![]() The "biasing" is like an adjustment to pair them into similarity so they both operate at the same degree or position as they move throughout their linear ranges together. The reason is that, many times you can build 2 items that seem or look identical but when you put them into operation they vary from one another. Example of biasing: A Fender guitar amp uses biasing on their dual power output tubes. ![]() The answer is no, no one who understands electronics well enough to design, build, or manipulate circuits can answer an easy, common question in layman's terms. It should suffice to say that in linear circuits this series resistance could reduce the gain-bandwidth product by giving more potency to Miller capacitance, as in any case where capacitances lurk in an increased-impedance environment. An editorial here might open by stating a firm belief that one has not applied a particularly linear discipline of spectral amplification if this is proven necessary, but that's for another time, and there are those who feel differently. The series resistance can also provide a certain meaning to Miller capacitance (collector-base) in the same way (or reveal the parasitic Miller cap) via the impedance increase, which could be good or bad but sort of brings linear amplification into the realm of inclusion of a series base resistor, particularly where interstage/open-loop gains are high and a slew-rate limitation must be imposed to avoid spontaneous oscillation. ![]() Analog or mixed (ADC) detection could probably make sense of it though, but now I'm headed out on a tangent based on random and frivolous guesses about your application. thermal runaway.īarring excessive resistance values and low current gains, it has little do with current gain, as any such design case would fundamentally tend to include transistor saturation on the real-time operational menu (i.e., using as a switch or other high-gain or logic-drive scenario rather than a linear amplifier) and the principal pitfall would be excessive resistance which could choke the transistor at an unreliable threshold, short of saturation (generally non-applicable in Darlington case), and this would be load-dependent (as a consequence of hFE), probably thermally adverse, and not CMOS-input-compliant. Speaking of which, when power transistors are to be paralleled, it may be more important to degenerate their emitters to prevent fallen hero syndrome, a.k.a. ![]() Whatever source or sink of current (output) is driving the transistor (an open collector / level shifter, a CMOS output, what have you) is ultimately to be driving such current to a silicon diode (or two in the Darlington case), for all it knows of the base-emitter junction(s) of the transistor(s) in question. Quite often for instance, current is set through an LED to meet its specifications in exactly this way. If the driving stage output is of 'relatively low' impedance (and is thus more of a voltage source in actuality) the series resistor must be present to convert it to a current source, just like in any other case of driving a diode or generalized low-impedance target. ![]()
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