4N25 - Phototransistor Optocoupler IC

2018年3月9日 - 0 Comments

4N25 Optocoupler IC

4N25 IC Pinout

4N25 Features and Specifications

IR LEDForward Voltage for turning ON: 1.25V-1.5V (Typically 1.3V, 1.5V being absolute maximum forward voltage)
IR LED Forward Current during ON: 10mA - 60mA (Typically 10mA, 60mA being absolute maximum forward current)
IR LED Reverse Voltage Maximum: 5V
IR LED反向电流最大值：100UA
晶体管的收集器和发射器之间的最大电压：70V
最大电流允许的槽晶体管收集器：100mA
Typical Rise Time: 2us
Typical Fall Time: 2us
No additional power needed to be applied for chip for making it work.

4N25 Equivalents

4N25 OPTOCOUPLER IChas many replacements like 4N26, 4N27, 4N28, 4N33,MCT2E, PC817. We need to check parameters and Pin configuration carefully before replacing. Replacing without taking voltage, current, and frequency parameters may lead to permanent damage.

Similar Opto-coupler ICs

MOC3021 (TRIAC based OPTOCOUPLER used to control AC RMS voltage), FOD3180 (High-Speed MOSFET),

Why to Use 4N25 OPTOCOUPLER

理解use ofleyu11.app consider:

Case1:您想将负载电路与控制电路分离。说你想控制一个小的速度DC motorby using MICROCONTROLLER PWM output. This setup is not feasible asmicrocontroller是敏感的设备。因此，为了隔离载荷电路并保护控制器免受电压波动的影响，我们使用了OptoCOPOPLER。

Case2:说你想触发一个场效应晶体管驱动高功率负载的电路。MOSFET触发电压通常为12V。MOSFET驱动器控制高功率负载所需的这些电压突发（+12V）无法从控制器中汲取。当控制器弹出 +3.3V或 +5V突发时。在那些情况下使用4N25 OPTOCOPLER芯片是理想的。

Case3:Consider we want to switch a 12V relay which is looping 220V AC fan according to RASPBERRY PI outputs. It is ideal to use 4N25 in this case, as 4N25 draws negligible amount of power considering a transistor or a MOSFET.

How to Use 4N25 OPTOCOUPLER

4N25 OPTOCOUPLER IChas two components integrated in it. One is INFRARED DIODE and another of INFRARED PHOTOTRANSISTOR. 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. The IR radiation emitted by IR LED will not be visible outside the chip. The whole issue of radiation will be working under background.

4N25 IC内部结构

理解OptoCOUPLERwe will consider a circuit shown below.

4N25 IC Circuit

我们将从微控制器中获取 +3.3电压脉冲，并将其驱动到IR二极管的正值。当IR二极管获得动力时，它将在内部发射红外线，当这些射线落在光线体上时，晶体管就会打开。当晶体管通过负载电路调整电流时，将在整个电动机上看到电压。因此，当微控制器电路提供高逻辑时，电动机旋转4N25芯片.

当控制器输出较低时，IR二极管输入会降低。因此，IR二极管在内部停止发射辐射。由于辐射被截止，因此光晶体管被关闭，因为辐射充当基本触发器。因此，其对高电阻状态的低阻力状态。具有高电阻，完整的电源电压出现在整个晶体管上，并且负载电路中的电流流量为零。因此电动机停止旋转。因此，当微控制器输入到4N25时，电动机停止旋转。

In this circuit you can see the motor draws power from the +12V battery source and not from the controller circuit. The PHOTOTRANSISTOR side secondary circuit here is in complete isolation with the CONTROLLER-PHTODIODE primary circuit. The resistors here are placed for limiting the currents in the circuit. Make a note the resistance values changed depending on voltages.

切换时间为4N25

在正常情况下，您无需考虑4N25芯片的切换延迟。这些延迟是4N25的响应时间延迟。当切换频率超过1MHz时，只需要考虑这个时机。

4N25 Switching Schematic and Timing

When the switching frequency goes higher, we need to take into account the two parameters of 4N25 in order to avoid the errors. These two parameters are RISETIME (tr+td) and FALLTIME (ts+tf). For understanding these parameters consider the circuit above as an example.

In here I_Fis the IR DIODE forward current. And Vo is the OUTPUT taken. Here Vo goes LOW when PHOTOTRANSISTOR is ON and Vo goes HIGH when PHOTOTRANSITOR is OFF. In another sense it is the voltage across the transistor and it represents the state of the PHOTOTRANSISTOR.

如图所示，考虑IR二极管具有功率，IR二极管发射辐射，并打开光晶体管。但是，正如您在图表中看到的那样，提供逻辑输入和在输出时较低的VO之间存在时间延迟。提供响应的延迟称为Risetime（TR+TD）。4N25的上升时间（TR+TD）为2U。

Similarly consider the IR DIODE power is cutoff, the PHOTOTRANSISTOR gets turned OFF. But as you can see in the graph there is time delay between LOGIC INPUT going LOW and Vo going HIGH at the OUTPUT. This delay in providing response is called FALLTIME (ts+tf). The FALLTIME (ts+tf) of the 4N25 is 2uS.

在这里，TD和TS位于纳米秒，因此通常被忽略了。

因此time delay responses of 4N25can get stacked leading to major errors. So during high frequencies one needs to take time delays into consideration.