HDSP-2301 HP [Agilent(Hewlett-Packard)], HDSP-2301 Datasheet - Page 42

• Manufacturer Part Number: HDSP-2301
• Description: Four Character 5.0 mm (0.20 inch) 5 x 7 Alphanumeric Displays
• Manufacturer: HP [Agilent(Hewlett-Packard)]

and the operating conditions
shown in equations (13), (14),
(15), and (16):
Adding in the junction-to-case
temperature rise as shown in
equation (22), the T
calculated as:
Intensity Control
An important consideration re-
garding display intensity is the
control of the intensity with re-
spect to the ambient lighting level.
In dim ambients, a very bright dis-
play will produce very rapid
viewer fatigue. Conversely, in
bright ambient situations, a dim
display will be difficult if not im-
Figure 30. Intensity Modulation
Control Using a One Shot
Multivibrator
V CC
150 K
T
T
TRIGGER
C
J
= 8 (1.40 C/W)
= 98 C
= 98 C + (20 C/W)
= 98 C + 22 C
= 120 C
(1.12 W) + 85 C
(1.12 W)
A 1
A 2
B 1
B 2
CLR
V CC
74122
15 F
CLAIREX
CL5 P5L
OR 500 K POT.
Q
Q
J
can be
FOR DECREASING
AMBIENT
ILLUMINATION
TO COL.
ENABLE
AN1016.30
(31)
(32)
possible to read and will also pro-
duce viewer fatigue and high error
rates. For this reason, control of
display intensity with respect to
the environment ambient intensity
is an important consideration. The
HDSP-2000 family of displays is
ideally suited for wide ranges of
ambient lighting since the inten-
sity of these displays can be
varied over a very wide dynamic
range. The propagation delay be-
tween the V
that the LEDs turn on or off is un-
der a microsecond, allowing
dynamic variations of over 2000 to
1 in display luminous intensity at
a 100 Hz refresh rate.
Figure 30 depicts a scheme which
will automatically control display
intensity over a range of 10 to 1 as
a function of ambient intensity.
This circuit utilizes a resettable
monostable multivibrator which is
triggered by the column enable
pulse. The duration of the
multivibrator output is controlled
by a photoconductor. At the end
of a column enable pulse, the
multivibrator is reset to insure
that column current is off prior to
the initiation of a new display
shift register loading sequence.
The output of this circuit is used
to modulate either the V
of the HDSP-2000 displays or the
column enable input circuitry.
For maximum reduction in dis-
play power, both inputs should
be modulated.
In the circuit shown in Figure 30,
the photocell may be replaced
by a 50 K potentiometer to
allow manual control of display
intensity.
Figure 31 shows a manually ad-
justable dimming circuit that
provides a very wide range of dis-
play intensity. With a 100 Hz
B
input and the time
B
inputs
display refresh rate, a 4000 to 1
dynamic range of display intensity
can be achieved. The Intersil
ICM7555 timer is used as a
retriggerable monostable
multivibrator. The output of the
timer is used to simultaneously
pulse width modulate V
play column current, and the
display supply current. Initially
the 100 pF capacitor is held dis-
charged by the timer. At the
negative transition of the trigger
input the timer would normally
allow the capacitor to charge,
however the 2N3906 transistor
keeps the capacitor discharged
until the trigger input goes high.
As soon as the trigger input goes
high, the capacitor is charged by a
constant current source formed
by the RCA CA3084 transistor ar-
ray. As soon as the voltage across
the capacitor reaches 2/3 V
output of the timer goes low, and
the timer discharges the capaci-
tor. The 2N3906 transistor always
discharges the capacitor when the
trigger is low, therefore the out-
put of the timer stays high if the
voltage across the capacitor never
reaches 2/3 V
shown, t can be varied exponen-
tially from .5 s to about 1900 s.
Since Q1 and Q2 are monolithic
transistors, t is relatively indepen-
dent of temperature.
Figure 31 also shows a circuit to
switch V
ing the time that the display is
blanked. When the 2N2219A tran-
sistor is off, the LM350 provides a
regulated 3 A 5 V output. How-
ever, when the 2N2219A transistor
is turned on, the output of the
LM350 regulator is reduced to
1.2 V. This reduces I
10 mA per display. Capacitive
loading of the regulator should be
minimized as much as possible to
maximize the switching speed.
34
CC
of the displays off dur-
CC
. For the values
CC
to under
B
, the dis-
CC
the