fig7 to insure that only one of the identical elements 17 or 19 is enabled at any time 0045 fig7 b describes one of two identical controlled elements 13 and 15 the objective in this embodiment is to apply the same magnitude of voltage between the gate and source terminals of the mosfet 709 as is applied across the gate and source of the mosfet 601 so that said mosfets become conductive simultaneously however since mosfet 709 is a p channel device while mosfet 601 is an n channel device and since the source terminal of mosfet 709 is elevated to the output voltage of the controlled power supply 1 which may vary widely during operation a level shifting circuit must be used to reference the voltage to be applied to the gate of mosfet 709 to said output voltage and also to invert the polarity of said applied voltage as compared to that applied to the mosfet 601 said level shifting inverting circuitry consists of resistors 701 702 703 704 706 and 707 along with amplifier 705 and transistor 708 said resistors may be chosen to provide voltage gain so that the magnitude of the voltage applied to the gate of mosfet 701 is some multiple of that applied to the gate of mosfet 601 in addition mosfet 709.