JP2006149056A - Dc-dc converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a low-ripple and high-accuracy output voltage achieved in the high accuracy of an output voltage at light loading. <P>SOLUTION: A high-side switch 15 and a low-side switch 14 are connected in series between an input voltage Vdd and ground potential, and an inductor 17 and a capacitor 18 are connected between a connector and an output terminal. A current detector 16 detects the current of the low-side switch 14 and outputs a current signal VIL. An error amplifier 3 compares a divided voltage of the output and a first reference voltage by using feedback resistors 1, 2 amplifies the difference of the comparison, and outputs an error signal VE. A control circuit 6 turns on the high-side switch 15 by using an output signal VX obtained by comparing the error signal VE of a first comparator 5 and the current signal VIL. A time for turning on the high-side switch is determined by an output of a latch circuit 10 that corresponds to a current IL of the inductor 17 inputted to a timer circuit 4, and the control circuit 6 is reset. The high-side switch 15 and the low-side switch 14 are complementarily turned on and off, to stabilize an output voltage Vout to a prescribed voltage. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention is a DC-DC converter that supplies a stable direct-current voltage to various electronic devices, and in particular, a DC that obtains a low ripple and high-accuracy output voltage by a control system that adjusts an off time of a switch that is a main component thereof. -It relates to a DC converter.

  In recent years, DC-DC converters are often used for power supplies for CPUs of personal computers. In general, a DC-DC converter is composed of an inductor, a high-side switch and a low-side switch connected in series between a power supply voltage and a ground potential, and the high-side switch and the low-side switch are repeatedly turned on and off alternately. Thus, the inductor repeatedly accumulates and releases magnetic energy, and the AC voltage generated at that time is rectified and supplied to the load as the output voltage.

  The output voltage is adjusted by the ratio of the on time in one cycle of the high side switch. The current that flows through the inductor is a triangular waveform that repeatedly increases and decreases when the switch is turned on and off. In the current mode control system, the peak or valley value is usually controlled to turn on or off the high-side switch. Control the time.

  In the on-time control, it is necessary to detect the current flowing through the high-side switch, and the detection circuit and its peripheral circuit are configured on the power supply voltage side. For this reason, the circuit configuration is complicated in order to accurately detect the current with respect to the power supply voltage assumed to fluctuate. On the other hand, the off-time control for detecting the current flowing through the low-side switch has a simple circuit configuration because the detection circuit and its peripheral circuits are set to the ground side.

Furthermore, with the recent trend of decreasing output voltage, the on-time of the high side switch tends to be shorter. In the on-time control method, detection and control must be performed while the high-side switch is on, but in the off-time control method, detection and control may be performed while the high-side switch is off. The control time can be taken longer. For the reasons described above, a device relating to an off-time control method has been devised as in Patent Document 1.
JP 2001-136737 A

  However, in the conventional technology having such a configuration, an intermittent operation is performed at a light load. This is because the switching operation is performed only when it is detected that the output voltage has dropped to the set voltage, and there is a problem that the DC deviation between the output voltage and the set voltage is maximum and ½ of the ripple voltage is generated.

  The present invention is directed to solving the problems of the prior art, and provides a DC-DC converter capable of obtaining a low ripple and high accuracy output voltage that realizes high accuracy of the output voltage at light load. With the goal.

  In order to achieve the above object, a DC-DC converter according to claim 1 according to the present invention has a synchronous rectifier topology and a valley current control buck conversion for outputting a lower output voltage from an input voltage. A high-side switch and a low-side switch coupled in series between an input voltage and a ground potential, and a switch coupling between the high-side switch and the low-side switch and an output terminal. An inductor; a current detector that measures a current flowing through the inductor; an error amplifier that outputs an error signal between a voltage divided by a first resistor and a second resistor connected in series to an output terminal; and a first reference voltage; and current detection A first comparator that compares the output of the error amplifier and the error amplifier, and a plurality of second comparisons that compare a voltage drop caused by the current detector and a plurality of reference voltages A latch circuit that connects the outputs of the plurality of second comparators, a control circuit that complementarily turns on and off the high-side switch and the low-side switch using the output of the first comparator, and a control circuit that uses the output of the latch circuit And a timer circuit for controlling the control circuit, wherein the on-time of the control circuit is varied according to the current flowing through the inductor.

  The DC-DC converter according to claim 2 is a DC-DC converter having a synchronous rectifier topology and having a valley current control buck converter for outputting an input voltage to a lower output voltage, A high-side switch and a low-side switch coupled in series between the input voltage and the ground potential, an inductor connected between the switch coupling portion between the high-side switch and the low-side switch and the output terminal, and a current for measuring a current flowing through the inductor A detector, an error amplifier that outputs an error signal between the first reference voltage and a voltage divided by a first resistor and a second resistor connected in series to the output terminal, and a first that compares the outputs of the current detector and the error amplifier. A comparator, a second comparator for comparing the voltage drop by the current detector and the second reference voltage, a voltage drop by the current detector and the third reference voltage A third comparator for comparing the voltage drop, a fourth comparator for comparing the voltage drop caused by the current detector and the fourth reference voltage, a latch circuit connecting the outputs of the second, third, and fourth comparators, and a first comparison A control circuit that complementarily turns on and off the high-side switch and low-side switch according to the output of the capacitor, and a timer circuit that controls the control circuit according to the output of the latch circuit, and the on-time of the control circuit is variable depending on the current flowing through the inductor It is characterized by doing.

  The DC-DC converter according to claim 3 is the DC-DC converter according to claim 1, wherein the timer circuit for controlling the on-time of the control circuit by the output of the latch circuit is a constant current source. A DC-DC converter characterized by comprising a circuit for charging a plurality of capacitors.

  A DC-DC converter according to a fourth aspect is the DC-DC converter according to the first or second aspect, wherein the timer circuit that controls the on-time of the control circuit by the output of the latch circuit includes a plurality of constants. It is characterized by comprising a circuit for charging a single capacitor by switching the current source.

  According to the above configuration, a circuit for monitoring the load current and varying the on-time is added to the DC-DC converter, and the peak current flowing through the inductor of the output terminal is controlled by the circuit to shorten the on-time at light load. Thus, continuous operation can be maintained even at light loads, and the output voltage can be made highly accurate.

  According to the present invention, in the method of controlling the off time of the high side switch, it is possible to operate in a continuous mode even at a light load, and to obtain an output voltage with higher accuracy in a wider load range than in the prior art. Compared to intermittent operation, the output ripple voltage during intermittent operation can be reduced because the on-time is shortened, and the output ripple voltage that caused the DC shift at the output terminal is reduced, resulting in higher output voltage accuracy. There is an effect that can be done.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a circuit diagram showing a schematic configuration of a DC-DC converter according to an embodiment of the present invention. In FIG. 1, 1 and 2 are feedback resistors, 3 is an error amplifier, 4 is a timer circuit, 5 is a first comparator, 6 is a control circuit for performing switching control, and 10 is a latch circuit comprising RS latches 7, 8, and 9. 11, 12 and 13 are second, third and fourth comparators, 14 is a low-side switch which is a rectifier, 15 is a high-side switch which is switching means, 16 is a current detector, 17 is an inductor, and 18 is smoothing means. This is a capacitor.

  The operation of the DC-DC converter in the present embodiment shown in FIG. 1 will be described below. A high-side switch 15 and a low-side switch 14 are connected in series between the input voltage Vdd and the ground potential, and an inductor 17 and a capacitor 18 are configured between the coupling portion and the output terminal of these switches to constitute a filter circuit. Connecting.

  The current detector 16 detects the current of the low side switch 14 and outputs a current signal VIL. The current detection circuit includes an error amplifier 3, a current detector 16, and a first comparator 5. The error amplifier 3 compares and amplifies the voltage obtained by dividing the output voltage Vout by the feedback resistors 1 and 2 and the first reference voltage, and outputs an error signal VE. The first comparator 5 compares the error signal VE with the current signal VIL of the voltage drop caused by the current detector 16.

  The control circuit 6 confirms that the low-side switch 14 is turned off by the input output signal VX from the first comparator 5 and turns on the high-side switch 15. This on-time is determined by an input signal to be described later to the timer circuit 4 and an output corresponding thereto. Further, the control circuit 6 is reset by the output of the timer circuit 4.

  As a result, the high side switch 15 and the low side switch 14 are complementarily turned on and off to operate to stabilize the output voltage Vout to a predetermined voltage.

  Next, description will be made with reference to FIG. 2 showing operation waveforms of the DC-DC converter in the present embodiment. FIG. 2A shows a waveform of continuous operation when the current IL flowing through the inductor 17 shown in FIG. 1 is large. When the current IL flowing through the inductor 17 decreases, the waveform of the intermittent operation as shown in FIG. Since the ON time is fixed during the intermittent operation shown in FIG. 2B, the waveform interval of the output ripple voltage ΔVrpl is the same as when the current flowing through the inductor 17 is large. For this reason, during intermittent operation, DC variation occurs in the output voltage Vout, making it difficult to output the output voltage Vout with high accuracy.

  In the DC-DC converter of the present embodiment, the range of continuous operation is widened because the on-time is varied in accordance with the current flowing through the inductor 17, and the output ripple voltage ΔVrpl is 1 as shown in the waveform of FIG. / N, and the accuracy of the output voltage Vout can be increased.

  The current signal VIL output from the current detector 16 is also input to the second, third, and fourth comparators 11, 12, and 13, respectively. As shown in FIG. 3, the operation waveforms (a), (b), and (c) represent the waveform of the LX voltage between the high-side switch 15 and the low-side switch 14. The LX voltage generates a voltage ΔV due to the ON resistance of the low side switch 14. This voltage ΔV increases as the current IL flowing through the inductor 17 increases. For this reason, when the current IL flowing through the inductor 17 increases, the timer circuit 4 operates and the on-time of the switch controlled by the control circuit 6 is lengthened.

  Therefore, the LX voltage is input to the RS latches 7 to 9 in the latch circuit 10 to which the outputs of the second, third, and fourth comparators 11, 12, and 13 are respectively input, and the second, third, and fourth comparisons are performed. The outputs of the units 11, 12 and 13 are held in the latch circuit 10.

  As shown in FIG. 3C, when the current flowing through the inductor 17 is large, the second, third, and fourth comparators 11, 12, and 13 operate, and the LX voltage reaches the voltage “−Vt”. As a trigger, the L2out, L3out, and L4out are output from the latch circuit 10 to the timer circuit 4.

  When the current flowing through the inductor 17 becomes small, the second and third comparators 11 and 12 operate and output L2out and L3out from the latch circuit 10 to the timer circuit 4.

  Further, when the current flowing through the inductor 17 becomes small, only the second comparator 11 operates and outputs L2out from the latch circuit 10 to the timer circuit 4.

  In this way, by preparing a plurality of comparators that are operated by the current flowing through the inductor 17, the on-time can be varied according to the value of the current flowing through the inductor 17.

  FIG. 4A is a circuit diagram showing a configuration of the timer circuit in the present embodiment. This operation will be described based on FIG. 4A with reference to FIG. Now, when all of L2out, L3out, and L4out are output from the latch circuit 10, the current IL flowing through the inductor 17 is large, so that the on-time is extended. Therefore, the on-time is extended by turning on the switches 23, 25, and 27 of the timer circuit 4. Further, the values are held by the RS latches 7, 8, and 9 until the LX voltage is lowered to “−Vt” next time.

  As shown in FIG. 4B, the time to turn on the switch of the control circuit 6 can be varied by changing the time of Ton2, 3, 4 according to the combination of turning on the switches 23, 25, 27. Can do.

  As described above, the timer circuit 4 can vary the on-time by the current IL flowing through the inductor 17. The second, third, and fourth comparators 11, 12, and 13 shown in FIG. 1, the RS latches 7, 8, and 9 of the latch circuit 10, and the switches 23, 25, and 27 of the timer circuit 4 shown in FIG. By using n current sources 24, 26, and 28, the ON time can be divided into n. In the example shown in FIG. 1 and FIG. 4 of the present embodiment, n = 3 is described. However, the present invention is not limited to this, and any number may be used.

  The timer circuit 4 may be configured to charge a plurality of capacitors with one constant current source as another configuration example.

  The DC-DC converter according to the present invention operates in a continuous mode even at a light load in a system for controlling the off time of the high side switch, obtains an output voltage with high accuracy over a wide load range, and turns on an intermittent operation. The output ripple voltage during intermittent operation can be reduced by shortening the time, the output ripple voltage can be reduced and the output voltage can be increased in accuracy, and the output is controlled by adjusting the ON time and OFF time of the switching means. -Useful for DC converters.

The circuit diagram which shows schematic structure of the DC-DC converter in embodiment of this invention An operation waveform (a) when a large current flows through the inductor in this embodiment, an intermittent operation waveform (b) in which the current flowing through the inductor is reduced, and an operation waveform (c) in which the time of the current flowing through the inductor is varied are shown. Figure The figure which shows the waveform (a) when the inductor current is small at the LX voltage in this embodiment, the waveform (b) when the inductor current is medium, and the waveform (c) when the inductor current is large. (A) of the timer circuit in the present embodiment is a circuit diagram showing the configuration, and (b) is a diagram showing the time of Ton.

Explanation of symbols

1, 2 feedback resistor 3 error amplifier 4 timer circuit 5 first comparator 6 control circuit 7, 8, 9 RS latch 10 latch circuit 11 second comparator 12 third comparator 13 fourth comparator 14 low side switch 15 high side Switch 16 Current detector 17 Inductor 18, 29 Capacitor 21 Constant current source 22 Reference current source 23, 25, 27 Switch 24, 26, 28 Current source 30 Comparator

Claims (4)

A DC-DC converter having a synchronous rectifier topology and having a valley current controlled buck converter for outputting an input voltage to a lower output voltage,
Measures the current flowing in the inductor, the high-side switch and the low-side switch coupled in series between the input voltage and the ground potential, the inductor connected between the switch coupling part between the high-side switch and the low-side switch and the output terminal A current detector that outputs, an error amplifier that outputs an error signal between a voltage divided by a first resistor and a second resistor connected in series to the output terminal and a first reference voltage, and outputs of the current detector and the error amplifier A plurality of second comparators for comparing a voltage drop caused by the current detector and a plurality of reference voltages, a latch circuit connecting outputs of the plurality of second comparators, A control circuit that complementarily turns on and off the high-side switch and the low-side switch by an output of the first comparator, and an output of the latch circuit. DC-DC converter, characterized by a timer circuit for controlling the control circuit to vary the current flowing through the on-time of the control circuit to the inductor Te. A DC-DC converter having a synchronous rectifier topology and having a valley current controlled buck converter for outputting an input voltage to a lower output voltage,
Measures the current flowing in the inductor, the high-side switch and the low-side switch coupled in series between the input voltage and the ground potential, the inductor connected between the switch coupling part between the high-side switch and the low-side switch and the output terminal A current detector that outputs, an error amplifier that outputs an error signal between a voltage divided by a first resistor and a second resistor connected in series to the output terminal and a first reference voltage, and outputs of the current detector and the error amplifier A first comparator that compares the voltage drop caused by the current detector and a second reference voltage, a third comparator that compares the voltage drop caused by the current detector and a third reference voltage, A fourth comparator for comparing a voltage drop caused by the current detector and a fourth reference voltage; a latch circuit connecting outputs of the second, third, and fourth comparators; A control circuit that complementarily turns on and off the high-side switch and the low-side switch by an output of a comparator; and a timer circuit that controls the control circuit by an output of the latch circuit; A DC-DC converter characterized by being variable according to the current flowing through the inductor.   3. The DC-DC converter according to claim 1, wherein the timer circuit that controls the on-time of the control circuit based on the output of the latch circuit is configured by a circuit that charges a plurality of capacitors by a constant current source.   3. The DC circuit according to claim 1, wherein the timer circuit that controls the on-time of the control circuit by the output of the latch circuit is configured by a circuit that switches a plurality of constant current sources and charges a single capacitor. DC converter.

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