one embodiment of this invention , applied to a starting circuit for an inverter , will be described with reference to fig2 . parts in fig2 which correspond to the parts in fig1 are denoted by the same referencenumerals , which will not be described in detail . in fig2 a dc - dc converter includes a starting circuit 20 according to this invention , instead of the conventional starting circuit 10 having thethyristor 8 of fig1 . a dc source voltage of a predetermined level is supplied through a resistorr 1 to the starting circuit 20 . one end of the resistor r 1 is connected to resistors r 2 and r 5 , a capacitor c 3 and further to an emitter electrode of a pnp transistor q 3 . the other endof the resistor r 5 is connected to the base electrode of the transistor q 3 to decide a base voltage therefor , and further to the collector electrode of a transistor q 4 . a resistor r 3 is connected in series with the resistor r 2 . the resistors r 2 and r 3 function as a voltage - divider . the connecting point between the resistors r 2 and r 3 is connected through a resistor r 4 to the base electrode of the transistor q 4 and to a collector electrode of the transistor q 3 . further , the base electrode of the transistor q 4 is connected through diodes d 1 and d 2 to one end of the feedback winding 5c of the output transformer 5 . a smoothing capacitor c 4 is connected between the base and emitter electrodes of the transistor q 4 . the other end of the capacitor c 3 is connected to one end of a starting winding 11e which is newly wound as a primary winding around the magnetic core of the input transformer 11 . the other end of the starting winding 11e is connected to the line 4b . accordingly , a discharge current of the capacitor c 3 flows through the starting winding 11e to induce secondary voltages at the secondary windings 11b and 11d . the other end ofthe starting winding 11e is connected further to one end of the primary winding 11a . the other end of the primary winding 11a is connected throughthe resistor r 6 to the feedback winding 5c of the output transformer 5to supply a part of the output of the output transformer 5 . with the application of the ac voltage source to the input terminals 1a and1b , a voltage of positive polarity is led out in the line 4a , while anothervoltage of negative polarity is led out in the line 4b . the voltage of positive polarity is applied through the resistor r 1 to the starting circuit 20 . the capacitor c 3 is gradually charged , and its charging current becomes nearly zero after a predetermined time . at the same time , the voltage across the capacitor c 4 gradually rises up , and it is applied to the base electrode of the transistor q 4 . when it rises above a certain level , for example , beyond 0 . 6 v , the transistor q 4 is put into its conductive state . accordingly , the collector voltage of the transistor q 4 lowers to put the transistor q 3 into the conductive state . when both the transistors q 3 and q 4 are thus put into the conductive state , the resistance between the one end of the capacitor c 3 and the line 4b becomes very low . accordingly , the capacitor c 3 is instantaneously discharged through the emitter - base circuit of the transistor q 3 and the collector - emitter circuit of thetransistor q 4 . the discharge current flows through the starting winding 11e to induce a predetermined voltage at the secondary winding 11bof the input transformer 11 . the induced voltage is applied to the base electrode of the transistor q 1 to put the latter into the conductive state . accordingly , a current from the line 4a flows through the transistor q 1 , the secondary winding 11c of the input transformer 11 , and the primary winding5a of the output transformer 5 to the capacitor c 1 . secondary voltagesare induced at the secondary windings 5b and 5c by the current flowing through the primary winding 5a . the output voltage of the secondary winding 5c is fed back to the primary winding 11a of the input transformer11 . the magnetic core of the input transformer 11 is presently saturated , so that the induced voltage of the secondary winding 11b becomes zero , andthe transistor q 1 is suddenly put into the non - conductive state . accordingly , as above described in fig1 the feedback voltage in the reverse polarity to the previous feedback voltage is applied to the primary winding 11a of the input transformer 11 to induce the voltage at the secondary winding 11d to put the transistor q 2 into the conductive state . with the conduction of the transistor q 2 , a currentfrom the capacitor c 2 flows through the primary winding 5a of the output transformer 5 , the secondary winding 11c of the input transformer 11 and the transistor q 2 to the line 4b . the output voltage of the secondary winding 5b is applied to the rectifying circuit 12 . the magneticcore of the input transformer 11 is again saturated , and the transistor q 2 is suddenly put into the non - conductive state . next , the voltage is induced at the secondary winding 11b to again put the transistor q 1 into the conductive state . as above described , the transistors q 1 and q 2 are alternately putinto the conductive or non - conductive state , so that a continuous pulse output voltage is obtained from the secondary winding 5b of the output transformer 5 . the pulse output voltage is rectified by the rectifying circuit 12 . a dc output is led out from the output terminals 14a and 14b . the output voltage of the other secondary winding 5c is rectified by the diodes d 1 and d 2 to obtain a negative voltage beyond a predetermined level at the base electrode of the transistor q 4 . with the application of the negative voltage , the transistor q 4 and accordingly , the transistor q 3 are put into the non - conductive state . as a result , as soon as the on - off operation of the transistors q 1 andq 2 is started , the operation of the starting circuit 20 is stopped . inthe circuit according to this invention , the charging voltage of the capacitor c 3 to start the switching operation of the transistors q 1 and q 2 can be adjusted in accordance with the load by making the resistors r 2 and r 3 variable , so that the starting operationcan be surely effected . according to this invention , for the inverter including a pair of transistors for oscillation , a starting circuit is provided which comprises a capacitor for imparting a starting voltage to one of the transistors , and a switching element for charging and discharging the capacitor , and a part of the output of the inverter is rectified and then applied to the starting circuit to put the latter into inactive condition . as soon as the inverter is put into its active condition , the starting circuit is put into the off - state with the application of a part of the output of the inverter . accordingly , the starting circuit does not become a load to the inverter in operation . moreover , the starting operation can be surely effected . while there have been described preferred embodiments of the invention , obviously modifications and variations are possible in light of the above teachings . it is , therefore , to be understood that within the scope of theappended claims , the invention may be practiced otherwise than as specifically described .