DIODE CIRCUITS 



that it is desired to rectify a certain voltage V, and current, 0-/max, we have: 

 minimum load resistance i^^min which will be connected = K//niax- Work 

 out the optimum inductance from L = 7?2,min/470, finding a swinging choke 

 whose inductance is this at maximum current /max- 



To load 



Figure 6.23 



Find the inductance of the swinging choke at low values of current from 

 the makers' characteristics or by experiment, and call this L'. 



Work out the maximum permissible bleeder resistance i?^, from L' — 

 RJ940. 



VOLTAGE MULTIPLIER RECTIFYING CIRCUITS 



A number of pieces of apparatus in electronics, such as Geiger tubes and 

 cathode ray tubes, require supplies of very low direct current and rather high 

 voltage, say more than 1,500 volts. It is possible to derive such suppHes by 

 conventional rectification of the output of a special high-voltage secondary 

 winding on the power transformer, but often inconvenient. If lower alter- 

 nating voltage supplies are available it is possible to generate the necessary 

 high-voltage required by special 'voltage multiplier' circuits. Since the 

 currents to be supplied are small these circuits are elaborations of the simple 

 capacitance-input half-wave circuit already described, and their regulation 

 is therefore poor. Somewhat simplified descriptions of these circuits and 

 their operation will now be given. 



Symmetrical voltage doubler {Figure 6.24) — When terminal A of the genera- 

 tor is positive with respect to terminal B current flows in the upper part of 



l^out=2V 



Figure 6.24 



the circuit, charging the upper capacitance to a voltage V, with the polarity 

 shown. When terminal A is negative with respect to terminal B the lower 

 part of the circuit is operative and the lower capacitance is charged, also to a 

 voltage V and with the polarity shown. Thus the output is 2V. 



The difficulty with this circuit is that both generator terminals are involved 

 in the circuit action, which means that the generator is not generally available 

 for supplying other rectifying circuits as well. By a modification of the 



106 



