Glossary a To F > 자유게시판

Voila - we turned an AC signal with peak-to-peak voltage of 10V into a DC signal with peak voltage of 20V. The multiplier can be stacked, although diode and capacitor leakage currents and other losses put some constraints on its scalability. The function of this diode is to begin conducting, due to the breakdown effect, when the terminal voltage gets dangerously high. The circuit on the left is, essentially, a band-pass filter: the capacitor needs the signal to change slowly enough to charge it up to an appreciable level - and above this frequency, serves as a shunt; but when the current is not changing fast enough, the inductor will begin conducting and will discharge the capacitor. When Vin2 is higher than Vin1, the right transistor will insist on getting the emitter voltage to a point where the left one no longer conducts - and so, the current flowing through the right R1 (and the associated voltage drop) will increase. 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.

A really interesting combination of the previous two circuits is a diode-based voltage multiplier: the output of a DC restorer can be used to gradually charge a capacitor to the peak output voltage, which is then used as a ground reference for another DC restorer. Many other RLC circuits can be designed, what are electric cables although these two approaches are most useful when easily understood dependence on source and load impedances is required. Operational amplifiers: advanced, differential push-pull voltage amplifiers with very high impedances (sometimes using JFET or MOSFET transistors), variable gain, temperature and supply voltage compensation, internal biasing, voltage drop compensation, and so forth - essentially designed to approximate a perfect amplifier within a fairly wide range of operating conditions. The power injector is the amplifier’s power supply. They are used in accurate sensing circuitry, in power management, in some types of oscillators, etc. Common examples include the LM193 family (LM293, LM393, LM2903); voltage threshold detectors (with internal, diode-based voltage references) are also available. For extremely high input impedances, TLC27L4 is a reasonably priced family of MOSFET-based chips; and for low-noise applications (e.g. audio processing), NE5534 is an affordable choice. One of the more popular chips suitable for single-supply operation are the LM124 family (including LM224, LM324, LM2902) and the LM158 family (LM258, LM358, LM2904) - all of which vary slightly, but are interchangeable in almost all uses.

The behavior of a high-pass filter fed with a square wave is perhaps even more interesting - with a voltage proportional to the rate of change of the input signal (hence the nickname: differentiator). Ohm's law states that the current needed to develop a particular voltage across the resistor will be proportional to the desired voltage, and inversely proportional to resistance; if R1 is reasonable, so is the collector-emitter current. Alas, when Vin later drops to 2V, Vout will stay at 5.4V - and because emitter voltage is now higher than base voltage, the transistor will not conduct. In all cases, the driving voltage applied to the base (or gate) must be high enough to trigger the transistor; that is, at least 0.6V in BJT, and at least 1-2V for most MOSFETs. 100k) resistors - and finally employed to drive the gate of a complementary MOSFET. Column C shows another arrangement that is not universally problematic, but should be avoided in switching where possible - and is all-too-common in hobbyist work: loading the emitter (BJT) or drain (MOSFET) - a configuration known as "common collector" or "common source". 3V. This circuit is shown in column B above. When the voltage is somewhere in between, though, both transistors may end up conducting, shorting the circuit - so caution must be exercised; this problem can be controlled by carefully biasing bases / gates using resistor-based voltage dividers, but it may affect switching performance.

This arrangement still suffers from the 0.6V bias - but this time, it can be solved more neatly than with AC coupling: by biasing both transistors into symmetrical, slight conduction when Vin is at the mid-point - and simply relying on the input signal to swing the ratio. So, instead, let's have a look at a more useful, if still modest, type of a simple transistor circuit: a voltage follower, also known as a buffer. A simple way to fix it is to have the input signal drive two complementary transistors at the same time, placed on both sides of the "out" node; this is known as a push-pull amplifier. The bottom line is that there is no way to predict the signal loss in these materials. Decibels - Decibels (dB) are commonly used to describe gain or loss in circuits. Digital electronics are a class of easy to understand circuits that use discrete voltage ranges and square waveforms to transmit and process data - most commonly, representing binary numbers for use in Boolean algebra: a signal close to 0V is meant to signify "0", and a signal close to Vcc signifies "1". The previous section discusses the use of transistors as binary switches operated in their saturation region - that is, the point where the resistance is minimal, and the admitted current is at its peak.