Datasheet PS2601, PS2601L, PS2602L, PS2603L, PS2604 Datasheet (NEC)

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)

Absolute Maximum Ratings Electric Characteristics

A = 25°C) (TA = 25°C)

Product name Features

PS2601 High isolation

*

PS2601L voltage

Internal

connection

CEO 5 k 80 50 80 to 600 3 5

High V
PS2602 (80 V MIN.)
PS2602L Single transistor

PS2603 High isolation

*

PS2603L voltage

High CTR 5 k 80 200 200 to 2500 100 100
PS2604 Darlington­ PS2604L transistor

PS2605 High isolation

*

PS2605L voltage

A.C. input 5 k ±80 50 80 to 600 3 5

CEO

High V
PS2606 (80 V MIN.)
PS2606L Single transistor

PS2607 High isolation

*

PS2607L voltage

A.C. input 5 k ±80 200 200 to 3400 100 100

High CTR
PS2608 Darlington­ PS2608L transistor

PS2621 High isolation

*

PS2621L voltage

Large input 5 k 150 50 20 to 50 3 5
PS2622 current
PS2622L Single transistor

PS2625 High isolation

*

PS2625L voltage

A.C. input 5 k ±150 50 20 to 50 3 5

Large input
PS2626 current
PS2626L Single transistor

PS2633 High isolation

*

PS2633L voltage

CEO 1000 to

High V

(300 V MIN.) 5 k 80 150 15000 100 100

High CTR
PS2634 Darlington­ PS2634L transitor

PS2651 High isolation

*

PS2651L2 voltage

CEO 5 k 80 50 50 to 400 3 5

High V

(80 V MIN.)
PS2652 Single transistor
PS2652L2

PS2653 High isolation

*

PS2653L2 voltage

High CTR 5 k 80 200 200 to 3400 100 100

Darlington­ PS2654 transistors
PS2654L2

(Vr.m.s.) (TYP) (TYP)

(T

BV I

F (mA) IC(mA) CTR (%) tr (µs) tr (µs)

* (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

R

L

Figure 2-1. Collector-Base Capacitance
CC-B of Phototransistor

3

Input
monitor

Vo

50%

Input

ton toff

90% 90%

Output

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.

PW = 100 µs

()

Duty = 1/10

VCC = 5 V

PS2601

IF = 5 mA

Input

monitor

51 Ω

Vo

R

L

= 100 Ω

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).

V

CC

= 5 V

PS2601

IF = 5 mA

Input

monitor

51 Ω

R

L

= 5 Ω

Vo

Input
monitor

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 (t

on, toff) and load resistance (RL) in a typical circuit (Test circuit 3)

having collector load resistance (5 kΩ) with the emitter grounded.

V

CC

= 5 V

R

L

= 5 Ω

PS2601

IF = 5 mA

Input

monitor

51 Ω

Vo

Input
monitor

Vo

Test Circuit 3

Graph 3

Up : Input 0.2 V/DIV
DOWN : Output 2 V/DIV

(50 µs/DIV)

5

Input
monitor

Vo

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.

V

CC

= 5 V

PS2601

IF = 5 mA

Input

Input

monitor

Vo

monitor

Insert resistor

of 200 kΩ here.

Test Circuit 4

(Emitter Follower)

51 Ω

R

BE

PS2601

R

R

L

= 5 Ω

L

= 5 Ω

Vo

Vo

Graph 4

Up : Input 0.2 V/DIV
DOWN : Output 2 V/DIV

(50 µs/DIV)

V

CC

= 5 V

IF = 5 mA

Input

monitor

Insert resistor

of 200 kΩ here.

Test Circuit 5

(Emitter Grounded)

51 Ω

R

BE

Graph 5

Up : Input 0.2 V/DIV
DOWN : Output 2 V/DIV

6

(50 µs/DIV)

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 R

BE 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. R

L characteristics and Fig. 2-4 shows the switching-time vs. RBE characteris-

tics.

1000

I

F =

5 mA

500

51Ω

200

I

F

= 5 mA VCC = 5 V
Sample Solid line:
Current transfer ratio of 166%

100

Dotted line:
Current transfer ratio of 274%
at Ir = 5 mA

50

VCC = 5V

x

I

Vo

R

L

t

f

t

s

20
10

Switching Time (µs)

5

2

1

100 500 1 k 5 k 10 k 50 k 100 k

Load Resistance RL (Ω)

Fig. 2-3 Switching-Time vs. RL Characteristics

1000

I

F =

10 mA

500

IF = 10 mA Vcc = 5 V

200

Sample Solid line:
Current transfer ratio of 166%

100

Current transfer ratio of 274%
at Ir = 5mA

51Ω

x

I

Dotted line:

Vcc = 5V

L

R

Vo

t f

t s

50

20
10

t

r

t

d

Switching Time (µs)

5

2

t r

t d

1

100 500 1 k 5 k 10 k 50 k 100 k

Load Resistance RL (Ω)

160

Vcc = 5 V, IF = 5mA
R

140

1 = 5Ω

Solid line: Emitter follower
Dotted line: Emitter grounded

120

100

80

60

Switching Time (µs)

40

ton

20

0

100 200 500 1000

Base-Emitter Resistance RBE (kΩ)

Fig. 2-4 Switching-Time vs. RBE Characteristics

160

VCC = 5 V, IF = 10mA
R

L

140

= 5Ω
Solid line: Emitter follower
Dotted line: Emitter grounded

120

100

t

toff

off

80

60

Switching Time (µs)

40

t

20

off

0

8

100 200 500 1000

8

Base-Emitter Resistance RBE (kΩ)

7

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 (I
emitter resistor (RBE).
Fig 2-5 shows the I

CEO vs. TA characteristics of a PS2601 optocoupler .

PS2601 ICEO-TA Characteristics

10000

IF = 0
V

CE

= 80V (40V for the

PS2603) 2601

(nA)

CEO

Solid line: PS2601
Dotted line: PS2603

1000

100

10

8

R

BE

=

RBE = 1M

R

BE

=1M

Ω

Ω

CEO) through the base-

1

R

BE

=100 M

Ω

Collector Dark Current I

0.1

- 20 0 20

40 60 80 100

Ambient T emperature TA (°C)

Figure 2-5. I

CEO 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.

Figure 2-6.

V

o

C

BE

R

L

Figure 2-7.

8

6a) CBE = No capacitance

Vo

Vin

6b) CBE = 10 pF

Vin

Vo

6d) CBE = 1000 pF

Vin

Vin

Vo

6c) C

BE = 100 pF

Vo

Graph 6

Up : Input Surge Voltage (Vin :1000 V/DIV)
DOWN : PS2601 output (VO: 1 V/DIV)

Vin

C

1-2

CBE

Test Circuit

9

5 V

Vo

470 Ω

Vin (dV/dt = 10 V/µs, 2 V/DIV)

CCB

Vin

Vo

(500 ns/DIV)

Graph 7-(a)
Input Voltage Fluctuation and Output

Vo (0.1 V/DIV)

Vin (dV/dt = 10 V/µs, 2 V/DIV)

Vo (0.1 V/DIV)

1000 pF

5 kΩ

C

CB

5 kΩ

Vin

Vo

(500 ns/DIV)

Graph 7-(b)
Effect of Collector-Base Capacitance on
Voltage Fluctuation

10

0.1

Output Voltage, Vo (V)

0.01

PS2601
R

L

1

= 5 kΩ

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

Graph 8-(a)

Vin

Vo

5 V

470 Ω

Up : Input Surge Voltage (Vin: 1000 V/DIV)
DOWN : PS2601 Output (Vo: 1 V/DIV)

(PS2601)

Vin

Base pin

Vo

Cut the base pin (pin 6)

(PS2601)

Graph 8-(b)

Vin

Vo

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 (R
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

V

CE

= 5 V

(PS2601)

50

40

(mA)

C

30

RBE =

200 kΩ
100 kΩ
50 kΩ
30 kΩ

8

20 kΩ

BE) that

20

10 kΩ

Collector Current I

10

0

123451020304050

Forward Current I

F (mA)

5 kΩ

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.

PS2601

r)

High-voltage

transistor (T

(µA)

CBL

200

100

50
40

30
20

10

CB

= 100V

V
(PS2601)

I

F

I

CBL

CTR = 274%

100V

A

CTR = 166%

CBL

I

Figure 2-10. Application to a
High Voltage Circuit

5
4

3

Collector-Base Photocurrent I

2

1

12345102030405080

Figure 2-11. I

13

CBL vs. IF Characteristic

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.

C

1-2

A

C

R

D

j

C

I

CBL

K

CB

T

r

C

BE

C

B

E

Figure 3-1. Equivalent Circuit (for PS2601 Optocoupler)

C

j : Junction capacity of LED

CBE : Base-emitter capacitance
RD : Resistor serially connected to LED
ICBL : Collector-base photocurrent generated by the light of the LED
C1-2 : Input-output capacitance
Tr : 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 (I

F) flowing through its light-emitting diode (LED). The CTR is expressed by:

I

CTR = x = 100 (%) ................(2)

IF

where IC = ICBL•hFE ..............................(3)

(hFE: D.C. current amplification factor of the phototransistor)

C

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:

I

CBL

I

CBL-I1

V

BE

R

BE

I

1

Figure 3-2.

C' = hFE' (ICBL-I1) = hFE' ( ICBL- )

I

•

IC' = hFE' • ICBL ( 1 - ) ................ (4)

• •

C' : Output current of an optocoupler having RBE

Note I

VBE

ICBL • RBE

VBE

RBE

hFE' : 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' VBE

= ( 1 - ) ................ (5)

IC hFE ICBL • RBE

As h

FE' is equal to hFE if IF = approx. 5 mA, IC = approx. 15 mA, and RBC > 100 kΩ, expression (5) is simplified as follows:

IC' VBE

= 1 - ................ (6)

IC ICBL • RBE

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 I

C') 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-R

BE characteristics.

1.0

0.8

0.6

0.4

CTR Relative V alues

0.2

0

1.0

Normalized to 1.0
at R

BE

= ×

IF = 1 mA, VCE = 5V

CTR = 274%

100

200 300 400 500 1000

Base Emitter Resistance RBE (kΩ)

CTR = 274%

CTR =166%

1.0
CTR = 274%

0.8

CTR =166%

0.6

0.4

CTR Relative V alues

0.2

0

8

100

200 300 400500 1000

Normalized to 1.0

BE

= ×

at R
IF = 5 mA, VCE = 5V

8

Base Emitter Resistance RBE (kΩ)

0.8

0.6

0.4

CTR =166%

CTR Relative V alues

0.2

0

100

200 300 400500 1000

Base Emitter Resistance RBE (kΩ)

Figure 3-3. ∆CTR-RBE Characteristics

Normalized to 1.0
at R

BE

= ×

IF = 10 mA, VCE = 5V

8

16

I

F

PS2601

R

BE

= 100 kΩ

Vo

Vcc = 10V

R

L

= 470 kΩ

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 (b).

RBE Serial to RL

VBE1

RL

V1

I

CBL

R

I

CBL

Figure 3-4 (a).

Open

V

BE

ICBL

RBE1

V

o

R

L

The output voltage V0, V1, and V2 of the above circuits (a), (b), and (c) are related as follows:

V1 hFE1 VBE

( 1 - ) ................ (7)

=

V2 hFE0 ICBL • RBE1

VBE2
V2 hFE2
V0 hFE0

= ( ) ................ (8)

1 -

1 +

CBL • RBE1

I

RL • hFE2

BE2

R

Figure 3-4 (c).

RBE Parallel to RL

BE2

V

BE2

V

2

R

L

When resistor R

BE 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

Vcc = 10 V
R

L

= 470 Ω

(a) RB open

CTR = 190%
(PS2601)

8

(b) RBE = 100 kΩ

6

4

Output voltage Vo (V)

2

(c) RBG = 100 kΩ

0

12 51020 50

Forward current IF (mA)

Figure 3-5. Vo vs. I

F 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.

PS2601

T

n1

I

b

R2 = 510 Ω

I

4

3

I

TTL

F

= 5 mA

I

A resistor of 510 kΩ
is inserted here.

I

R

0

0

= 1 kΩ

I

1

R

1

= 2 kΩ

Figure 4-1. Circuit Design Example

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 Tr1 must be 0.8 V or less. Accordingly, I2

must be as follows:

VCC - VCE 5 - 0.8

I2 ⊕ = = 8.2 (mA) ................(9)

R2 0.51 (kΩ)

Therefore I3 = I2 + I4 = 8.2 + 1.6 = 9.8 (mA) ................(10)

Vcc = 5 V

V

OUT

G

Let's assume that hFE of transistor Tr1 is 40 (worst). Ib must be as follows:

I3 9.9 (mA)

Ib ⊕ = = 0.247 (mA) ................(11)

hFE 40

Similarly, let's assume that VBE of transistor Tr1 is 0.8 V (worst), I1 must be as follows:

VBE 0.8

I1 = = = 0.4 (mA) ................(12)

R1 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 0.647(mA)

CTR = x 100 = x 100 = 21.6% ................(14)

IF 3 (mA)

18

Accordingly, the CTR value including reduction of CTR by time elapse, temperature change, and insertion of R

BE 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

0.8

0.6

0.4

CTR Relative V alue

0.2

0

010101010

234 5

Time (Hr)

Figure 4-2. Change of CTR with
Time (PS2601)

IF = 20 mA
T

A

= 25˚C

IF = 5 mA
T

A

= 60˚C

Normalized to CTR
test conditon
I

F

IF = 5 mA
T

A

= 25˚C

= 5 mA, V

CE

1.2

1.0

0.8

0.6

0.4

= 5V

CTR Relative V alue

0.2

0

-55 -40 -20 20 40 60 80 1000

Ambient Temperature TA (°C)

Figure 4-3. CTR-Relative-Value vs.

A Characteristics

T

Normalized to 100
at T

A

= 25˚C

I

F

= 5 mA, VCE = 5 V

19

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 High isolation Abundant I/O functions High CTR High V

Product Voltage (TYP) (MIN) (TYP)
name

PS2501 D.C. input, Single 300% 80V tr = 3 µs
PS2501L (*) transistor output tr = 5 µs

PS2502 D.C. input, Darlington 2000% 40V tr, tf = 100 µs
PS2502L (*) pair transistor output

5 kVac
PS2505 A.C. input, single 300% 80V tr = 3 µs
PS2505L (*) transistor output tr = 5 µs

PS2506 A.C. input, Darlington 2000% 40V tr, tf = 100 µs
PS2506L (*) pair transistor output

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.

CEO Response

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

8765

1234

1,3. Anode
2,4. Cathode
5,7. Emitter
6,8. Collector

10.2 MAX

6.53.8

MAX

4.55

MAX

2.8

MIN

1.34

0.65

0.50±0.10

2.54

7.62

0.25

M

0 to 15˚

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

4.55

2.8

PS250X-4

6.53.8

MAX

MAX

MIN

1.34

6.5

3.8

5.1 MAX

MAX

0.65

2.54

20.3 MAX

0.50±0.10

0.25 M

7.62

2.54

0 to 15˚

7.62

43

12

1. Anode

2. Cathode

3. Emitter

4. Collector

16151413

12117810 9

1234

56

1,3,5,7. Anode
2,4,6,8. Cathode
9,11,13,15. Emitter
10,12,14,16. Collector

PS250X-2

4.55

MAX

2.8

MIN

1.34

0.65

0.50±0.10

0.25

M

0 to 15˚

Figure 3. Package Dimensions (Units in mm) (PS2501, PS2502, PS2505, and PS2506)

22

Lead Bending type (Gull-wing)

PS250XL-1

3.8

MAX.

1.34±0.10

PS250XL-4

5.1 MAX

0.25 M

2.54

20.3 MAX

7.62

6.5

9.60±0.4

2.54

1. Anode

2. Cathode

3. Emitter

4. Collector

0.05 to 0.2

0.9±0.25

7.62

6.5

43

12

16 15

12

14 137810 9

12 11

34

56

1,3,5,7. Anode
2,4,6,8. Cathode
9,11,13,15. Emitter
10,12,14,16. Collector

PS250XL-2

3.8

MAX.

1.34±0.10

10.2 MAX

0.25 M

2.54

7.62

6.5

9.60±0.4

87

65

12

34

1,3. Anode
2,4. Cathode
5,7. Emitter
6,8. Collector

0.05 to 0.2

0.9±0.25

3.8

MAX.

1.34±0.10

9.60±0.4

0.25 M

0.05 to 0.2

0.9±0.25

Fig. 4 Package Dimensions (Units in mm) (PS2501L, PS2502L, PS2505L, and PS2506L)

23

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 I

C 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 I

F 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

1.0

0.8

0.6

0.4

CTR Relative V alue

0.2

Standard characteristics

IF = 5 mA
T

A = 60˚C

IF = 20 mA
T

A = 25˚C

IF = 5 mA
T

A = 25˚C

CTR Relative V alue

1.2

1.0

0.8

0.6

0.4

0.2

Standard value
Continuous supply of 20 mA (I

TA = 60˚C TA = 25˚C

F

)

0

Figure 5.

23 4 56

10 10 10 10 10

010101010

2345

Time (Hr) Time (Hr)

Figure 6.

CTR vs. TA Characteristics (TA: Ambient Temperature)

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.

CTR

of phototransistor

Light-emission

efficiency of LED

TA TA TA

Figure 7. CTR vs. TA Characteristics

FE

h

24

Figure 8-(a) to Figure 8-(g) show CTR vs. TA characteristics under various conditions.

(a)

1.2

1.0

Standard characteristics
I

F

= 5 mA, VCE = 5V

(b)

1.50

1.25

Standard characteristics

I

F

= 1 mA, VCE = 5V

0.8

0.6

0.4

0.2

CTR Relative V alue

0

-50 -25 0 25 50 75 100

Normalized to

1.0 at T

Ambient T emperature TA (°C) Ambient T emperature TA (°C)

(c)

1.6

1.50

1.25

1.00

0.75

0.50

CTR Relative V alue

0.25

0

-50 -25 0 25 50 75 100

Standard characteristics
I

F

= 0.3 mA, VCE = 5V

Normalized to

1.0 at T

Ambient T emperature TA (°C)

(e)

1.2

1.0

Standard characteristics
CTR = approx. 300%

A

= 25˚C

A

= 25˚C

CTR Relative V alue

CTR Relative V alue

1.00

0.75

0.50

0.25

0

-50 -25 0 25 50 75 100

Normalized to

1.0 at T

(d)

1.2

1.0

0.8

0.6

0.4

0.2

0

-50 -25 0 25 50 75 100

Standard characteristics
CTR = approx. 200%

Normalized to

1.0 at T

A

= 25*C

I

F

= 5 mA,VCE = 5V

Ambient T emperature TA (°C)

(f)

1.2

1.0

Standard characteristics
CTR = approx. 400%

A

= 25˚C

0.8

0.6

0.4

CTR Relative V alue

0.2

0

-50 -25 0 25 50 75 100

Normalized to

1.0 at T
I

F

= 5 mA,VCE = 5V

Ambient T emperature TA (°C)

(g)

1.2

1.0

0.8

0.6

0.4

CTR Relative V alue

0.2

0

-50 -25 0 25 50 75 100

Standard charcteristics
CTR = approx. 500%

Normalized to

1.0 at T
I

F

= 5 mA, VCE = 5V

Ambient T emperature TA (°C)

A

= 25˚C

A

= 25˚C

CTR Relative V alue

0.8

0.6

0.4

0.2

0

-50 -25 0 25 50 75 100

Normalized to

1.0 at T

A

I

F

= 5 mA, VCE = 5V

Ambient T emperature TA (°C)

= 25˚C

25

CTR vs. IF Characteristics (IF: Forward Current Flowing Through the LED)

The current transfer ratio (CTR) depends upon the magnitude of a forward current (I

F). 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 I

F 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

V

CE

= 5V

500

400

Sample A

300

Sample B

CTR (%)

200

100

0

0.1 0.5 1 5 10 50

Forward Current IF (mA)

Figure 9. CTR vs. I

F Characteristics (Standard Value)

Response Characteristics

The response characteristics of optocouplers are the same as those phototransistors. The fall time t

f 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

500

Standard characteristics

V

CC

= 5 V TA = 25˚C

R

L

= 4.7 kΩ TA = 85˚C

1000

500

Standard characteristics

V

CC

= 5 V TA = 25˚C

R

L

= 10 kΩ TA = 85˚C

200
100

t

off

50

t

s

20

t

Response Time (µs)

10

on

5

t

2

d

1

0510

Forward Current IF (mA)

Figure 10. Response-Time vs. I

F

Characteristics

1000

500

200

Standard characteristics

I

F = 10 mA TA = 25˚C

R

L = 3 kΩ TA = 85˚C

toff

100

200

t

off

100

50

t

s

20

Response Time (µs)

10

t

on

5

t

2

d

1

0510

Forward Current I

Figure 11. Response-Time vs. I

F (mA)

F

Characteristics

1000

500

Standard characteristics

I

F

= 10 mA TA = 25˚C

R

L

= 10 kΩ TA = 85˚C

t

off

200

t

100

s

50

20

ts

10

Response Time (µs)

ton

5

50

20
10

Response Time (µs)

5

td

2

1

0510

VCC (V)

Figure 12. Response-Time vs. VCC
Characteristics

2

1

0510

V

CC (V)

Figure 13. Response-Time vs. V
Characteristics

For reference, a voltage-gain vs. frequency characteristic using CTR as a parameter is shown below.

CC

t

on

t

d

27

5

0

Standard
characteristics

Test Circuit and Condition

-5

-10

-15

Voltage Gain (dB)

-20

-25
100 500 1 k 5 k 10 k 50 k 100 k 500 k

1 kΩ 51 Ω

330 µF

CTR = 156%
CTR = 186%

CTR = 304%

V

CC

C

= 2.25 mA

I

1 kΩ

= 10 V

V O

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

1.1

1.0

(V)

F

0.9

0.8

Forward Voltage V

0.7

0.6

0.5

I

F

= 10 mA

I

F

= 5 mA

I

F

= 1 mA

-30 0 25 50 75 100

Ambient T emperature TA (°C)

Figure 15. V

F vs. TA Characteristics

28

(nA)

18

15

10

5

0.50 1.0 1.5 2.0

Standard
characteristics
CTR = 200%

IF = 10 mA,
T

A

= 85˚C

IF = 8 mA,TA = 85˚C

IF = 8 mA,
T

A

= 25˚C

IF = 10 mA, TA = 25˚C

CEO

10000

5000

(1 µA)

1000

500

100

50

Standard characteristics
CTR = approx. 400%

VCE = 80 V

40 V
24 V
10 V

5 V

(nA)

CEO

10000

5000

(1 µA)

1000

500

100

50

Standard characteristics
CTR = approx. 100%

VCE = 80 V

40 V
24 V
10 V

5 V

10

5

1

Collector Cut-off Current I

0.5

0.1

-50 -25 0 25 50 75 100

Figure 16. I

0.3

0.2

(V)

CE (sat)

0.1

Voltage V

Collector Saturation

10

5

1

Collector Cut-off Current I

0.5

0.1

-50 -25 0 25 50 75 100

Ambient T emperature TA (°C) Ambient T emperature TA (°C)

CEO vs. TA Characteristics

CTR = approx. 200%

CTR = approx. 400%

Figure 17. I

0.3

0.2

(V)

CE (sat)

0.1

Voltage V

Collector Saturation

CEO vs. TA Characteristics

CTR = approx. 200%

CTR = approx. 400%

0

-50 -25 0 25 50 75 100

Ambient T emperature TA (°C) Ambient T emperature TA (°C)

Figure 18. VCE (sat) vs. TA Characteristics

0.20

(V)

0.15

CE (sat)

0.10

Voltage V

Collector Saturation

0.05

-50 -25 0 25 50 75 100

Ambient T emperature TA (°C)

Figure 20. VCE (sat) vs. TA Characteristics

CTR = 400%

330%

200%

IF = 1 mA
I

C

= 1 mA

IF = 5 mA
I

C

= 1 mA

29

0

-50 -25 0 25 50 75 100

Figure 19. V

(mA)

C

Collector Current I

Collector Saturation Voltage V

Figure 21. I

IF = 5 mA
I

C

= 4 mA

CE (sat) vs. TA Characteristics

CE (sat) (V)

C vs. VCE (sat) Characteristics

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

0

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 (I

C) 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 V

CE (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

1.0

0.8

0.6

0.4

CTR Relative V alue

0.2

0

10 10 10 10 10 1

Standard values Continuous supply of
I

F

TA = 60˚C

5432

Time (Hr)

Figure 22. CTR vs. Time Characteristics (Standard Value)

= 1 mA

TA = 25˚C

30

CTR vs. Temperature Characteristics

Normalized to

1.0 at T

A

= 25˚C

I

F

= 1 mA, VCE = 2V

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0

-50 -25 0 25 50 75 100

Standard characteristics
CTR = approx. 2500%

Figure 23-(a) to 23-(f) show CTR vs. Temperature Characteristics under various conditions.

23-(a)

1.4
Standard characteristics

1.2

1.0

0.8

0.6

CTR relative value

0.4

Normalized to

A

0.2

1.0 at T
I

F

= 25˚C

= 1 mA, VCE = 2V

0

-50 -25 0 25 50 75 100

Ambient T emperature TA (°C)

23-(c)

1.4
Standard characteristics

1.2

1.0

23-(b)

1.4
Standard characteristics

1.2

1.0

0.8

0.6

CTR Relative V alue

0.4

Normalized to

1.0 at T

0.2

A = 25˚C

I

F = 0.3 mA, VCE = 2V

0

-50 -25 0 25 50 75 100

Ambient T emperature T

A (°C)

23-(d)

0.8

0.6

0.4

CTR Relative V alue

0.2

0

-50 -25 0 25 50 75 100

Ambient T emperature T

23-(e)

1.4

1.2

1.0

0.8

0.6

CTR Relative V alue

0.4

0.2

0

-50 -25 0 25 50 75 100

Ambient T emperature TA (°C)

Normalized to

A

1.0 at T
I

Standard characteristics
CTR = approx. 3500%

Normalized to

1.0 at T
I

= 25˚C

F

= 0.1 mA, VCE = 2V

A (°C)

A

F

= 25˚C

= 1 mA, VCE = 2V

31

CTR relative value

Ambient T emperature T

A (°C)

23-(f)

1.4

1.2

1.0

0.8

0.6

CTR Relative V alue

0.4

0.2

0

-50 -25 0 25 50 75 100

Standard characteristics
CTR = approx. 4500%

Normalized to

1.0 at T

A

I

F

= 25˚C

= 1 mA, VCE = 2V

Ambient T emperature TA (°C)

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
V

CE

= 2V

6000

5000

4000

CTR (%)

3000

2000

1000

0

0.05 0.1 0.5 1 5 10 50

Forward Current IF (mA)

Figure 24. CTR vs. I
(PS2502, PS2506)

F Characteristics (Standard Value)

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

2

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.

(LED2) (LED1)

1

4

2

3

Figure 2. PS2501-1

4

3

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)

V

CC

= 10 V

AC 100 V

11 kΩ

PS2505-1

Figure 3. 100 Vac Direct Input Circuit

+

Input signal

AC 100 V

0
_

LED light
emission

output

Output signal

LED 1

LED 2

+

0

Figure 4. Input/Output Signal

LED 1

LED 2

100 Ω

LED 1

Output signal

LED 2

Deviation due to
the differences in
light emission and
coupling efficiencies
of LEDs

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

Station line
(75 V

r.m.s.

, 16 HZ)

PS2501-1

+
0
_

+
0
_

Example 1: AC-DC converter

V

CC

V

CC

AC 100V

PS2505-1

+
0

_

(a) AC input compatible optocoupler

(bidirectional input)

Example 2: Detection of a telephone bell signal

Station line

r.m.s., 16 HZ)

(75 V

AC 100 V

+
0

(b) Conventional optocoupler

(one-direction input)
(Full-wave rectification by means of
diode bridge)

PS2501-1
+
0

PS2505-1

+
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

AC 100 V

PS2505-2

AC 100V

Common

PS2501-2

Common

(a) AC input compatible optocoupler

(bidirectional input)

(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)

I

F1

I

C1

IC2
CTR2 =
IF2 x (current flowing in LED2)

36

A

A

F2

I

LED 2 LED 1

A

IC2

VCE = 5 V

Figure 5. CTR Measuring Circuit

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

Forward voltage VF IF = ±10 mA 1.1 1.4 V

Diode

Pin-to-pin capacitance C

t V = 0, f = 1.0 MHZ 50 pF

Transistor Collector cutoff current I

CEO VCE = 80 V, IF = 0 100 nA

Current transfer ratio CTR(IC/IF)IF = ± 5 mA 80 300 600 %

CE = 5.0 V

V

Collector saturation voltage V

CE(sat) IF = ±10 mA 0.3 V

IC = 2.0 mA

Insulation resistance R1-2 Vin-out = 1.0 kV 10

11

Input-to-output capacitance C1-2 V = 0, f = 1.0 MHZ 0.5 pF

Coupled VCC = 10 V,

Rise time tr IC = 2 mA, 3 µs

RL = 100Ω
VCC = 10 V,

Fall time tf IC = 2 mA, 5 µs

RL = 100Ω
IF = 5 mA,

Transfer efficiency ratio CTR1/CTR2 VCE = 5.0 V 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).

Ω

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07/17/2000

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