why totem pole outputs cannot be connected together

Starting with the two equations for the circuit which includes the two resistors, the logic gate output Vout, and the transistor base emitter voltages: VbeH=(Vcc*R2)/(R2+R1)-(VoutH*R2)/(R2+R1) VbeL=(Vcc*R2)/(R2+R1)-(VoutL*R2)/(R2+R1) where VbeH is Vbe when the logic gate output is high at the voltage VoutH, and where VbeL is the 'target' Vbe when the logic gate output is low at the voltage VoutL. The main idea is that the transistor has to turn fully on and fully off with the respective gate output voltage limitations. Hello again, Here are some calculations that illustrate the problems with the circuit and how they can be corrected. Maybe swap but also change the 4.7k to a smaller value, like 3.9k or maybe 3.3k. Swapping values may just barely allow the transistor to turn on, but changing the values a bit could be better, and of course adding that diode would ensure proper operation with the right resistor values. It may be necessary to place a silicon diode in series with the emitter of that transistor, and then the output would look more like a logic high anyway once we get the resistor values right. If it is around 1ma then we probably dont have to worry too much, but if it has to power a small LED then we'd have to think a little more. If you can find that information that would help. Unfortunately we dont know the load at the collector of the transistor so it's a bit impossible to specify any exact values for the two resistors that would ensure both proper turn on and proper turn off. What you could do is assume the output of the gate goes from 0.5v for a low to 3.5v for a high and go from there. The other thing though is that you have to ensure that the transistor can turn on fully too, and if you swap the two resistors the only resistor that can turn it on would be the 4.7k so that would be a reduction in base emitter current of about 1/5 what it was, roughly, plus the 1k would pull it up a lot so there's a chance that it may not turn on at all which is also not good. Any higher and the transistor will begin to conduct.

If the supply is 5v that would mean the base should be about 4.7 volts as a minimum i would say. To turn that transistor completely off, the base voltage has to be close the +Vcc. The combination of 4.7 and 1k like that only raises the output by about 0.26 volts, which does not seem like enough. Hi, That's the same impression i get when i consider the max output of the LS02 gate for a logic high.

Why totem pole outputs cannot be connected together