Jeff, Beta is most definitely a factor in the current gain of an emitter follower. This is most important with a linear regulator where the load is driven by the emitter. The beta determines the current gain of the pass transistor and how much current must be driving the base. If a transistor had <1 beta it would do no good for a reference voltage to have a pass transistor.
beta = Ic/Ib the collector to base gain and relationship. The H parameters HFE (DC beta) and Hfe (AC beta). A transistor is not determined by its beta, but its operation and is still a transistor with a bets<1. Maybe not a good one, but still is, hi. A capacitor's capacitance is not a function of any applied signal. That's like saying something is red only if one sees it. A diode is different. Its properties are determined by external signals. This is one reason engineers consider it active. It changes and activity affects a circuit by how voltages and currents are applied. A capacitor or inductor or resistor, passive devices, do not change how they react. 73, ron, n9ee/r >From: Jeff DePolo <[EMAIL PROTECTED]> >Date: 2007/10/24 Wed PM 09:15:59 CDT >To: [email protected] >Subject: RE: RE: RE: RE: RE: RE: RE: [Repeater-Builder] Re: duplexer isolation >and reciev > >> Beta is the current gain of a transistor, HFE and Hfe. > >Finally something we can agree on. But the way you used "beta" was >referring to the net gain of a *circuit* using a transistor in >emitter-follower >configuration, which I don't think is the correct use for the term, and >which is why I put "beta" in quotes in my reply. > >> 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. > >A transistor is capable of gain, thereby making it an active device. It's >gain (or lack thereof) in a maldesigned circuit doesn't change the fact that >the device, itself, is still capable of power gain. > >A dead transistor with an hFE of < 1, in my opinion, makes it no longer a >transistor. If we're going to consider broken or burned-out components in >our discussions, we're never going to get anywhere... > >> 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. > >Under your definition, if there is a change in one of its properties of a >device when energy is supplied to it, the device is active, do I understand >that right? A diode's capacitance changes with applied voltage, OK, I >concur. The voltage across a resistor changes with current through it. An >inductor's reactance changes with frequency. The resistance in a length of >copper wire changes with temperature. So I guess all of these are active >devices? > > Ron Wright, N9EE 727-376-6575 MICRO COMPUTER CONCEPTS Owner 146.64 repeater Tampa Bay, FL No tone, all are welcome.
