What is a typical diode voltage that saturates an optocoupler?

[zape]

nec 2571 is the optocoupler model

[eccerr0r]

Re: What is a typical diode voltage that saturates an optocoupler?

The datasheet says the diode voltage typical drop is 1.2V at 10mA. Maximum current is 50mA. As with all diodes, it's current that enables it, depending on the exact optocoupler you get, the saturation voltage for one unit can destroy another.

The transistor saturation voltage is 0.3V at 2mA.

[zape]

Re: What is a typical diode voltage that saturates an optocoupler?

1 have around 1v drop on the diod.
what Vce should I expect on the other end?
I suspect bad optocoupler because I have 10v Vce where I expected less than 1v

[budm]

Re: What is a typical diode voltage that saturates an optocoupler?

1) How is this opto being used/connected?
2) How much is the current on the LED side?
3) Read about how to read data sheet, look at CTR: https://cdn.badcaps-static.com/pdfs/...85b94d258d.pdf
http://electronicsbeliever.com/opto-...r-explanation/

[eccerr0r]

Re: What is a typical diode voltage that saturates an optocoupler?

1V is probably 'off' though at cusp of turning on. You need to measure current through the diode somehow to really know how far 'on' it is.

[zape]

Re: What is a typical diode voltage that saturates an optocoupler?

the diode current is 0.15 mA

[budm]

Re: What is a typical diode voltage that saturates an optocoupler?

0.15mA? That can't be right, the Ice will be low also so the Transistor will not be saturating. What is the Voltage source and how is the LED side is driven?
That is very very low, no wonder the Vf is only 1V. If you look at page 8 the Graph of Forward current VS Forward Voltage you will see what the Vf will be at around 0.15mA, about 1V @25c
What kind of circuit are we dealing with here?

[zape]

Re: What is a typical diode voltage that saturates an optocoupler?

The led is powered by 3.3v stby pulling down to ground via transistor and 470 Ohm resistor (that's how I measured the LED current). But I now checked the 3.3_stby voltage and it drops to ~2v when I try to power on the PSU!
So I think the problem is not in the optocoupler but in the Vstby source.

[budm]

Re: What is a typical diode voltage that saturates an optocoupler?

It will help if you tell us what kind of power supply you are working on and also provide good clear straight shot pictures of the top and bottom side of the board.