User Manual

67
Lesson 8 4N35
Introduction
The 4N35 is an optocoupler for general purpose application. It consists of gallium arsenide
infrared LED and a silicon NPN phototransistor. When the input signal is applied to the LED in
the input terminal, the LED lights up. After receiving the light signal, the light receiver then
converts it into electrical signal and outputs the signal directly or after amplifying it into a
standard digital lev el. Thus, the transition and transmission of electricity-light-electricity is
completed. Since light is the media of the transmission, meaning the input terminal and the
output one are isolated electrically, this process is also be known as electrical isolation.
Components
-1 * 4N35
-1 * LED
-1 * 220 Ohm Resistor
- 1* 1k Ohm Resistor
- Some jump wires
Principle
4N35
The 4N35 is an optocoupler for general purpose application. It consists of gallium arsenide
infrared LED and a silicon NPN phototransistor.
What an optocoupler does is to break the connection between signal source and signal
receiv er, so as to stop electrical interference. In other words, it is used to prevent interference
from external electrical signals. 4N35 can be used in AV conversion audio circuits. Broadly it
is widely used in electrical insulation for a general optocoupler.
See the internal structure of 4N35 above. Pin 1 and 2 are connected to an infrared LED. When
the LED is electrified, it'll emit infrared rays. To protect the LED from burning, usually a resistor
(about 1K) is connected to pin 1. Then the NPN phototransistor is power on when receiv ing
the rays. This can be done to control the load connected to the phototransistor. Even when
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