Author Topic: LED based optoisolator that can work from 5V 150uA 300Hz signal  (Read 1282 times)

0 Members and 1 Guest are viewing this topic.

Online PsiTopic starter

  • Super Contributor
  • ***
  • Posts: 10385
  • Country: nz
LED based optoisolator that can work from 5V 150uA 300Hz signal
« on: November 22, 2020, 03:30:29 am »
I'm trying to help someone remotely and it would be much easer if I could point them to
an optoisolator that will accept a 5V, 150uA input signal directly to the LED. Data freq is 300hz.

As you would expect all the normal optos just don't get bright enough at 150uA to switch NPN hard enough to generate a good output, even with 500k pullup on a darlington opto.
Digital optos would work, but the person doesn't have easy access to 5V to power it on the input side.

With such high efficiency leds available today you would think there must be something that can handle low currents.
I've seen led's that are pretty bright on 150uA

Does such a thing exist?
« Last Edit: November 22, 2020, 03:34:08 am by Psi »
Greek letter 'Psi' (not Pounds per Square Inch)
 

Offline wraper

  • Supporter
  • ****
  • Posts: 17952
  • Country: lv
Re: LED based optoisolator that can work from 5V 150uA 300Hz signal
« Reply #1 on: November 22, 2020, 04:04:10 am »
Say SFH608-5 should work IMHO. CTR is Rated at 0.5mA, so I guess it should still work at 0.15mA with significantly degraded CTR. There is also SFH618A-5 which has the same CTR specs, however it also has a graph showing that at 0.1mA it's still functional.
« Last Edit: November 22, 2020, 04:13:44 am by wraper »
 
The following users thanked this post: WattsThat

Offline wraper

  • Supporter
  • ****
  • Posts: 17952
  • Country: lv
Re: LED based optoisolator that can work from 5V 150uA 300Hz signal
« Reply #2 on: November 22, 2020, 04:20:47 am »
LDA111 Darlington should work as well according to the graph. https://www.ixysic.com/home/pdfs.nsf/0/66F34A78811BAA3985256A2C00693C54/$file/Lda111.pdf
 

Offline Zero999

  • Super Contributor
  • ***
  • Posts: 20357
  • Country: gb
  • 0999
Re: LED based optoisolator that can work from 5V 150uA 300Hz signal
« Reply #3 on: November 22, 2020, 12:19:01 pm »
I'm trying to help someone remotely and it would be much easer if I could point them to
an optoisolator that will accept a 5V, 150uA input signal directly to the LED. Data freq is 300hz.

As you would expect all the normal optos just don't get bright enough at 150uA to switch NPN hard enough to generate a good output, even with 500k pullup on a darlington opto.
Digital optos would work, but the person doesn't have easy access to 5V to power it on the input side.

With such high efficiency leds available today you would think there must be something that can handle low currents.
I've seen led's that are pretty bright on 150uA

Does such a thing exist?
How about a low current digital isolator, such as the ISO7021?
https://www.ti.com/lit/ds/symlink/iso7021.pdf
 

Online PsiTopic starter

  • Super Contributor
  • ***
  • Posts: 10385
  • Country: nz
Re: LED based optoisolator that can work from 5V 150uA 300Hz signal
« Reply #4 on: November 25, 2020, 11:14:03 am »
How about a low current digital isolator, such as the ISO7021?
https://www.ti.com/lit/ds/symlink/iso7021.pdf

That would require a power connection on the input side, which is problematic.
Greek letter 'Psi' (not Pounds per Square Inch)
 

Online PsiTopic starter

  • Super Contributor
  • ***
  • Posts: 10385
  • Country: nz
Re: LED based optoisolator that can work from 5V 150uA 300Hz signal
« Reply #5 on: November 25, 2020, 11:21:46 am »
Greek letter 'Psi' (not Pounds per Square Inch)
 

Offline mikeselectricstuff

  • Super Contributor
  • ***
  • Posts: 14117
  • Country: gb
    • Mike's Electric Stuff
Re: LED based optoisolator that can work from 5V 150uA 300Hz signal
« Reply #6 on: November 25, 2020, 12:04:01 pm »
Another option may be to use a small pulse transformer.
On the primary side, have the input switch a transistor to short the winding.
On the secondary, feed it with a ~1-10MHz squarewave via a resistor, and measure the loading cause by the transistor being on or off.
 
Youtube channel:Taking wierd stuff apart. Very apart.
Mike's Electric Stuff: High voltage, vintage electronics etc.
Day Job: Mostly LEDs
 

Online BrianHG

  • Super Contributor
  • ***
  • Posts: 8275
  • Country: ca
    • LinkedIn
Re: LED based optoisolator that can work from 5V 150uA 300Hz signal
« Reply #7 on: November 25, 2020, 08:02:35 pm »

Digital optos would work, but the person doesn't have easy access to 5V to power it on the input side.

Does such a thing exist?
Digital isolators exist without that 5v supply input.  They are a little slower than the ones with the dedicated VCC pin, yet still at least 10x faster than the typical opto.  Need to search TI.com.  I also believe that some of the 1 channel TI parts allow the input VCC to be connected to the input data and power the 2 of them together to switch on, and 0v on both pins for off on the output side with some degradation on switch-on time.

Here is a normal 40ua input normal LED opto, but slower than the data isolator and pricey at 3$:
https://www.digikey.com/en/products/detail/broadcom-limited/ACPL-K70A-500E/11594302
 
The following users thanked this post: Psi

Online BrianHG

  • Super Contributor
  • ***
  • Posts: 8275
  • Country: ca
    • LinkedIn
Re: LED based optoisolator that can work from 5V 150uA 300Hz signal
« Reply #8 on: November 26, 2020, 03:55:19 am »
I tried googling 'led simulated optoisolator'.
Silicon Labs make some, but they require at least 1ma at the input to work, though they are fast.

Check their 'Si873x' series.  Though, I cannot tell is the 1ma requirement is the activation minimum current, or, if that figure is due to the simulated input current diode curve.  Maybe it will switch on before the current reaches 1ma.
 
The following users thanked this post: Psi

Online PsiTopic starter

  • Super Contributor
  • ***
  • Posts: 10385
  • Country: nz
Re: LED based optoisolator that can work from 5V 150uA 300Hz signal
« Reply #9 on: November 26, 2020, 08:25:09 am »
Here is a normal 40ua input normal LED opto, but slower than the data isolator and pricey at 3$:
https://www.digikey.com/en/products/detail/broadcom-limited/ACPL-K70A-500E/11594302

I think you have found the one. :)
Greek letter 'Psi' (not Pounds per Square Inch)
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf