A New Circuit for Low-Cost Electronic Ballast

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
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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
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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.
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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
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AN-1074
Results with fixed frequency, R1= 1.2K:
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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
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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.
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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
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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.
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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
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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.
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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
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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.
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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
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AN-1074
Results with frequency modulation, R1= 200ohm: PF = 0.938
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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
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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.
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17
AN-1074
Figure 12 shows the frequencies at the minimum of the bus and at the maximum
VBUS = 150V, frequency 53KHz
18
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AN-1074
VBUS = 320V, frequency 64KHz
Figure 12: VS pin and frequencies at the minimum of the bus and at the maximum.
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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
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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.
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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
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AN-1074
Figure 15 shows the frequencies at the minimum of the bus and at the maximum.
VBUS = 150V, frequency 58.6 KHz
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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
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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
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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
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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
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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
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