MCP23017无法正确点亮LED

你是如何测量电流的？你的仪表在测量时的负载电压是多少？我将测量电阻两端的电压降，使用欧姆定律。在VID 4.5V的IO 8MA上，GPIO引脚在VOL 0.6V处标示，所以不要期望驱动20毫安LED而不可能发生奇怪的事情。您确实先读过数据表，不是吗？



      以下为原文

    How are you measuring the current? Whats the burden voltage of your meter when measuring?
 
I would measure the voltage drop across the resistor and use ohms law.
 
The GPIO pins are spec'ed at Vol 0.6V at Io 8mA with Vdd 4.5V so don't expect to drive a 20 mA LED without strange things possibly happening.
 
You did read the data sheet first, didn't you?

事实上，输出的额定值为3Ma（输出高压D090规格），在数据表中没有VI曲线，但所有部件都有VI曲线。端口的输出电阻决定输出电压与输出电流之间的关系。在这种情况下，它可以是0.7V/3Ma～200欧姆最大。你的测量显示（3.3-2.3）/10A＝100欧姆。这个输出电阻随电压和温度而变化，并且不是真正的线性，所以最好不要依赖它。正如Coprand所说的，你没有看到23017数据表来确定它的能力。



      以下为原文

    Actually the outputs are rated for 3mA (Output high-voltage D090 spec)
 
There's no VI curve in the datasheet, but all parts have a VI curve. The output resistance of the port determines the relationship between output voltage and output current. In this case it may be 0.7V/3mA ~ 200 ohms max. Your measurements show (3.3-2.3)/10A = 100 ohms.
 
This output resistance varies with voltage and temperature and is not really linear, so best not to rely on it for things like this. As crosland said, it doesn't appear you read the 23017 datasheet to determine it's capability.

是的，当我在I/O和Gnd之间阅读时，OP确实更有意义。



      以下为原文

    Yeah, the OP does make more sense when read as LED between I/O and Gnd.

谢谢你的回复。用数字电表，如果我把LED连接到带有电阻的3.3电压调节器上，它就显示出正确的20mA。你还可以通过LED的亮度来判断它是不正确的。在5伏特的时候，Vdd试过了，但是仍然不能得到20mA和足够亮的光。是的，我是H。AVE读取数据表，引用“输出电流源于任何输出Pi25Ma”，那么你是如何做到这一点的？事实上，输出额定为3mA（输出高压D090规格）“这不是说“-3毫安”和“- 0.7伏”（20 - 3和4.5 - 0.7）在4.5伏特，而不是输出额定在那？如果你不能用这个来驱动大于3Ma的LED，那么你建议哪个端口扩展器？谢谢戴维



      以下为原文

    Thanks for the replies.
Using a digital meter, if I connect led to the 3.3 voltage regulator with resistance it shows the correct 20ma.
You can also tell by the brightness of the led that it is not correct.
Have tried it with Vdd at 5 volts but still unable to get 20ma and a bright enough light.
Yes I have read the Data sheet, which quotes "output current sourced by any output pin 25ma", so how do you achieve that?
"Actually the outputs are rated for 3mA (Output high-voltage D090 spec)"
Does that not say "-3.0 ma" and "-0.7 volts" (giving 20 - 3 and 4.5 - 0.7) at 4.5 volts not the output is rated at that?
 
If you cannot use this to drive LEDs greater than 3ma then which port expander device do you suggest?
 
Thanks David
  
  
 

再看一看，它是在绝对最大额定值下。这不是说“我可以提供20mA”。它说：“确保你永远不会从PIN中抽取超过20Ma，或者芯片会被损坏。”哦，地面。你想开什么样的LED？现代LED在5Ma下非常明亮。正如其他人所暗示的，大多数芯片可以吸收比它们所能提供的电流更多的电流。因此，将阳极连接到电源更为常见，并且驱动引脚低到发光二极管。



      以下为原文

   
Have another look WHERE you are reading that.
It is under the ABSOLUTE MAXIMUM RATINGS section.
That is not saying "I can supply 20mA".
It is saying "It is your job to ensure that you never draw more than 20mA from the pin, or the chip will be damaged."
e.g. that can happen if you short a high output to ground.
 
What sort of LEDs are you trying to drive? Modern LEDs are pretty bright at 5mA.
 
As others have hinted, most chips can sink more current than they can source.
For that reason it is more common to connect the anode to your supply, and drive the pin low to light an LED.
 

在任何长度的时间内，你绝对不会操作任何设备，因为电流从芯片中流出，所以电流是负的。如果你的LED连接在输出引脚（阳极）和接地（阴极）之间，那么额定值是3Ma。如果你把LED连接在Vdd（阳极）和引脚（阴极）之间，那么额定值是8Ma。这一次的电流是积极的，因为它是流入芯片。你需要学习如何更全面地解释数据表。谁说，任何端口扩展器的目的是驱动LED在20毫安。有16个引脚，可能会有320毫安流入或流出芯片。为什么你固定在20毫安的LED？你确定你没有犯同样的错误，从数据表中选择最大持续电流（这是你所起诉的）。大多数现代高亮度LED在足够低的电流下亮度足够高。您可能需要专用LED驱动器或某种类型的缓冲器。



      以下为原文

   
You never operate any device at it absolute maximum ratings for any length of time.
 

The current is negative because it's flowing out of the chip. If your LED is connected between the output pin (anode) and ground (cathode) then the rating is 3mA.
 
If you connect the LED between Vdd (anode) and the pin (cathode) then the rating is 8mA. This time the current quoted is positive as it is flowing into the chip.
 
You need to learn how to interpret data sheets more thoroughly.
 

Who says any port expander is designed to drive LEDs at 20 mA. With 16 pins that would potentially be 320 mA flowing into or out of the chip.
 
Why are you fixated on 20 mA for the LED? Are you sure you are not making the same mistake and choosing the maximum continuous current from the data sheet (which LED are you suing). Most modern high brightness LEDs are more than bright enough on much lower currents.
 
You may need a dedicated LED driver or a buffer of some sort.