39 respectively finally in channel 84 the outputs of the and and nand circuits 94 and 96 are applied to switches e and e 39 respectively since the switches are all identical we will only describe in detail the switches d and d 39 in channel 82 the signal from circuit 94 in channel 82 is inverted by an inverter 102 and applied by way of a resistor 104 to the base of a transistor 106 forming with a second transistor 108 a darlington pair having a high input impedance and a relatively low output impedance the emitter of transistor 108 is connected to the output of power supply 68 and to the base of transistor 106 via a biasing resistor 109 the collectors of the two transistors 106 and 108 are connected to the terminal d of the delta wound stator 12 as illustrated in fig4 switch d 39 includes an inverter 112 which inverts the output from circuit 96 in channel 82 and applies it to the base of a transistor 114 which along with a second transistor 116 forms a darlington pair the output of inverter 112 is also connected via a resistor 118 to the source of positive voltage v2 the collectors of transistors 114 and 116 on the other hand are applied to stator terminal d while the transistor 116 emitter is connected to ground by way of a resistor 122 and via a biasing resistor 124 to the base of transistor 114 finally stator terminal d is coupled to ground via a diode 124 and to source v1 by a diode 126 referring now to fig1 and 4 in channel 82 when signals a and b are both high.