AN-3002

APPLICATION NOTE

2

REV. 4.00 4/30/02

The resulting LED forward current that will keep the output

circuitry conducting is shown as the result of proper design.

Figure 3. Pulse Train Waveforms

A desired sine wave to be present is shown in Figure 4.

The resulting LED forward current that will keep the output

circuitry conducting is shown as the result of proper design.

Figure 4. Sine Wave Waveforms

Matrices Opto-Coupling

With the low input LED current advantage of the 6N139, the

ability to drive matrices with but one TTL output is now pos-

sible as shown in Figure 5.

Figure 5. Opto-Coupling out of Matrices

Non-Loading Line Receiver

For virtual non-loading, the 6N139 is compatible with the

differential amplifier circuit of Figure 6.

Figure 6. Differential Amplifier Drive

For a virtual no-load optoisolator circuit use:

X=Non-latching output circuitry to follow

LED=Input diode of 6N139

Current requirement at “in” will be less than 20 micro

Amperes.

Example:

circuit will respond nicely to TTL “0” and “1” levels. That is,

a “0” at “In” will cause LED current resulting in the conduc-

tion of the output circuitry. Conversely, a “1” at “In” will

result in no LED current. Notice that depending upon which

collector the LED is in series with it will give the option of

LED current flowing with a “0” or a “1” at “In”.

6N139 Output Circuitries

The following are two examples of 6N139 output circuitry.

One latching (Figure 7); the other non-latching (Figure 8),

but both capable of driving a TTL gate directly.

Referring to Figure 7 and assuming that the “RESET” has

been actuated by a momentary ground and no input signal is

being received, all transistors shown are non-conducting

(Output high, “1”). The arrival of an input signal will cause

all transistors to turn on. (Output low, “0”). The PNP transis-

tor, being turned on by the output transistor, will in turn latch

that same output transistor or until the “RESET” is again

initiated.

In Figure 8, where no signal is being received, the input

transistor is not conducting. The output transistor is very

slightly conducting. The 4.7M

Ω resistor causing this slight

conduction will not bring the “Output” to a “0” level.

The purpose of this slight conduction is to reduce the

turn-on delay time. When a signal is received, both input

INPUT

(Volts)

+

t=0

OUTPUT

(Volts)

5.0

0.4

LED

(mA)

1.0

0.5

0

INPUT

(Volts)

+

0

t=0

OUTPUT

(Volts)

5.0

0.4

LED

(mA)

1.0

0.5

0

1 of 16

ACTIVE

LOW

SCAN

CONTROL

16 X 16

MATRIX

5V

5.5K

Ω

RESISTORS

ALL

ARE INPUT DIODES OF 6N139

IN

10K

Ω

or

here

+V

6N139

AS EXAMPLE

LED

0.5 mA

X

1mA

+V