Concise Electronics for Geeks > 자유게시판

Just as importantly, it achieves much better regulation over a wide range of possible loads. The problem with this is that all real-world loads will develop some voltage across them in normal operation; this raises the emitter or source voltage accordingly - perhaps close to, or even above, the driving base / gate voltage. This negative voltage will prevent that MOSFET from turning on until the charge is dissipated through the voltage divider (which takes time proportional to the capacitances and resistances involved) - and the gate is positive enough again. The behavior of the first circuit - known as a half-wave rectifier - should be fairly clear: the diode conducts, and therefore creates a voltage across the resistor (a dummy load), only if the first input is more positive than the other; in this circuit, diode breakdown voltage is selected high enough not to interfere with this process. First, we need to find an equivalent resistor that, when placed across the terminals of our 9V battery, would conduct just 20 mA. 5RC, the capacitor will be more than 99% charged, with almost no current flowing - and a voltage equivalent to that of the power source will be present across its terminals.

An unexpected low-pass filter distortion seen in a digital signal is usually indicative of excessive capacitance of the signal path, perhaps because the connection is too long, or runs too close to others; while a high-pass pattern may indicate a broken trace or cut wire, forming an unwelcome capacitor in series with the source of the signal. Low-pass and high-pass filters can be cascaded to form band-pass or band-stop filters; identical filters can also be stacked to achieve a steeper response curve (n-th order filters, with gn frequency transmission function). C product, and therefore, what are electric cables the same frequency response. Because gates are not expected to directly drive significant loads (several milliamps is usually the limit), CMOS transistors are selected so that their resistances and voltage response characteristics eliminate the risk of short-circuit damage when input voltage is somewhere between ground and Vcc; that said, output voltage levels and other gate characteristics are guaranteed to be sane only within certain specific ranges of "0" and "1" inputs.

At this point, the left transistor will turn on, and create a negative voltage on the gate of the other MOSFET, turning it off for a while. The MOSFET transistor shown in column A generally does not require a resistor, at least at low signal frequencies, because it does not allow any appreciably long-lived current to flow through the gate (at very high frequencies, the small but non-zero gate-source capacitance becomes a factor, though). For example, AND gates may be employed to make sure that the input or output stage is active only when the clock signal is high; modified flip-flops may be used to detect clock signal state transitions and initiate actions on rising or falling edges; and binary counters may be used to ensure that a particular number of clock cycles passes between any two operations, or to select the appropriate part of a circuit to use when executing a sequence of calculations. Diodes are also commonly used to build constant-current sources, such as this circuit: this arrangement will admit only as much current as needed to create a particular voltage across the constant "sense" resistor, R2, regardless of the potentially variable voltage drop seen across the connected load.

The previously discussed modifications of the voltage follower circuit - to allow adjustable voltage amplification and push-pull operation - are just as applicable to this regulator. In many cases, this is not a big deal - the capacitor and the resistors can be selected with the interesting range of frequencies in mind; but fundamentally, the follower is no longer maintaining direct relationship between input and output voltages - and merely between their rates of change. Relying on this intrinsic gain is usually not a good idea for production-grade circuits, as the parameter can change significantly at a whim - but by looking at its general order of magnitude, you can see what input impedance would be appropriate. Transistor drivers: one of the most rudimentary classes of integrated circuits, these chips consists of a modest number of individual transistors, often with protective resistors and diodes, to be used as line drivers (i.e., impedance converters). The ability to spot these waveforms is actually extremely useful when debugging digital circuits, where square wave signals are used extensively.