as indicated above , apparatus in accordance with the invention may be considered to comprise a novel integration or combination of a bucking - type switch - mode regulator and a flyback - type switch mode - regulator , such as are noted above in connection with fig3 and 4 . thus , the circuit described hereinafter as a preferred embodiment of the invention has , in essence , two directions or modes of operation , in a first of which circuit performance is analogous to that exemplified by a bucking - type regulator , and in the second of which analogous to that exemplified by a flyback - type regulator . in continuous running operation , the result provided is a high degree of voltage output control , in which the output voltage is not dependent upon the load , unlike the conditions prevailing in conventional supply circuits such as those illustrated in fig1 and 2 . one particular preferred embodiment of a control in accordance with the invention is illustrated in fig5 . as seen there , the apparatus 50 includes a pair of fet switching branches 52 and 54 , each of which is connected between the b + supply line 56 and the system ground 58 . fet branch 52 includes a pair of directly - connected power fets 60 and 62 , whose common junction point 64 is connected to a load 66 and provides the effective drive excitation for the same . the load 66 may be considered , for purposes of illustration , to be a wheelchair drive motor analogous to the motors 12 , 12a discussed above in connection with fig1 and 2 ; however , as will be readily understood , in the broader connotations of the invention the load 66 could be any of a number of different particular devices , typically of an electromagnetic character but not necessarily so . each of the power fets 60 , 62 is shown as having a diode 61 , 63 , respectively , connected across it in opposite conductive polarity to that represented by the b + line 56 . preferably , diodes 61 and 63 are internal to the fets themselves , i . e ., a diode action provided by the multiple - layer construction of the field effect transistors . such an effect is provided , for example , in the power fets ( mosfets ) sold by siemens which are designated their type buz 10h , which provides desirable operating characteristics for the electrical wheelchair application indicated ( as well as other such applications ). in the wheelchair application described , a typical drive motor for use as load 66 may be a twelve - volt , seven to ten amp ( operating current ) d . c . motor , or a comparable twenty - four volt ( four to five amp operating current ) motor such as that sold by motor products of owosso of owosso , mich .) and designated as their model jas 15c . as will be understood , the particular power fets selected for use should have operating characteristics ( such as their conducting resistance and maximum current - carrying capability ) matched to the particular motor selected . the second fet circuit branch 54 is configured somewhat similar to branch 52 , discussed above , including a pair of directly - connected fets 68 and 70 ; unlike fets 60 and 62 , however , fets 68 and 70 need not be high - power devices , since their function is to provide a control voltage sense ( as discussed below ); consequently , fets 68 and 70 may be low - power devices , and need not have an internal diode feature as discussed above . an example of a particular fet which may be used to implement fets 68 and 70 is the siliconix vn 10 km . as illustrated , the common junction 72 of fets 68 and 70 is connected along a path 74 and through resistor 76 to a circuit junction point 78 , and this point is also connected , along a circuit branch 80 , to the aforementioned drive point 64 for fets 60 and 62 . consequently , it will be observed that the two midpoints 64 and 72 of fet circuit branches 52 and 54 are in effect balanced against one another at circuit point 78 , and this point is coupled along a circuit path 82 to one input of a comparator 84 , whose output is in turn coupled back through an &# 34 ; op amp &# 34 ; 85 to the circuit input , in a manner to be described subsequently . the other input of comparator 84 is derived from a resistive voltage divider branch 87 connected across the two fet circuit branches 52 and 54 , between b + line 56 and ground 58 . voltage divider branch 87 includes a pair of complementary resistors 88 , 90 , whose relative proportions determine the value of a reference voltage appearing at their common connection point 92 . this reference voltage is coupled as a second input to comparator 84 along a circuit path 94 , as illustrated . the control gate 68a of low - power fet 68 is coupled back to the control gate 60a of power fet 60 , and the control gate 70a of low - power fet 70 is coupled back to this same input signal condition , which is present at input junction point 96 . the input control gate 62a of power fet 62 receives an opposite - polarity version of the input signal initially present at circuit point 96 , the initial input being inverted by an inverter 98 . thus , it will be apparent that power fets 60 and 62 operate in a directly opposite manner with respect to one another , and that sensing circuit branch 54 functions in a manner which is in effect the opposite of that attributable to fet circuit branch 52 . both such oppositely - varying signals are combined at the circuit nodal point 78 , and applied to one input of comparator 84 . the control signal initially provided to circuit 50 as an input emanates from a control device 116 , to which a positive - polarity input supply is connected . as will be understood , such a control unit should have a manually operable member such as a push switch or slide switch ( or &# 34 ; joy stick ,&# 34 ; etc .) by which the operator can readily change speed and operational direction , such changes being brought about by changes in the effective pulse width outputted from the device , by which one may change the duty cycle applied to the drive motor 66 . the output pulses from control 116 are balanced against ( differentially combined with ) the integrated output of comparator 84 , which is coupled back through an integrator 85 as an input to a differential amplifier designated 86 , to whose other input the control 116 is also coupled . in a switch - mode device such as that under discussion , the control unit 116 will be a variable pulse generator , which may be manipulated by the wheelchair operator to control the speed and direction ( i . e ., forward or reverse ) desired for the wheelchair under any given condition . such a device , for example , may be implemented by using a typical commercially - available separate - component pulse generator and pulse - width modulator , or a special - purpose hybrid variable pulse - width controller device , which is also available as a standardized commercial component . as a very basic example of the control 116 , a single - frequency chopper may be used to produce a triangular waveform and an output level - select control determines the zero - point of the triangular wave , by which the period or width of the repetitive triangular pulse is determined . typically , a pulse - type controller such as that referred to above is operated at a comparatively low frequency ( e . g ., 80 hz ), but it is more preferred , in accordance with this invention , to operate at a much higher frequency ( e . g ., 25 khz ), which provides for inaudible operation as well as for increased control capability . in using such higher frequencies , the above - noted mosfet switches are particularly desirable for use since they are high - speed devices which ensure full half - cycle conduction without overlap ( simultaneous conduction ) between the conduction periods of the respective circuit portions . to further enhance such high - frequency operation , a fast - acting ( high - speed ) fet driver may be used as an interface device between the pulse - width modulator and the fet gates , for example a unitrode ( uc ) 3707 device . in accordance with the foregoing , it may be seen that as input pulses emanating initially from controller 116 are applied to the control electrodes of the respective fets in circuit branches 52 and 54 , as for example to apply a forward excitation to the drive motor or other load 66 , the pulsing command signal from the controller functions to set a duty cycle and thus apply a desired drive voltage to the load which constitutes a proportional part of the b + voltage carried on conductor 56 . for purposes of illustration , it may be considered that during such forward - direction commands fet 60 will be driven into and out of conduction at the pulse repetition rate produced by the controller , whereas fet 62 will be receiving opposite - polarity control voltage and will thus be non - conductive during such time . fets 60 and 62 operate in an opposite manner ; thus when reverse or opposite - direction motion is commanded , the opposite polarity and opposite fet conduction characteristic will prevail , resulting in circuit nodal point 64 receiving opposite - polarity control voltage , causing current flow through load 66 to be in the opposite direction under such conditions . the drive actuation voltage appearing at circuit nodal point 64 is also applied , through conductors 80 and 79 , to node 78 , where it is balanced against the voltage present at the common junction 72 of fets 68 and 70 ( which represents the no - load voltage ). this composite sense voltage is compared with the selected resistively - determined reference voltage which is present at nodal point 72 . by so doing , the power supply apparatus 30 actually regulates the operative output voltage appearing across load 66 , rather than merely applying a predetermined excitation thereto on an open - loop basis . in effect , the control voltage at node 78 is an ongoing and instantaneous representation of actual load excitation compared to no - load excitation ; in fact , under actual no - load conditions , the excitation present at node 78 will be one - half that of the applied voltage from conductor 76 because each point in time when fet 60 is driven into conduction and nodal point 64 goes positive , circuit branch 74 is also driven into conduction , but through both fets 68 and 70 . by comparing the actual voltage present at circuit node 78 with that present at circuit junction 72 , which is resistively divided by resistors 68 and 70 , an error signal is obtained which is a direct function of the voltage drop across the load 66 . thus , if the load is drawing heavy current , a comparatively higher voltage will appear at circuit point 78 , in relation to the resistively - divided voltage present at circuit point 72 . accordingly , the disclosed power supply circuitry operates to establish an output voltage , or working voltage , independently of load conditions , contrary to conventional supplies which are very substantially load - dependent . in an &# 34 ; idle &# 34 ; condition , without loading of the motor or other controlled device , the current flow through the motor or equivalent inductance will rise and fall symmetrically about zero if the motor or other load device is drawing no average current . if an operating mode is set by actuation of controller 116 , current flow through the motor ( or other equivalent load ) will alternately rise and partially discharge , to maintain the set voltage , and it will do so even if there is no load applied to the motor . thus , the particular operation achieved by setting a given duty cycle , by manipulation of the controller , is not changed to any significant degree by conditions actually encountered or presented through the load , e . g ., load variations , pulsations , etc . in the illustrative example of an electric wheelchair drive motor control , the advantages of such an apparatus will be immediately clear ; that is , the operator selects a set speed by actuation of the controller , and that speed is very closely maintained even though the terrain being traversed may vary in its surface characteristics , angle of inclination , etc . should the wheelchair encounter a downward slope of significant gradient , the motor will be driven by gravitational effects to produce back emf , which will be constructively used ; i . e ., as regenerative feedback , returning power to the supply rather than dissipating it in the form of lost heat energy , etc ., and dynamic braking also will occur inasmuch as point 84 , representative of the input to the load , will be connected to ground through a very small resistance , ( i . e . the conducting resistance of fet 62 ), and this all occurs without the requirement for any special sensing and / or switching . it may thus be seen that the present invention provides very extensive control functions for maintaining particularly selected applied voltages , in some respects resembling switch - mode regulator circuitry and performance characteristics and to some extent resembling a combination of both a bucking - type regulator and a flyback regulator , running continuously and in an integrated , mutually cooperative manner providing for extensive control of operating ( load ) voltages . of course , it is to be understood that the desirable applications for such a device are extensive and diverse , including numerous specific uses in addition to the electrical wheelchair apparatus discussed above as an illustrative example , particularly where the load to be controlled characteristically involves significant and comparatively randomized variations and pulsations . in the electric wheelchair example , however , it is to be noted that the apparatus of the invention provides all of the desired control characteristics , including careful and continuous speed control , dynamic braking , and regenerative feedback , with commensurate operational efficiency , while involving only a relatively simple circuit with comparatively few components . at the same time , the safety margin is extensive , since component overload and burnout is essentially eliminated , including in particular the motor being controlled as well as the control itself . it is to be expected that other applications for the disclosed apparatus will likely involve analogous advantages and safety factors , the range of likely application including practically all circumstances where voltag agile power supplies are desirable ; in fact , the apparatus provided herewith could well serve the purpose of a standard power function generator . that is , depending upon the control signal used as the initial input , various waveforms could be generated for any given purpose , with characteristic close control , essentially no overshoot , and with very agile voltage output - variation capabilities . the above description is that of a preferred embodiment of the invention . various changes and alterations can be made without departing from the spirit and broader aspects of the invention as set forth in the appended claims , which are to be interpreted in accordance with the principles of patent law , including the doctrine of equivalents .