Connect with us

Phototransistor minimum Vcc

Discussion in 'General Electronics Discussion' started by G1234, Nov 29, 2017.

Scroll to continue with content
  1. G1234


    Nov 29, 2017
    Hi, I am a software maker dipping my hands in HW.
    I want to use a phototransistor in a standard resistor/phototransistor circuit on a 1.8v Arduino board.
    What is the minimal Vcc I can use with components like below?
    Will it work with 1.8v ?

    Attached Files:

  2. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    The parameter too look for is Collector-Emitter saturation voltage. It is ~0.4 for all these couplers. Therefore your output will go up to 1.8 V -0.4 V = 1.4 V for a logic high.
    An 1.8 V arduino's logic threshold should be at ~ 0.9 V (1/2 * 1.8 V), therefore 1.4 V should be detected as logic high without problems.

    Note that the above calculation is valid for saturation of the phototransistor which means the transistor is illuminated to dribe a higher current than is provided by the resistor Re. Re limits the current to Ie = 1.4 V / Re. A sensible value for Re is e.g. 10 kΩ for a current of 0.14 mA.
    G1234 likes this.
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day