2-29
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 VF values for driver circuit
design and maximum power
dissipation may be calculated
using the VFMAX models:
Standard Red HDSP-4820 series
VFMAX = 1.8 V + IPeak (10 Ω)
For: IPeak ≥ 5 mA
AlGaAs Red HLCP-J100 series
VFMAX = 1.8 V + IPeak (20 Ω)
For: IPeak ≤ 20 mA
VFMAX = 2.0 V + IPeak (10 Ω)
For: IPeak ≥ 20 mA
HER (HDSP-4830) and Yellow
(HDSP-4840) series
VFMAX = 1.6 + IPeak (45 Ω)
For: 5 mA ≤ IPeak ≤ 20 mA
VFMAX = 1.75 + IPeak (38 Ω)
For: IPeak ≥ 20 mA
Green (HDSP-4850) series
VFMAX = 2.0 + IPeak (50 Ω)
For: IPeak > 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:
IVAVG = (IFAVG/IFAVG DATA
SHEET)ηpeak)(IVDATA
SHEET)
Where:
IVAVG is the calculated time
averaged luminous intensity
resulting from IFAVG.
IFAVG is the desired time
averaged LED current.
IFAVG DATA SHEET is the data
sheet test current for IVDATA
SHEET.
ηpeak is the relative efficiency at
the peak current, scaled from
Figure 4 or 10.
IV DATA SHEET is the data sheet
luminous intensity, resulting
from IFAVG DATA SHEET.
For example, what is the
luminous intensity of an HDSP-
4830 driven at 50 mA peak 1/5
duty factor?
IFAVG = (50 mA)(0.2) = 10 mA
IFAVG DATA SHEET = 10 mA
ηpeak = 1.3
IV DATA SHEET = 3500 µcd
Therefore
IVAVG = (10 mA/10 mA)
(1.3)(3500 µcd)
= 4550 µcd