參數(shù)資料
型號: PS2621
廠商: NEC Corp.
英文描述: Optocoupler Applications
中文描述: 光耦應(yīng)用
文件頁數(shù): 19/38頁
文件大小: 223K
代理商: PS2621
18
V
CC
- V
CE
5 - 0.8
I2
= = 8.2 (mA) ................(9)
R
2
0.51 (k
)
Therefore I
3
= I
2
+ I
4
= 8.2 + 1.6 = 9.8 (mA) ................(10)
Let's assume that h
FE
of transistor T
r1
is 40 (worst). I
b
must be as follows:
I
3
9.9 (mA)
I
b
= = 0.247 (mA) ................(11)
h
FE
40
Similarly, let's assume that V
BE
of transistor T
r1
is 0.8 V (worst), I
1
must be as follows:
V
BE
0.8
I
1
= = = 0.4 (mA) ................(12)
R
1
2 (k
)
Therefore, the output current I
0
of the optocoupler is
I0
I
1
+ I
b
= 0.647 (mA) ................ (13)
If forward current I
F
is 3 mA (worst) (normally I
F
= 5 mA), the CTR is calculated as follows:
I
0
0.647(mA)
CTR = x 100 = x 100 = 21.6% ................(14)
I
F
3 (mA)
CIRCUIT DESIGN EXAMPLE (USING THE PS2601)
Fig. 4-1 shows a design example of an optocoupler circuit having a base-emitter resistor for improvement of response ability.
The minimum current transfer ratio (CTR) required for TTL operation is calculated as follows:
Current I
4
must be 1.6 mA to drive the TTL and the collector-emitter voltage of transistor T
r1
must be 0.8 V or less. Accordingly, I
2
must be as follows:
A resistor of 510 k
is inserted here.
PS2601
I
F
= 5 mA
I
0
I
1
Vcc = 5 V
V
OUT
G
I
3
I
4
T
n1
I
b
R
2
= 510
TTL
R
0
= 1 k
R
1
= 2 k
Figure 4-1. Circuit Design Example
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