Electronic apparatus for biological research electronicappara00dona Year: 1958 Figure similarly for diode (2) and the potential at D {Figure ): in fact it is even longer. Suppose point A is positive to earth but has passed its peak and is negative going: diode (1) is conducting and diode (2) is cut off. As A is falling there is a tendency for the inductance current to fall, which the induc- tance combats by generating a back across itself, the sense of which is to make B more negative than E. If the potential at E is stabilized, the effect of the back is to depress the
Electronic apparatus for biological research electronicappara00dona Year: 1958 Figure similarly for diode (2) and the potential at D {Figure ): in fact it is even longer. Suppose point A is positive to earth but has passed its peak and is negative going: diode (1) is conducting and diode (2) is cut off. As A is falling there is a tendency for the inductance current to fall, which the induc- tance combats by generating a back across itself, the sense of which is to make B more negative than E. If the potential at E is stabilized, the effect of the back is to depress the potential at B, so that A can go further negative before diode 1 is cut off. Thus the conduction time of diode 1 is extended. The benefit conferred by the long conduction time is very low Potential ot/4 Rjtential ofD Potential of/A Fbtential at C Diode '^ Diode '^ Diode 1 2 1 conducting conducting conducting Figure peak diode current and so low voltage drops. The same applies in the case of diode 2 and hence the regulation of the circuit is good. There is a difficulty with choke-input circuits which requires bearing in mind. Referring to Figure , if the load is accidentally removed the inductance current is drastically reduced and so, therefore, is the contribution of the inductance to the operation of the circuit. When this happens the arrangement reverts to the capacitance-input type of rectifier and the output voltage rises from its normal value of about 2K/7r to V. This may cause serious damage, and to prevent it happening it is necessary to ensure that some load is always present. Such a load is called a 'bleeder' (R^, in Figure ). It can be shown that if for a 50 cycle supply L > i?imax/940 the output voltage will not rise above its normal value. This value of L is known as the 'critical inductance'. Design procedure is therefore as follows: given 105
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