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  #1  
Old 05-15-2014, 09:50 PM
OSOO OSOO is offline
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Default Using AD8561

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:

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Old 05-15-2014, 10:41 PM
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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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Old 05-15-2014, 11:07 PM
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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 !?
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Old 05-16-2014, 03:51 AM
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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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Old 05-17-2014, 12:28 AM
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This is the updated schematic:


https://www.dropbox.com/s/2p4o2woa11...517_032540.jpg
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Old 05-17-2014, 12:50 AM
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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.
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Old 05-18-2014, 08:51 PM
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Thank you rony
the problem is solved
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