“OPERAZIONI”-UNIVERSAL

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;

 

— high-speed;

 

— precision, accuracy up to a tenth of a percent;

 

— Micropower;

 

— 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