NEC PS2651

California Eastern Laboratories
Optocoupler
Applications
DESIGNING FOR OPTOCOUPLERS WITH BASE PIN
GENERAL
Optocouplers (optical couplers) are designed to isolate electrical output from input for complete elimination of noise. They have
been used conventionally as substitutes for relays and pulse transformers. Today's current technology in the area of microcomputers creates new applications for optocouplers.
This manual describes the characteristics of typical optocouplers. Also included are notes on designing application circuits for
typical optocouplers (with a base pin) for better comprehension. NEC's typical optocouplers with or without base pins are listed
on the following pages.
1
PS2600 Series Optocouplers (6-Pin Dual-in-Line Package)
Product name
PS2601
* PS2601L
PS2602
PS2602L
PS2603
* PS2603L
PS2604
PS2604L
PS2605
* PS2605L
PS2606
PS2606L
PS2607
* PS2607L
PS2608
PS2608L
PS2621
* PS2621L
PS2622
PS2622L
PS2625
* PS2625L
PS2626
PS2626L
PS2633
* PS2633L
PS2634
PS2634L
PS2651
* PS2651L2
PS2652
PS2652L2
PS2653
* PS2653L2
PS2654
PS2654L2
Internal
connection
Absolute Maximum Ratings
(TA = 25°C)
Electric Characteristics
(TA = 25°C)
Features
High isolation
voltage
High VCEO
(80 V MIN.)
Single transistor
High isolation
voltage
High CTR
Darlingtontransistor
High isolation
voltage
A.C. input
High VCEO
(80 V MIN.)
Single transistor
High isolation
voltage
A.C. input
High CTR
Darlingtontransistor
High isolation
voltage
Large input
current
Single transistor
High isolation
voltage
A.C. input
Large input
current
Single transistor
High isolation
voltage
High VCEO
(300 V MIN.)
High CTR
Darlingtontransitor
High isolation
voltage
High VCEO
(80 V MIN.)
Single transistor
High isolation
voltage
High CTR
Darlingtontransistors
BV
(Vr.m.s.)
IF (mA)
IC(mA)
CTR (%)
5k
80
50
80 to 600
5k
80
5k
±80
50
80 to 600
3
5k
±80
200
200 to 3400
100
200
tr (µs)
(TYP)
3
200 to 2500
tr (µs)
(TYP)
5
100
100
5
100
5k
150
50
20 to 50
3
5
5k
±150
50
20 to 50
3
5
5k
80
150
1000 to
15000
100
100
5k
80
50
50 to 400
3
5
5k
80
200
200 to 3400
100
100
* (with a base pin)
Note: A product name followed by letter L indicates a product having leads formed for surface mount.
2
There are two kinds of optocouplers (a light emitting diode (LED) as an input and a phototransistor as an output) according to the
type of output transistor: Single transistor type and Darlington-transistor type.
The single-transistor type optocouplers are used to perform high-speed switching (with high-speed response). The Darlingtontransistor type optocouplers are used to obtain a large output current by utilizing a small input current (independently of switching
speeds).
Designing the circuits properly will improve the PS2601 optocoupler (Single Transistor type) by having a base pin in terms of
switching speed, elimination of noise in input signals, and output leakage current (collector dark current, and application to highvoltage circuits).
APPLICATIONS OF OPTOCOUPLER BASE PINS
INCREASING SWITCHING SPEED
The switching speed of an optocoupler with a base pin can be increased by inserting a resistor between the base and the emitter
of its phototransistor even when the optocoupler is applied to a large load resistance.
Generally, the phototransistor of an optocoupler such as the PS2601 has a large photo-sensitive area on it. Accordingly, the
junction capacitance (CC-B) between the collector and the base of the phototransistor is great (up to 20 pF) and as a result its
response speed (turn-off time toff) is low. The relationship between turn-off time toff and collector-base capacitance CC-B is
expressed by:
toff × CC-B x hFE x RL ................(1)
where
toff : Turn-off time (See Fig. 2-2.)
CC-B : Collector-base capacitance
hFE : D.C. current amplification factor
RL : Load resistance
Cc-B
RL
Figure 2-1. Collector-Base Capacitance
CC-B of Phototransistor
3
50%
Input
ton
toff
90%
Output
90%
10%
10%
Figure 2-2. ton/toff Measuring Points
As judged from expression (1), the turn-off time toff is affected by collector-base capacitance CC-B, D.C. current amplification
factor hFE, and load resistance LR. In actual circuit design, CC-B and hFE are fixed. Accordingly, the turn-off time is significantly
affected by the resistance of load RL.
Graph 1 shows the relationship between response speed (ton,toff) and load resistance (RL) in typical emitter follower (test circuit 1)
having a load resistance of 100 Ω.
= 100 µs
( PW
Duty = 1/10 )
VCC = 5 V
PS2601
IF = 5 mA
Input
monitor
Vo
Input
monitor
51 Ω
RL = 100 Ω
Vo
Test Circuit 1
Graph 1
Up
: Input 0.2 V/DIV
DOWN : Output 0.5 V/DIV
(50 µs/DIV)
4
Graph 2 shows the relationship between response speed (ton, toff) and load resistance (RL) in a typical emitter follower (Test
circuit 2) having a greater load resistance (5 kΩ).
VCC = 5 V
PS2601
IF = 5 mA
Input
monitor
Input
monitor
Vo
51 Ω
RL = 5 Ω
Test Circuit 2
Vo
Graph 2
Up
: Input 0.2 V/DIV
DOWN : Output 2 V/DIV
(50 µs/DIV)
As shown in Graph 2, the turn-off time for load resistance of 5 kΩ is about 100 µs. Similarly, the turn-off time for load resistance
of 100 kΩ is 1 to 2 ms. This is also true when the load resistance is connected to the collector of the phototransistor.
Graph 3 shows the relationship between response speed (ton, toff) and load resistance (RL) in a typical circuit (Test circuit 3)
having collector load resistance (5 kΩ) with the emitter grounded.
VCC = 5 V
RL = 5 Ω
PS2601
Vo
Input
monitor
IF = 5 mA
Input
monitor
Vo
51 Ω
Test Circuit 3
Graph 3
Up
: Input 0.2 V/DIV
DOWN : Output 2 V/DIV
(50 µs/DIV)
5
To reduce the turn-off time toff of a test circuit having a greater resistance, insert a resistor RBE between the emitter and the base
of the phototransistor. See Test circuit 4 and Test circuit 5. Graph 4 and 5 show their input and output waveforms.
VCC = 5 V
PS2601
IF = 5 mA
Input
monitor
Vo
Input
monitor
51 Ω
RBE
RL = 5 Ω
Insert resistor
of 200 kΩ here.
Vo
Test Circuit 4
(Emitter Follower)
Graph 4
Up
: Input 0.2 V/DIV
DOWN : Output 2 V/DIV
(50 µs/DIV)
VCC = 5 V
RL = 5 Ω
PS2601
Vo
Input
monitor
IF = 5 mA
Vo
Input
monitor
51 Ω
RBE
Insert resistor
of 200 kΩ here.
Test Circuit 5
(Emitter Grounded)
Graph 5
Up
: Input 0.2 V/DIV
DOWN : Output 2 V/DIV
(50 µs/DIV)
6
The turn-off time can be greatly reduced by the base-emitter resistance (RL). In Test circuit 4, the turn-off time of the test circuit
having resistance RL is about 1/30 of that of the test circuit without the resistance. This is because the carrier (photocurrent)
stored in the collector-base capacitor (CC-B) is quickly released through the base-emitter resistor (RBE). However, note that part
of a photocurrent generating on the base of the phototransistor flows through the RBE resistor and reduces the current transfer
ratio (CTR). Compare the voltage level of the output waveform in Photo 4 with that of the output waveform in Photo 2. The
current transfer ratio of the test circuit having a base-emitter resistor of 200 kΩ is half or less of that of the test circuit without the
resistance. (See 3.3 for reduction of the current transfer ratio CTR.)
For reference, Fig. 2-3 shows the switching-time vs. RL characteristics and Fig. 2-4 shows the switching-time vs. RBE characteristics.
1000
Switching Time (µs)
100
50
500
Vo
51Ω
200
VCC = 5V
IF =
Ix
10 mA
51Ω
IF = 5 mA VCC = 5 V
Sample Solid line:
Current transfer ratio of 166%
Dotted line:
Current transfer ratio of 274%
at Ir = 5 mA
200
ts
20
10
tr
100
Vcc = 5V
tf
Vo
tf
RL
Switching Time (µs)
500
1000
IF =
5 mA I x
RL
ts
IF = 10 mA Vcc = 5 V
Sample Solid line:
Current transfer ratio of 166%
Dotted line:
Current transfer ratio of 274%
at Ir = 5mA
50
20
10
5
5
td
tr
2
2
td
1
1
100
500
1k
5k
10 k
50 k 100 k
100
Load Resistance RL (Ω)
500
1k
5k
10 k
50 k 100 k
Load Resistance RL (Ω)
Fig. 2-3 Switching-Time vs. RL Characteristics
160
160
140
VCC = 5 V, IF = 10mA
RL = 5Ω
Solid line: Emitter follower
Dotted line: Emitter grounded
120
Switching Time (µs)
120
100
100
toff
80
60
toff
80
60
40
40
ton
toff
20
20
100
200
500
1000
100
200
500
1000
Base-Emitter Resistance RBE (kΩ)
Base-Emitter Resistance RBE (kΩ)
Fig. 2-4 Switching-Time vs. RBE Characteristics
7
8
0
0
8
Switching Time (µs)
140
Vcc = 5 V, IF = 5mA
R1 = 5Ω
Solid line: Emitter follower
Dotted line: Emitter grounded
STABILIZING OUTPUT LEVELS
When an optocoupler is used with the base pin of its phototransistor open, the collector dark current (ICEO) flows as a base
current. The current is amplified as a collector current and could make the output level of the phototransistor unstable. To
eliminate this unwanted base current and make the output level stable, flow the collector dark current (ICEO) through the baseemitter resistor (RBE).
Fig 2-5 shows the ICEO vs. TA characteristics of a PS2601 optocoupler.
PS2601 ICEO-TA Characteristics
1000
IF = 0
VCE = 80V (40V for the
PS2603) 2601
Solid line: PS2601
Dotted line: PS2603
RBE =
8
Collector Dark Current ICEO (nA)
10000
100
10
RBE = 1MΩ
RBE =1MΩ
1
RBE =100 MΩ
0.1
- 20
0
20
40
60
80
100
Ambient Temperature TA (°C)
Figure 2-5. ICEO vs. TA Characteristics
ELIMINATION OF INDUCED NOISE
Generally, machine-controlling equipment generates induced noise which may cause malfunctions. This unwanted noise in input
signals can be isolated by means of optocouplers. However, if the noise is too strong, it may be switched to the output through
the input-output capacitance C1-2 of the optocoupler. This unwanted noise in the output can be removed in the following manner.
Insert a capacitor (preferably 100 pF) between the base and the emitter of the phototransistor of the optocoupler. This capacitor
delays response and suppresses malfunctions.
Graph 6-(a) to 6-(d) show how an external noise (surge voltage of 1000 V/µs at rise time) is eliminated as the capacitance of the
base-emitter capacitor.
A fluctuation in the collector-emitter voltage caused by the on/off operation of a power switch at the output of the optocoupler
causes a base current to flow through the collector-base capacitor (CCB), which causes a malfunction.
In Fig. 2-7, for example, an instantaneous base current flows through the collector-base capacitor (CCB) of the optocoupler. The
current is multiplied by hFE (as a collector current) and causes an output voltage on both ends of the load resistance. It seems as
if an input signal was applied to the optocoupler. Graph 7-(a) shows the waveforms. This unwanted instantaneous induction
current can be eliminated by inserting a capacitor CBE between the emitter and the base of the phototransistor. Graph 7-(b)
shows the waveforms. Fig. 2-8 shows the output-voltage vs. CBE characteristics.
Vo
CBE
RL
Figure 2-6.
Figure 2-7.
8
6a) CBE = No capacitance
6b) CBE = 10 pF
Vin
Vin
Vo
Vo
6c) CBE = 100 pF
6d) CBE = 1000 pF
Vin
Vin
Vo
Vo
Graph 6
Up
: Input Surge Voltage (Vin :1000 V/DIV)
DOWN : PS2601 output
(VO: 1 V/DIV)
C1-2
5V
Vo
CBE
Vin
Test Circuit
9
470 Ω
Vin (dV/dt = 10 V/µs, 2 V/DIV)
CCB
Vin
Vo
Vo (0.1 V/DIV)
5 kΩ
(500 ns/DIV)
Graph 7-(a)
Input Voltage Fluctuation and Output
CCB
Vin (dV/dt = 10 V/µs, 2 V/DIV)
Vin
Vo
1000 pF
5 kΩ
Vo (0.1 V/DIV)
(500 ns/DIV)
Graph 7-(b)
Effect of Collector-Base Capacitance on
Voltage Fluctuation
10
PS2601
RL = 5 kΩ
Output Voltage, Vo (V)
1
0.1
0.01
100
1000
Base-Emitter Capacitance, CBE (pF)
Figure 2-8. Vo vs. CBE Characteristics
As mentioned above, noise induced by the fluctuation of supply voltage can be removed by proper treatment of the base pin. For
switching of input free from induced noise at normal switching speed, optocouplers with a base pin such as the PS2602 series
are available. If the base pin of an optocoupler is left unused or opened, it typically will pick up external noise. Cutting off the
base pin is also effective in order to prevent it from picking up external noise. See Graph 8-(b).
11
(PS2601)
Vin
Base pin
Vo
Graph 8-(a)
Up
: Input Surge Voltage (Vin: 1000 V/DIV)
DOWN : PS2601 Output
(Vo: 1 V/DIV)
Cut the base pin (pin 6)
(PS2601)
Vin
Vo
Graph 8-(b)
5V
Vo
470 Ω
Vin
Test Circuit
12
ELIMINATION OF INPUT SURGES
Unwanted external noise and output leakage currents (e.g., collector current IC) of a preceding transistor may cause the lightemitting diode (LED) of an optocoupler to light involuntarily. Usually, a circuit (connecting a resistor in parallel to the LED) is
provided to absorb such input surges. To prevent malfunction of an optocoupler, it is also effective to insert a resistor (RBE) that
increases the input threshold current (by the use of the input-output characteristics) between the base and the emitter of the
phototransistor. In this case, the current transfer ratio (CTR) must be low. (See 3.3 for Reduction of CTR.)
60
VCE = 5 V
(PS2601)
50
Collector Current IC (mA)
8
RBE =
200 kΩ
40
100 kΩ
50 kΩ
30
20 kΩ
30 kΩ
20
10 kΩ
10
5 kΩ
0
1
2
3
4 5
10
20
30 40 50
Forward Current IF (mA)
Figure 2-9. IC vs. IF Characteristics (Example)
APPLICATION TO HIGH POTENTIAL CIRCUIT
The withstanding voltage between the collector and the emitter of the PS2601 optocoupler is 80 V (MAX). To make the
optocoupler available to higher withstanding voltages, use the collector-base junction photodiode as a light-sensitive element and
connect a high-voltage circuit to the output of the optocoupler. In this case, the output of the photodiode must be amplified
because it is smaller than the usual output.
Fig. 2-10 shows an example of an optocoupler applied to a high-voltage circuit. In this sample circuit, the photocurrent (ICBL) of
the optocoupler is fed to the base of the high-voltage transistor and a current (IF) passes forward through the light-emitting diode
(LED). Fig. 2-11 shows the ICBL vs. IF characteristics. Before working on applications outside the rated values of the
optocouplers, evaluate the practical circuits fully by contacting CEL.
Collector-Base Photocurrent ICBL (µA)
200
High-voltage
transistor (Tr)
PS2601
ICBL
VCB = 100V
(PS2601)
100
100V
IF
50
40
30
ICBL
A
CTR = 274%
CTR = 166%
20
10
5
4
3
2
Figure 2-10. Application to a
High Voltage Circuit
1
1
2
3 4 5
10
20
Figure 2-11. ICBL vs. IF Characteristic
13
30 40 50
80
NOTES ON USE OF OPTOCOUPLER BASE PIN
This chapter explains the reduction of a current transfer ratio of an optocoupler whose base and emitter are connected by a
resistor (RBE) and other optocouplers that seem to be significant in the treatment of the base pin of an optocoupler.
EQUIVALENT CIRCUIT (FOR PS2601 OPTOCOUPLER)
Fig. 3-1 shows an equivalent circuit of a single-transistor optocoupler such as the PS2601.
C1-2
A
C
CCB
RD
Cj
ICBL
Tr
CBE
K
B
E
Figure 3-1. Equivalent Circuit (for PS2601 Optocoupler)
Cj
CBE
RD
ICBL
C1-2
Tr
: Junction capacity of LED
: Base-emitter capacitance
: Resistor serially connected to LED
: Collector-base photocurrent generated by the light of the LED
: Input-output capacitance
: Amplifying transistor
DEFINITION OF CURRENT TRANSFER RATIO (CTR)
A current transfer ratio (CTR) of an optocoupler indicates the rate of an output current IC of its phototransistor to a forward input
current (IF) flowing through its light-emitting diode (LED). The CTR is expressed by:
IC
CTR =
x = 100 (%) ................(2)
IF
where IC = ICBL•hFE ..............................(3)
(hFE: D.C. current amplification factor of the phototransistor)
14
REDUCTION OF CURRENT TRANSFER RATIO (CTR) BY INSERTION OF BASEEMITTER RESISTOR
A resistor (RBE) connected to the base and emitter pins of an optocoupler causes the reduction of the output current (reduction of
current transfer ratio). This is because a part (I1) of the base current flows through the base-emitter resistor and causes a voltage
equivalent to the emitter-base voltage (VBE). The base current is reduced by this current component (I1) and, as the result, the
current transfer ratio (CTR) goes down. The output current IC' is expressed as follows:
ICBL
ICBL-I1
VBE
RBE
I1
Figure 3-2.
IC' = hFE' (ICBL-I1) = hFE' ( ICBL•
• • IC'
= hFE' • ICBL ( 1 -
Note IC'
hFE'
VBE
ICBL • RBE
VBE
RBE
)
) ................ (4)
: Output current of an optocoupler having RBE
: Amplification factor of an optocoupler having RBE
Accordingly, the ratio of output current IC' (of the optocoupler having RBE) to output current IC (of the optocoupler with the base
open) is expressed by:
IC'
hFE'
IC
hFE
=(1-
VBE
ICBL • RBE
) ................ (5)
As hFE' is equal to hFE if IF = approx. 5 mA, IC = approx. 15 mA, and RBC > 100 kΩ, expression (5) is simplified as follows:
IC'
IC
=1-
VBE
ICBL • RBE
................ (6)
15
Expression (6) indicates that the current transfer ratio (CTR) is significantly affected by the value of ICBL • RBE. For example, if
the forward current IF of the light-emitting diode is smaller (that is, ICBL is smaller) or if the base-emitter resistance RBE is smaller,
the reduction rate (rate of IC') becomes greater.
The above CTR reduction must be considered when inserting a resistor between the emitter and the base of the phototransistor
of the optocoupler to increase the switching speed. The performance of the optocoupler might become unstable because the
CTR will be affected by time elapse or temperature change (even if it is initially stable).
Fig. 3-3 shows the ∆CTR-RBE characteristics.
1.0
1.0
Normalized to 1.0
at RBE = ×
IF = 1 mA, VCE = 5V
CTR = 274%
0.8
CTR Relative Values
CTR Relative Values
0.8
0.6
CTR = 274%
0.4
CTR =166%
CTR =166%
0.6
0.4
0.2
0.2
Normalized to 1.0
at RBE = ×
IF = 5 mA, VCE = 5V
0
100
200
300 400 500
1000
1.0
CTR = 274%
CTR =166%
CTR Relative Values
0.6
0.4
0.2
Normalized to 1.0
at RBE = ×
IF = 10 mA, VCE = 5V
0
200
300 400 500
1000
8
100
300 400 500
1000
Base Emitter Resistance RBE (kΩ)
Base Emitter Resistance RBE (kΩ)
0.8
200
8
100
Base Emitter Resistance RBE (kΩ)
Figure 3-3. ∆CTR-RBE Characteristics
16
8
0
The reduction of a CTR is greatly affected by the positional relationship between load resistor RL and base-emitter resistor RBE,
as shown in Fig. 3-4 (b) and 3-4 (c).
Figure 3-4 (a).
Figure 3-4 (b).
Figure 3-4 (c).
Open
RBE Serial to RL
RBE Parallel to RL
ICBL
ICBL
RBE1
VBE
ICBL
RBE2
VBE1
Vo
VBE2
V2
V1
RL
RL
RL
The output voltage V0, V1, and V2 of the above circuits (a), (b), and (c) are related as follows:
V1 hFE1
=
V2 hFE0
V2 hFE2
V0 = hFE0
(1-
VBE
) ................ (7)
ICBL • RBE1
VBE2
ICBL • RBE1
RL • hFE2
1+
RBE2
1-
(
)
................ (8)
When resistor RBE is serially connected to resistor RL (see Fig. 3-4 (c)), the reduction of a CTR becomes greater even if hFE2 is
approximately equal to hFE0 in expression (8) as the expression includes RL as a parameter.
Fig. 3-5 shows typical V0 vs. IF characteristics of the above circuits (a), (b), and (c).
10
Output voltage Vo (V)
8
Vcc = 10 V
RL = 470 Ω
CTR = 190%
(PS2601)
PS2601
(a) RB open
Vcc = 10V
IF
(b) RBE = 100 kΩ
RBE = 100 kΩ
6
Vo
4
RL = 470 kΩ
2
(c) RBG = 100 kΩ
0
1
2
5
10
20
50
Forward current IF (mA)
Figure 3-5. Vo vs. IF Characteristics
17
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.
Vcc = 5 V
PS2601
R2 = 510 Ω
IF = 5 mA
TTL
I0
A resistor of 510 kΩ
is inserted here.
VOUT
I4
R0 = 1 kΩ
Tn1
I1
I3
R1
= 2 kΩ
Ib
G
Figure 4-1. Circuit Design Example
The minimum current transfer ratio (CTR) required for TTL operation is calculated as follows:
Current I4 must be 1.6 mA to drive the TTL and the collector-emitter voltage of transistor Tr1 must be 0.8 V or less. Accordingly, I2
must be as follows:
I2 ⊕
VCC - VCE
5 - 0.8
=
= 8.2 (mA) ................(9)
0.51 (kΩ)
R2
Therefore I3 = I2 + I4 = 8.2 + 1.6 = 9.8 (mA) ................(10)
Let's assume that hFE of transistor Tr1 is 40 (worst). Ib must be as follows:
Ib ⊕
I3
9.9 (mA)
=
hFE
= 0.247 (mA) ................(11)
40
Similarly, let's assume that VBE of transistor Tr1 is 0.8 V (worst), I1 must be as follows:
VBE
I1 =
0.8
=
R1
= 0.4 (mA) ................(12)
2 (kΩ)
Therefore, the output current I0 of the optocoupler is
I0 ⊕ I1 + Ib = 0.647 (mA) ................ (13)
If forward current IF is 3 mA (worst) (normally IF = 5 mA), the CTR is calculated as follows:
I0
CTR =
0.647(mA)
x 100 =
IF
x 100 = 21.6% ................(14)
3 (mA)
18
Accordingly, the CTR value including reduction of CTR by time elapse, temperature change, and insertion of RBE must be 21.6 %
or more.
A design example of an optocoupler circuit that operates for at least ten years is shown below (using Fig. 3-3, 4-2 and 4-3). The
major causes of CTR reduction area as follows:
(From Fig. 3-3)
CTR-relative-value vs. RBE characteristics
15% down (with respect to initial value, RBE = ×)
(From Fig. 4-2)
CTR change with time (10 years, Ta = 60 °C)
40% down (with respect to initial value, 0 year)
(From Fig. 4-3)
CTR-relative-value vs. ambient-temperature characteristics
(Ta = 60 °C)
15% down (with respect to initial value ta = 25 °C)
Considering the above characteristics and safety factor = 2 (twice margin), the recommended CTR is:
21.6 x 1.4 x 1.15 x 1.15 x 2 = 80%.................(15)
(Reference)
1.2
1.0
1.0
IF = 20 mA
TA = 25˚C
IF = 5 mA
TA = 60˚C
0.8
0.6
CTR Relative Value
CTR Relative Value
1.2
IF = 5 mA
TA = 25˚C
0.4
Normalized to CTR
test conditon
IF = 5 mA, VCE = 5V
0.2
0
0
10 2
10 3
10 4
0.8
0.6
0.4
10 5
Normalized to 100
at TA = 25˚C
IF = 5 mA, VCE = 5 V
0.2
Time (Hr)
0
Figure 4-2. Change of CTR with
Time (PS2601)
-55 -40
-20
0
20
40
60 80
Ambient Temperature TA (°C)
Figure 4-3. CTR-Relative-Value vs.
TA Characteristics
19
100
PS2500-SERIES MULTI-CHANNEL OPTOCOUPLERS
GENERAL
Recently, optocouplers have been supplanting relays and pulse transformers for complete noise elimination, level conversion,
and high-potential isolation. Microprocessor systems are requiring more and more optocouplers on the limited area of PC boards
for I/O interface and other purposes. For these requirements, NEC has manufactured multi-channel optocouplers having 4 pins
(for one channel) to 16 pins (for four channels). These multi-channel optocouplers are called the PS2500 series optocouplers.
The PS2500 series optocouplers are divided into PS2501, PS2502, PS2505, and PS2506 according to their functions.
(PS2501L, PS2502L, PS2505L, and PS2506L have leads formed for surface installation.)
This manual describes features, structures, and basic characteristics of the PS2500 series optocouplers.
FEATURES, STRUCTURES, AND PACKAGE DIMENSIONS
Features
The major feature of PS2500 is very high isolation voltage between input and output (substantially two to three times that of the
conventional PS2400 series optocouplers). This can be proved because none of the 1300 test optocouplers were destroyed in a
strict product test (applying 10 kVac to each optocoupler for one minute). The improvement in dielectric strength of the PS2500
optocouplers has been accomplished by the double molding package structure.
In addition to high isolation voltage, the PS2500 optocouplers boast high heat resistance and high moisture resistance. Table 1
lists the major features of the PS2500 series optocouplers.
Features
Product
name
High isolation
Voltage
Abundant I/O functions
High CTR
(TYP)
High VCEO
(MIN)
Response
(TYP)
PS2501
PS2501L (*)
D.C. input, Single
transistor output
300%
80V
tr = 3 µs
tr = 5 µs
PS2502
PS2502L (*)
D.C. input, Darlington
pair transistor output
2000%
40V
tr, tf = 100 µs
PS2505
PS2505L (*)
A.C. input, single
transistor output
300%
80V
tr = 3 µs
tr = 5 µs
PS2506
PS2506L (*)
A.C. input, Darlington
pair transistor output
2000%
40V
tr, tf = 100 µs
5 kVac
Table 1. Features of PS2500 Optocouplers
Note: Tested in oil (In the air, unwanted arc discharging will occur at 6 to 7 kVac.)
* The product name followed by letter L is for a product having leads for surface mount.
20
Optocoupler Structure
Figure 1 shows the internal perspective view of a PS2500 optocoupler and Figure 2 shows the sectional view of the optocoupler.
Figure 2 below shows the optocoupler in a light-tight epoxy resin housing, and a light-sensitive element (phototransistor or photo
Darlington transistor) with light-transmittable epoxy resin medium between them. A light signal emitted by the LED is transferred
to the photosensitive transistor via the internal resin medium.
Both the housing resin and the internal resin have the same expansion coefficient. Namely, the optocoupler elements are molded
twice with epoxy resin. (This structure is referred to as a double molding structure.)
The high isolation voltage is obtained by the long adjacent area of the inner and outer resins (inner boundary) and identical
expansion coefficient of the inner and outer resins (eliminating arc discharges on the inner boundary).
Figure 1. Internal perspective view of optocoupler
Outer resin (Black)
Inner resin (White)
Inner boundary
Figure 2. Sectional view of optocoupler
21
Dimensions
Figures 3 and 4 show the dimensions of the PS2500 series optocouplers. The PS2500 series optocouplers are very compact
and fit for high-density installation on PC boards. For example, the package area occupied by a single channel of the PS2500
series is half that of the PS2600 series (6-pin Dual in-line package).
PS250X-1
PS250X-2
4 3
8 7 6 5
5.1 MAX
10.2 MAX
1 2 3 4
2.54
Anode
Cathode
Emitter
Collector
0 to 15˚
0.25 M
7.62
0.65
1.34
PS250X-4
161514131211 10 9
20.3 MAX
3.8
MAX
6.5
1 2 3 4 5 6 7 8
1,3,5,7.
Anode
2,4,6,8.
Cathode
9,11,13,15. Emitter
10,12,14,16. Collector
2.54
7.62
0.65
4.55
MAX
2.8
MIN
2.54
Anode
Cathode
Emitter
Collector
4.55
MAX
2.8
MIN
0.65
2.8
MIN
4.55
MAX
7.62
0.50±0.10
1.34
1.34
1,3.
2,4.
5,7.
6,8.
6.5
1.
2.
3.
4.
3.8
MAX
3.8
MAX
6.5
1 2
0.50±0.10
0.25 M
0 to 15˚
Figure 3. Package Dimensions (Units in mm) (PS2501, PS2502, PS2505, and PS2506)
22
0.50±0.10
0.25 M
0 to 15˚
Lead Bending type (Gull-wing)
PS250XL-1
PS250XL-2
4 3
8 7 6 5
5.1 MAX
10.2 MAX
1 2
1 2 3 4
1.
2.
3.
4.
Anode
Cathode
Emitter
Collector
1,3.
2,4.
5,7.
6,8.
7.62
0.9±0.25
9.60±0.4
9.60±0.4
1.34±0.10
1.34±0.10
0.25 M
0.25 M
PS250XL-4
16 15 14 13 12 11 10 9
20.3 MAX
1 2 3 4 5 6 7 8
1,3,5,7.
Anode
2,4,6,8.
Cathode
9,11,13,15. Emitter
10,12,14,16. Collector
3.8
MAX.
6.5
9.60±0.4
0.05 to 0.2
7.62
2.54
6.5
3.8
MAX.
2.54
0.9±0.25
1.34±0.10
0.25 M
Fig. 4 Package Dimensions (Units in mm) (PS2501L, PS2502L, PS2505L, and PS2506L)
23
0.05 to 0.2
0.05 to 0.2
7.62
6.5
3.8
MAX.
2.54
Anode
Cathode
Emitter
Collector
0.9±0.25
CHARACTERISTICS OF PS2501 AND PS2505 OPTOCOUPLERS
Current Transfer Ratio (CTR)
The current transfer ratio (CTR) of an optocoupler is the ratio of the value of output current IC to the value of input forward current
IF (IC/IF x 100%). The CTR is a parameter equivalent to the D.C. current amplification factor hFE of a transistor.
The CTR is one of the most significant characteristics of optocouplers, as well as isolation voltage. In circuit designing, CTR must
be considered first of all because the CTR:
1 varies as time goes by,
2 is affected by ambient temperature, and
3 is dependent upon forward current IF flowing through the LED.
Both PS2505 and PS2506 optocouplers (bidirectional input type) have two current transfer ratios (CTRs) because they have two
LEDs in the input. For further information, refer to Applications of Optocouplers for A.C. input.
Change of CTR over time
The current transfer ratio (CTR) of an optocoupler is determined by the light-emission efficiency of the LED (emitting infrared
light), efficiency of light transmission between the LED and the phototransistor, light sensitivity of the phototransistor, and hFE of
the transistor.
The change of a CTR over time is mainly caused by reduction of the light-emission efficiency of the LED. Generally, the CTR is
reduced to a greater extent as the forward current IF increases or as the operating temperature increases. Figure 5 and 6
respectively show estimated changes of CTRs of PS2501 and PS2505 optocouplers over time.
Estimated change of CTRs with time lapse (Standard values)
1.2
1.2
Standard value
Continuous supply of 20 mA (IF)
Standard characteristics
1.0
CTR Relative Value
CTR Relative Value
1.0
0.8
0.6
TA = 60˚C TA = 25˚C
0.4
0.2
IF = 5 mA
TA = 60˚C
IF = 20 mA
TA = 25˚C
IF = 5 mA
TA = 25˚C
0.8
0.6
0.4
0.2
0
10 2
Figure 5.
10 3
10 4
10 5
10 6
0
Time (Hr)
10 2
Figure 6.
10 3
10 4
10 5
Time (Hr)
CTR vs. TA Characteristics (TA: Ambient Temperature)
CTR
Light-emission
efficiency of LED
hFE of phototransistor
The CTR-Temperature characteristic is greatly affected by the total characteristics of light-emission efficiency of the LED and hFE
of the phototransistor as the light-emission efficiency has a negative temperature coefficient and hFE has a positive temperature
coefficient. See Figure 7.
TA
TA
Figure 7. CTR vs. TA Characteristics
24
TA
Figure 8-(a) to Figure 8-(g) show CTR vs. TA characteristics under various conditions.
(b)
(a)
1.2
1.50
Standard characteristics
IF = 5 mA, VCE = 5V
Standard characteristics
IF = 1 mA, VCE = 5V
1.25
CTR Relative Value
CTR Relative Value
1.0
0.8
0.6
0.4
0.2
Normalized to
1.0 at TA = 25˚C
1.00
0.75
0.50
Normalized to
1.0 at TA = 25˚C
0.25
0
0
-50
-25
0
25
50
75
-50
100
Ambient Temperature TA (°C)
0
75
100
1.2
Standard characteristics
CTR = approx. 200%
CTR Relative Value
Standard characteristics
IF = 0.3 mA, VCE = 5V
1.25
1.00
0.75
0.50
Normalized to
1.0 at TA = 25˚C
0.25
1.0
0.8
0.6
0.4
Normalized to
1.0 at TA = 25*C
IF = 5 mA,VCE = 5V
0.2
0
0
-50
-25
0
25
50
75
-50
100
-25
0
25
50
75
100
Ambient Temperature TA (°C)
Ambient Temperature TA (°C)
(e)
(f)
1.2
1.2
Standard characteristics
CTR = approx. 400%
Standard characteristics
CTR = approx. 300%
CTR Relative Value
1.0
CTR Relative Value
50
Ambient Temperature TA (°C)
1.6
1.50
0.8
0.6
0.4
Normalized to
1.0 at TA = 25˚C
IF = 5 mA,VCE = 5V
0.2
1.0
0.8
0.6
0.4
Normalized to
1.0 at TA = 25˚C
IF = 5 mA, VCE = 5V
0.2
0
0
-50
-25
0
25
50
75
-50
100
(g)
1.2
Standard charcteristics
CTR = approx. 500%
1.0
0.8
0.6
0.4
Normalized to
1.0 at TA = 25˚C
IF = 5 mA, VCE = 5V
0.2
0
-50
-25
0
25
50
75
-25
0
25
50
75
Ambient Temperature TA (°C)
Ambient Temperature TA (°C)
CTR Relative Value
25
(d)
(c)
CTR Relative Value
-25
100
Ambient Temperature TA (°C)
25
100
CTR vs. IF Characteristics (IF: Forward Current Flowing Through the LED)
The current transfer ratio (CTR) depends upon the magnitude of a forward current (IF). When IF goes lower or higher than a
proper magnitude, the CTR becomes smaller. Figure 9 shows the CTR vs. IF characteristics.
Note that rate changes of CTRs are very diffrent at low IF magnitude (approx. 5 mA), middle IF magnitude (approx. 5 mA), and
high IF magnitude (approx. 20 mA). Namely, the CTR depends heavily upon the magnitude of forward current IF in lower and
higher current ranges.
For low-input and high-output switching, see Chapter 4.
600
Standard characteristics
VCE = 5V
500
CTR (%)
400
Sample A
300
Sample B
200
100
0
0.1
0.5
1
5
10
50
Forward Current IF (mA)
Figure 9. CTR vs. IF Characteristics (Standard Value)
Response Characteristics
The response characteristics of optocouplers are the same as those phototransistors. The fall time tf is expressed by:
tf RL•hFE•CCB
RL: Load resistance
hFE: Amplification factor
CCB: Collector-base capacitance
If RL is too high, tf becomes too high to be fit for high-speed signal transmission. Select the proper load resistance for the desired
signal rate. Similarly, the collector current must fully satisfy the minimum value of the CTR, CTR vs. TA characteristics, and CTR
vs. time characteristics. Otherwise, the phototransistor will operate unsaturated, causing lower response characteristics and
malfunction.
Figures 10 to 13 show the response-time vs. forward current characteristics and response-time vs. VCC characteristics, using load
resistance and ambient temperature as parameters.
26
1000
1000
Standard characteristics
VCC = 5 V
TA = 25˚C
RL = 4.7 kΩ
TA = 85˚C
500
500
200
100
Response Time (µs)
200
Response Time (µs)
Standard characteristics
VCC = 5 V
TA = 25˚C
RL = 10 kΩ
TA = 85˚C
toff
50
ts
20
ton
10
toff
100
50
ts
20
10
ton
5
5
td
2
td
2
1
1
0
5
10
0
Forward Current IF (mA)
200
200
toff
100
50
20
ts
10
Standard characteristics
IF = 10 mA
TA = 25˚C
RL = 10 kΩ
TA = 85˚C
toff
500
Response Time (µs)
Response Time (µs)
1000
Standard characteristics
IF = 10 mA
TA = 25˚C
RL = 3 kΩ
TA = 85˚C
500
10
Figure 11. Response-Time vs. IF
Characteristics
Figure 10. Response-Time vs. IF
Characteristics
1000
5
Forward Current IF (mA)
ton
ts
100
50
20
10
ton
5
5
td
2
td
2
1
1
0
5
10
0
5
VCC (V)
VCC (V)
Figure 13. Response-Time vs. VCC
Characteristics
Figure 12. Response-Time vs. VCC
Characteristics
For reference, a voltage-gain vs. frequency characteristic using CTR as a parameter is shown below.
27
10
5
Standard
characteristics
Voltage Gain (dB)
0
Test Circuit and Condition
-5
1 kΩ
51 Ω
VCC = 10 V
330 µF
-10
IC = 2.25 mA
CTR = 156%
-15
VO
CTR = 186%
1 kΩ
CTR = 304%
-20
-25
100
500 1 k
5 k 10 k
50 k 100 k
500 k
Frequency f (HZ)
Figure 14. Voltage-Gain vs. Frequency Characteristics
(Standard Value) (PS2501, PS2505).
Other Temperature Characteristics
Almost all characteristics of optocouplers are apt to be affected by ambient temperature (see 3.1.2). Figures 15 to 21 show how
VF (Forward Voltage), ICEO (Collector Cut-Off Current), and VCE (sat) (Collector Saturation Voltage) are affected by ambient
temperature.
1.2
IF =
Forward Voltage VF (V)
1.1
IF =
1.0
10 m
A
5 mA
IF =
1m
A
0.9
0.8
0.7
0.6
0.5
-30
0
25
50
75
100
Ambient Temperature TA (°C)
Figure 15. VF vs. TA Characteristics
28
10000
(1 µA)
1000
500
VCE = 80 V
40 V
24 V
10 V
5V
100
50
10
5
1
0.5
0.1
-50
-25
0
25
50
Standard characteristics
CTR = approx. 100%
5000
Collector Cut-off Current ICEO (nA)
Collector Cut-off Current ICEO (nA)
10000
Standard characteristics
CTR = approx. 400%
5000
75
(1 µA)
1000
500
VCE = 80 V
40 V
24 V
10 V
5V
100
50
10
5
1
0.5
0.1
-50
100
-25
Ambient Temperature TA (°C)
0
0.3
75
100
0.3
CTR = approx. 200%
Collector Saturation
Voltage VCE (sat) (V)
CTR = approx. 200%
0.2
CTR = approx. 400%
0.1
0.2
CTR = approx. 400%
0.1
IF = 1 mA
IC = 1 mA
IF = 5 mA
IC = 4 mA
0
0
-50
-25
0
25
50
75
100
-50
-25
0
25
50
75
100
Ambient Temperature TA (°C)
Ambient Temperature TA (°C)
Figure 18. VCE (sat) vs. TA Characteristics
Figure 19. VCE (sat) vs. TA Characteristics
0.20
18
0.15
Collector Current IC (mA)
15
Collector Saturation
Voltage VCE (sat) (V)
50
Figure 17. ICEO vs. TA Characteristics
Figure 16. ICEO vs. TA Characteristics
Collector Saturation
Voltage VCE (sat) (V)
25
Ambient Temperature TA (°C)
CTR = 400%
330%
200%
0.10
IF = 10 mA, TA = 25˚C
IF = 8 mA,
TA = 25˚C
10
IF = 10 mA,
TA = 85˚C
IF = 8 mA,TA = 85˚C
5
Standard
characteristics
CTR = 200%
IF = 5 mA
IC = 1 mA
0.05
-50
-25
0
25
50
75
0
100
0.5
1.0
1.5
2.0
Collector Saturation Voltage VCE (sat) (V)
Ambient Temperature TA (°C)
Figure 21. IC vs. VCE (sat) Characteristics
Figure 20. VCE (sat) vs. TA Characteristics
29
At normal temperature (TA = 25 °C), the collector cut-off current ICEO is very little (about 1 nA (at VCE = 80 V and CTR = about
400% )), but it will be multiplied by about 10 at an increment of 25°C. This needs to be kept in mind when using a small output
current (IC) of an optocoupler with a high load.
The rate change of VCE (sat) (Collector Saturation Voltage) is about 0.7% per °C at ambient temperature of 0°C to 70°C. In circuit
design, the collector output current IC should be determined under the condition of half or less of the CTR rated values. Otherwise, the saturation voltage VCE (sat) will become greater.
CHARACTERISTICS OF PS2502 AND PS2506 OPTOCOUPLERS
The PS2502 and PS2506 optocouplers are higher in sensitivity than the PS2501 and PS2505 optocouplers and can be driven by
low currents.
CTR-Related Characteristics
The PS2502 and PS2506 optocouplers assure CTR ⊕ 200% at IF = 1 mA and can be directly driven by CMOS output signals.
See 3.1 for CTR definition and characteristics.
Change of CTR Over time
Figure 22 shows the CTR vs. time characteristics of the PS2502 and PS2506 optocouplers.
1.2
Standard values Continuous supply of
IF = 1 mA
1.0
CTR Relative Value
TA = 25˚C
0.8
TA = 60˚C
0.6
0.4
0.2
0
10
102
103
104
10 5
10
Time (Hr)
Figure 22. CTR vs. Time Characteristics (Standard Value)
30
CTR vs. Temperature Characteristics
Figure 23-(a) to 23-(f) show CTR vs. Temperature Characteristics under various conditions.
23-(b)
23-(a)
1.4
1.4
Standard characteristics
1.2
1.0
1.0
CTR Relative Value
CTR relative value
Standard characteristics
1.2
0.8
0.6
0.4
Normalized to
1.0 at TA = 25˚C
IF = 1 mA, VCE = 2V
0.2
0
-50
-25
0
25
50
75
0.8
0.6
0.4
Normalized to
1.0 at TA = 25˚C
IF = 0.3 mA, VCE = 2V
0.2
0
-50
100
-25
0
1.4
1.2
1.0
CTR relative value
CTR Relative Value
100
Standard characteristics
CTR = approx. 2500%
Standard characteristics
1.2
0.8
0.6
0.4
Normalized to
1.0 at TA = 25˚C
IF = 0.1 mA, VCE = 2V
0.2
-25
0
25
50
75
1.0
0.8
0.6
0.4
Normalized to
1.0 at TA = 25˚C
IF = 1 mA, VCE = 2V
0.2
0
-50
100
-25
0
25
50
75
100
Ambient Temperature TA (°C)
Ambient Temperature TA (°C)
23-(f)
23-(e)
1.4
1.4
Standard characteristics
CTR = approx. 3500%
1.2
Standard characteristics
CTR = approx. 4500%
1.2
CTR Relative Value
CTR Relative Value
75
23-(d)
23-(c)
1.4
1.0
0.8
0.6
0.4
Normalized to
1.0 at TA = 25˚C
IF = 1 mA, VCE = 2V
0.2
0
-50
50
Ambient Temperature TA (°C)
Ambient Temperature TA (°C)
0
-50
25
-25
0
25
50
75
1.0
0.8
0.6
0.4
Normalized to
1.0 at TA = 25˚C
IF = 1 mA, VCE = 2V
0.2
100
0
-50
-25
0
25
50
Ambient Temperature TA (°C)
Ambient Temperature TA (°C)
31
75
100
CTR vs. IF Characteristics
As shown in Figure 8, the CTR of a single-transistor output optocoupler (such as the PS2501 and PS2505 optocouplers) is at
most 20% in a low-current area (e.g. IF = 0.1 mA). However, the CTR of a Darlington-transistor output optocoupler (such as the
PS2502 and PS2506 optocouplers) can be greater than 200% in a low-current area (e.g. IF = 0.1 mA).
Figure 24 shows the CTR vs. IF characteristics of the PS2502 and PS2506 optocouplers.
7000
Standard characteristics
VCE = 2V
6000
CTR (%)
5000
4000
3000
2000
1000
0
0.05 0.1
0.5
1
5
10
50
Forward Current IF (mA)
Figure 24. CTR vs. IF Characteristics (Standard Value)
(PS2502, PS2506)
CONCLUSION
Demand for optocouplers featuring higher insulation and noise elimination is steadily increasing. At the same time, various
problems (change of characteristics by ambient temperature and time elapse) will occur in their circuit design. We hope this
manual will be helpful in solving such problems.
32
APPLICATION OF AC INPUT COMPATIBLE OPTOCOUPLER
INTRODUCTION
With the rapid penetration and diversification of electronic systems, demand for optocouplers is strengthening. Most popular are
products featuring compact design, low cost, and high added value.
To meet the market needs, NEC is expanding the optocoupler. This manual focuses on optocouplers compatible with AC input,
and covers configuration, principles of operation, and application examples.
CONFIGURATION (INTERNAL PIN CONNECTION DIAGRAM)
1
(LED2)
2
(LED1)
4
1
4
3
2
3
Figure 2. PS2501-1
Figure 1. PS2505-1
Figure 1 shows the internal pin connection of the AC input compatible optocoupler PS2505-1, and Figure 2, of the optocoupler
PS2501-1. The most significant difference from the optocoupler (PS2501-1) is that the PS2505-1 incorporates an input circuit
with two LEDs connected in reverse parallel. In the optocoupler (PS2501-1), one LED is connected in the input circuit so that the
LED emits light to provide a signal when a current flows in one direction (1-2 in Figure 2) (one-direction input type).
However, in the configuration shown in Figure 1, when a current flows in direction 1 to 2, LED1 emits light to send a signal, and
when it flows from 2 to 1, LED2 emits light to send a signal (bidirectional input type). Namely, even if the voltage level between 1
and 2 varies, and the positive and negative polarities are changed, either of two LEDs emits light to send a signal. This means
that the one direction input optocoupler permits DC input only, while the bidirectional input type permits AC input as well. Therefore, the PS2505-1 is described as an AC input compatible optocoupler.
The next section describes the status of output signals when 100 Vac power is directly input to an AC input compatible
optocoupler (PS2505-1) via a current limit resistor.
33
DIRECT INPUT OF 100 Vac
Figure 3 shows the circuit diagram when 100 Vac power is directly input to an AC input compatible optocoupler via a current limit
resistor. The relationship between input and output signals is as shown in Figure 4.
(LED2) (LED1)
VCC = 10 V
AC 100 V
Output signal
11 kΩ
100 Ω
PS2505-1
Figure 3. 100 Vac Direct Input Circuit
+
Input signal
AC 100 V
0
_
LED light
emission
output
LED 1
Output signal
LED 2
LED 1
LED 2
LED 1
Deviation due to
the differences in
light emission and
coupling efficiencies
of LEDs
LED 2
+
0
Figure 4. Input/Output Signal
Graph 1 Upper: 100 Vac Input Signal 100 V/DIV
Lower: Output Signal 1 V/DIV
As described above, when an AC input compatible optocoupler is used, an AC input signal can be extracted as a full-wave
rectified output signal. The output signal is smoothed by inserting a capacitor in the last stage of the circuit of a phototransistor if
necessary.
In the one-direction input optocoupler (PS2501 series), when an AC signal is to be input, it must be full-or half-wave rectified by a
diode bridge or CR circuit. On the other hand, the AC input compatible optocoupler permits direct input of an AC signal. This
enables simpler configuration, space saving, and reduced design cost.
The next section demonstrates three examples of applications.
34
APPLICATION EXAMPLES
Example 1: AC-DC converter
VCC
VCC
AC 100 V
AC 100V
PS2505-1
PS2501-1
+
+
+
0
_
0
0
(a) AC input compatible optocoupler
(bidirectional input)
(b) Conventional optocoupler
(one-direction input)
(Full-wave rectification by means of
diode bridge)
Example 2: Detection of a telephone bell signal
Station line
(75 Vr.m.s., 16 HZ)
Station line
(75 Vr.m.s., 16 HZ)
PS2505-1
PS2501-1
+
+
+
0
0
0
_
_
_
(a) AC input compatible optocoupler
(bidirectional input)
(b) Conventional optocoupler
(one-direction input)
(rectification by CR circuit)
35
Example 3: Sequencer circuit input section
Common
PS2501-2
AC 100 V
AC 100V
PS2505-2
(a) AC input compatible optocoupler
(bidirectional input)
Common
(b) Conventional optocoupler
(one-direction input)
(Full-wave rectified by diode bridge)
PRECAUTIONS FOR DESIGN
The AC input compatible optocoupler is identical to the conventional optocoupler except for the presence of two LEDs connected
in reverse parallel in the input circuit. Therefore, the circuit configuration can be designed as conventionally. The difference is
that there are two types of current transfer ratios (CRT) because two LEDs are connected in the input circuit. The two CTRs are
not necessarily the same, owing to the differences in light emission and coupling efficiencies of LEDs. Consequently, this causes
deviation in output signal level. The differences are rated under the item of the current efficiency ratio (CTR1/CTR2) for electric
characteristics.
Current transfer ratio (CTR1/CTR2)
IC1
CTR1 =
IF1 x (current flowing in LED1)
IC1
IF1
A
IC2
A
CTR2 =
IF2 x (current flowing in LED2)
IC2
A
IF2
LED 2
LED 1
Figure 5. CTR Measuring Circuit
36
VCE = 5 V
The transfer efficiency ratio (CTR1/CTR2) is rated as 0.3 (MIN.), 1.0 (TYP.), and 3.0 (MAX.). Assuming that CTR1 is 200%, CTR2
is in the range of 66 to 600%. Therefore, an AC input compatible optocoupler should be designed to operate with CTR 66 to
600%. For reference, the electric characteristics of the AC input compatible optocoupler (PS2505 series) are as follows:
Electric Characteristics (TA = 25°C)
ITEM
CODE
CONDITIONS
MIN.
TYP.
MAX.
UNIT
1.4
V
Forward voltage
VF
IF = ±10 mA
1.1
Pin-to-pin capacitance
Ct
V = 0, f = 1.0 MHZ
50
Collector cutoff current
ICEO
VCE = 80 V, IF = 0
Current transfer ratio
CTR(IC/IF)
IF = ± 5 mA
VCE = 5.0 V
Collector saturation voltage
VCE(sat)
IF = ±10 mA
IC = 2.0 mA
Insulation resistance
R1-2
Vin-out = 1.0 kV
Input-to-output capacitance
C1-2
V = 0, f = 1.0 MHZ
0.5
pF
Rise time
tr
VCC = 10 V,
IC = 2 mA,
RL = 100Ω
3
µs
Fall time
tf
VCC = 10 V,
IC = 2 mA,
RL = 100Ω
5
µs
Transfer efficiency ratio
CTR1/CTR2
Diode
Transistor
Coupled
IF = 5 mA,
VCE = 5.0 V
80
300
pF
100
nA
600
%
0.3
V
Ω
1011
0.3
1.0
3.0
For the external drawing, absolute maximum ratings, and characteristics curves, refer to the specific documents (AC input
compatible multi-optocoupler series).
EXCLUSIVE NORTH AMERICAN AGENT FOR
RF, MICROWAVE & OPTOELECTRONIC SEMICONDUCTORS
CALIFORNIA EASTERN LABORATORIES • Headquarters • 4590 Patrick Henry Drive • Santa Clara, CA 95054-1817 • (408) 988-3500 • Telex 34-6393 • FAX (408) 988-0279
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07/17/2000
DATA SUBJECT TO CHANGE WITHOUT NOTICE
37