. Electronic apparatus for biological research . 0 -1 -2 -3 -4 -5" Collector voltage Figure (a swing of 4-5 V) and from 1-25 mA to 5-75 mA (a swing of 4-5 mA) so the maximum power output for a sinusoidal signal is 4-5 V X 4-5 mA 8 2-5 mW The power supplied to the output stage is 6 V X 3-5 mA = 21 mW, so the efficiency of the stage is 2-5/21 X 100 per cent = 12 per cent. Thus far the procedure is exactly as for valves. In using a working point V^ = —2-5, Z,. = 3-5 mA, our transistor parameters are probably not far from those quoted by the makers for -2, L — 3 mA, which are /5 = 47 50
. Electronic apparatus for biological research . 0 -1 -2 -3 -4 -5" Collector voltage Figure (a swing of 4-5 V) and from 1-25 mA to 5-75 mA (a swing of 4-5 mA) so the maximum power output for a sinusoidal signal is 4-5 V X 4-5 mA 8 2-5 mW The power supplied to the output stage is 6 V X 3-5 mA = 21 mW, so the efficiency of the stage is 2-5/21 X 100 per cent = 12 per cent. Thus far the procedure is exactly as for valves. In using a working point V^ = —2-5, Z,. = 3-5 mA, our transistor parameters are probably not far from those quoted by the makers for -2, L — 3 mA, which are /5 = 47 500 a 13 kQ To secure a standing collector current of 3 mA we need a base 'bias' current defined by the bias resistor R^. The quickest way to find the proper value of 7?3 is by experiment with the particular transistor in use. As a pointer to the approximate value required, if we regard /? as a measure of IJIj, (actually, of course, ^ is dljdl^) then to get a collector current of 3 mA we need a base bias current of 3 mA/47 = 64 juA. Since the base and emitter are practically at the same potential, the whole battery voltage appears 685
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