Driving the Advanced Power TOPLED
Application Note
Introduction
Response Curve of the Advanced
Power TOPLED
LEDs are currently used in many application
areas. In the automobile sector, nearly all
dashboards utilize LEDs for backlighting. For
new application areas which require a higher
light output, even more efficient and
powerful LEDs are needed. Brake lights,
turn signals and fog lights, for example,
require powerful LEDs in order to fulfil
statutory regulations.
Every application requires the selection of
an appropriate LED. The Advanced Power
TOPLED (APT) serves to complement the
Power TOPLED and Golden Dragon power
components. With a maximum power
consumption of approximately 0.5W and
high optical efficiency, this package fills the
light output gap between the Power
TOPLED and the Golden Dragon (Figure1).
Above a certain threshold voltage, the LED
is conductive and exhibits a steep If - Vf
response curve (see Figure 2). In the
reverse direction, the LED blocks the flow of
current.
Figure 1: Comparison of the power
consumption of different LED packages
Figure 2: Typical forward response curve
for the LAG67F at Ta = 25°C (see
LAG67F datasheet)
This application note describes the electrical
characteristics of the Advanced Power
TOPLED along with various electrical
simulations.
For comparison, the minimum and maximum
response curve for Voltage Group 4A of the
LA G67F are shown in the following figure
(Figure 3).
December, 2013
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200
180
160
140
If / mA
120
100
80
60
40
LA G67F - 4A - MIN
20
LA G67F - 4A MAX
0
1,5
1,7
1,9
2,1
2,3
2,5
Uf / V
Figure 3: Comparison of minimum and maximum response curve of the LA G67F–4A,
simulated with PSpice
The following figure (Figure 4) shows the
comparison of an Advanced Power
TOPLED (LYG67B) and a Power TOPLED
(LYE67B) in HOP2000 chip technology,
simulated in PSpice.
Both response curves were simulated at
room temperature for LEDs from Voltage
Group3 (typical response curve). In
comparison to the Power TOPLED, the APT
exhibits a clearly steeper response curve.
200
150
If / mA
100
50
0
1,5
1,7
1,9
2,1
2,3
2,5
2,7
LA G67F - 4A - MAX
LA E67F - 4A - MAX
-50
Uf / V
Figure 4: Comparison of the Advanced Power TOPLED (LAG67F-4A-MAX) and Power
TOPLED (LA E67F-4A-MAX).
December, 2013
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It can be seen that the response curve for
the APT is steeper than the one of the
Power TOPLED.
Vf-Grouping of
Power TOPLED
the
Advanced
The selection of voltage groups for the
Advanced Power TOPLED is similar to that
of the Power TOPLED, with a grouping
current of 140mA, however.
The LAG67F and the LY G67B are divided
into the following voltage subgroups:
Voltage Subgroup 3B: 2.05V – 2.20V
Voltage Subgroup 4A: 2.20V – 2.35V
Voltage Subgroup 4B: 2.35V – 2.50V
Voltage Subgroup 5A: 2.50V – 2.65V
Driving the
TOPLED
Advanced
Power
When driving the APT, care should be taken
that the maximum permissible operating
conditions are not exceeded. First of all, it is
important that the forward current does not
exceed a constant maximum of 200mA
throughout the entire input voltage range
(for the LAG67F and the LYG67B). This
should be insured with appropriate driver
circuitry. Secondly, the maximum junction
temperature of 125°C must not be
exceeded. This must be insured with
appropriate thermal management (see also
the application note: “Thermal Management
of SMT LEDs“).
This application note only discusses the
electrical characteristics of the APT; the
thermal characteristics are not discussed.
Details of the thermal characteristics can be
obtained
from
the
above-mentioned
application note.
For the following simulations, these
assumptions are always valid: The
simulation
results
are
immediately
ascertained after power-on, at room
December, 2013
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temperature. No thermal effects are
considered. Corresponding to a typical
battery voltage within the automobile sector,
an input voltage of 13.5V (minimum 9V,
maximum 16V), is chosen. Analogously, the
results can also be transferred to other
application areas by using other input
voltages.
Serial
Connection
with
Advanced Power TOPLED
the
In a further simulation, the behavior of
voltage subgroup 4A was investigated. The
resistance in each path was chosen such
that a current of 140mA was supplied,
corresponding to the middle response curve
of voltage subgroup 4A (Figure 5).
In order to simulate the worst case, four
LAG67F LEDs from the lower edge of
subgroup 4A were used in the left path
(LAG67F-4A-MIN). In the right path, four
LAG67F LEDs from the upper edge of
subgroup 4A were used (LAG67F-4AMAX).
VCC
146.9mA
R1
133.4mA
R2
31.4
31.4
146.9mA
D1
133.4mA
D5
LA_G67F-4A-MIN
LA_G67F-4A-MAX
146.9mA
D2
133.4mA
D6
VCC
V1
LA_G67F-4A-MIN
LA_G67F-4A-MAX
13.5Vdc
146.9mA
D3
133.4mA
D7
280.2mA
0
LA_G67F-4A-MIN
LA_G67F-4A-MAX
146.9mA
D4
133.4mA
D8
LA_G67F-4A-MIN
LA_G67F-4A-MAX
0
Figure 5: Serial connection for the
LAG67F: left path: Voltage Group 4A
Minimum, right path: Voltage Group 4A
Maximum
240
200
If / mA
160
120
LA G67F-4A-MIN
LA G67F-4A-MAX
80
40
0
7
8
9
10
11
12
13
14
15
16
V_VCC / V
Figure 6: Current through D1 and D5 vs input voltage
The LEDs from the lower edge of voltage
subgroup 4A draw a current of around
147mA, while the LEDs from the upper edge
of voltage group 4A draw a current of
around 133mA at a supply voltage of 13.5V.
In the above diagram (Figure 6), the
behavior of the two paths is shown for the
entire input voltage range. The slight
spreading is due to the differences of the
minimum and maximum response curves.
In comparison, a matrix connection for a
single voltage subgroup was simulated, as
is the case for the LAG67F (Figure 7).
VCC
R1
15.7
D1
D5
LA_G67F-4A-MIN
LA_G67F-4A-MAX
D2
D6
VCC
Matrix
Connection
with
Advanced Power TOPLED
the
V1
LA_G67F-4A-MIN
LA_G67F-4A-MAX
13.5Vdc
D3
D7
0
LA_G67F-4A-MIN
In the matrix connection, the same LEDs
were used as with the serial connection. In
contrast however, the LEDs were connected
to each other with a cross connection. In
addition, only one series resistor was used
for the entire circuit. This series resistor was
chosen such that a typical current of about
140mA was present at each LED.
December, 2013
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LA_G67F-4A-MAX
D4
D8
LA_G67F-4A-MIN
LA_G67F-4A-MAX
0
Figure 7: Matrix connection with the
LAG67F: left path: Voltage Group 4A
Minimum, right path: Voltage Group 4A
Maximum
In this case also, the resistance was chosen
such that the current through each path was
exactly 140mA, corresponding to the middle
response curve of the voltage subgroup 4A.
In order to demonstrate the worst case once
again, LEDs from the upper edge (LA G67F4A-max) and the lower edge (LA G67F-4Amin) of voltage group 4A were employed
(Figure 8).
This simulation shows a distinct difference
between the maximum current value of
165mA and the minimum current value of
115mA at a voltage of 13.5V (Figure 9).
For LEDs with the lower forward voltage, the
maximum current of 200mA is exceeded for
battery voltages greater than 14.8V.
VCC
281.4mA
R1
15.7
165.6mA
D1
115.8mA
D5
LA_G67F-4A-MIN
LA_G67F-4A-MAX
165.6mA
D2
115.8mA
D6
VCC
V1
LA_G67F-4A-MIN
LA_G67F-4A-MAX
13.5Vdc
165.6mA
D3
115.8mA
D7
281.4mA
0
LA_G67F-4A-MIN
LA_G67F-4A-MAX
165.6mA
D4
115.8mA
D8
LA_G67F-4A-MIN
LA_G67F-4A-MAX
0
Figure 8: Current distribution at a battery
voltage of 13.5V in the matrix connection
300
250
If / mA
200
150
100
LA G67F-4A-MIN
LA G67F-4A-MAX
50
0
7
8
9
10
11
12
13
14
15
16
V_VCC / V
Figure 9: Current through D1 and D5 vs input voltage:
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Overdrive Protection
In addition to the limiting resistors and the
obligatory reverse protection diode, a PTC
(positive temperature coefficient) resistor
can be connected in series with the two LED
paths.
appropriate driver device. In the following
example, the TLE4242G from Infineon was
used for current regulation (see Figure 11).
VCC
5V
The PTC resistor has a positive temperature
coefficient; that is, the resistance of the
component becomes greater with increased
temperature. The resistance of the PTC
increases when the ambient temperature
increases, or when the LEDs are driven at
higher levels, resulting in a warming of the
LEDs themselves, and thus a warming of
the PTC. As the resistance of the PTC
increases, the current through the circuit is
reduced. In this way, the current through the
LEDs can be limited.
R4
10k
ST
PWM
I
Q
TLE 4242G
REF
GND
D11
D
LY_G67B-3-mean
C1
D12
47n
0
LY_G67B-3-mean
0
D13
LY_G67B-3-mean
D14
LY_G67B-3-mean
RREF
0.86
0
VCC
Figure 11: Current regulation with the
TLE 4242G. The above circuit was not
simulated; after construction of the
circuit, the measurement data was
recorded and displayed in the following
diagram.
RT1
PTC
t
D9
Reverse protection diode
R1
R2
D1
D5
LA_G67F-4A-MIN
The circuit was designed such that the
current through the Advanced Power
TOPLEDs at a nominal battery voltage of
13.5V is approximately 200mA.
LA_G67F-4A-MAX
D2
D6
LA_G67F-4A-MIN
LA_G67F-4A-MAX
D3
D7
LA_G67F-4A-MIN
LA_G67F-4A-MAX
D4
Stromregler TLE 4242G
D8
LA_G67F-4A-MIN
250
LA_G67F-4A-MAX
200
0
150
I (LED) / mA
Figure 10: Serial connection with a PTC
resistor
Kennlinie TLE 4242G
100
50
Driving the Advanced Power
TOPLED with a Current Driver
0
0,0
2,0
4,0
6,0
8,0
10,0
12,0
14,0
16,0
18,0
20,0
U (Batterie) / V
An elegant solution for regulating the current
through a series of LEDs is to use an
December, 2013
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Figure 12: LED current in relation to
supply voltage with the TLE 4242G
Above a battery voltage of about 6V, the
current begins to flow through the LEDs. At
around 9V, ~190mA of current flows through
the APTs. This current remains constant
throughout the entire battery voltage range
of 9-16V. The current first collapses at a
voltage below 9V. At lower supply voltages,
however, an increase in forward voltage
leads to a breakdown of current. This must
therefore be taken into account if the LEDs
are to be illuminated at lower supply
voltages.
The advantage of using a current regulator
as opposed
to driving the LEDs with
resistors can be seen here. The current
through the LEDs remains constant over the
entire voltage range of the battery. More
importantly, at a nominal battery voltage, the
current through the LED amounts to
practically the maximum value of 200mA.
The LED can therefore be fully driven at a
nominal battery voltage, whereas the LED
with a series resistor must be powered with
considerably less current in this case. Since
a higher current level also leads to a higher
intensity level, this permits the same number
of LEDs to produce more light. On the other
hand, current regulation permits one to
achieve the same light intensity with fewer
LEDs than that of a resistive circuit.
Conclusions
The Advanced Power TOPLED can be
driven with a resistor if the maximum current
throughout the entire supply voltage range
and the maximum permissible junction
temperature are not exceeded. It is
recommended, however, that the circuitry
utilize individual serial paths for diode
illumination, since the current distribution
from a pure matrix circuit can lead to
overdriving the LEDs.
The use of a current regulator has a positive
effect on LED performance.
Author: Markus Hofmann
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