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參數(shù)資料
| 型號： | LM3914VX |
| 元件分類： | 顯示驅動器 |
| 英文描述： | LED Display Driver |
| 中文描述： | LED顯示驅動器 |
| 文件頁數(shù)： | 8/12頁 |
| 文件大小： | 236K |
| 代理商： | LM3914VX |
Application Hints
(Continued)
A 20W, 8
X
; 30W, 4
X
AMPLIFIER
Givens:
Power Output
20W into 8
X
30W into 4
X
1V Max
Input Sensitivity
Input Impedance
100k
Bandwidth
20 Hz–20 kHz
g
0.25 dB
Equations (1) and (2) give:
20W/8
X
30W/4
X
Therefore the supply required is:
g
23V
@
2.24A, reducing to . . .
g
21V
@
3.87A
With 15% regulation and high line we get
g
29V from equa-
tion (3).
A
V
t
20
c
8
1
V
OP
e
17.9V
V
OP
e
15.5V
I
OP
e
2.24A
I
OP
e
3.87A
Sensitivity and equation (4) set minimum gain:
e
12.65
We will use a gain of 20 with resulting sensitivity of 632 mV.
Letting R
IN
equal 100k gives the required input impedance.
For low DC offsets at the output we let R
f2
e
100k. Solving
for R
f1
gives:
R
f2
e
100k
100k
20
b
1
The bandwidth requirement must be stated as a pole, i.e.,
the 3 dB frequency. Five times away from a pole gives 0.17
dB down, which is better than the required 0.25 dB. There-
fore:
R
f1
e
e
5.26k; use 5.1k
f
L
e
20
5
e
4 Hz
f
h
e
20k
c
5
e
100 kHz
Solving for C
f
:
C
f
t
1
2
q
R
f1
f
L
e
7.8
m
F; use 10
m
F
The recommended value for C
C
is 5 pF for gains of 20 or
larger. This gives a gain-bandwidth product of 6.4 MHz and
a resulting bandwidth of 320 kHz, better than required.
The breakdown voltage requirement is set by the maximum
supply; we need a minimum of 58V and will use 60V. We
must now select a 60V power transistor with reasonable
beta at I
Opeak
, 3.87A. The TIP42, TIP41 complementary pair
are 60V, 60W transistors with a minimum beta of 30 at 4A.
The driver transistor must supply the base drive given 5 mA
drive from the LM391. The MJE711, MJE721 complementa-
ry driver transistors are 60V devices with a minimum beta of
40 at 200 mA. The driver transistors should be much faster
(higher f
T
) than the output transistors to insure that the R-C
on the output will prevent instability.
To find the heat sink required for each output transistor we
use equations (7), (9), and (10):
P
D
e
0.4 (30)
e
12W
i
JA
s
150
§
C
b
55
§
C
12
i
SA
s
7.9
b
2.1
b
1.0
e
4.8
§
C/W
If both transistors are mounted on one heat sink the thermal
resistance should be halved to 2.4
§
C/W.
The maximum average power dissipation in each driver is
found using equation (8):
(7)
e
7.9
§
C/W for T
AMAX
e
55
§
C
(9)
(10)
P
DRIVER(MAX)
e
12
30
e
400 mW
Using equation (9):
i
JA
s
155
b
55
0.4
e
237
§
C/W
8
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相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| LM3914VX/NOPB | 功能描述:LED照明驅動器 DOT/BAR DISPLAY DRVR RoHS:否 制造商:STMicroelectronics 輸入電壓:11.5 V to 23 V 工作頻率: 最大電源電流:1.7 mA 輸出電流: 最大工作溫度: 安裝風格:SMD/SMT 封裝 / 箱體:SO-16N |
| LM3915 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Dot/Bar Display Driver |
| LM3915J/A+ | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:LED Display Driver |
| LM3915N | 制造商:Texas Instruments 功能描述: 制造商:Texas Instruments 功能描述:IC LED DISPLAY DRIVER 3915 DIP18 |
| LM3915N/A+ | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:LED Display Driver |
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