dc/dc converter

Abstract

The present invention provides a DC / DC converter that compares a second error signal with a predetermined threshold to generate a light load signal. A zero-crossing signal indicating the end of the regeneration period of the inductor is generated. When the light load signal and the zero cross signal are output, the intermittent operation permission signal is output after the first predetermined time has elapsed, and the intermittent operation is performed. At this time, the low-pass filter is switched to a time constant larger than that at the time of steady operation. In intermittent operation, when the zero-crossing signal is not output for a second predetermined period and the second error amplification signal is smaller than the threshold value, the switching element is turned off, and when the second error amplification signal is greater than the threshold value, the switching element is turned on. Pass. When the switching element is turned off, pulses are superimposed to lower the first error signal for a predetermined time. Furthermore, when the output voltage is lower than a predetermined value, the low-pass filter is switched to the same small time constant as in the stable operation.

Description

Technical field [0001] The present invention relates to a DC / DC converter. Background technique [0002] As a method of generating a stable voltage lower than the input voltage, a non-isolated step-down chopper circuit is widely used. However, since the switching operation is continued even when the load becomes light, such as during standby, the lighter the load, the lower the power conversion efficiency. [0003] In order to solve this problem, proposed Picture 11 The DC / DC converter shown (Patent Document 1). The error signal COMP is compared with a predetermined threshold value Vsk_Lo to detect light load. The error signal COMP is generated by comparing the voltage FB with the reference voltage Vref. The voltage FB is the output voltage V through the resistor Rfb1 and the resistor Rfb2. out It is obtained by splitting. When the load becomes light, since the voltage FB rises, the error signal COMP output from the error amplifier 14 falls. Therefore, when the error signal COM...

AI Technical Summary

Problems solved by technology

The light-load detection comparator 23 compares the error amplification signal COMP with the light-load detection first threshold Vsk_Lo to perform light-load detection. Therefore, there is the following problem: the more the output voltage V out Under the small condition, the current level for light load determination (light load detection threshold) becomes larger, and the intermittent oscillation operation is also performed in the heavy load area where the stable oscillation operation is originally intended.

Therefore, the intermittent oscillation frequency is lower than the human audible range (20kHz or less), and when a ceramic capacitor is used as the output capacitor 10, there is a problem of generating sound due to the piezoelectric effect

[0012] In addition, as a third problem, there is a problem that, since there is no current difference between the load current that enters the intermittent oscillation operation and the load current that leaves the intermittent oscillation operation, the operation becomes unstable in the load region near the threshold value.

[0013] With regard to Patent Document 2, although the above-mentioned second problem can be reduced, the first and third problems cannot be solved.

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