What is CTR of optocoupler at different LED currents?

[treez]

Hello,
I am wondering what is the actual spread of CTR for the PS2501-1-K-A optocoupler, when considered over all the LED currents?

Page 6 of the datasheet says its CTR = 300-600%.

Then the graph on top right of page 8 shows CTR vs diode current, but does not say which opto family each graph corresponds to. Do you know?

PS2501-1-K-A optocoupler datasheet:-
**broken link removed**

 

[ysba]

Hi,

Do you really need to know the curve for that specific group?

I see this curve as a generic one, just to show how the CTR behaves over LED currents and over each unity. Saying that your opto belong to "K" group means that its curve will be more likely "Sample A" curve. For other groups in which CTR spreads, the curve can be any. Each unit will have its own curve.

Once I worked with a common EL817 optocoupler and there was huge variations in CTR. It was an analog signal read by a MCU throught an optocoupler. In order to compensate CTR variance, I made an auto-adjust routine. In production, a known input is applied to the circuit, and the firmware looks for a gain that causes the desired reading for that input. Then this gain is stored and used during normal operation.

 

[treez]

Do you really need to know the curve for that specific group?

Yes because it is opto for use in smps feedback loop.

Saying that your opto belong to "K" group means that its curve will be more likely "Sample A" curve.

There is nothing in the datasheet to suggest that the "sample A" curve (top right graph of page 8 of datasheet) belongs to the "K" group of optocouplers. (K group is described on page 7 of datasheet)

 

[ysba]

What I meant is that "sample A" curve shows how a 400% CTR @ 5mA unit behaves over LED currents, independent of what group the optocoupler belongs. Choosing a specific group just guarantee that you can have less variation between units. I don't think different groups will have different curves, since groups are defined after manufacturing. They test every unit, and the ones that have best specs are sold with higher price.

 

[treez]

Thanks, could you give a figure for what would be the lowest CTR of the PS2501-1-K-A optocoupler when it has 2mA flowing in its opto-diode. (I am sure it is less than 300, but how much less)

(opto datasheet is in top post)

 

[treez]

The graph of CTR vs LED current for the PS2501-1-K-A optocoupler (page 8, top right, of datasheet) is for Vce=5V.
Please tell what would the CTR be if …………
1)..the Vce was >5V
2)…the Vce was <5V

Opto datasheet is in top post

 

[ysba]

Looks like group K minimum CTR function fits well in sample B curve (comparing page 6 with the chart in page 8, marked in red at image below). Follwing the curve down to 2mA, it shows a CTR about 245% (marked in blue).



- - - Updated - - -

I found this two useful texts about optocoupler:

1) http://www.renesas.eu/products/opto/technology/ctr/
2) http://www.renesas.com/products/opto/technology/usage/index.jsp

The first one is about what are the factors that affect CTR (IF, temperature and aging).

The second is about how to use an optocoupler. VCE should be choosen according to the kind of application (switching or linear). VCE doesn't affect opto CTR, is is a consequence. The CTR*IF product tells what would be the maximum optocoupler's output current, and there are curves in the datasheet that tells how VCE behaves over output currents.