| 主权项 |
1. A switching power supply device comprising:
a switching controller of a non-linear control type, for generating an output voltage from an input voltage by performing on/off control of a switching element according to a result of comparison of a feedback voltage with a reference voltage; and an on-period setter for monitoring a switch voltage appearing at an end of the switching element so as to set, based on a duty of the switch voltage, an on-period of the switching element in the switching controller, wherein the on-period setter increases the on-period of the switching element the higher the duty of the switch voltage is, and decreases the on-period of the switching element the lower the duty of the switch voltage is, wherein the on-period setter includes:
a first voltage generation circuit for generating a first voltage according to charging/discharging operation of a capacitor;a second voltage generation circuit for generating a second voltage according to the duty of the switch voltage; anda first comparator for generating a first control signal by comparing the first voltage with the second voltage, wherein the first voltage generation circuit includes:
a constant-current source for generating a constant charge current that does not depend on the input voltage;a capacitor connected to the constant-current source; anda charge/discharge switch for switching between charging and discharging of the capacitor according to the on/off control of the switching element, wherein the second voltage generation circuit includes:
a level shifter for shifting a level of the switch voltage;a buffer for shaping a waveform of an output of the level shifter; anda filter for generating the second voltage by smoothing an output of the buffer, and wherein the constant-current source and the level shifter operate by being fed with a same internal supply voltage. |
