Simple, Versatile Control IC Dims Fluorescent Ballasts

designfeature
Andre Tjokrorahardjo
Applications Engineer,
Lighting Systems and Applications
International Rectifier, El Segundo, Calif.
Simple, Versatile Control IC
Dims Fluorescent Ballasts
F
luorescent dimming systems can satisfy visual comfort, and reduce
utility costs through daylight harvesting, demand reduction, scheduled
dimming, and other strategies. A dimming electronic ballast is an essential part of this system.
To perform dimming functions, the ballast must be configured to
understand an input signal from the control device, and act upon the
current flowing through the lamp. Typically, this is a challenging task
for the ballast designer and is usually achieved using a complex, high-pin-count control IC.
The IRS2530D is a new dimming ballast control IC in a compact 8-pin form-factor
(Fig. 1). This DIM8TM is a 600-V half-bridge driver IC that includes all the necessary
functions for preheat, ignition, and dimming control of the lamp, and protects the
circuit against line and lamp fault conditions. With only eight pins to accomplish all
dimming ballast functions, the IC can minimize component count and simplify design,
and is flexible enough to be used with various dimming control methods.
Several reference-design kits have been created to help with the evaluation of the
IRS2530D. Each of these kits uses a different dimming control method, and they cover
various input voltages and lamp types. A complete description of each kit is available
at International Rectifier’s lighting website (www.irf.com/product-info/lighting/).
The IRS2530D is simple to use
with any analog and digital
control method available for
dimming fluorescent lamps.
In addition, it can implement
dimming control for LEDs.
Power Line
Communication
Analog Dimming
Fig. 2 shows the schematic of a dimmable
3-Way
electronic
ballast
for driving a 26-W
quad-pin CFL from a
Wireless IR
CFL
220-Vac line with an
isolated 1- to 10-Vdc
dimming input. The
Triac
ballast comprises an
Dimming
Wall
EMI filter to block balInterface
Dimmer
last-generated noise,
Linear Fluorescent
a rectifier and bus
capacitor to convert ac
line input into a dc bus
0 to 10 V Analog
voltage, a control IC
and half-bridge to proDigital
duce high-frequency
square-wave voltage,
LED
Switch
and a resonant output
Fig. 1. The IRS2530D is a 600-V half-bridge driver IC with all the necessary functions for preheat, ignition, and stage for preheating,
dimming control of the lamp. Plus, it protects the circuit against line and lamp fault conditions.
igniting, and running
0°
1° 2°
3°
L1
L2
N
1 0 10 0 1 0 1 1 1
26 Power Electronics Technology | March 2010
Reprinted by permission of Power Electronics Technology magazine.
www.powerelectronics.com
dimmingcontrollers
L
RF1
0.47 R
0.5 W
220 Vac
Line
Input
Full-Bridge
Rectifier
EMI Filter
LF
1 mH
0.2 A
BR1
600 V
0.5 A
RVCC1
360 k
N
RVCC2
360 k
Bus Cap
CF
47 nF
400 V
D2
1N4148
D1
11 V
VCC
1
0.1 µF
COM
CVCC2
2
CDIM 10 nF DIM
3
CVCO 2.2 nF VCO
4
CPH
0.68 µF
D4
RVCO
1N4148
1.5 k
R4
15 k
D3
1N4148
T1
2x30 mH
R1
100 k
R2
470 k
R3
1.8 k
C2
0.1 µF
Half-Bridge
Control IC
RLIM2
10 R
IRS2530D
DC Dimming
Reference
Input
+
1 to 10 V
C1
DIM
INPUT 0.1 µF
-
CBUS +
10 µF
RLIM1
350 Vdc
10 R
1 µF
CVCC1
CFB
0.1 µF
VB
8
HO
7
VS
6
LO
5
RHO
10 R
MHS
IRFU320
LRES: A
2.3 mH
CBS
0.1 µF
RLO
10 R
MLS
IRFU320
CVS
1 nF
1 kV
CSNUB
1 nF
1 kV
DCP2
1N4148
RVS2
82 k
EF20
airgap
= 1 mm
CDC
47 nF
400 V
LRES:B
5 turns
CRES
4.7 nF
1.6 kV
OSRAM
DULUX
T/E
26 W/840
CH1 0.18 µF
RLMP2
470 k
CH2 0.18 µF
DCP1
18 V
0.5 W
RLMP1
220 k
RFB
1k
Resonant
Output Tank
LRES:C
5 turns
RCS
7.5 R
RVS1
82 k
Isolation
Current
Sensing
Fig. 2. The ballast contains an EMI filter, rectifier, bus capacitor, control IC, and half-bridge to produce high-frequency square wave voltage, and a resonant output
stage for preheating, igniting, and running the lamp.
the lamp. The current-sensing resistor and the isolated dimming reference input are additional components needed for
dimming application. The IRPLDIM4E reference design kit
does not include the isolation section of the circuit.
X1A
L
220 V AC Line
Input
N
X1B
RF1
0.47 R
0.5 W
DC Reference Generator for Quad-Level Switch Dimming System
LF
1 mH/200 mA
CF
0.1 µF
275 Vac
When power is initially turned on, the bus capacitor
(CBUS) charges up, and resistors RVCC1 and RVCC2
supply the micro-power current to the IRS2530D. After
the VCC voltage reaches above UVLO threshold, the half-
R3
120 k
BR1
600 V
0.5 A
C3
10 n
R1
150 k
R2
150 k
DIN
600 V
1A
C2
0.1 µF
C1
330 µF
R9
100 k
VDD
1
P2
2
P3
3
P4
4
RVCC1
360 k
R5
24 k
D2
5.1 V
RVCC2
360 k
VSS
8
P7
7
P6
6
P5
5
R6
10 M
+
R7
100 k
C7
0.1 µF
VCC
1
CVCC
COM
1 µF
2
CDIM 10 n DIM
3
CVCO 2.2 n VCO
4
CPH
0.68 µF
IC1
IRS2530D
R10
100 k
C6
2.2 µF
IC2
PIC12F629
D1
5.1 V
CBUS
10 µF
350 V
R4
120 k
RVCO
1.5 k
R8
56 k
VB
8
HO
7
VS
6
LO
5
RHO
1O R
CBS
0.1 µF
RLO
10 R
RLMP1
470 k
CFB
0.1 µF
RFB
1k
MHS
IRFU320
LRES:A
2.3 mH
CDC
EF20
47 n
airgap = 1 mm 400 V LRES:B
Five turns
CVS
1n
1 kV
MLS
IRFU320
CRES
4.7 n
1,600 V
DCP1
1N4148
RLMP2
1M
DCP1
17 V
0.5 W
26 W
CFL
Lamp
CH1
0.1 µF
CH2
0.1 µF
LRES:C
5 turns
RCS
7.5 R
1%
Fig. 3. The IRPLDIM5E is a quad-level switch-dimming fluorescent ballast that operates from a 220-Vac line and drives a 26-W quad-pin CFL.
www.powerelectronics.com March 2010 | Power Electronics Technology
Reprinted by permission of Power Electronics Technology magazine.
27
dimmingcontrollers
Voltage
Doubler
DC Reference Generator
for 3-Way Dimming System
BR1:D1
DF10S
BR1:D2
DF10S
RPU
220 k
LF
1 mH
C3
47 µF
200 V
PL 1
CF
0.068 µF
400 V
RSUPPLY
1M
RVCC1
11 R
RVCC2
11 R
CVCC1
2.2 µF
R3
1M
PL 2
0
1
Live
30
1
2
C2
0.1 µF
C1 250 V
0.1 µF
250 V
Common
3
3-Way
Socket
Screw Base
Neutral
Q3
MMBTA42
Q4
MMBTA42
R4
1M
R6
1M
RPU
0.47/0.5 W
DZI
68 V
Q1
STP7NK40Z
CVCC2
0.1 µF
CDIM
0.01 µF
CVCO
2.2 n
R5
220 k
C4
47 µF
200 V
BR1:D3
DF10S
BR1:D4
DF10S
CPH
0.47 µF
VCC
VB
8
1
COM
2
DIM
3
VCO
IRS2530D
120 V AC
Line
2
R17 1 M
R7
1k
RDIM
C5 10 k
10 µF
CFB
0.1 µF
VS
6
LO
5
4
RVCO
1.5 k
HO
7
RFB
1k
RHO
11 R
CBS
0.1 µF
RLO
11 R
Q2
STP7NK40Z
RLMP1
100 k
RLMP2
1M
CSNUB
1 n/1 kV
DCP2
1N4148
DCP1
1N4148
LRES:A
2.2 mH
EF20
CDC
airgap 47 n/
= 1 mm 400 V
CRES
4.7 n/1.6 kV
LRES:B
5 Turns
CH1
220 µF
32-W Spiral
CFL Lamp
CH2
220 µF
LRES:C
5 Turns
RCS
8.2 R/1%/1 W
Fig. 4. The IRPLCFL8U is a three-way switch-dimming electronic ballast driving a 32-W spiral CFL from a 120-Vac line.
bridge starts to oscillate at the maximum frequency. The
charge-pump circuit (CVS, DCP1, and DCP2) takes over
as the main supply circuit for the IC and keeps the VCC at
the internally clamped 15.6 V.
An internal current source at the VCO pin charges up
the external capacitor (CPH). Output frequency decreases
as the CPH charges and, at the same time, the lamp filaments are preheated using the secondary winding from the
resonant inductor. As the frequency decreases toward the
resonant frequency of the output stage, the voltage across
the lamp increases. After it reaches a high enough voltage to
ignite the lamp, lamp current begins to flow. The resonant
output stage transitions to a series-L, parallel RC circuit with
the Q-value and operating point determined by the user’s
dim level.
Ac lamp current is sensed by the resistor RCS, and the
resulting ac voltage is coupled with the dc dimming reference voltage from isolation through feedback resistor (RFB)
and feedback capacitor (CFB). This dc + ac signal is then fed
into the DIM pin of the IRS2530D and is regulated by the
control loop, such that the valley of the ac voltage always
stays at COM.
When the dc reference voltage at the DIM pin is
decreased for dimming, the valleys of the ac voltage are
pushed below COM. The dimming control circuit increases
the frequency to decrease the gain of the resonant tank circuit, and thus the ac lamp current, until the ac valleys at the
DIM pin are at COM again.
The opposite happens when the dc reference is increased
to increase the brightness level. In this way, the dimming
control circuit keeps the ac lamp current peak-to-peak
amplitude regulated to the desired value at all dc dim level
settings.
Quad-Level Switch Dimming
Another dimming control method is quad-level switch dimming, which uses the on/off switch to control the dimming
level. When the switch is turned off and then turned back
on in less than one second, the dimming level is reduced by
one level.
If the dimming level is already at the minimum, this
action will cycle the dimming level back to the maximum. If
the switch is turned off for more than one second, dimming
will stay at the last level.
The IRPLDIM5E is a quad-level switch-dimming
fluorescent ballast which drives a 26-W quad-pin CFL
from a 220-Vac line. Fig. 3 shows the schematic of the
IRPLDIM5E.
The circuit in Fig. 3 is similar to the IRPLDIM4E, except
for the circuitry to generate the dc dimming reference
voltage. A microcontroller is used to provide the reference
voltage and to determine whether to switch to the next
dimming level.
The micro-controller used here is the PIC12F629, which
contains some EEPROM non-volatile memory that allows
the microcontroller to store the last dim level setting before
shutting down after power is switched off. This enables
the ballast to start up at that same setting when power is
restored, no matter how long the ballast has been off.
Pin 5 of the microcontroller generates a fixed-frequency
square wave signal with four different duty cycles, which
correspond to four dimming levels. The square wave signal
28 Power Electronics Technology | March 2010
Reprinted by permission of Power Electronics Technology magazine.
www.powerelectronics.com
dimmingcontrollers
then goes through the low-pass filter to produce the dc
reference voltage.
Pin 6 of the microcontroller is connected to the bridge
rectifier through a filter circuit with a very short delay. This
allows the microcontroller to detect when ac power has
been removed and restored quickly.
The VDD supply capacitor, C1, is large enough to allow
the microcontroller to continue to run for more than one
second after ac power has been removed from the ballast.
The microcontroller starts a timer as soon as it detects that
the power is switched off. If power is restored within one
second, the microcontroller will reduce the duty cycle one
level, and thus reduce the dc reference by one step. If the
level is already at the minimum, it will cycle back to the
maximum duty cycle.
filaments are connected. In the second position, the first
filament (PL1) is connected across the ac line for the lowest brightness setting. Resistor R5 pulls up the dc dimming
reference across resistor R7 and capacitor C5 to set the
minimum brightness.
The third position, which corresponds to the medium
brightness setting, uses R6 to pull up the dc dimming reference. In the fourth position, parallel resistors R5 and R6 set
the dc dimming reference for the high brightness setting.
The level of brightness can be modified as needed by changing the value of R5, R6, and R7. Transistor Q3 and Q4
ensure that the dc reference voltage is high enough at the
high brightness, setting since both of these transistors will be
switched on in this case.
Phase-Cut (Triac) Dimmer
Three-Way Switch dimming
Virtually all domestic and professional dimming systems are
based on triacs, also known as phase-cut dimmers. These
devices conduct once they have been fired, only while the
current flows in excess of the holding current of the device.
These dimmers work very well with a resistive load—such
as an incandescent light bulb—as the triac continues to
conduct after it is fired, until very close to the end of the
half-cycle.
A traditional CFL ballast, in which there is no power
factor correction, only draws current from the mains near
the peak of the mains voltage where the storage capacitor
charges—and not during the remainder of the mains halfcycle. The inability of traditional CFL ballasts to sustain
conduction of the triac will cause severe flickering when
used with such a dimmer.
The three-way dimming system is widely adopted in the
U.S. The system consists of a special lamp socket that has a
four-position switch and a bulb with a modified screw base.
For incandescent lamps, the bulb has two filaments and two
connections on the lamp screw base.
The IRPLCFL8U is a three-way switch-dimming electronic ballast driving a 32-W spiral CFL from a 120-Vac
line. Fig. 4 shows the ballast, together with the three-way
socket and the modified lamp base. The interface circuit
includes a voltage doubler (D1, D2, D3, D4, C1, and C2)
in place of a rectifier and a circuit to generate the dc dimming reference voltage (R3, R4, R5, R6, R7, RPU, Q3, Q4,
DZ1, and C5).
The first socket switch position is “off,” in which no
F1
0.47 R
0.5 W
L
120 V
Triac
Input
C1
33 nF
250 V
D1
600 V
1A
L1
2.7 mH
0.15 A
C2
33 nF
250 V
D4
D2
RVCC1
100 k
C4
6.8 nF
1 kV
D3
RVCC2
100 k
C3
33 nF
250 V
C5
4.7 nF 1 kV
N
+
VCC
COM
2
R2
100 k
R3
100 k
CDIM 10 µF
D5
1N4148
D6
10 V
0.5 W
DIM
3
R4
100 k
VB
8
1
CVCC
1 µF
CVCO 2.2 µF
VCO
IRS2530D
CBUS
22 µF
200 V
C6
1.0 µF
R6
15 k
CPH
0.68 µF
RHO
10 R
HO
7
VS
6
LO
RLO
10 R
RVCO
1.5 k
RLMP1
220 k
CFB
0.1 µF
RFB
1k
MHS
IRFU320
CBS
0.1 µF
5
4
R5
100 k
Triac Interface
LRES
1.25 mH
1A
CVS
1 µF
1 kV
MLS
IRFU320
DCP2
1N4148
DCP2
10 V
0.5 W
CDC
47 nF
400 V
CRES
4.7 nF
1.6 kV
LRES:B
CH1
0.1 µF
CFL Lamp
CH2
0.1 µF
LRES:C
RCS
7.5 R/1 W
1%
DC Reference Generator for
Triac Dimming System
Fig. 5. A triac-dimmable CFL ballast driving a single 15-W spiral CFL from a 120-Vac input.
www.powerelectronics.com March 2010 | Power Electronics Technology
Reprinted by permission of Power Electronics Technology magazine.
29
dimmingcontrollers
Application note AN-1153 describes a triac-dimmable
CFL ballast driving a single 15-W spiral
CFL from a 120-Vac input. Fig. 5 shows
the schematic of the ballast.
Capacitors C2, C3, C4, and C5 are
used to interface with the triac in the
dimmer so that the ballast can maintain
triac conduction until almost the end of
the mains half-cycle. There is also circuitry that detects the firing angle of the
triac and adjusts dc reference voltage to
set the lamp current.
The voltage waveform at the junction of D1 and D4 is equivalent to the
output voltage of the dimmer. This will
be a phase-cut approximated sine wave with a dc offset,
such that the negative peak is at ground. This is reduced by
the voltage divider network of R2 and R3, which is then fed
into D5 and D6.
Only the signal representing the positive half-cycle of the
mains is left at the anode of D6, which is then converted to
a dc level via the filter of R4 and C6. Because the minimum
dimming level occurs at a point where the dimmer is still
capable of providing enough output for the ballast to operate, this voltage will never actually be zero. The dc level is
further reduced with the voltage divider network of R5 and
R6, and used as the dc dimming reference voltage.
digital dimming systems are relatively new.
Because of the simplicity of its dimming control method, the IRS2530D
can be easily utilized for both methods.
The ballast designer needs to determine
how to generate the proper dc voltage
reference from the dimming control
method being used.
Analog dimming methods include
0- to 10-Vdc, phase-cut dimmers, and
three-wire phase controls, as well as
photo-sensor, motion-sensor, and wireless infrared. The dc voltage reference
can be generated by a voltage divider
using a combination of resistors, photoresistors, potentiometers, or rheostats.
The dc voltage reference should be properly set, as it
should not be too high to limit power loss in the currentsense resistor, and not too low to avoid noise problems at the
minimum dimming level. The IRS2530D datasheet (www.
irf.com/product-info/datasheets/data/irs2530d.pdf) explains
how to properly set the dc reference and the current sense
resistor.
Digital dimming offers a number of advantages compared
to analog: simplified wiring, a high degree of granularity for
control accuracy, and two-way communication. Another
advantage of this system is its capability to perform logarithmic dimming level. Since the human eye is much more sensitive to lower rather than higher light levels, the logarithmic
light output appears to be linear.
The most prominent of digital dimming methods is the
open-standard two-wire interface digital addressable lighting
interface (DALI). To work with digital dimming methods,
Digital dimming
offers a number of
advantages compared
to analog methods,
including simplified
wiring, a higher
degree of control
accuracy, and twoway communication
Other Dimming Systems
There are various dimming control methods available for
fluorescent applications. In general, dimming control can
be categorized into two methods: analog and digital. While
analog dimming systems are well-established and common,
L
RF1
0.47 R
0.5 W
120 V AC
Line
Input
LF
1 mH
0.2 A
BR1
600 V
0.5 W
RVCC1
360 k
N
CF
47 nF
400 V
CBUS
10 µF
350 Vdc
LED
Current
Reference
Setting
RVCC2
360 k
Modified Output
Stage for LEDs
RLIM1
10 R
RLIM2
10 R
1 µF
CVCC1
0.1 µF
CVCC2
COM
CDIM 10 nF
DIM
CVCO 0.1 nF
VCC
VB
2
3
VCO
RHO
10 R
8
1
IRS2530D
DC Dimming
Reference Input
+
HO
7
VS
6
CBS
0.1 µF
LO
5
4
REMAX
200 k
RLMP1
220 k
RPOT1
10 k
RMIN
430 R
CFB
0.1 µF
RLO
10 R
LRES:A
2.3 mH
EF25
airgap
= 1mm
MHS
IRF730
MLS
IRF730
CSNUB
1 nF
1 kV
DCP2
1N4148
CRES
4.7 nF
1.6 kV
D1
MUR160
D2
MUR160
D4
MUR160
D3
MUR160
6
HBLEDs
750 mA
DCP1
18 V
0.5 W
RFB
1k
RCS
2.5 R/1 W
1%
Fig. 6. The IRS2530D ballast can be used to control and dim the current of an offline LED.
30 Power Electronics Technology | March 2010
Reprinted by permission of Power Electronics Technology magazine.
www.powerelectronics.com
dimmingcontrollers
a dimming ballast designed around the
IRS2530D requires a microcontroller to
communicate with digital protocols. The
microcontroller interprets data from the
digital control, and generates the square
wave signal with fixed frequency but
varying duty-cycle, which corresponds
to the desired dimming level.
Dimmable LED Drivers
The dimming
control loop of the
IRS2530D keeps
the amplitude of
the LED current
regulated by
adjusting the
frequency of the
half-bridge switching
circuit
Unlike a fluorescent lamp, an LED
requires constant current control and
does not need to be preheated or ignited. The IRS2530D can also be used to
control and dim LED current. Fig. 6
shows the schematic of an offline LED
driver using the IRS2530D.
The circuit is a resonant-mode circuit that has been slightly modified from the IRPLDIM4E
circuit. Since it is no longer necessary to preheat and ignite
the load, the output stage has been modified to become a
series L-C-LED configuration. The resulting square-wave ac
voltage at the output is converted to positive full wave rectified voltage using an additional full-bridge rectifier.
Ac current sensing is still performed by the current-sensing resistor (RCS). This provides a direct ac measurement
of the full wave rectified LED current amplitude. This ac
signal is then coupled with the dc voltage from the current
reference setting onto the DIM pin of the IRS2530D. The
dimming control loop of the IRS2530D keeps the amplitude
of the LED current regulated by continuously adjusting the
frequency of the half-bridge switching circuit, such that the
nominal rms LED current is maintained within the manufacturer’s specifications.
When the dc reference voltage is decreased for dimming,
the IRS2530D increases the frequency to decrease the gain
of the resonant tank circuit and thus decrease LED current.
This control scheme keeps LED current constant over line,
load, and temperature variations for any given dimming
reference input, and will work for any number of LEDs in
series.
The above LED control circuit is almost similar to the
IRPLDIM4E dimming fluorescent ballast circuit. Any of the
dimming fluorescent ballast methods described above can be
easily translated to an LED control circuit. The dimming
control loop of IRS2530D allows the circuit to be scaled to
any number of LED in series. To work with LEDs with different current ratings, the current-sense resistor and dc reference settings need to be adjusted accordingly.
www.powerelectronics.com March 2010 | Power Electronics Technology
Reprinted by permission of Power Electronics Technology magazine.
31