C
2
0.1µF
R
3
100kΩ
A
1
C
1
0.1µF
R
2
1MΩ
2
1MΩ
4
R
1
1MΩ
40pF
20dB/decade
f
–3dB
=
75Ω
1MΩ
R
3
(2πR
2
C
2
)
λ
OPT301
8
5
V
O
FIGURE 12. DC Restoration Rejects Unwanted Steady-State Background Light.
6
1/2
REF200
100µA
100µA
2
1MΩ
1
4
10V to 36V
40pF
2N2222
75Ω
1/2
REF200
λ
OPT301
8
3
5
20kΩ
4-20mA
(4mA Dark)
IN4148
R
1
22.5kΩ
R
2
65Ω
Calculations shown provide a dark output of 4mA.
Output is 20mA at a photodiode current of
I
D max
. Values shown are for I
D max
max = 1µA.
R
1
=
1.014
X
10
6
(1 – 2500 I
D max
)
26,000
(1 – 2500 I
D max
)
– 994,000Ω
R
2
=
– 26,000Ω
FIGURE 13. 4-20mA Current-Loop Transmitter.
®
11
OPT301