Switching power supply circuit provided with protection function

A switching power supply circuit, provided with a protection function, comprising:

• a transformer having a primary winding, a secondary winding and a tertiary winding;
• a primary-side rectifying circuit for converting an alternating-current power to a direct-current power;
• a primary-side electrolytic capacitor for smoothing the direct-current power from the primary-side rectifying circuit;
• a secondary-side rectifying circuit for converting an alternating-current power, outputted by the secondary winding of the transformer, to a direct-current power;
• a secondary-side electrolytic capacitor for smoothing the direct-current power outputted from the secondary-side rectifying circuit;
• a tertiary-side rectifying and smoothing circuit for converting an alternating-current power, outputted by the tertiary winding of the transformer, to a direct-current power and smoothing thereof;
• a switching circuit for repeatedly opening and closing the primary winding of the transformer that inputs a voltage of the primary-side electrolytic capacitor;
• a pulse width control circuit for controlling the pulse width of drive signals that control opening and closing of the switching circuit;
• a secondary-side electrolytic capacitor deterioration detecting circuit for detecting deterioration of the secondary-side electrolytic capacitor;
• and
• a stop-signal generation circuit for inputting a deterioration detection signal from the secondary-side electrolytic capacitor deterioration detecting circuit, wherein the protection function is provided in such a way that
• the secondary-side electrolytic capacitor deterioration detecting circuit inputs an output voltage of the tertiary-side rectifying and smoothing circuit;
• and
• the stop-signal generation circuit generates a stop-signal triggered by a deterioration detection signal from the secondary-side electrolytic capacitor deterioration detecting circuit, then in turn the pulse width control circuit discontinues providing drive signals to the switching circuit, causing the operation of the switching power supply circuit stopped.

A switching power supply circuit, provided with a protection function, comprising:

• a transformer having a primary winding, a secondary winding and a tertiary winding;
• a primary-side rectifying circuit for converting an alternating-current power to a direct-current power;
• a primary-side electrolytic capacitor for smoothing the direct-current power from the primary-side rectifying circuit;
• a secondary-side rectifying circuit for converting an alternating-current power, outputted by the secondary winding of the transformer, to a direct-current power;
• a secondary-side electrolytic capacitor for smoothing the direct-current power outputted from the secondary-side rectifying circuit;
• a tertiary-side rectifying and smoothing circuit for converting an alternating-current power, outputted by the tertiary winding of the transformer, to a direct-current power and smoothing thereof;
• a switching circuit for repeatedly opening and closing the primary winding of the transformer that inputs a voltage of the primary-side electrolytic capacitor;
• a pulse width control circuit for controlling the pulse width of drive signals that control opening and closing of the switching circuit;
• a primary-side electrolytic capacitor deterioration detecting circuit for detecting deterioration of the primary-side electrolytic capacitor;
• a secondary-side electrolytic capacitor deterioration detecting circuit for detecting deterioration of the secondary-side electrolytic capacitor;
• and
• a stop-signal generation circuit for inputting deterioration detection signals from the primary-side electrolytic capacitor deterioration detecting circuit and the secondary-side electrolytic capacitor deterioration detecting circuit, wherein the protection function is provided in such a way that
• the primary-side electrolytic capacitor deterioration detecting circuit inputs a voltage of the primary-side electrolytic capacitor;
• the secondary-side electrolytic capacitor deterioration detecting circuit inputs an output voltage of the tertiary-side rectifying and smoothing circuit;
• and
• the stop-signal generation circuit generates a stop-signal triggered by a deterioration detection signal either from the primary-side or secondary-side electrolytic capacitor deterioration detecting circuit, then in turn the pulse width control circuit prohibits providing drive signals to the switching circuit, causing the operation of the switching power supply circuit stopped.