In recent years, widespread integrated circuit, which is a nearly complete unit (amplifier, radio or audio frequencies, a detector, etc.) or radios in General. However, for all its appeal (especially for mass production of narrow-purpose machinery) excessive specialization of IC circuit is devoid of flexibility and impedes the solution of diverse tasks assigned to the electronics. Report that and produced a huge number of more versatile chips, the so — called operational amplifiers (op-amps).
Being essentially an integral DC amps with high gain, designed to work with a variety of external circuits negative feedback (OS), “operativniki” familiar to experienced hams. Master these universal components of modern electronics and also beginners, which is addressed in the first place, this material.
Depending on the type of the selected OS it is possible to obtain at the output proportional to the input signal gain, a non-linear function of its, math. To navigate in such a vast sea of information helps (especially at first) a quick reference document, tailored to the most typical examples include OU and perform at this task (see table).
Paying tribute to such an important parameter of the ow, as the voltage gain K, Which decreases with increasing input signal frequency, it is impossible, however, not take into account other characteristics. Because the inputs “operatsionniy” answer internal differential circuit, to the extent it effectively amplifies the differential voltages applied to these inputs; this corresponds to a differential input impedance Rвх. Supplied to the inputs of the voltage should not exceed the value Uдф.max, in order to avoid distortion of the input signal and the output OU of order.
It’s also important to note that in the absence of the input signal, the output may experience some signal due to currents flowing through the internal resistance of the signal source. It is also possible the inclusion among the inputs of the “operatsionniy” balancing resistor that sets the necessary bias voltage UCM.
Examples of the most common inclusions of operational amplifiers and perform the functions
In table DA1 — Oh. k is the gain, Ewha woman, IIN, VOUT, is the voltage and current at input and output.
Limit output current IOUT OU.max defines the minimum resistance of the attached load RL.min. Speaking of which, it should be noted that many modern versions of OU have cascade protect from overload and short circuit.
These options are almost all good-quality directories OU.
Making sure to practice a truly universal amplifier capabilities “operativnikov”, however, we must acknowledge a certain predisposition to some of their specialization. Moreover, even taken to subdivide the shelter into several types:
— for General use on the basis of which are built assemblies of equipment with a total error of about one percent;
— precision, accuracy up to a tenth of a percent;
— programmable individual parameters which can be changed by external control circuits.
It should also be noted that OU is designed primarily for bipolar food to the midpoint; to organize it manages (the”scheme” methods) and with a unipolar power supply.
Well, now that made a little tour of the main properties and parameters of op-amp, it is useful to consider some examples of using these semiconductor devices in radio Amateur practice. Perhaps, the greatest distribution was received here “operativniki”, working as “Deputy” application specific integrated circuits — preamplifiers audio frequency. In particular, the recognition and success followed (and still following!) schematic uzch for a portable radio with output power up to 0.3 W.
Fig. 1. Schematic and topology pseudospectral Board audio amplifier on the chip КР140УД8А and two transistors КТ815А
Modernized by the author of the version of the device (Fig. 1) with the functions of pre-amplifier good chip DA1 type КР140УД8А. Push-pull power amplifier works perfectly on the transistors VT1, VT2 of different conductivity type. With the release of the latest 2 OU served feedback circuit R6, R3, C2.
The selection of resistor R5 in the absence of a set signal on the emitters of transistors resting voltage equal to half the Range.. the Rest is in accordance with a circuit diagram collected on pseudospectral Board of plastic foil where the placement of the electronic components shown “to the light”, that is, the cut in the foil conductive paths.
In this homemade uzch may apply KLS capacitors (C1, C3), K50-6 (C2, C4), resistors MLT-0,125 and dynamic head of BA1 with a capacity of 0.5—2 watts with the resistance of the voice coil of about 8 Ohms.
Although OU does not belong to the high-frequency instrument, some modifications allow fans to collect radio receivers, the main advantage of which is simplicity of construction and small dimensions. Good results are obtained, for example, “operativniki” type КР140УД1Б (Fig. 2), allowing single supply miniature batteries GB1 type L1028.
Fig. 2. Circuit diagram and circuit Board micropreemie on the basis of the operational amplifier
The signal SV is perceived magnetic antenna WA1. Dedicated tuned into resonance oscillating circuit L1С1С2 it goes to the input of op-amp. In the bowels “of operatsionniy” occur the gain of the radio signal, its detection and amplification of the sound component that is announced ear microphone BF1 type TM-4.
Best mode for working of the operational amplifier КР140УД1Б can be set at a constant current resistor R1, and the appropriate selection of the capacitance of the capacitor C4 (in the range of 20-200 FSC) to mark the area of the range where it is desirable to have increased sensitivity.
The proposed option was developed based on the fixed reception the most respected owner of a local radio station. The capacitor C2 here — Garant rough, and S1 —accurate settings. If you wish, instead you can put a variable condenser type KP-180, in order to have a smooth restructuring of the resonant circuit (receiver General) on several radio stations.
Coil And in the author’s version of a wound wire, PELCO-0,12 on a ferrite core with permeability of 400 marks with a length of 40-60 mm; number of turns is of the order of hundreds. Decent type capacitors KLS (C2, C4) and K53-1 (C3), turn — КТ4-21, resistor MLT-0,125. The circuit Board is performed by the already described technology.
Fig. 3. Schematic audio oscillator (a) and device to search for hidden wiring (b)
In conclusion, two interesting technical solutions based on OU, the implementation of which are quite capable of any, even the novice hobbyist. First, there is nothing like a sound frequency generator with positive OS between output and input (Fig. For). Variable resistor R1 is needed here to create the OS — a through the diodes VD1, VD2. “Shells” R2 adjusts the frequency of the oscillations of the sound range defined by the circuit elements R1, C2.
When connecting the power supply outlet 1 have a periodic triangular signal, and the output 2 is of a rectangular shape. For recording one of the outputs is fed to a sufficiently powerful amplifier.
Appreciated will, I think, appreciated by readers and the latest of the proposed solutions (Fig. 3b). It is compact and sensitive device for locating electrical wiring behind the plaster.
When the antenna WA1 (metal rod or a foil strip on the Board) located near a current-carrying conductor, leads it “seeeye 50 Hz” amplified КР140УД1208, and at terminal 6 “of operatsionniy” voltage appears, causing the led АЛ307Б to apply quite a strong bright red. Conversely, the area of the broken wire light will turn off.