://www.irf.com/ Data and specifications subject to change without notice. 12/9/2004 CRES