The first ICDCamplifier was the 709, introduced by Fairchild in the mid 1960s. The 709 by today's standard has many shortcomings, and a whole family of amplifiers has been produced. The commonest is the 741 which has been described as the Universal Component. A DCamplifier chip in its simplest form has just six connections. The positive supply, negative supply and the output are obvious. The amplifier has two inputs. These are known, respectively, as the non inverting and the inverting inputs. The amplifier amplifies the voltage between the two inputs. Let us assume, therefore, that the input is connected to 0V and an input signal applied to the +ve input. It will be found that the output moves in the same sense as the output. If we reverse the input connections, and connect the signal to the input, and the +ve input to 0V, the output will move in the opposite sense to the input. The terms 'inverting' and 'non inverting' thus refer to the sense of the inputs with respect to the resulting output. DC amplifiers are characterised by very high gains; 200,000 being typical for the common 741. Normally supplies of a 15V are used, so an input voltage of less than 1mV will cause the output to saturate. In practice, all DC amplifiers are invariably used with negative feedback which, in conjunction with high gains, gives very predictable results.
DC amplifiers are used in instrumentation, audio circuits, filter design and industrial control. By the early 1980s they had become a universal component. Research DC Amplifiers
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Matt and Leela Probert
Abbreviations
Research DC Amplifiers
