PC847 Optocoupler Alternative

Discussion in 'General Electronics Chat' started by jonhamil, Oct 9, 2011.

  1. jonhamil

    Thread Starter New Member

    Oct 9, 2011
    Hi there - I am new to these forums, so please be gentle!

    I am refurbishing an old 8085 microcontroller based product (simple production line controller). It uses a fair few Sharp PC847 (marked as PC817) opto isolators / opto couplers. These are quad versions of the Sharp PC817 opto.

    According to the datasheet the device will degrade over time - given that this product is about 20 years old, I think it would be prudent to replace them. However RS only stock the PC817 single device, not the PC847. they do suggest an alternative: Siemens ILQ615. The comparison shows key differences are on maximum current tranfer ratio. The Sharp device goes up to 600% and the Siemens part goes to 125%. I do not properly understand CTF - can anyone advise if this is obviously ok?

    Really appreciate any helpful advice which any can offer?

    Many thanks,

  2. bertus


    Apr 5, 2008

    You could take a look at the TLP621-4.

  3. jonhamil

    Thread Starter New Member

    Oct 9, 2011
    Spot-on, thanks very much indeed :)
  4. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    CTR is Current Transfer Ratio and measures how much output current you get for a given input currrent.

    Example: If you drive a 200% CTR device with 10mA of base current you can expect 20mA out of the transistor.

    So bigger is better, and without a careful analysis don't replace a 600% device with a 125% one.