Switching power supply circuit

A switching power supply circuit comprising:

• a transformer having a core comprising a magnetic material of amorphous metal and a primary-side winding and a secondary-side winding wound around the core;
• a switching element series-connected to the primary-side winding of said transformer, for flowing current through the primary-side winding of said transformer according to a pulsive drive signal;
• a primary-side current detection circuit for detecting the current flowing through the primary-side winding of said transformer;
• plural circuit elements for rectifying and smoothing a voltage generated in the secondary-side winding of said transformer to generate an output voltage;
• a secondary-side voltage detection circuit for detecting the output voltage generated by said plural circuit elements;
• a storage unit for storing a data table including setting information on threshold values of at least a primary-side current and a secondary-side voltage;
• and
• a digital signal processor for referring to the setting information stored in said storage unit to control a pulse width in the drive signal such that the secondary-side voltage becomes constant when the primary-side current is smaller than the threshold value, maintain the pulse width in the drive signal when the primary-side current exceeds the threshold value, and stop switching operation of said switching element when the secondary-side voltage is lower than the threshold value.

A switching power supply circuit comprising:

• a choke coil having a core comprising a magnetic material of amorphous metal and a winding wound around the core;
• a switching element connected to one terminal of said choke coil, for flowing current through said choke coil according to a pulsive drive signal;
• a switching current detection circuit for detecting the current of said switching element;
• plural circuit elements for rectifying and smoothing a voltage generated in a connection point between said choke coil and said switching element to generate an output voltage;
• and
• a control circuit for generating said drive signal based on at least a detection result of said switching current detection circuit, and limiting a period for flowing the current in the winding of said choke coil.

A switching power supply circuit comprising:

• a choke coil having a core comprising a magnetic material of amorphous metal and a winding wound around the core;
• a switching element connected to one terminal of said choke coil, for flowing current through said choke coil according to a pulsive drive signal;
• a switching current detection circuit for detecting the current of said switching element;
• plural circuit elements for rectifying and smoothing a voltage generated in a connection point between said choke coil and said switching element to generate an output voltage;
• a voltage detection circuit for detecting the output voltage generated by said plural circuit elements;
• a storage unit for storing a data table including setting information on threshold values of at least the current of said switching element and an output voltage;
• and
• a digital signal processor for referring to the setting information stored in said storage unit to control a pulse width in the drive signal such that the output voltage becomes constant when the current of said switching element is smaller than the threshold value, maintain the pulse width in the drive signal when the current of said switching element exceeds the threshold value, and stop switching operation of said switching element when the output voltage is lower than the threshold value.