The resistors here are placed for limiting the currents in the circuit. The PHOTOTRANSISTOR side secondary circuit here is in complete isolation with the CONTROLLER-PHTODIODE primary circuit. Optoisolator Transistor with Base Output. 4N25 Specifications: Voltage - Isolation: 5000Vrms Input Type: DC Output Type: Transistor with Base Current - Output / Channel: 50mA Voltage.
In this circuit you can see the motor draws power from the +12V battery source and not from the controller circuit. Download schematic symbols, PCB footprints, pinout & datasheets for the 4N25 by Vishay Semiconductor Opto Division. Thus the motor stops rotating when the microcontroller input to 4N25 gets LOW. With HIGH RESISTANCE the complete supply voltage appears across the transistor and current flow in the load circuit gets ZERO. So its LOW RESISTANCE state to HIGH RESISTANCE states. Since radiation is cutoff the PHOTOTRANSISTOR gets turned OFF since the radiation acts as BASE TRIGGER. With that the IR DIODE stops emitting radiation internally. I have researched this forum and seen posts that suggest that a 4N25 optical isolator can not be used for an analog circuit, just switching circuits. Unlike most dimmers it does not simply connect the dash lights through a variable resistor to ground. When the controller output goes LOW, the IR DIODE input goes LOW. I have a sensitive an unusual dash dimmer switch on my vehicle.
Thus the motor rotates when microcontroller circuit provides HIGH logic to the 4N25 chip. When transistor gets tuned ON the current flows through load circuit and the voltage will be seen across the motor. Isolation voltage shall be measured using the following method. When IR DIODE gets powered it will emit Infrared rays internally, when these rays fell on the PHOTOTRANSISTOR the transistor gets turned ON. 4N25 Series/4N26 Series/4N27 Series/4N28 Series. Pin 6 (the base of the transistor) is used to tweak the sensitivity of the optocoupler. When the LED in the 4N25 turns on, it causes the input output to go LOW because there is a direct path opened to ground. We will get the +3.3Voltage pulses from a microcontroller and these are driven to the POSITIVE of IR DIODE. The transistor side of the 4N25 (pin 4, 5, and 6) reproduces a signal by always being high except for when the LED gets turned on. The whole issue of radiation will be working under background.įor understanding the OPTOCOUPLER we will consider a circuit shown below. The IR radiation emitted by IR LED will not be visible outside the chip. The IR DIODE is connected between terminals 1 and 2, the PHOTOTRANSISTOR is connected at terminals 4, 5 and 6.The internal setup of two components can be seen below. One is INFRARED DIODE and another of INFRARED PHOTOTRANSISTOR. 4N25 OPTOCOUPLER IC has two components integrated in it.