You may recognize this.
There is an excellent online Falstad simulator link below which follows this aequation above which does not model saturation. So I added diodes to resemble the effects of saturation. Other simulators like pspice, LTspice, and Micro-Cap x64 are excellent at using real models but poor at slow motion interactive real simulation. (unfortunately it is not like a real scope that has signal trigger Sync and more like a fast strip chart.
Imagine the NPN is two PN:NP junctions. When Vce = 0 collector PN junction is conducting and draining the current gain to nothing. It may start draining hFE at Vce=2V if you are near maximum current. But they only specify saturated in all datasheets as Vce(sat) = xxx mV.
You must memorize the diode exponential law of current vs voltage. look it up. This applies to transistors for Ic vs Vbe which is exponential. But when we add an emitter resistor we get Vbe+Ve which then becomes more linear because of this effective hFE property. There is also some internal r
E which I show by lower case r. In fact, every diode or PN junction has series Rs and this matches the Vce(Sat)/Ic=Rce for any small or power transistor. The more power a bigger package can dissipate, the lower Rce will be.
Now to understand saturation, imagine the NPN transistor has two PN diodes across C-B and B-E that reduce the current gain hFE when V(BC) goes from -ve to + ve at Vce=Vbe now the current gain reduces rapidly as the C-B junction is forward biased. The collector in linear mode acts as a current source (more or less) but when Vce drops below 1V or so it it starts to act like a voltage source in the saturated state, so we call this now an inverting switch. Now none of this non-ideal saturation is shown in the Schockley Equation above.
If you can read a scope, I have put a power transistor with a triangular 0 to 5V linear sweep up and down from a 50 ohm signal generator so you can see the exponential base and collector current. I added the 2 diodes which sort of emulates what is inside the non-ideal (real) transistor.
You can learn a hundred things from these plots. Each plot shows the peak max min and avg. for each trace and the node is labelled like Vbe, Vce, Ib, Ic, Pd=Vce*Ic
See how many you can find in the relationships by usingyour mouse over Rc and thumbwheel to raise it to> 10k then drop it down to 100 ohms then towards 0.
Remember that you do not add these diodes, I only added them to simulate saturation. My Falstad SIM uses the Schockley equation with fixed hFE (you can change it) and does not model saturation which exists in all transistors.
This might be a 2N3055 but wasn't modelled exactly here for demo purposes.
Summary
he behavior of a bipolar junction transistor (BJT), possibly an NPN transistor like the 2N3055, and discussing the effects of saturation on its characteristics.
Let me break down the key points:
- Simplified Model and Saturation:
- The model presented is simplified and does not explicitly model saturation.
- Saturation is briefly mentioned, and it is noted that datasheets typically specify the saturation voltage (Vce(sat)).
- Saturation is characterized by the collector-emitter voltage (Vce) dropping below a certain threshold (around 1V).
- Diode Exponential Law:
- The diode exponential law is mentioned, and it's noted that this law applies to transistors when considering the collector current (Ic) versus base-emitter voltage (Vbe).
- Adding an emitter resistor (Re) can make the relationship more linear due to the effective hFE property.
- Emitter Resistance (re):
- Internal emitter resistance (rere) is introduced, and it's noted that the addition of an emitter resistor (Re) makes the relationship more linear.
- Collector-Emitter Resistance (Rce):
- The collector-emitter resistance (Rce) is discussed, and it's mentioned that every diode or PN junction has series resistance (Rs).
- Vce(sat)/Ic=Rce is highlighted, and it's noted that the lower Rce is, the more power a transistor can dissipate.
- Behavior in Saturation:
- In saturation, the transistor is described as acting like an inverting switch, and the current gain (hFE) reduces rapidly.
- Simulation with Falstad:
- A simulation using Falstad is mentioned, where a power transistor with diodes emulating non-ideal behavior is displayed.
- Plots of various parameters like Vbe, Vce, Ib, Ic, and Pd are simulated.
- Experimentation with Parameters:
- Experimentation is encouraged by adjusting parameters such as Rc to observe the effects on the relationships.
- Scope Readings:
- Learning to read a scope is critical, and various relationships in the plots are highlighted, including peak, max, min, and average values for different traces.
It seems like you want to do hands-on, and simulation is a practical approach to understanding the behavior of transistors, especially in saturation, and how certain parameters and resistances influence their characteristics. This kind of experimentation and observation is crucial for understanding real-world transistor behavior beyond theoretical models