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  1. R

    Transistors

    Everyone should read the link in post #69, where Winfield Hill illustrates the voltage control vs current control design philosophy. Very interesting read. Ratch
  2. R

    why we need Load resistor?

    Perhaps not under some circumstances. But the Power Transfer Theorem (PTT) does not address whether the source is capable of supplying the needed power, or the load is capable of receiving all the available power, or whether the damping factor is OK, or whether the frequency range is...
  3. R

    Transistors

    Joules per coulomb is the correct MKS unit of voltage. Actually, "elementary charge" is a better term to use instead of unit charge. Someone could say "unit of charge", and you could wonder if he meant MKS units or whatever. The elementary charge unambiguously means the smallest atomic charge...
  4. R

    Transistors

    No, electrons and protons each carry a unit charge of opposite polarity. One coulomb contains 6.24E18 unit charges, and one unit charge is 1.60E-19 coulombs. http://en.wikipedia.org/wiki/Elementary_charge
  5. R

    Transistors

    A joule/coulomb is not the same as a joule per unit charge. A joule per electron would be 6.24E18 joules per coulomb of electrons. Joules per unit charge is not a MKS unit. Yes, a 9 volt battery does mean it has an energy density difference of 9 volts between its terminals. Whether it can...
  6. R

    why we need Load resistor?

    The ability of the source to provide sufficient power, or the ability of the load to dissipate all the power it receives, has nothing to do the the Power Transfer Theorem. That is an unrelated consideration analogous to making sure a resistor's dissipation is sufficient for the current through...
  7. R

    Transistors

    That is basically correct, but if you refer to current in a electric field, then you mean power. If you mean charge movement in an electric field, then that's energy. Energy has units of volt-charge, not volts alone. Voltage is the energy density of the charge. The fact that you can show...
  8. R

    Transistors

    One can always invert a relationship mathematically and say that either one causes the other. But the true test of what causes what is the physics of the system. That is why I delved into the diffusion aspects of a BJT and averred that it was voltage controlled. I know of no current...
  9. R

    Transistors

    Believing, feeling or thinking something is so is not proof that it is.
  10. R

    Transistors

    He said that changing the voltage source to the base through a resistor will change the Ic. It will, but he never said that it proves the transistor is voltage controlled. I first made that statement about voltage control, and used a physics argument to substantiate my assertion. He said...
  11. R

    Transistors

    I disagree. I interpret him as saying that whatever the sum of the emitter and Vbe are, the Ic is controlled by Vbe. He never says that Vbe is constant. Voltage change on the base causing change in Ic sounds like voltage control to me. I don't agree. The physics say that voltage is...
  12. R

    why we need Load resistor?

    What you say about matching the load with the source is true, IF the source impedance cannot be changed. BUT, if the source impedance can be lowered, then more power will be transferred than if the source were equal to the load. Ratch
  13. R

    Transistors

    No, we both aver that a BJT is voltage controlled. The difference is that you cannot explain the control of diffusion with a current. The diffusion is controlled by a Vbe voltage that increases/decreases the barrier voltage caused by the creation of the depletion region where a PN junction...
  14. R

    Transistors

    The base determines the charge carrier flow between the emitter and the collector by controlling the diffusion process by adjusting Vbe. Once the charge carriers leave the emitter and enter the base, they are swept into the collector by the higher collector voltage. Increasing the collector...
  15. R

    Temperature compensating a transistor?

  16. R

    Temperature compensating a transistor?

    Ah, now we got some resistance in the emitter. That should improve the temperature stability. I would also try to reduce the 100k resistor in the base to 10k or even 1k if you can get away with it. Ratch
  17. R

    Transistors

    That is why it is beneficial to put some resistance R in the emitter leg. This resistance gets betatized by the negative feedback. Then you are controlling the current by applying voltage across the much larger R*(beta+1), which swamps out the much smaller now irrelevant resistance of the...
  18. R

    Transistors

    The exponential behavior of the voltage to current of a junction diode is due to the fact that it uses diffusion to transport its charge carriers instead of electric fields like a plain conductor does. Other applications like an ink drop spreading throughout a glass of water also show this same...
  19. R

    Temperature compensating a transistor?

    You are running the worst possible configuration for a BJT. You have high base resistance and low emitter resistance. That shunts the thermal current generated in the collector into the base emitter junction where it gets "betatized" (read amplified) by the transistor. By making the base...
  20. R

    Transistors

    I have not studied the saturation region of the BJT very much, so I am not going to comment on something I know little about. It is somewhat more complicated than the active region. I do plan one day to peruse it, however. Ratch
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