Jeff, Beta is the current gain of a transistor, HFE and Hfe. No one would design a transistor with a beta of less than one, but they do exist for transistors can become defective. It is common for a new transistor to have a beta of 100, but after hours of use decrease to 20. A good design recognizes this and adapts. They can also decrease to less than 1. Usually one replaces them, but they are still acting as a transistor. An emitter follower will have power gain only if the transistor has a beta, HFE or Hfe, greater than 1, but is active in any case. Having gain, voltage, current or power, does not determine if a component is active. It is how the component reacts to the energy.
Yes diodes and transistor have junction capacitance, resistance, but get their properties from entirely different means than passive devices such as a resistor. Junction capacitance is a function of energy supplied to the device. A capacitor does not change its properties based on energy supplied, unless one exceeds its specs. A diode does. A transistor and diode change their properties based on the energy supplied. This makes both active. As for the Quantum Mechnicancs this was over 40 years ago. One must know high level calculus understanding the wave and heat flow equations to follow. On one of my exams the instruction was to come up with the equation for current flow in a diode. Only took about 3 pages. The 2nd question was how much current was flowing with given parameters, holes, doping density, and some others. If you got the first correct it was easy. If one goes thru these derivations one can see a diode is a very active device. 73, ron, n9ee/r >From: Jeff DePolo <[EMAIL PROTECTED]> >Date: 2007/10/23 Tue PM 08:52:14 CDT >To: Repeater-Builder@yahoogroups.com >Subject: RE: RE: RE: RE: RE: RE: [Repeater-Builder] Re: duplexer isolation and >reciever n > > >> Sorry, but I totally disagree about a diode not being active. >> If having to have gain then many devices such as a transistor >> emitter follower with a beta of <1 would not be an active device. > >I assume you're using the term "beta" to really mean current gain of the >stage. On my planet, an emitter-follower stage can't have a current gain of >< 1. Please draw me a schematic of an emitter-follower circuit that does. > >Or better yet, point me to a data sheet for a transistor that has a beta >(hFE) spec of less than one. > >An emitter-follower is a current-gain stage. Assuming the voltage remains >constant (or nearly so, minus the junction drop), but current increases, it >provides POWER GAIN, which DOES make it an active stage. > >> Maybe if you had studied the equations with Quantum Mechanics >> for a diode you might understand this. > >You don't need quantum mechanics to show that a diode is a passive device. >But I'll indulge you; please explain how a diode (just a plain old silicon >junction diode) qualifies as an active device using quantum mechanics. > >> A diode follows some >> of the same equations as a transistor. > >So? A diode also "follows some of the same equations" as a capacitor, a >resistor, an inductor, or even a fuse for that matter depending on how its >used in a circuit. What's your point? > > --- Jeff > > Ron Wright, N9EE 727-376-6575 MICRO COMPUTER CONCEPTS Owner 146.64 repeater Tampa Bay, FL No tone, all are welcome.
