Switching power supply

A switching power supply comprising:

• at least one transformer having primary and secondary windings isolated from each other;
• one or more switching elements for on-off control of D.C. input voltage applied to said primary winding;
• said at least one transformer inducing a D.C. output voltage for a load connected to the secondary winding in response to the D.C. input voltage applied to the primary winding, said secondary winding having a winding resistance;
• a detection circuit for sensing current flow in said secondary winding without the need for a separate current-sensing element, said detection circuit connected to one terminal of the secondary winding for detection of a voltage drop which is proportional to the load current and which is caused by the winding resistance of the secondary winding in association with operation of the switching elements, said detection circuit detecting the voltage drop from one terminal of the secondary winding to produce output current detection signals through a filter network non-magnetically coupled therewith for rejection of signals within a switching frequency region from the output voltage induced in the secondary winding;
• a current sharing terminal connected to a transmitting line for carrying the output detection signals from the current detection circuit;
• and
• a pulse width control circuit for supplying the driving signals to said one or more switching elements to hold the D.C. output voltage constant, said pulse width control circuit controlling pulse widths of the driving signals supplied to the switching elements so that as an electric potential at the current sharing terminal increases more load current will be allowed to flow.

A switching power supply comprising:

• at least one transformer having primary and secondary windings isolated from each other;
• one or more switching elements for on-off control of D.C. input voltage applied to said primary winding;
• said at least one transformer inducing a D.C. output voltage for a load connected to the secondary winding in response to the D.C. input voltage applied to the primary winding;
• a choking coil coupled to the secondary winding and having a winding resistance;
• and
• a detection circuit for sensing current flow in said secondary winding without the need for a separate current-sensing element, said detection circuit connected to one terminal of the choking coil for detection of a voltage drop which is proportional to load current and which is caused by the winding resistance of the choking coil in association with operation of the switching elements, said detection circuit detecting the voltage drop from one terminal of the choking coil to produce output current detection signals.

A switching power supply comprising:

• at least one transformer having primary and secondary windings isolated from each other;
• one or more switching elements for on-off control of D.C. input voltage applied to said primary winding;
• said at least one transformer inducing a D.C. output voltage for a load connected to the secondary winding in response to the D.C. input voltage applied to the primary winding;
• a choking coil interposed in a transmitting line of the D.C. output voltage and having a winding resistance;
• a detection circuit for sensing current flow in said secondary winding without the need for a separate current-sending element, said detection circuit connected to one terminal of the choking coil for detection of a voltage drop which is proportional to load current, and which is caused by the winding resistance of the choking coil in association with operation of the switching elements, said detection circuits detecting the voltage drop from one terminal of the choking coil to produce output current detection signals
• a current sharing terminal connected to a second transmitting line carrying the output detection signals from the current detection circuit;
• and
• a pulse width control circuit for supplying driving signals to said one or more switching elements and keeping the D.C. output voltage constant, said pulse width control circuit controlling pulse widths of the driving signals so that as an electric potential at the current sharing terminal increases more load current will be allowed to flow.