Switching Power Supply Circuit with Protective Function

摘要

A switching power supply circuit includes a transformer having primary, secondary and tertiary windings; a primary-side rectifying-and-smoothing circuit that converts AC power to DC power then smoothes it; a secondary-side rectifying-and-smoothing circuit that smoothes secondary-side power; a tertiary-side rectifying-and-smoothing circuit that smoothes power from the tertiary winding; a switching circuit that switches the primary winding; a pulse width control circuit that controls the switching of the switching circuit; an output-error detecting circuit that detects a deviation of a secondary-side DC output voltage from a reference voltage; and a ripple-voltage detecting-and-controlling circuit that detects a ripple-voltage of the secondary-side DC output voltage and stop-controls the output-error detecting circuit, wherein a stop-control signal from the ripple-voltage detecting-and-controlling circuit causes the output-error detecting circuit to stop outputting, then a drive signal to the switching circuit is stopped, thus the operation of the switching power supply circuit is stopped.

主权项

1. A switching power supply circuit with protective function for preventing a disruption of a switching power supply device due to a deterioration of an electrolytic capacitor, comprising:
a transformer having a primary winding, a secondary winding and a tertiary winding; a primary-side rectifying circuit that converts AC power to DC power; a primary-side electrolytic capacitor that smoothes the DC power outputted from the primary-side rectifying circuit; a secondary-side rectifying circuit that converts AC power outputted from the secondary winding of the transformer to DC power; a secondary-side electrolytic capacitor that smoothes the DC power outputted from the secondary-side rectifying circuit; a tertiary-side rectifying and smoothing circuit that converts AC power outputted from the tertiary winding of the transformer to DC power and smoothes the DC power; a switching circuit that repeatedly switches the primary winding of the transformer which inputs a voltage of the primary-side electrolytic capacitor; a pulse width control circuit that controls the pulse width of a drive signal for controlling the switching of the switching circuit; an output-error detecting circuit that detects a deviation of a secondary-side DC output voltage outputted by the secondary-side rectifying circuit and the secondary-side electrolytic capacitor from a predetermined reference voltage and controls the pulse width control circuit; and a ripple-voltage detecting and controlling circuit that extracts a ripple-voltage component of the secondary-side DC output voltage and stop-controls the output-error detecting circuit when the ripple-voltage component exceeds a predetermined voltage, wherein a stop-control signal from the ripple-voltage detecting and controlling circuit causes the output-error detecting circuit to stop outputting, which in turn causes the pulse width control circuit to stop providing a drive signal to the switching circuit, and then an operation of the switching power supply circuit is stopped.