# Speed of the electrons

Discussion in 'Physics & Math' started by c'est moi, Jan 29, 2002.

1. ### leopoldValued Senior Member

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17,455
i see you have evaded the question in my last post.
i worded it in such a way that google isn't going to be much help unless you know a little about what you are looking for.
which one?
like i said before, there are 3 basic amplifier configurations.
can you name at one of them?
name, as in what it's called in the field.
yes, there are 2 types of BJT, one works with positive supplies the other works with negative.
current in both types flows from negative to positive.
i know of no transistor amplifier circuit that operates with an open base.
post the schematic of such an amplifier.
okay, i'm done with you.
i directly challenge you to post a schematic with the transistor in normal conduction with a Vbe of 5 volts.

3. ### Prof.Laymantotally internally reflectedRegistered Senior Member

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http://www.electronics-tutorials.ws/blog/darlington-transistor.html

If the base is open then there is no current flow in the circuit, but it can then be used as an amplifier for a signal wave without losing the signal wave. If it operated without 5 volts at the base then it would lose the signal wave that was being input into the circuit.

On this page it assumes, that the voltage is positive so the current flow is described backwards. In electronic flow theory of high power devices this is a very common circuit, and it is said normally that the current flows into the base of the transitor, that is a square wave thats volatage is negative. Also notice that the collector and emitter positions are reversed from the top of the circuit to the bottom of the circuit, for the PNP configuration and the NPN configuration. Electron flow is then in the opposite direction.

5. ### leopoldValued Senior Member

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17,455
the page you posted is for a darlington pair, pair as in two.
the gain is approx. beta squared and the resulting heat loss is that of a single transistor.
the page you posted mentions nothing about the Vbe of a single transistor.

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8. ### Prof.Laymantotally internally reflectedRegistered Senior Member

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It is and 2 + 2 = 4. It is just to trivial of a question for most people to even bother putting it into a web site. It is what you call a dumb question. The page I gave says that it is driven by logic gates, most IC use 5 volts. The voltage would have to be - 5 volts at the base of the circuit in order for it to amplify the electronic high of a signal. It then cuts off during a electronic low signal. So then it would have to use IC that put out a negative voltage as an electronic high or "one".

9. ### Prof.Laymantotally internally reflectedRegistered Senior Member

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That is an NPN transitor not a PNP transitor. The arrow doesn't point to the base so it is not a PNP.

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go away.

11. ### Prof.Laymantotally internally reflectedRegistered Senior Member

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"To cause the Base current to flow in a PNP transistor the Base needs to be more negative than the Emitter (current must leave the base) by approx 0.7 volts for a silicon device or 0.3 volts for a germanium device with the formulas used to calculate the Base resistor, Base current or Collector current are the same as those used for an equivalent NPN transistor and is given as."

It looks I found your answer, but it also assumes current flows from positive to negative, even though the electric charge of electrons are negative, go figure. Sometimes I wonder if most people even know what directions electrons actually travel in inside of electronics, no more than the speed they are moving. http://bjttransistor.wordpress.com/2012/07/14/the-pnp-transistor/

It really doesn't matter because they can be designed to work at any voltage at the base. It just depends on the specifications of the compentents involved. In Radar used in the military the transistors are designed to turn on with - 5 volts from a negative power source. The electron flow is then into the base of the transistor. This allows the transitor to operate coming straight from an input of an oscillator. Otherwise it would require more cicuitry in order for them to operate, but a radar is a high power system so then you wouldn't want to lower the input voltage to something less than 5 volts. Rule of electronics is to use the least amount of components possible, and designing a transistor for a signal amplifier that runs on - 5 volts would then require less components. They are not needed to be energy efficient, they require a lot of power.

Also a low voltage at the base of a transistor can allow for electronic interference. If it has to be - 5 volts than the output of the radar itself will not alter its own function. I think I recal this being mentioned now, and that is also another reason for the uncle capacitors I mentioned earlier. If the input of the PNP's only had to be 0.3 volts then activating it would also activate all of the transistors, that would cause a major malfunction.

12. ### Prof.Laymantotally internally reflectedRegistered Senior Member

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Great link, I think a lot of people that think electrons are attracted to a negative charge could really use a supported living community. They have just been in field for too long and had to try and figure out how they worked on their own without a proper education in the field. Electron flow in a circuit can be very fast even with a small positive charge. It doesn't take long for a voltage level to drop or change completely.

Electrons do stay in orbitals or valence shells that are electron clouds. These orbitals are distances around the atom where the wavelengths of the electrons match up and then they jump between these orbitals where the wavelength would cancel itself out. The frequency of light absorbed and emitted from these electrons will then be at a frequency that is determined by what orbitals the electrons of the specific atoms are in.