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#1
05-15-2014, 09:50 PM
 OSOO Junior Member Join Date: Feb 2014 Posts: 34

Hi,
I have AD8561 IC ,and I don't know how to use it in my comparator circuit ,why it has 2 output pins ? and what is the function of the latch pin ? do I have to use it in my circuit ?

for example this circuit:

#2
05-15-2014, 10:41 PM
 crutschow Senior Member Join Date: Mar 2008 Location: L.A. USA Posts: 6,323 Blog Entries: 1

The circuit has differential outputs which are used where a high speed differential signal is needed. You can use just one output, if desired.

The latch is also an optional input, used to latch the output in its last state, if desired.

But I wouldn't think you need such a high speed comparator for that optical application. Note that you need a pull-down resistor for the output of detector to ground to rapidly pull the voltage to 0V when the detector turns off.
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Zapper
Curmudgeon Elektroniker
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#3
05-15-2014, 11:07 PM
 OSOO Junior Member Join Date: Feb 2014 Posts: 34

So why my circuit is not working , I connected pin 1 to 6v power supply and pin4 and pin6 to ground ,and V+ the reference voltage from the voltage divider which ~1v ,(I used a 46k resistor rather than 100k in the circuit schematic above ) ,the V- is connected to the output of the phototransistor though a potentiometer which is 3v ,when the light is interrupted this voltage become ~0v ,but the output voltage still high even if the reference voltage is greater the V- voltage ,why !?
#4
05-16-2014, 03:51 AM
 crutschow Senior Member Join Date: Mar 2008 Location: L.A. USA Posts: 6,323 Blog Entries: 1

Do you have a resistor from the photo-transistor output to ground as I mentioned in my previous post. Otherwise the leakage current at that node may maintain the signal voltage high or, at best, it will very slowing leak to zero. If you measure that voltage, the input resistance of the voltmeter will pull the node low and you will measure 0V.

Edit: I don't see a pot in your schematic. Please post an updated schematic.
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Zapper
Curmudgeon Elektroniker
#5
05-17-2014, 12:28 AM
 OSOO Junior Member Join Date: Feb 2014 Posts: 34

This is the updated schematic:

https://www.dropbox.com/s/2p4o2woa11...517_032540.jpg
#6
05-17-2014, 12:50 AM
 ronv Senior Member Join Date: Nov 2008 Location: Tucson AZ. Posts: 982

You may need to ground the latch pin. The chip also has 2 grounds - in your case V- and ground. Add some resistance in series with the LED or it may burn your IC or the LED.
 The Following User Says Thank You to ronv For This Useful Post: OSOO (05-18-2014)
#7
05-18-2014, 08:51 PM
 OSOO Junior Member Join Date: Feb 2014 Posts: 34

Thank you rony
the problem is solved

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