NE587 Philipss, NE587 Datasheet - Page 7

• Manufacturer Part Number: NE587
• Description: LED decoder/driver
• Manufacturer: Philipss

Philips Semiconductors Linear Products
However, a major portion of this power dissipation (P
because the current source output is operating with 3.25V across it.
In practice, the outputs operate satisfactorily down to 0.5V, and so
the extra voltage may be dropped external to the integrated circuit.
Suppose the worst-case V
the maximum V
required to keep the display active, and hence 2.0V may be dropped
externally with a resistor from V
calculated by:
assuming worst case I
Hence now
P
and
P
If a diode (or 2) is used to reduce voltage to the display, then the
voltage appearing across the display driver will be independent of
the number of “ON” segments and will be equal to
V
Where n is the number of diodes used, power dissipation can be
calculated in a similar manner.
In a multiplexed display system, the voltage drop across the digit
driver must also be considered in computing device power
dissipation. It may even be an advantage to use a digit driver which
August 31, 1994
D MAX
D av
S
R
LED decoder/driver
- V
S
= 5.0
F
= 5.25 50 + 1.25
= 525mW
- nV
= V
7 x I
(V
CC
d
S
2.0
, V
30 + 1.25
- V
SEG
E
D
I
CC
V
for the LED display is 2.25V. Only 2.75V is
- R
+
0.8V
X
10
SEG
7
5
CC
of 30mA.
7
(
1
2
I
25 = 306 mW.
/V
SEG
W rating)
S
30mW
CC
supply is 4.75 to 5.25V, and that
)
to V
7
S
. The value of this resistor is
I
SEG
K
DC
D MAX
) is
536
drops an appreciable voltage, rather than the saturating PNP
transistors shown in Figure 9. For example a Darlington PNP or
NPN emitter-follower may be preferable. Figure 8 shows the NE591
as the digit driver in a multiplexed display system. The NE591 output
drops about 1.8V which means that the power dissipation is evenly
distributed between the two integrated circuits.
Where V
optimized for minimum system power dissipation and/or cost.
Clearly, good regulation in the V
so this supply can be made much cheaper than the regulated 5V
supply used in the rest of the system. In fact, a simple unsmoothed
full-wave rectified sine wave works extremely well if a slight loss in
brightness can be tolerated. A transformer voltage of about
3-4.5V
shown below:
The duty cycle for this system depends upon V
characteristics of the display driver.
With
The duty cycle is approximately 60%.
V
V
S
F
= 2.0V
= 4.9V peak
RMS
S
I
and V
SEG
works well in most LED display systems. Waveforms are
V
S
CC
are two different supplies, the V
S
supply is totally unnecessary, and
S
Product specification
, V
F
S
and the output
supply may be
NE587