. Electronic apparatus for biological research. Electronic apparatus and appliances; Biology -- Research. COMPLETE PIECES OF TRANSISTOR APPARATUS due to Potok and Wales'. This is a voltmeter of sensitivity of 1 MQ/V. On applying the voltage to be measured, V, at the input terminals, a current V/R flows out of the base of the transistor, causing an increase in collector current §{VIR) which is indicated by the meter. A is the main collector supply battery. In the absence of any test voltage an emitter-to- collector leakage current (1 + ^)Ic(o) flows, and this is 'backed-off' on the meter by cu
. Electronic apparatus for biological research. Electronic apparatus and appliances; Biology -- Research. COMPLETE PIECES OF TRANSISTOR APPARATUS due to Potok and Wales'. This is a voltmeter of sensitivity of 1 MQ/V. On applying the voltage to be measured, V, at the input terminals, a current V/R flows out of the base of the transistor, causing an increase in collector current §{VIR) which is indicated by the meter. A is the main collector supply battery. In the absence of any test voltage an emitter-to- collector leakage current (1 + ^)Ic(o) flows, and this is 'backed-off' on the meter by current from an auxiliary battery via the associated variable S«t2ero -o- â AAAAA R ⦠o- 50nA Fsn 1- Figure resistor, which forms the 'set-zero' control. Due to the temperature dependence of /^(o), a different zero setting will be frequently required. Zero-drift with temperature change can be offset by using two transistors in a push-pull circuit. Figure shows an example due to Johnson*. The arrangement converts a 0-50 ^A movement into an apparatus having full-scale deflection for 2 ^A. Unfortunately there is nothing in this type of circuit to prevent the rise of collector current with rising temperature. Such a rise may take the transistor working points outside their working regions, so that correct amplification cannot take Figure We have seen that the inclusion of resistance in the emitter circuit serves to off"set the effects of temperature. We have also seen that such a resistance introduces negative feedback and reduces gain. In coupled circuits, where there is a definite minimum frequency at which the circuit is required to operate, this feedback may be eliminated by shunting the emitter resistance with a large capacitance; in direct-coupled circuits there is no such frequency and another method is necessary. The technique is to use the transistor equivalent of the long-tailed pair in valves {Figure ). This is a differenti
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