Why this optical switch is so special?

Hello experts,
I found only QVE00112 ( https://www.fairchildsemi.com/ds/QV/QVE00112.pdf ) from Fairchildsemi shares the power supply between its sensor and emitter. Other similar parts from OPTEK ( **broken link removed** ) or Honeywell ( **broken link removed** )all leave the emitter power supply to user interface independent with sensor power supply. I am wondering what should be taken into accout when chosing between these two typies of optical switches. Anyone could explain it?

Thanks in advance.

All three look very, very similar and basic parameters such as supply voltage Vcc=5V, Vf≈1.7V (@20mA), tr=70ns and tprp=5µs and others, are identical ..
And in most cases you would connect the diode supply to Vcc too ..
The only differences are in package dimensions ..
Regards,
IanP

IanP said:

All three look very, very similar and basic parameters such as supply voltage Vcc=5V, Vf≈1.7V (@20mA), tr=70ns and tprp=5µs and others, are identical ..
And in most cases you would connect the diode supply to Vcc too ..
The only differences are in package dimensions ..
Regards,
IanP

Click to expand...

Hello IanP,
Thanks for your quick reply.
How about the resistor in series with the emitter diode? In QVE00112, this resistor have been already integrated in package. But in other two parts, user have to add an external resistor. It's not convenient. Am I right?

No integrated resistor may be inconvinient in some situations but signals from this optical swirch go to a PCB anyhow, and if I were designing a PCB for this circuit I would allow for a 0Ω resistor just in case you can not replace this part with identical one but you can easily obtain those without integrated resistors..
Rgards,
IanP

IanP said:

No integrated resistor may be inconvinient in some situations but signals from this optical swirch go to a PCB anyhow, and if I were designing a PCB for this circuit I would allow for a 0Ω resistor just in case you can not replace this part with identical one but you can easily obtain those without integrated resistors..
Rgards,
IanP

Click to expand...

Indeed, I have used QVE00112. If I must replace it, I must add two lines plusing an external resistor. Any tradeoff to make such modification minimum?

Probably the easiest way of making such a modification is to use a surface mount resistor in, say, 0805 package.
Cut the track on the PCB and make ≈2mm gap. Clean copper on both sides of the track and gently soder this 0805 resistr at both sides .. and its done ..
If you do it tidely it may not look at all like a modofication ..
Regards,
IanP