COMPLETE PIECES OF TRANSISTOR APPARATUS 



base of the amplifying transistor TR^, whose emitter is suppHed with 

 reference voltage from the Zener diode. Departures of the output voltage 

 from the desired value alter the collector current of TR^ and hence the 



Stabilized 

 ref. voltage 



-o — 



5mA 



Unstabilized 

 supply 



-o + 



Zener 

 diode 



Figure 45.50 



base current of TR2. The main output current, flowing from emitter to 

 collector of TRg, is changed in such a sense as to correct the original 

 departure. 



— o- 



Unstabilized 

 supply in 



Stabilized 

 supply out 



+ 



Zener 

 diode 



— ^r 



Figure 45.51 



Even better performance can be secured by matching the high output 

 impedance of TR^ to the low input impedance at the base of TR2 by a third 

 transistor in earthed collector, producing an arrangement like Figure 45.53. 



Auxiliary 

 negative 

 supply 



Stabilized 



supply 



out 



Unstabilized 

 supply in 



+ 



Figure 45.52 



Evans and CarrolP^ obtained a stabilized output of —6 V from an unstabilized 

 input of —8 V and an auxiliary supply of —9. The output resistance was 

 less than 0-3 Q and the stabilization ratio better than 1/20,000. 



Lloyd^^ has described a transistor stabilizer which produces an output 

 of 6 V at up to 2 amps from an input of 7-8 V J:: 10 per cent. This would 

 clearly be of value for supplying the heaters of valves in direct-coupled 

 amplifiers. Five transistors are used. There is a 3 stage error amplifier, in 

 which the transistors are in earthed emitter, whose output feeds the control 

 transistor via a matching transistor in earthed collector. It is claimed that 



707 



