Need opto coupler alternative

[FriedMule]

Hi, I am trying to find an alternative to the H11F1M opto coupler that also act as an variable resistor. What I am seeking is something like a combined Voltage / Current variable resistor combined with an digital isolator, but I plan on letting analog signal go trough.

EDIT: forgot, the data does not have to be the same, I am just looking for the same functionality, what are that type of chip called?

https://avtronic.eu/medias/h11f1m/h11f1m.pdf

 

[abraxalito]

You could look into a slightly different implementation of the same function. The Silonex isolators here are based on a photocell rather than a phototransistor : Special Purpose | Isolators | DigiKey

 

[FriedMule]

You could look into a slightly different implementation of the same function. The Silonex isolators here are based on a photocell rather than a phototransistor : Special Purpose | Isolators | DigiKey

Haven heard of that, but I am trying to avoid diodes, since they degrade over shorter time then many other chips.

 

[abraxalito]

They all use LEDs which are diodes. Yes they do degrade over time, its a well known drawback of using optocouplers. As far as I'm aware the only differences are in the receiving element - phototransistor, photodiode or photocell.

 

[FriedMule]

They all use LEDs which are diodes. Yes they do degrade over time, its a well known drawback of using optocouplers. As far as I'm aware the only differences are in the receiving element - phototransistor, photodiode or photocell.

There do exists digital isolators, that work on a different princip, but I do not understand if they do only work with digital signal or if they can be adjusted to different risistances?

 

[abraxalito]

Yes - the digital isolators I've come across use capacitive coupling or magneto-resistive elements. I haven't seen any analog versions using that tech.

 

[FriedMule]

Yes - the digital isolators I've come across use capacitive coupling or magneto-resistive elements. I haven't seen any analog versions using that tech.

Okay, but there have to be an alternative to Opto's?

 

[FriedMule]

I am wondering if a digital pot do isolate the controlling voltage from the signal, going trough the resistive part of the pot? Or in other word are they totally isolated from each other?

 

[jan.didden]

Some digital pots have separate digital control ground and analog pot ground. Those would have total isolation between control and pot.
But I think the max difference between the two ground and supply voltage is probably very limited.

Why is the possible ageing of photocell emitter diode a problem for you? If you use something like an IL300 with one photodiode in a feedback loop (see app note section of the data sheet) you have both isolation and almost perfect linear transfer.

Jan

 

[FriedMule]

Some digital pots have separate digital control ground and analog pot ground. Those would have total isolation between control and pot.
But I think the max difference between the two ground and supply voltage is probably very limited.

Why is the possible ageing of photocell emitter diode a problem for you? If you use something like an IL300 with one photodiode in a feedback loop (see app note section of the data sheet) you have both isolation and almost perfect linear transfer.

Jan

Degradation of the diode is maybe not a problem, but the circuit shall be on 24/7 for as long the elderly woman I know is living. It's a bipper that shall remind her to lock the door, check the stove while cooking and so on.
I think that the maximum voltage will be about 2V and the controlling voltage, do I 100% decide, dependent on what an e-pot demands.

 

[Mark Tillotson]

Digipots are not galvanically isolated at all, they are just CMOS transmission gates and on-die resistor networks. Some have internal level-shifting circuitry so the digital control signals can be anywhere within the analog supply range, but they are not isolated.


Its vaguely possible someone's grafted on an optocoupler to one, but basically you'd use a separate digital isolator with a digipot if you needed isolation, and that rules out chips with I2C bus (which has bidirectional signals).

 

[jan.didden]

Well, we talk about degradation of the diode in terms of slight change of voltage or emissivity in the ppm range at a particular current maybe, but that will not by a long shot impair functionality, if that is your worry.
There will be a lot more parts in your circuitry that change a lot more over time.

Jan

 

[FriedMule]

I know this is outside my original question, but after reading all your great comments, I think I'll stick to Opto's and that do make me wonder about the non linearity of most Opto's. The IL300 looks like it can somewhat compensate for that but how do I know if an Opto is with variable resistance and if it is linear, without having to look trough every schematic out there?

 

[jan.didden]

Not wanting to second guess you, but why do you need a linear, stable opto for something that needs to beep once in a while ??

Jan

 

[FriedMule]

Not wanting to second guess you, but why do you need a linear, stable opto for something that needs to beep once in a while ??

Jan

I don't but was just wondering about linearity. I have to say that i am a totally noob, so I grab any chance I've got to learn more and therefore my "outside subject" question


I am also wondering on how one would manage to adjust power to the opto. One demands max 1.4V 50uA to min 1.4V 0.2uA. I can't see how you could adjust that via i.e. a logarithmic pot to adjust the volume?

 

[jan.didden]

I don't but was just wondering about linearity. I have to say that i am a totally noob, so I grab any chance I've got to learn more and therefore my "outside subject" question


I am also wondering on how one would manage to adjust power to the opto. One demands max 1.4V 50uA to min 1.4V 0.2uA. I can't see how you could adjust that via i.e. a logarithmic pot to adjust the volume?

You want to drive such a LED with a variable current. Optical output is, to a first degree, related to current through the LED, not the voltage across it.

The nice thing about the IL300 is that it has 2 matched receiver diodes in the package. So you use one of them in the driving circuit to linearize the input/output transfer, and then the output of the other diode, being isolated, is also the same and linear as it is matched to the diode at the driving circuit. There's some nice apps in the data sheet.
You can use that to isolate analog audio to better than -80dB THD.

Jan

 

[FriedMule]

You want to drive such a LED with a variable current. Optical output is, to a first degree, related to current through the LED, not the voltage across it.

The nice thing about the IL300 is that it has 2 matched receiver diodes in the package. So you use one of them in the driving circuit to linearize the input/output transfer, and then the output of the other diode, being isolated, is also the same and linear as it is matched to the diode at the driving circuit. There's some nice apps in the data sheet.
You can use that to isolate analog audio to better than -80dB THD.

Jan

Thanks sounds great!
Do the IL300 also have variable resistance? I have been told that most of the opto couplers works as a relay, either on or off, no in between.
Sorry my noob question here but how do I (what to search and learn about) do to make a pot, adjust current in uA ranges?

 

[jan.didden]

You really should read its data sheet, it has a very good explanation (section Theory of Operation or How it Works) and several app notes. Much better than me reciting it here ;-)

Jan

 

[FriedMule]

You really should read its data sheet, it has a very good explanation (section Theory of Operation or How it Works) and several app notes. Much better than me reciting it here ;-)

Jan

I have tried to read several datasheet and compared many, that's why I did ask about variable resistance, to me do wary few datasheet show any possibility to be variable. The PC619 and H11F1M chip shows it, but other do just show max current and do only show on resistance as one number.
But I'll try to read on the IL300 again


EDIT: I try to read this datasheet: https://www.vishay.com/docs/83622/il300.pdf