US-12627232-B2 - DC/DC converter having a coil connected to a connection point between two switches connected in series

US12627232B2US 12627232 B2US12627232 B2US 12627232B2US-12627232-B2

Abstract

A DC/DC converter has a coil connected to a connection point between a main switch and a subordinate switch connected in series; and alternately turns on/off the main switch and the subordinate switch, thereby converting a direct current input voltage into a predetermined direct current output voltage. The DC/DC converter includes a current mode detection unit for detecting either a continuous current mode in which a current flowing through the coil does not pass through a zero point, or a discontinuous current mode in which the current flowing through the coil passes through the zero point, when the subordinate switch is ON; and a subordinate switch control unit for controlling the ON time of the subordinate switch in a next or later cycle, based on a time from turning-off of the subordinate switch until a voltage at the connection point reaches a predetermined threshold value.

Inventors

Kousuke Hayakawa

Assignees

TOREX SEMICONDUCTOR LTD.

Dates

Publication Date: 20260512
Application Date: 20221020
Priority Date: 20211021

Claims (8)

1 . A DC/DC converter which has a coil connected to a connection point between two switching means that are connected in series; uses, as a main switching means, one switching means of the two switching means that is being turned on when energy is stored in the coil, and uses, as a subordinate switching means, another switching means of the two switching means that is being turned on when the energy stored in the coil is sent out to an output side; and performs a switching action for alternately turning on/off the main switching means and the subordinate switching means, thereby converting a direct current input voltage into a predetermined direct current output voltage, the DC/DC converter, comprising: a current mode detection means for detecting either a continuous current mode in which a current flowing through the coil does not reach zero, or a discontinuous current mode in which the current flowing through the coil reaches zero, when the main switching means is turned OFF; and a subordinate switch control means for controlling an ON time of the subordinate switching means in a next or later cycle, based on a time from turning-off of the subordinate switching means until a voltage at the connection point reaches a predetermined threshold value lying within a range between a minimum value and a maximum value of the voltage, wherein if the discontinuous current mode is detected based on results of detection by the current mode detection means, the subordinate switch control means performs a correction on the controlled ON time of the subordinate switching means in the next or later cycle, wherein the subordinate switch control means exercises control based on a value of a voltage which varies in one direction so as to rise or fall depending on the time from the turning-off of the subordinate switching means until the voltage at the connection point reaches the predetermined threshold value, and which falls or rises by a constant amount in a direction opposite to the direction of varying so as to rise or fall similarly in each cycle, and wherein the subordinate switch control means compares the value of the voltage which varies in one direction so as to rise or fall depending on the time from the turning-off of the subordinate switching means until the voltage at the connection point reaches the predetermined threshold value, and which falls or rises by the constant amount in the direction opposite to the direction of varying so as to rise or fall similarly in each cycle, with a value of a voltage varying in the one direction by rising or falling in value depending on the ON time of the subordinate switching means, to exercise control.
2 . The DC/DC converter according to claim 1 , wherein the subordinate switch control means is adapted to control the ON time of the subordinate switching means in the next or later cycle so that a polarity of the current flowing through the coil is not reversed.
3 . The DC/DC converter according to claim 1 , wherein the subordinate switch control means decreases a rise rate of the voltage, which rises depending on the time from the turning-off of the subordinate switching means until the voltage at the connection point reaches the predetermined threshold value, thereby performing the correction.
4 . The DC/DC converter according to claim 1 , wherein the subordinate switch control means increases the value of the voltage, which falls in each cycle, thereby performing the correction.
5 . A DC/DC converter which has a coil connected to a connection point between two switches that are connected in series; uses, as a main switch, one switch of the two switches that is being turned on when energy is stored in the coil, and uses, as a subordinate switch, another switch of the two switches that is being turned on when the energy stored in the coil is sent out to an output side; and performs a switching action for alternately turning on/off the main switch and the subordinate switch, thereby converting a direct current input voltage into a predetermined direct current output voltage, the DC/DC converter, comprising: a current mode detection unit configured to detect either a continuous current mode in which a current flowing through the coil does not reach zero, or a discontinuous current mode in which the current flowing through the coil reaches zero, when the main switch is turned OFF; and a subordinate switch control unit configured to control an ON time of the subordinate switch in a next or later cycle, based on a time from turning-off of the subordinate switch until a voltage at the connection point reaches a predetermined threshold value lying within a range between a minimum value and a maximum value of the voltage, wherein if the discontinuous current mode is detected based on results of detection by the current mode detection unit, the subordinate switch control unit performs a correction on the controlled ON time of the subordinate switch in the next or later cycle, wherein the subordinate switch control unit exercises control based on a value of a voltage which varies in one direction so as to rise or fall depending on the time from the turning-off of the subordinate switch until the voltage at the connection point reaches the predetermined threshold value, and which falls or rises by a constant amount in a direction opposite to the direction of varying so as to rise or fall similarly in each cycle, and wherein the subordinate switch control unit compares the value of the voltage which varies in one direction so as to rise or fall depending on the time from the turning-off of the subordinate switch until the voltage at the connection point reaches the predetermined threshold value, and which falls or rises by the constant amount in the direction opposite to the direction of varying so as to rise or fall similarly in each cycle, with a value of a voltage varying in the one direction by rising or falling in value depending on the ON time of the subordinate switch, to exercise control.
6 . The DC/DC converter according to claim 5 , wherein the subordinate switch control unit is adapted to control the ON time of the subordinate switch in the next or later cycle so that a polarity of the current flowing through the coil is not reversed.
7 . The DC/DC converter according to claim 5 , wherein the subordinate switch control unit decreases a rise rate of the voltage, which rises depending on the time from the turning-off of the subordinate switch until the voltage at the connection point reaches the predetermined threshold value, thereby performing the correction.
8 . The DC/DC converter according to claim 5 , wherein the subordinate switch control unit increases the value of the voltage, which falls in each cycle, thereby performing the correction.

Description

CROSS REFERENCE TO RELATED APPLICATIONS This application is the United States national phase of International Patent Application No. PCT/JP2022/039076 filed Oct. 20, 2022, and claims priority to Japanese Patent Application No. 2021-172741 filed Oct. 21, 2021, the disclosures of which are hereby incorporated by reference in their entireties. BACKGROUND OF THE INVENTION Field of the Invention This invention relates to a DC/DC converter and, more specifically, to that useful when applied to driving in two drive modes, i.e., a PWM mode adapted for a heavy load and a PFM mode for a light load. Description of Related Art As a DC/DC converter, wide use is made of one which has a coil connected to a connection point between two switching means connected in series, and performs a switching action for alternately turning on/off the main switching means (one of the two switching means which is turned on when energy is stored in the coil), and the subordinate switching means (the other of the two switching means which is turned on when the energy stored in the coil is sent out to the output side), thereby converting a direct current input voltage into a predetermined direct current output voltage. As a type of such a DC/DC converter, a proposal has been made for one equipped with a subordinate switch control means, which controls the ON time of the subordinate switching means in a next or later cycle, based on a time elapsing from the turning-off of the subordinate switching means until a predetermined threshold value lying within a range between the minimum value and the maximum value of the voltage of the rising waveform of the connection point (in the case of a step-down type) is reached, in an attempt to prevent, without fail, a harmful phenomenon due to the reversal of the polarity of a current flowing through the coil. This type of DC/DC converter has become publicly known (see JP 4674661). The DC/DC converter disclosed in JP 4674661 has faced the following problem: If there are two current modes, i.e., a continuous current mode (CCM) in which a coil current flowing through the coil does not pass through a zero point, and a discontinuous current mode (DCM) in which the coil current flowing through the coil passes through the zero point, during the switching action of the switching means, an error occurs between control in the continuous current mode and control in the discontinuous current mode. In detail, with the DC/DC converter disclosed in JP 4674661, the period from the turning-off of the subordinate switching means until the voltage at the connection point reaches the predetermined threshold value may be longer in the discontinuous current mode than in the continuous current mode. The reason is as follows: In the continuous current mode, after the subordinate switching means is turned off, the voltage at the connection point instantaneously rises vertically. In the discontinuous current mode, on the other hand, after the subordinate switching means is turned off, ringing is induced in the voltage at the connection point owing to resonance of the coil and parasitic capacity present at the connection point, so that the above voltage rises gently. That is, compared with the time until the threshold value is reached in the former case, the time until the threshold value is reached delays in the latter case. With the DC/DC converter disclosed in JP 4674661, as noted above, a deviation arises between the time from the turning-off of the subordinate switching means until the voltage at the connection point reaches the predetermined threshold value in the continuous current mode and that in the discontinuous current mode. The deviation causes the error between the predetermined control in the continuous current mode and that in the discontinuous current mode. As a result, a phenomenon in which the coil current flows backward from the output side to the ground side may occur. Such a phenomenon results in an outputted charge being discarded into the ground GND, thus inducing a decrease in the efficiency of the DC/DC converter. SUMMARY OF THE INVENTION The present invention has been accomplished in the light of the prior art as described above. It is an object of the invention to provide a DC/DC converter which is driven in a continuous current mode and a discontinuous current mode, and which can exercise predetermined control accurately without causing an error when controlling the ON time of a subordinate switching means in a next cycle based on a time from the turning-off of the subordinate switching means until a voltage at a connection point connected to an end of a coil reaches a predetermined threshold value. A first aspect of the present invention for attaining the above object is a DC/DC converter which has a coil connected to a connection point between two switching means connected in series; uses as a main switching means one switching means of the two switching means being turned on when energy is stored i