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  1. R

    Transistors / hfe / Active region conflicts

    You can never control Vbe with Ib. You can only fool yourself into thinking you do. Connect a voltage source across a one ohm resistor. Set the voltage to one volt. You should be assured that the voltage source is controlling the current present in the resistor. Now insert an ammeter in...
  2. R

    Transistors / hfe / Active region conflicts

    Yes, feedback and other design techniques are used in design to mitigate the exponential response of Ic to Vbe. For that reason, it could be said in a contrarian manner that Vbe is considered of primary importance. Otherwise, so much design effort would not be lavished on it. However, that is...
  3. R

    Transistors / hfe / Active region conflicts

    Most of the current present in the emitter-base junction (Ie) passes on thru the base collector junction and into the collector circuit. Only a small fraction of this current passes out of the base terminal, and is considered waste current. Are you saying that this waste current is determining...
  4. R

    Transistors / hfe / Active region conflicts

    No, the physics of the BJT cannot explain how base charge flow controls Vbe. A base current source contains the voltage that will control the BJT. If you set the base current, then Vbe will conform to that current. The base current is set by external means, whereas the Vbe is applied to the...
  5. R

    Relationship of frequency and capacitance.

    Yes, a large capacitance value is need to store enough energy to supply the load for the period of time when the input sinusoidal goes below the desired DC output. The AC is turned into pulsating nonalternating current by a rectifier. Ratch
  6. R

    Relationship of frequency and capacitance.

    OK, attached are a couple of pages from the Schaum's Outline Series, Electric Circuits. The circuit problem 8.12 is rather useless because there is no selectivity and its impedance is somewhat low, but it delivers on being resonant at all frequencies. Ratch
  7. R

    Relationship of frequency and capacitance.

    Yes, you are correct. It is never a good idea to answer a post late at night. For a series resonant circuit, there is only one frequency. For a parallel resonant circuit, some folks and textbooks like to define 3 resonant frequencies. One is where the L and C reactance are equal, a second...
  8. R

    Relationship of frequency and capacitance.

    Not quite. A reactance opposes a current by inducing a back voltage. It does not produce heat because it stores energy in an electric or magnetic field, and gives it back to the circuit later. It is also frequency dependent. A resistor opposes a current by reducing the energy density of the...
  9. R

    Relationship of frequency and capacitance.

    Its ability to store energy. It works like this. Suppose you apply a relatively low frequency signal to a capacitor. The slow frequency assures that there is time to pump a lot of charge onto one plate and delete it from the opposite plate as the voltage rises. But if there is a point where...
  10. R

    Relationship of frequency and capacitance.

    No, it does not make sense and yes, you are misunderstanding. Never forget that a capacitor is a energy storage device. It does this by separating charge quantities. When a capacitor is energized by an applied voltage, electrons accumulate on one plate and deplete on the opposite plate. This...
  11. R

    Transistors / hfe / Active region conflicts

    Yes, in BJT design, we try to minimize the nonlinear response of Vbe through judicious use of external components. I was not referring to design, but instead what controls the BJT internally as a device alone. By the way, drift current if very minimal in a forward biased diode as compared to...
  12. R

    Transistors / hfe / Active region conflicts

    Yes, but those terminals are directly bonded to the internal semiconductor slabs. That is as close to the internals of a BJT as an applied voltage can get. Besides, BJT physics says that Ic and Ib are determined by Vbe. No, base current is waste current that cannot be eliminated. Base...
  13. R

    Transistors / hfe / Active region conflicts

    You are neglecting to mention something. Vbe is the internal voltage that defines and controls what Ib and Ic will be, because voltage controls the current according BJT physics. A external current source by definition cannot be considered to be the internal control of a device. That would...
  14. R

    Transistors / hfe / Active region conflicts

    You are wrong about that, and here is why. By your reasoning, the base driven by a current source controls the collector of a BJT through Vbe. But, Vbe acts directly on the internals of the BJT, specifically the depletion region to control the diffusion current. The forced base current from a...
  15. R

    Transistors / hfe / Active region conflicts

    Before you can make that statement, you are obligated to show where my discourse in post #30 is in error. I have tried to explain to you how the physics of the BJT show the voltage Vbe lowers the barrier or back-voltage of the depletion region, thereby permitting more diffusion charge carriers...
  16. R

    Voltage drop from supply

    Charge flows, current does not. Current exists or is present. "Current flow" literally means "charge flow flow". That is redundant and ridiculous. The decrease in voltage is probably due to your power supply unable to sustain that voltage at the increased current the motor wants. You did...
  17. R

    Transistors / hfe / Active region conflicts

    Vbe does control the base current according to the physics of the transistor, so it is relevant. Just because its particular value can be ignored when it is forced to comply with a desired current does not mean it is not controlling the base current along with the collector current. The base...
  18. R

    Transistors / hfe / Active region conflicts

    I don't believe in magic. The current is supplied by the current source. Even so, transistors work independently of the circuit. Their contribution along with the rest of the circuit make the final output response. Yes, desired response requires external components. What better way to...
  19. R

    Transistors / hfe / Active region conflicts

    I aver that at the same temperature, the base current, Vbe, and collector current of a BJT will be the same in a circuit as it would be if the transistor were isolated from the circuit and run only on voltage sources. Ratch
  20. R

    Transistors / hfe / Active region conflicts

    Not so, if the device were connect to nothing, then no input current would be present. Damnable Physics! One can do many things which are forbidden by common sense, but that leads to perdition. It is the current source that is supplying the Vbe voltage. It is the Vbe that is controlling the...
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