Little Question.

Discussion in 'General Electronics Chat' started by Voltboy, Sep 4, 2007.

  1. Voltboy

    Thread Starter Active Member

    Jan 10, 2007
    197
    0
    Hello.
    I just got anew phototransistors and some LM339 Quad Comparators.
    Before using the phototransistors and the LM339 I want to know what mean each specification (I dont wanna burn anything).
    About the phototransistor (the datasheet is http://www.fairchildsemi.com/ds/QS%2FQSE113.pdf)
    and I want to know what mean Collector-Emmiter Dark Current, Collector Emitter Breakdown and Emitter Collector Breakdown.
    I'm using the PT as a switch and it will be connected to a 3v battery, so to be sure is it ok to connect the negative terminal of the battery (cathode) to the emmiter and the positive terminal (anode) to the collector (Its and NPN).

    About the LM339 (datasheet at http://www.fairchildsemi.com/ds/LM%2FLM339.pdf )
    To be sure about the Vcc and Gnd pins, should I connect the positive terminal of battery (anode) to the Vcc and the negative terminal (cathode) to the Gnd, right?
     
  2. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    I think it would be helpful if you would draw up your proposed circuit schematic at least in the area of the phototransistor so that we can see what you have in mind.

    What you have is the IR detector. Did you plan on obtaining an IR LED to use as an IR light emitter?

    hgmjr
     
  3. Voltboy

    Thread Starter Active Member

    Jan 10, 2007
    197
    0
    I'm not sure which circuit I'll use, please recommend me which one is best, umm, i think the comparator one have the pins wrong, the 4 needs to be where the 5 is and the 5 where the 4.
    The circuit is for a Fire detecting robot, so I'm not using an IR LED, I will activate it with fire.

    In the datasheet of the PT, the Emitter-Collector Breakdown minimum voltage is 5. That means that to pass the PT to an active mode there most be 5V or more , or it means that if you put more than 5v between emitter-collector it get ruined (burned or something)??

    Yoda
     
  4. nanovate

    Distinguished Member

    May 7, 2007
    665
    1
    It means that you could ruin it if you exceed that by even a little. Treat it like a reverse breakdown of a diode... the current will increase dramatically with a small increase in voltage. ALL the specs in the "Absolute Maximum Ratings" are Do NOT exceed or the device will likely fail. Dark current is like leakage current. You'll also want to look at the saturation voltage at a given light intensity to determine you lowest VCE(on) will be when you plug it into your circuit.
     
  5. Voltboy

    Thread Starter Active Member

    Jan 10, 2007
    197
    0
    Sorry, but I got other question, there is Emitter-Collector voltage at 5v so if it exceed 5v it get ruined, but there is Collector-Emitter voltage at 30v, what the difference between both?
     
  6. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    The phototransistor in question is an NPN device. It should normally be operated with the collector more positive that the emitter. In these cases, the Voltage at the collector can be more positive than the emitter by 30 volts. The spec for the voltage emitter-to-collector defines the case when the emitter is more positive than the collector. This is not a normal operating condition but the manufacturer has graciously provided this parameter so that if the condition is likely the designer knows what to limit the voltage to in order to avoid damaging the device.

    hgmjr
     
  7. Voltboy

    Thread Starter Active Member

    Jan 10, 2007
    197
    0
    So after reviewing all what you guys told to me, this will be my final circuit, R1 is 1.5k Ohm so the circuit will have only 1mA (because the On-State collector max is 1.5mA)
    If you have anything to say about it just post it.

    Regards
    Yoda
     
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