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  1. R

    [HELP] - Basic AND gate problem

    I was concerned only with the logic, not with the hardware. Ratch
  2. R

    Capacitors

    The difference is that in a resistor, the charge flows continuously at a constant voltage. In a capacitor, the charge flow will decrease until it stops when the capacitor is energized to the applied voltage. The definition of charge flow through a component needs to be more defined than just...
  3. R

    Capacitors

    davenn, "NOTE the overall charge of the capacitor remains zero/balanced The number of negative charges on one plate will be balanced by an equal number of positive charges on the other plate The energy is stored in the electric field that is formed between the plates" Correct, I have said many...
  4. R

    [HELP] - Basic AND gate problem

    The current limiting resistor is not part of the logic circuit. Do what you have to do to keep the LEDs safe from the applied voltage. Ratch
  5. R

    Capacitors

    Laplace, "So we can see electrons going into one wire of the capacitor, and we see electrons coming out of the other wire of the capacitor, but no current exists through the capacitor?" Yes, that is correct. "Is that because it is not the same electrons going in as are coming out?" No, while...
  6. R

    [HELP] - Basic AND gate problem

    Wouldn't putting 2 switches in series make a 2 input AND gate? Four switches in series make a 4 input AND gate. Ratch
  7. R

    Capacitors

    Please understand that a capacitor does not let current exist through it. If it did, it would be considered "leaky" and defective. A perfect dielectric has a infinite resistance. So how does an AC ammeter register alternating current when an alternating voltage is applied to a capacitor? The...
  8. R

    Assistance with Transistor Theory

    It doesn't matter. A good current source contains a resistor external to the BJT, and the current source is not open. Great applications can be made with current sources and a BJT, but the BJT is still controlled by Vbe. Ratch
  9. R

    Assistance with Transistor Theory

    Ian Getreu, I think we both agree on how the BJT operates. "I do disagree with your comment about the models. The best models, such as the Gummel-Poon, are based on the physics of the device so they do explain how the BJT works." I am not convinced. Looking over the Gummel-Poon (G-P) model...
  10. R

    Assistance with Transistor Theory

    An ideal current source has an infinite voltage to propel the charge through the infinite resistance. By the definition, the ideal current source dispenses a defined constant current, therefore the circuit cannot be considered open. The Vbe of the BJT will be a particular value with a constant...
  11. R

    Assistance with Transistor Theory

    Ian Getreu, "I would like to address the question of whether a BJT should be considered as current driven or voltage driven. To a certain extent, the answer is 'both" or "either"." I believe you are answering the question, "What is the best design method?" If you are asking about whether the...
  12. R

    Assistance with Transistor Theory

    Ian Getreu, I agree with just about everything you said above. I can say more about charge flow (current), however. Current consists of charge carrier movement of any polarity. There are just as many positive charges in the universe as negative ones. Examples are semiconductor holes...
  13. R

    Assistance with Transistor Theory

    I was talking about both to illustrate my point. Ratch
  14. R

    Assistance with Transistor Theory

    I never said the collector current controls Vbe. In fact, I said many times the Vbe controls the Ic. But if you adjust Ic by applying a voltage across Re through the base-emitter, naturally Vbe is going to adjust to a value in accordance with the BJT transconductance present at that current...
  15. R

    Assistance with Transistor Theory

    Again, you are talking about the circuit consisting of an external resistor and a BJT. You would not be able to say the base current is controlling the Vbe unless the BJT collector current was controlled by the Vbe. The fact that the BJT is a transconductance amplifier enables the Vbe to...
  16. R

    Assistance with Transistor Theory

    A BJT cannot tell what is connected to it. In its active region, it always acts independently as a transconductance amplifier. If you drive the BJT with a current source, then you have a circuit consisting of a BJT and a external resistor, which is not the same as a BJT alone. The BJT does...
  17. R

    Assistance with Transistor Theory

    A real world current source does not have an infinite resistance or infinite voltage to drive it. Therefore a current source attached to the BJT base is composed of a very large external resistance and a very large voltage. That setup is not the same as an open circuit where no current at all...
  18. R

    Assistance with Transistor Theory

    I believe we said that the base current is proportional to the collector current. Vbe is what causes the waste base current and controls collector current. You mention a model again. Remember, a model simulates what a device does, but not how the device does it. Driving a BJT with a current...
  19. R

    Assistance with Transistor Theory

    You will have to ask a semiconductor fabrication man that question. I remember reading about some lab prototyping transistors with high betas, but they could not transfer the method to a production line. Also, secondary effects caused by the modifications needed made the transistors unsuitable...
  20. R

    Assistance with Transistor Theory

    I never said, and I don't think anyone else did either, that you should be concerned about the miniscule changes that occur in Vbe when large changes happen Ic. Setting the voltage across Re determines the current in Ic and Vbe takes care of itself. Just set the Vb bias around 0.7 volts higher...
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