IRF IRPLMB1E Programmable run frequency Datasheet

IRPLMB1E
International Rectifier • 233 Kansas Street, El Segundo, CA 90245 USA
IRPLMB1E - 25W 230VAC small size ballast using IR2520D
By
Cecilia Contenti
Topics Covered
Overview
Features
Electrical Characteristics
IR2520D Ballast Control IC
Circuit Description
Miniballast Circuit Diagram
Functional Description
Fault Conditions
Miniballast Layout
Design Tip: AUto-restart Option
Design Procedure to adapt the
design to different lamp types
1. Overview
Small sizes ballasts (often called Matchbox ballasts) are becoming very common in Europe to drive a wide
range of lamps with power between 18W and 26W like PLC 18W, PLT 18W, TC-L 18W, TC-L 24W, TC-F 18W,
TC-F 24W, TC-DEL/TEL 26W, T5 24W, T8 18W, T5C 22W and TR 22W. Limiting the maximum power to 25W
the design does not need to conform to THD and PF requirements and this allows saving the PFC stage
reducing the components count and maintaining a very small size.
The MINIBALLAST1 is an electronic ballast for driving 26W compact fluorescent lamps from 220VAC. The
circuit provides all of the necessary functions for preheat, ignition and on-state operation of the lamp and
also includes the EMI filter and the rectification stage. The ballast size is 36mmx55mm.
The circuit is built around the IR2520D Ballast Control IC. The IR2520D provides adjustable preheat time,
adjustable run frequency to set the lamp power, high starting frequency for soft start and to avoid lamp flash,
fault protection for open filament condition and failure to strike, low AC line protection and auto-restart after
line brownout conditions. The IR2520D is a low-cost solution with only 8 pins and allows the component
count for the complete solution to be reduced down to 19 components.
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IRPLMB1E
2. Features
!
!
!
!
!
! operating frequencies determined by bi-polar tran-
Programmable run frequency
Programmable preheat time
Open filaments and no-lamp protection
Failure to Strike and deactivated-lamp protection
Low AC line protection
3. Electrical Characteristics
Pin
(W)
21
22
24
24.2
24.5
Iinrms
(mA)
160
160
168
168
168
Vbusav
(V)
280
290
300
310
320
Freq.
(KHz)
40.3
40.3
40.3
40.3
40.3
PF
0.63
0.625
0.62
0.62
0.61
THD
(%)
115
117
118
118
118
4. IR2520D Ballast Control IC
The IR2520D is intended for driving CFL and TL
lamps in CFL or matchbox (small size ballasts)
applications. The IR2520D integrates all of the
necessary functions for preheat, ignition and on-state
operation of the lamp, plus, lamp fault protection and
low AC-line protection, together with a complete high
and low-side 600V half-bridge driver. The IR2520D
has only 8 pins and fits into a standard SOIC8 or
DIP8 package. The IR2520D has been designed to
overcome the disadvantage of discrete selfoscillating solutions while maintaining low cost.
In the CFL market, the self-oscillating bipolar
transistor solution is still more popular than a
ballast control IC plus FETs solution due to lower
cost. This approach is very simple in nature but has
disadvantages including:
! DIAC or additional circuit required for starting,
additional free-wheeling diodes required
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!
!
!
!
Input Power: 24W @ 220VAC
Input Current: 168mArms @ 220VAC
Starting Frequency: 100KHz
Average Run Frequency: 40KHz
Ballast turn-on voltage: 120VAC
Ballast turn-off voltage: 70VAC
Input
(VAC)
200
210
220
230
240
!
sistor storage time and toroid saturation (not easy to
design, very dependent on tolerances in production
and difficult to set the frequencies precisely),
unreliable “always hot” PTC thermistor used for
preheat that often fails in the field,
no protection against lamp non-strike or open
filaments conditions,
no smooth frequency ramping during ignition,
capacitive mode operations,
high crest factor in the lamp current.
These can result in high susceptibility to components
and load tolerances and/or catastrophic failure of
ballast output stage components and a short lamp
life. The IR2520D includes adaptive zero-voltage
switching (ZV, adaptive run frequency for zero-voltage switching), internal crest factor and non-zero
voltage switching (ZVS) protection, as well as an integrated bootstrap diode. The heart of this IC is a
voltage controlled oscillator (VCO) with externally
programmable minimum frequency and a 0-5VDC
analog voltage input. One of the biggest advantages
of the IR2520 is that it uses the VS pin and the RDSon
of the low-side half-bridge MOSFET for over-current
protection and to detect non-ZVS conditions. An
internal 600V FET connects the VS pin to the VS sensing circuitry and allows for the VS pin to be accurately measured during the time when pin LO is
high, while withstanding the high DC bus voltage
during the other portion of the switching cycle when
the high-side FET is turned on and VS is at the DC
bus potential. This eliminates the need for a highprecision current sensing resistor that is typically
used to detect over current. Please refer to the
IR2520D datasheet for further information on the
IR2520D including electrical parameters, state
diagram and complete functional description.
As a result of the IR2520 features, the MINIBALLAST1
circuit using the IR2520D is a complete matchbox
solution that offers better reliability and longer lamp
life than self oscillating solutions while reducing
component count and ballast size.
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IRPLMB1E
5. Circuit Description
The schematic for MINIBALLAST1 is shown in figure
5.1. The BOM with the components values is shown
in table 5.2.
The ballast incorporates a fuse, EMI filter, input rectifier, bus capacitor, half-bridge, control and output
stage. The output stage is the classical resonant
circuit consisting of an inductor, LRES, and a capacitor, CRES. The circuit is built around the IR2520D
Ballast Control IC. The IR2520 provides adjustable
preheat time, adjustable run frequency to set the lamp
power, high starting frequency (about 2.5 times fmin)
to avoid lamp flash, capacitive mode protection for
open filament condition and current crest factor
protection for failure to strike or no lamp conditions.
The AC line input voltage is rectified to provide a bus
voltage of approximately 300 volts. The start up
resistor, Rsupply (in the reference design we have 2
resistors, Rsupply and Rsupply 2 in series), is sized
such that they can supply the micro-power current
during under-voltage lockout (UVLO). When VCC
exceeds the UVLO+ threshold, the IR2520 begins to
oscillate and the charge pump circuit (CSNUB, DCP1
and DCP2) supplies the current to VCC that causes
the internal 15.6V zener clamp to regulate.
The IR2520 Ballast Control IC controls the frequency
of the half-bridge programming the right parameters
on the lamp to provide lamp preheat, lamp ignition,
running mode, low AC line protection and lamp/
ballast fault protection.
RSUPPLY
DCP2
LAMP
BR1
MHS
F1
VCC
1
LF
CF
COM
2
FMIN
3
RFMIN
CVCO
VCO
4
IR2520
CVCC
CBUS
VB
8
HO
7
VS
6
CBS
LRES
CSNUB
LO
5
CRES
MLS
CDC
DCP1
Fig. 5.1) MINIBALLAST1 Circuit Diagram
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IRPLMB1E
Item #
Qty
1
1
International
Rectifier
Manufacturer
Part Number
2
1
Dale
CW-1/2
Resistor, 0.5Ohm, 1/.2W
F1
3
1
Panasonic
ECQ-U2A104ML
Capacitor, 0.1uF 275 VAC
CF
Digikey
P10730-ND
4
1
LF
DF10S
Description
Bridge Rectifier, 1A 1000V
Epcos
B82145-A1105-J
EMI Inductor, 1mH 370mA
Digikey
M5830-ND
RF Chockes 1mH 200mA
Reference
BR1
5
1
Wima
MKS2 Series
Capacitor, 47nF 400V
6
1
Panasonic
EEU-EB2V100
Capacitor, 10uF 350VDC 105C
CDC
CBUS
7
1
Panasonic
ECJ-3VB1H104K
Capacitor, 0.1uF 50V 1206
CBS
8
1
Panasonic
ECJ-3VF1E474Z
Capacitor, 0.47uF 25V 1206
CVCO
9
1
Panasonic
ECY-3YB1E105K
Capacitor, 1uF 25V 1206
CVCC
10
1
AVX
1812AA681J
Capacitor, 680pF 1KV SMT 1812
CSNUB
11
1
Wima
MKP4 Series
Capacitor, 4.7nF 1KV Polypropylene
CRES
12
1
International
Rectifier
IR2520D
IC, Ballast Driver
IC BALLAST
13
1
VOGT
5752602600
Inductor, 2.25mH, 5%, 1Apk
LRES
14
2
International
Rectifier
IRFU320
Transistor, MOSFET
MHS, MLS
15
2
Panasonic
Resistor, 1M, 1206, 100V
RSUPPLY1, RSUPPLY2
16
1
Panasonic
ERJ-8ENF6812V
Resistor, 68.1K, 1%, 1206
RFMIN
17
2
Diodes
LL4148DICT-ND
Diode, 1N4148 SMT DL35
DCP1, DCP2
18
1
WAGO
235-202
Connector, 2 terminal
X1
19
1
WAGO
235-204
Connector, 4 terminal
X2
Total
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TABLE 5.2) MINIBALLAST1 Bill Of Materials.
Lamp type: Spiral CFL 26W, Line Input Voltage: 190-240 VAC. Note: Different lamp types may require BOM
changes.
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6. Functional Description
Figure 6.1 shows the voltage across the lamp and
the current in the resonant inductor LRES during
Startup, Preheat, Ignition and Run Mode.
At startup, VCO is 0V and the frequency is very high
(about 2.5 times fmin). This minimizes voltage spikes
and lamp flash at startup. The frequency ramps down
towards the resonant frequency of the high-Q ballast
output stage, causing the lamp voltage and lamp
current to increase. During this time, the filaments of
the lamp are pre-heated to the emission temperature to guarantee a long lamp life. The frequency
keeps decreasing until the lamp ignites. If the lamp
ignites successfully, the IR2520D enters RUN Mode.
If the minimum frequency has been chosen below
or very close to the resonant frequency, the IC will
work near resonance and will adjust the frequency
continuously to maintain ZVS at the half-bridge and
to minimize the losses in the FETs. If the minimum
frequency has been chosen higher than the resonant frequency the IR2520D will work at the minimum frequency.
Figure 6.2 shows the current across the resonant
inductor and the voltage across the lamp filaments
at the startup.
Fig. 6.1:
Voltage across the lamp (yellow waveform) and current in
the resonant inductor (green waveform) during Startup,
Preheat, Ignition and Run Mode
When power is turned on, the IR2520D goes into
Under Voltage Lockout (UVLO) mode.
The UVLO mode is designed to maintain a very low
(<200uA) supply current and to guarantee that the IC
is fully functional before the high- and low-side output drivers are activated. During UVLO, the high- and
low-side driver outputs (LO and HO) are both low
and pin VCO is pulled down to COM for resetting the
starting frequency to the maximum.
Once VCC reaches the startup threshold (UVLO+),
the IR2520D turns on and the half-bridge FETs start
to oscillate. The IC goes into Frequency Sweep Mode.
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Figure 6.2:
Voltage across the lamp filaments (yellow) and current
in the resonant inductor (green) at the startup.
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Figure 6.3 shows the VS (HB) Voltage, the lamp
voltage and the lamp current during Run Mode.
Figure 6.3:
VS (HB) Voltage (blue), Lamp Voltage (yellow) and the
Lamp Current (green) during Run Mode.
7. Fault Conditions
In case of fault conditions such as open filaments,
failure to strike, deactivated lamp or no lamp, the
IR2520D will go into Fault Mode. In this mode the
oscillator is latched off. To reset the IC back to preheat mode, VCC must be recycled below and above
the UVLO thresholds. Resetting the mains does this.
In case of low AC line, the IR2520D will automatically increase the frequency to maintain ZVS. In this
way, the ballast will work at a lower power during a
low AC line condition and will operate at the proper
power again when the line increases again.
7.1. Failure To Strike/ Deactivated Lamp Protection
This protection relies on the crest factor protection
together with the non-ZVS circuit of the IR2520D, both
enabled when the voltage in pin VCO reaches 4.6V.
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In order to detect failure to strike conditions, the
IR2520D performs an internal crest factor measurement for detecting excessive dangerous currents or
inductor saturation that can occur during a lamp nonstrike fault condition or deactivated lamp condition.
The IR2520D measures the VS pin during the entire
on-time of the low-side MOSFET. Should the peak
current exceed the average current by a factor of 4
during the on-time of LO, the IC will enter Fault Mode
and both gate driver outputs will be latched ‘low’.
Performing the crest factor measurement provides
a relative current measurement that cancels temperature and/or tolerance variations of the RDSon
of the low-side half-bridge MOSFET and does not
need to be programmed differently for different
lamp types. During normal operation, the current
will increase until the lamp ignites. After lamp ignition the current will decrease down to the nominal current. Should a lamp non-strike condition
occur where the filaments are intact but the lamp
does not ignite, the lamp voltage and output stage
current will increase during the ignition ramp until
excessive currents occur or the resonant inductor saturates. The non-ZVS circuit or the crest
factor circuit will detect this condition and the IC will
enter Fault Mode and both gate driver outputs will be
latched ‘low’. This will prevent damaging of the halfbridge MOSFETs.
Fig. 7.1 shows the inductor current and the lamp
voltage in case of failure to strike condition together
with the VCO pin voltage. At initial turn-on of the ballast, the frequency will ramp down from fmax, through
resonance, to fmin. If the lamp does not ignite, the
inductor current will saturate and high-voltages will
occur across the lamp as the frequency sweeps
through resonance. The voltages and currents in the
output stage will decrease as the frequency continues to decrease to the capacitive side of resonance.
The voltages and currents will be low but hard-switching will occur (non-ZVS). When the frequency reaches
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IRPLMB1E
fmin (VCO > 4.6V), the non-ZVS and crest-factor protection will be activated and the frequency will increase again to try and maintain ZVS. The frequency
will sweep back through resonance (from the capacitive side) and the crest-factor protection will shutdown the IC on the first event when the inductor saturates to a level where the crest factor exceeds 3 (see
Fig. 7.1).
Fig. 7.2 shows pin LO, pin VS and the current in the
resonant inductor during shutdown, with a shorter
time scale. The final shortened pulse of LO just before shutdown (Fig. 7.2) occurs due to the internal
1us blank time of the crest-factor detection during
each turn-on rising edge of LO (to provide immunity
to noise and transients).
Fig. 7.2:
4 is the current in the resonant inductor, 2 is pin VS (HB
Voltage), 3 is pin LO
7.2. Open Filaments Protection
Fig. 7.1:
4 is the current in the resonant inductor, 2 is the lamp
voltage, 3 is the voltage in pin VCO
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The open filament protection relies on the non-ZVS
circuit of the IR2520D, enabled when pin VCO
reaches 4.6V. Should an open filament lamp fault
occur, hard-switching will occur at the half-bridge and
the non-ZVS circuit inside the IR2520 will detect this
condition, increase the frequency each cycle and shut
down when VCO decreases below 1V; both gate
driver outputs will be latched ‘low’. This will prevent
hard-switching and damaging of the half-bridge
MOSFETs.
Fig. 7.3 shows the pin VCO and pin VS at the shutdown with open filament. As you can see, at startup
pin VCO charges from 0V up to 4.6V, at 4.6V the
non-ZVS circuit is enabled, CVCO discharges and
the frequency increases. When the voltage on pin
VCO decreases below 1V we have latched shutdown.
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IRPLMB1E
Fig. 7.4 shows pin VCO and pin VS (HB Voltage) at
the shutdown with a shorter time scale. The FMIN
pin can be used as trigger as this pin transitions
from 5V to COM when the IC enters fault mode or
UVLO-.
Fig. 7.4:
1 is the voltage in pin FMIN, 3 is the voltage in pin
VCO, 2 is pin VS
Fig. 7.3:
3 is the voltage in pin VCO and 2 is pin VS
7.3. Low AC line Protection
As you can see from figure 7.5, varying the AC line
from 220V to 130VAC the ZVMCS circuit of the IR2520
increases automatically the frequency to maintain
ZVS.
When the mains voltage decreases, the resonant
frequency increases, becoming close to the run
frequency. This will cause non-ZVS. The IR2520
will detect non-ZVS and increase the frequency
continuously as long as non-ZVS is detected. This
will protect the half-bridge MOSFETs against
hard-switching.
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IRPLMB1E
8. MINIBALLAST Layout
The Layout of the Reference Kit MINIBALLAST1 is
shown in Fig. 8.1.
The critical components are CVCC, CVCO, RFMIN
and CBOOT. They must be placed as close as
possible to the pins of the IR2520D. The ground of
CCVO, RFMIN and CVCC need to be connected to
pin COM of the IR2520D and this ground path
must be connected to the power ground at a single
point
Figure 7.5:
VS PIN for AC line 220V (on the top) and AC line
130V (on the bottom)
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IRPLMB1E
Figure 8.1: MINIBALLAST1 Layout
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9. Design Tip: Auto-restart Option
The design can be modified to include re-lamp/autorestart option as shown in Fig. 9.1.
The resistors Rsupply must be moved across the
upper lamp filament and the lamp connected to the
bus voltage, instead than to ground. When the lamp
is replaced, Rsupply together with the upper filament
of the lamp provide a path from the DC bus to supply
the micro-power current to the IR2520 and to restart
the IR2520 as soon as VCC exceeds the UVLO+
threshold. Rsupply need to be able to handle high
voltage. If using SMD components, 2 resistors are
needed.
RSUPPLY
DCP2
LAMP
BR1
MHS
F1
VCC
1
LF
CF
COM
2
FMIN
3
RFMIN
CVCO
VCO
4
IR2520
CVCC
CBUS
VB
8
HO
7
VS
6
CBS
LRES
CSNUB
LO
5
CDC
CRES
MLS
DCP1
Fig. 9.1: Circuit Modification to include auto-restart option
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IRPLMB1E
10. Design Procedure to adapt the design
to different lamps types
The design with the IR2520D is very simple because
it only has 2 control pins: VCO (0-5VDC oscillator
voltage input) and FMIN (minimum frequency setting). To modify the design for a higher lamp power,
you will need to modify RFMIN, CVCO, LRES and
CRES. Make sure that FETs and inductors are rated
to the current you need with the new lamp and that
VCC is stable. To modify the design to a lower lamp
power, you will need to decrease RFMIN and only in
some case to modify also CVCO, LRES and CRES.
In most cases you can use FETs and inductors with
lower current ratings.
Pin FMIN is connected to ground through a resistor
(RFMIN). The value of this resistor programs the minimum frequency (fmin) of the IC and the starting frequency of the IC (2.5xfmin). The IR2520 will work in
run mode at the minimum frequency unless nonZVS is detected. Generally, to work with constant frequency, the minimum frequency needs to be chosen
above the resonant frequency of the low-Q R-C-L
circuit. In this case, one can increase the value of
RFMIN to decrease the frequency and increase the
lamp power, or, decrease the value of RFMIN to increase the run frequency and decrease the lamp
power.
Pin VCO is connected to ground through a capacitor
(CVCO). The value of this capacitor programs the
time the frequency needs to ramp down from 2.5
times fmin (fmax) to fmin.
One can increase the capacitor value to increase the
preheat time, or, decrease the capacitor value to decrease the preheat time.
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The suggested design procedure is as follows:
1) Use the BDA software to calculate LRES
and CRES.
Select the input configuration without PFC,
select the IR2156 IC and select single lamp
current mode configuration. Select the new
lamp in the database or add the lamp pa
rameters by hand selecting the “Advanced”
option.
Calculate the operating point and chose the
right values of L and C that satisfy:
1.1)
Run frequency (best working range) 4050KHz
1.2)
C as small as possible to minimize
losses (suggested value 4.7nF)
1.3)
L values you have available
2)
While measuring LO, apply 15V from pin
VCC to pin COM and adjust the value of
RFMIN to obtain the right minimum frequency (it is suggested set fmin = run frequency obtained with the BDA software).
Increase RFMIN to decrease the minimum
frequency or decrease RFMIN to increase
the minimum frequency.
3)
Apply the AC input and check preheat, ignition and run states of the lamp.
3.1) If the lamp ignites during preheat, the pre
heat current is too small or the starting volt
age across the lamp is too big, increase
the value of CRES to decrease the voltage
across the lamp during preheat and startup
while increasing the preheat current. LRES
may need to be decreased to maintain the
same power and the same frequency.
3.2) If the IC works at a frequency > fmin, in
crease CRES or LRES to decrease the reso
nant frequency avoiding hard-switching, or,
decrease the value of the snubber capaci
tor CSNUBBER (a CSNUBBER minimum
value of 680pF is suggested to make sure
VCC stays above the UVLO-).
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IRPLMB1E
3.3) If VCC drops, increase the value of
CSNUBBER or CVCC
4)
Adjust the value of RFMIN to have the right
power on the lamp (increase RFMIN to increase power or decrease RFMIN to decrease power) and the value of CVCO to set
the correct preheat time (increase CVCO to
increase the preheat time and decrease
CVCO to decrease the preheat time).
5)
Test the ballast over the entire input range
and make sure that the frequency does not
change dramatically in your working range.
Select the value of RSUPPLY to have startup
at the correct AC line voltage. Increase the
value of RSUPPLY to start the IC at higher
AC voltages and decrease the value of
RSUPPLY to start the IC at lower AC voltages.
6)
Test your lamp life (number of starts). A good
design should guarantee at least 5,000
starts. To increase the number of starts, increase CRES or the preheat time (CVCO)
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. 3/14/2004
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