7
Electrical/Optical
These versatile bar graph arrays
are composed of ten light emit-
ting diodes. The light from each
LED is optically stretched to form
individual elements. The Red
(HDSP-4820) bar graph array
LEDs use a p-n junction diffused
into a GaAsP epitaxial layer on a
GaAs substrate. The AlGaAs Red
(HLCP-J100) bar graph array
LEDs use double heterojunction
AlGaAs on a GaAs substrate. HER
(HDSP-4830) and Yellow (HDSP-
4840) bar graph array LEDs use
a GaAsP epitaxial layer on a GaP
substrate. Green (HDSP-4850)
bar graph array LEDs use liquid
phase GaP epitaxial layer on a
GaP substrate. The multicolor bar
graph arrays (HDSP-4832/4836)
have HER, Yellow, and Green
LEDs in one package.
These displays are designed for
strobed operation. The typical
forward voltage values can be
scaled from Figures 5 and 11.
These values should be used to
calculate the current limiting
resistor value and typical power
consumption. Expected maxi-
mum V
F
values for driver circuit
design and maximum power
dissipation may be calculated
using the V
FMAX
models:
Standard Red HDSP-4820 series
V
F
MAX = 1.8 V + I
Peak
(10
Ω)
For: I
Peak
≥
5 mA
AlGaAs Red HLCP-J100 series
V
F
MAX = 1.8 V + I
Peak
(20
Ω)
For: I
Peak
≤
20 mA
V
F
MAX = 2.0 V + I
Peak
(10
Ω)
For: I
Peak
≥
20 mA
HER (HDSP-4830) and Yellow
(HDSP-4840) series
V
F
MAX = 1.6 + I
Peak
(45
Ω)
For: 5 mA
≤
I
Peak
≤
20 mA
V
F
MAX = 1.75 + I
Peak
(38
Ω)
For: I
Peak
≥
20 mA
Green (HDSP-4850) series
V
F
MAX = 2.0 + I
Peak
(50
Ω)
For: I
Peak
> 5 mA
Figures 4 and 10 allow the
designer to calculate the
luminous intensity at different
peak and average currents. The
following equation calculates
intensity at different peak and
average currents:
I
V
AVG = (I
F
AVG/I
F
AVG DATA
SHEET)η
peak
)(I
V
DATA
SHEET)
Where:
I
V
AVG is the calculated time
averaged luminous intensity
resulting from I
F
AVG.
I
F
AVG is the desired time
averaged LED current.
I
F
AVG DATA SHEET is the data
sheet test current for I
V
DATA
SHEET.
η
peak
is the relative efficiency at
the peak current, scaled from
Figure 4 or 10.
I
V
DATA SHEET is the data sheet
luminous intensity, resulting
from I
F
AVG DATA SHEET.
For example, what is the
luminous intensity of an HDSP-
4830 driven at 50 mA peak 1/5
duty factor?
I
F
AVG = (50 mA)(0.2) = 10 mA
I
F
AVG DATA SHEET = 10 mA
η
peak
= 1.3
I
V
DATA SHEET = 3500
µcd
Therefore
I
V
AVG = (10 mA/10 mA)
(1.3)(3500
µcd)
= 4550
µcd
AGILENT [ AGILENT TECHNOLOGIES, LTD. ]
