Hello Ratch and Winterstone,
Ratch:
I agree with your last statement, that we dont want to reject the model when some operating condition is marginal to the method. However i was under the impression that it worked well and accurately for almost any operating point except maybe saturation. The posts on that other site didnt seem to suggest that there was a limit to the operating point as he even mentioned scaling re with collector current starting at 1ma. I would then be led to believe that if we had anything over 1ma it should work.
Also, the spice simulation seems to work just fine with 0.65 volts on the base, and also i have done a few designs where the base emitter voltage was assumed to be 0.65.
So then what would you say is the appropriate operating conditions?
Winterstone:
Well see we were calling it the "voltage control method" just to have something to call this method. It's not that we really wish to control the current, just to calculate a single operating point. The post linked to in Ratch's post clearly indicates we can do this because it even delves into multiple stage DC coupled amplifiers. Without being able to calculate the operating point it would be worthless for that.
Also, when a transistor part number is given in a schematic it does not have the "Is" value written next to it. It also does not have the Beta value written next to it. All it has is the part number written next to it or in a parts list. So when we see the circuit we see "2N2222A" but that's it. No Is, no Beta, but we still have to analyze it. So my point was if we have a hard time finding Is we have a hard time calculating the collector current using the exponential formula. The post linked to stated that the Beta is all over the place. So we dont know Beta exactly, but we dont seem to know Is exactly either.
Ratch:
I agree with your last statement, that we dont want to reject the model when some operating condition is marginal to the method. However i was under the impression that it worked well and accurately for almost any operating point except maybe saturation. The posts on that other site didnt seem to suggest that there was a limit to the operating point as he even mentioned scaling re with collector current starting at 1ma. I would then be led to believe that if we had anything over 1ma it should work.
Also, the spice simulation seems to work just fine with 0.65 volts on the base, and also i have done a few designs where the base emitter voltage was assumed to be 0.65.
So then what would you say is the appropriate operating conditions?
Winterstone:
Well see we were calling it the "voltage control method" just to have something to call this method. It's not that we really wish to control the current, just to calculate a single operating point. The post linked to in Ratch's post clearly indicates we can do this because it even delves into multiple stage DC coupled amplifiers. Without being able to calculate the operating point it would be worthless for that.
Also, when a transistor part number is given in a schematic it does not have the "Is" value written next to it. It also does not have the Beta value written next to it. All it has is the part number written next to it or in a parts list. So when we see the circuit we see "2N2222A" but that's it. No Is, no Beta, but we still have to analyze it. So my point was if we have a hard time finding Is we have a hard time calculating the collector current using the exponential formula. The post linked to stated that the Beta is all over the place. So we dont know Beta exactly, but we dont seem to know Is exactly either.