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PNP or NPN Transistors

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Nigel Goodwin said:
I'm getting that 'going down to open a bottle of cider feeling' :p
I must start earlier than you do (on the clock). I'll probably have mine in about 4 hours.:D
 
dknguyen said:
Unstable. Oscillations.
As a comparator with both inputs tied to the same voltage, right? That is the very reason God gave us hysteresis.:D
 
Roff said:
As a comparator with both inputs tied to the same voltage, right? That is the very reason God gave us hysteresis.:D

Still doesn't explain how the op-amp/comparator knows whether or not it's working off of a dual-supply or single-supply with only two power pins!

I guess you could use a zener diode regulating from the high-side to get a comparator to output a low that is always a certain voltage below the high-side power rail. But I don't think that is how it is done.
 
dknguyen said:
Still doesn't explain how the op-amp/comparator knows whether or not it's working off of a dual-supply or single-supply with only two power pins!

I guess you could use a zener diode regulating from the high-side to get a comparator to output a low that is always a certain voltage below the high-side power rail. But I don't think that is how it is done.
MAX912 has +V, -V, and GND pins.
Any op amp with only 2 power pins can work with either dual or single supplies. You just have to obey the common mode input voltage range. The output will limit at the rail voltages, minus whatever internal saturation it incurs. You must have seen this sticky, right?
 
dknguyen said:
Still doesn't explain how the op-amp/comparator knows whether or not it's working off of a dual-supply or single-supply with only two power pins!

The output of a (single-ended) operational amplifier is referred to the reference voltage of the circuit, that is the common ground point if you use a dual supply.
 
dknguyen said:
Still doesn't explain how the op-amp/comparator knows whether or not it's working off of a dual-supply or single-supply with only two power pins!

I guess you could use a zener diode regulating from the high-side to get a comparator to output a low that is always a certain voltage below the high-side power rail. But I don't think that is how it is done.


too many transitors in the schematic for me to follow, but mabey you can work it out https://www.electro-tech-online.com/custompdfs/2008/01/LM741.pdf

page 4

only thing i can see is a potential divider just at the output (i think thats what it is)
 
That's an op amp isn't it? Don't dual-supply op-amps wired as comparators saturate at the negative rails for a LO output and at the positive rails for a HI output? The MAX912 (comparator) always outputs a ~1V LO and a 3V high regardless of the bipolar or unipolar operation.
 
dknguyen said:
Don't dual-supply op-amps wired as comparators saturate at the negative rails for a LO output and at the positive rails for a HI output?
Yes, but some comparators (like the LM311) that can operate from a dual supply have a GND pin and their output stage, basically an open collector transistor, can be connected to 0 V. So, the low level will be about 0 V.
Hope this makes sense.
 
I know. But the op-amps thta have me mystified are the ones that only have two power pins (not 3, it's fairly obvious how those work). The MAX913 for example.
 
Oh, it does! Funny I never noticed it. I've been working with it on my schematics for the past week. I'm pretty sure they're wired up though.
 
eng1 said:
I'm looking at the datasheet from maxim-ic.com. That comparator does have a GND pin.
Dk, I just told you the same thing in my last post. Pay attention!:D
 
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