JP2001286128A - Switching regulator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a switching regulator capable of reducing undershoot when a load rapidly increases and also curtailing the time until the output voltage is stabilized as well. SOLUTION: A switching element Tr11 and a resistor R10 connected to the switching element are connected between a source side of a switching element Tr10 and a choke coil CL10, and an output voltage of the coke coil CL10 and a reference voltage Vref10 are compared. Then, the switching element Tr11 is switched by a comparator 10 having hysteresis.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a switching regulator.

[0002]

2. Description of the Related Art Generally, a chopper type step-down switching regulator mainly comprises a choke coil L20, a diode Di20 and a smoothing capacitor C, as shown in the circuit diagram of FIG.
It comprises L20, switching element Tr20 and control circuit 21.

In the circuit configuration of FIG. 2, a charging current flows from an input Vin20 by first turning on a Tr20, and a choke coil L
The energy is stored in the power supply 20 and the power is supplied to the output Vout20. Next, by turning off Tr20, a discharge current flows to the output with the back electromotive force of the choke coil L20 due to the stored energy, and power is supplied to the output Vout20.

Further, the control circuit 21 monitors the output voltage and stabilizes the output voltage by controlling the ON time of the Tr 20.

As described above, the output voltage is stabilized. However, abrupt changes in load depend on the response of the system shown in FIG. 2 and the capacitance of the smoothing capacitor CL20.
Overshoot and undershoot occur. Here, the choke coil is what slows down the response of the system.
L20. Usually, an appropriate choke coil L20 is selected in consideration of the oscillation frequency of the control circuit 21, load current, ripple, and the like.

[0006]

In the conventional switching regulator, when the load suddenly increases, the current is supplied through the choke coil, so that the slope depends on the inductance value (L value) of the choke coil. Increase. As a result, there is a problem that a large undershoot occurs depending on the time constant of the L value of the choke coil even if the response speed of the control circuit is fast.

[0007]

In order to solve the above-mentioned problems, the present invention provides another path between the input and the output via a switch. Then, when the load fluctuates rapidly, an undershoot can be suppressed by supplying a current through another path and supplying power to the output.

[0008]

Embodiments of the present invention will be described below with reference to the drawings.

[0009]

FIG. 1 is a circuit diagram of a chopper type step-down switching regulator showing a first embodiment of the present invention. Choke coil L10, diode Di10, smoothing capacitor CL1
0, the switching element Tr10, and the control circuit 11 are the same as in the related art.

The difference from the conventional example shown in FIG. 2 is that a switching element Tr11 and a resistor R10 are interposed between the source side of the switching element Tr10 and the output side of the choke coil L10, and the switching element Tr11 is controlled. That is, a comparator 10 and a reference voltage Vref10 of the comparator 10 are added. Here, the comparator 10 is a countermeasure against undershoot when the load current (hereinafter, Iout) suddenly increases. The comparator 10 has a hysteresis to detect an undershoot at the time of a load change and release the undershoot at a desired output voltage.

FIG. 3 shows the current operation (IL) and the output voltage (Vout) on the output side of the coil when Iout increases sharply, for the conventional operation and the operation of the present invention.

First, the choke coil L10 and the diode Di1
The operation of the conventional basic circuit represented by 0, the smoothing capacitor CL10, the switching element Tr10, and the control circuit 11 is shown by the thick dotted line in FIG. As shown in FIG. 3, at the time of load fluctuation, the coil current increases while having a time constant (Td3) of the inductance value of the coil, in order to allow the coil to pass a current large enough to allow the rapidly increased Iout to flow. The undershoot increases in proportion to the time constant.

Next, an operation according to the present invention in which undershoot is reduced is shown by a thick solid line in FIG. Td1 indicates the time required for switching from the current path of the conventional switching regulator to another path according to the present invention, and Vref10 is the output voltage value at that time. As shown in FIG. 1, Vout is input to the positive side and Vref10 is input to the negative side of the input of the comparator 10. Since the comparator 10 is for countermeasures against undershoot, Vref10 is set to the output voltage set value−α. α is a value that determines the amount of undershoot. If the value of α is too large, the undershoot increases, and if it is too small, voltage fluctuation (ripple voltage) due to switching is caught.
It is necessary to take measures such as increasing the smoothing capacitor CL10 and decreasing the ripple voltage itself. In consideration of this, it is appropriate that the α value is about 100 mV to 200 mV.

In the normal state, since Vout10 is larger than Vref10, the comparator 10 outputs high (H), and PchTr11
Is turned off and performs the same operation as the conventional switching regulator. When Vout10 becomes smaller than Vref10 due to undershoot when the load suddenly increases, the comparator 10 outputs low (L), and the PchTr11
Turn ON. At this time, the current flows through the resistor R10 and IL
Can be launched quickly. Td2 shown in FIG. 3 is the IL time constant according to the present invention. By reducing this time constant, undershoot is reduced.

Another feature is that the transistor Tr11 is connected from the source side of the transistor Tr10, but this is to prevent the destruction of the transistor Tr10 due to a large peak current flowing when the load is changed to the path R10. Here, it is necessary to select Tr11 having a large allowable current Id.

FIG. 4 is a chopper type step-down switching regulator circuit diagram showing a second embodiment of the present invention. The difference from the first embodiment shown in FIG. 1 is that a choke coil L41 is interposed between the drain side of Tr41 and the output side of choke coil L40, and that the source side of Tr41 is connected to the drain side of Tr40. By performing the operation shown in FIG. 3 similarly to the first embodiment, it is possible to reduce the undershoot at the time of load change.

As described above, since the magnitude of the undershoot depends on the time constant of the choke coil, it is necessary to select a choke coil L41 having an inductance value smaller than that of L40 and to shorten the time constant.

Further, since the regulator operates by switching according to the coil characteristics, when the current path at the time of a load change passes through the choke coil L41, it is connected to the drain side of the switching element L40. At that time, since a large peak current flows when the path is switched to the L41 path during a load change, it is necessary to select a Tr40 having a large allowable current Id.

FIG. 5 is a circuit diagram of a chopper type step-down switching regulator showing a third embodiment of the present invention. The purpose of the present invention is to reduce the undershoot at the time of a load change as in the first embodiment.
The Nch Tr51 is interposed between the source side and the output side of the choke coil, and the gate of the Tr51 is provided with Vref51 instead of being controlled by the comparator.

In order to turn off Tr51 in the normal state and turn on Tr51 when the load fluctuates, Vref51 corresponds to the following equation.

Vref51 = Vout50 + Vth51-β (1) When it is desired to set the undershoot at about 100 mV to 200 mV, the undershoot is reduced by setting β = 100 mV to 200 mV.

Further, similarly to the second embodiment, Tr51 has an allowable current Id.
You need to choose the big one.

FIG. 6 is a circuit diagram of a chopper type step-down switching regulator showing a fourth embodiment of the present invention. The purpose of the present invention is to reduce the undershoot at the time of load change as in the first embodiment.
Nch Tr61 is connected between the source side of the transistor and the output side of the choke coil, and resistors R60 and Tr61 are connected between the gate of Tr61 and the output.
The point is that C60 is interposed between the gate and the ground (GND). Here, R60 and C60 are RC circuits.

In the normal state, Vth61 of Tr61 is 0V and Tr6
Since 1 is OFF, the same operation as the conventional switching regulator is performed. When Vout60 drops due to undershoot when the load suddenly increases, a voltage difference (Vgs) occurs between the gate and the source of Tr61. This is Tr61
Both gate and source are connected to output, but Tr61
Is connected to the output voltage via the CR circuit, so that the gate voltage has a time constant of C × R, and the gate voltage does not change immediately even if the output voltage changes. Here, when Vgs becomes larger than Vth61, Tr61 turns ON, and current is supplied through the path of Tr61.

[0025]

As described above, the switching regulator according to the present invention has an effect of suppressing an undershoot by supplying a current to the output through another path and supplying power to the output when the load fluctuates suddenly.

[Brief description of the drawings]

FIG. 1 is an overall circuit diagram of a chopper type step-down switching regulator according to a first embodiment of the present invention.

FIG. 2 is an overall circuit diagram of a conventional chopper type step-down switching regulator.

FIG. 3 is an operation explanatory diagram of the first embodiment of the present invention.

FIG. 4 is an overall circuit diagram of a chopper type step-down switching regulator according to a second embodiment of the present invention.

FIG. 5 is an overall circuit diagram of a chopper type step-down switching regulator according to a third embodiment of the present invention.

FIG. 6 is an overall circuit diagram of a chopper type step-down switching regulator according to a fourth embodiment of the present invention.

[Explanation of symbols]

 Vin10,20,40,50,60 ・ ・ ・ Input voltage Vout10,20,40,50,60 ・ ・ ・ Output voltage Tr10,11,20,40,41,50,51,60 ・ ・ ・ Pch transistor Tr61 ・・ ・ Nch transistor L10,20,40,41,50,60 ・ ・ ・ Choke coil Di10,20,40,50,60 ・ ・ ・ Diode CL10,20,40,50,60 ・ ・ ・ Smoothing capacitor C60 ・・ ・ Capacitors RL10,20,40,50,60 ・ ・ ・ Load resistance R10,60 ・ ・ ・ Resistance 10,40 ・ ・ ・ Comparator Vref10,40,51 ・ ・ ・ Reference voltage 11,21,41,51,61 ... Control circuits

Claims (4)

[Claims] 1. A switching regulator having a configuration in which a switching element 1, a choke coil, a diode, and a smoothing capacitor are provided between an input and an output.
A switching regulator comprising a switching element 2 and a resistor between an input and an output, and a comparator for monitoring the output voltage and controlling the switching element 2 is added. 2. The switching regulator according to claim 1, wherein said resistor is replaced with a choke coil. 3. A switching regulator having a configuration in which a switching element 1, a choke coil, a diode, and a smoothing capacitor are provided between an input and an output.
A switching regulator, wherein a reference voltage for applying and controlling a constant voltage to a gate of the switching element 2 is applied between the input and the output via the switching element 2. 4. The switching regulator according to claim 3, wherein an RC circuit is provided between a gate of said switching element 2 and an output.