JP2869371B2 - Power supply control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plurality of switching power supply circuits mounted on a power supply device and having different characteristics (specifically, a switching power supply circuit of a normal rectification type and a synchronous rectification type). And a power supply control device for driving each independently.

[0002]

2. Description of the Related Art In recent years, electronic devices have become smaller and more sophisticated and multifunctional, and a power supply device incorporated in the electronic devices has a plurality of power supplies corresponding to loads (machines and circuits) having different characteristics. It has a switching power supply circuit. Here, a pulse width modulation type control integrated circuit (PWM control IC) is generally used for drive control of the switching power supply circuit, and has a number of control systems corresponding to a load or a power supply circuit. When a plurality of switching power supply circuits are independently operated in the same power supply device, an interference phenomenon (switching beat) based on a plurality of switching operations may occur in the device. This, for example, when two switching power supply circuits, each of which to be operating in the switching frequencies f ₁ and f _2, that the low frequency corresponding to the difference between two switching frequencies (f ₁ -f ₂₎ is generated Is due.

In the conventional power supply device, in order to prevent the occurrence of the switching beat, the timing of the switching operation of the switching power supply circuit which operates independently is synchronized with each other. Means of unifying and using a waveform signal (triangular wave voltage) has been used. FIG. 4 schematically shows a power supply control device configured to prevent the occurrence of such switching beats and a power supply device having the same. The control device CD in FIG. 4 is roughly divided into a first control system 1 and a second control system.
, An oscillation circuit 3, a reference voltage source 4, and an accessory circuit 5. Here, the oscillating circuit 3 outputs a triangular wave voltage at a predetermined oscillating frequency, the reference voltage source 4 outputs a voltage with high stability as a reference level, and the accessory circuit 5 prevents output short-circuit protection and low-input malfunction prevention. The oscillation circuit 3, the reference voltage source 4, and the accessory circuit 5 are shared by each control system.

The control system 1 includes a first switching power supply circuit P
S1 is driven and controlled. Basically, the error amplifier Err1, the comparator Comp1, and the output buffer Buf are controlled.
1 As an operation of the control system 1, first, a feedback signal (FB1) is received from the switching power supply circuit PS1, and is compared with a reference voltage (V _REF ) in an error amplifier Err1 to obtain an error signal. The comparator Comp1 compares the error signal with the triangular wave voltage from the oscillation circuit 3 and generates an on-duty pulse output signal (PO1) corresponding to the output voltage. This pulse output signal (PO1) is supplied to the switching element of the switching power supply circuit via the output buffer Buf1, whereby the switching power supply circuit PS1 is driven and controlled so that the output voltage becomes constant.

Here, the accessory circuit 5 outputs an operation stop signal when an abnormality occurs in the switching power supply circuit PS1, and the output buffer Buf1 inhibits passage of the pulse output signal PO1 when receiving the operation stop signal, and the switching power supply The operation of the circuit PS1 is stopped. The control system 2 drives and controls the second switching power supply circuit PS2, and includes an error amplifier Err2, a comparator Comp2, and an output buffer Buf2. The operation is the same as that of the control system 1, and the description is omitted.

[0006] In recent years, there has been a strong demand for downsizing of the power supply device due to the recent portable electronic devices. In reducing the size of the power supply device, the switching frequency of the switching element is increased for the purpose of reducing the inductance and the capacitor, which are components of the switching power supply circuits (PS1, PS2). This switching frequency is determined by the oscillation frequency of the triangular wave voltage output from the oscillation circuit 3 of the control device CD. The oscillation frequency generally used is several hundred [kHz], but currently several [MHz].
There are even things. On the other hand, when an electronic device is made portable, a battery is used as a power supply source, and thus there is a strong demand for a power supply device with low power consumption. To reduce the power consumption of the power supply device, it is necessary to improve the efficiency of each switching power supply circuit, and a synchronous rectification method may be employed as a means for improving the efficiency of the switching power supply circuit.

In this synchronous rectification method, the loss caused by the on-state collector-emitter voltage generated in the transistor is smaller than the loss caused by the forward drop voltage generated in the diode. The generated loss is reduced, and the efficiency of the switching power supply circuit can be improved. However, in practice, when a transistor is used as a rectifying element, a loss is involved in the on / off operation, and the loss increases rapidly as the switching frequency increases. As a result, depending on the switching frequency, the loss is smaller in the normal rectification method using a diode than in the synchronous rectification method using a transistor. Incidentally, in the current semiconductor device, in order to obtain the benefit of improving the efficiency of the switching power supply circuit by adopting the synchronous rectification method, the switching frequency is about 200 [kHz].
Is said to be the limit.

In the synchronous rectification method using a transistor as a rectifying element, it is necessary to drive the transistor as a rectifying element in a complementary manner in synchronization with the operation of the switching element, which further requires circuits and components. . Therefore, the switching power supply circuit employing the synchronous rectification system is larger in size than the case of employing the normal rectification system at the cost of improving the efficiency, and as a result, the size of the power supply device is increased.

[0009]

In order to achieve a good balance between miniaturization and high efficiency of a power supply device, for example, a switching power supply circuit of a normal rectification system is applied to a load with low power consumption to reduce the size. In order to achieve high efficiency by applying a synchronous rectification type switching power supply to a load that consumes a large amount of power, such as a normal rectification type and a synchronous rectification type switching power supply circuit according to the characteristics of the load. May be appropriately arranged. However, if the switching power supply circuit of the normal rectification type and the synchronous rectification type are actually used together, the conventional power supply control device as shown in FIG. 4 uses a reference waveform signal (triangular wave voltage) for the purpose of preventing the occurrence of a switching beat. ) Is shared by the respective control systems, so that the pulse output signal (P
There is a problem in that only one type of switching frequency O) exists.

In other words, the switching frequency required for miniaturization and the switching frequency required for high efficiency (synchronous rectification) are in conflict with each other, so that either one of miniaturization and high efficiency is sacrificed. You have to do it. Therefore, the present invention makes it possible to independently operate a plurality of switching power supply circuits having different characteristics including the normal rectification method and the synchronous rectification method under switching conditions suitable for each, while preventing the occurrence of switching beats. Accordingly, it is an object of the present invention to provide a power supply control device capable of achieving a good balance between miniaturization and high efficiency of the power supply device.

[0011]

According to the present invention, a plurality of control systems are provided so that independent control can be performed for a plurality of power supply circuits. In the control device for the power supply of the pulse width modulation system in which the output signals are synchronized, among the plurality of control systems,
The pulse frequency of the pulse output signal of at least one control system is set to a frequency lower than (1 / n) of the pulse frequency of another control system by frequency dividing means. Specifically, a frequency dividing means is provided for a control system that supplies a pulse output signal to a switching power supply circuit using a synchronous rectification method,
Alternatively, a frequency dividing means is added to the oscillating means, and a reference waveform signal whose frequency is reduced by the frequency dividing means is supplied to a control system which supplies a pulse output signal to a switching power supply circuit using a synchronous rectification method. And

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A feedback signal corresponding to an output voltage of a switching power supply circuit is compared with a reference voltage,
A plurality of control systems including an error amplifier for generating an error signal corresponding to the deviation and a comparator for comparing the error signal with the triangular wave voltage and generating an on-duty pulse output signal corresponding to the output voltage are configured. A reference voltage source and an accessory circuit are provided, and the output reference voltage V _REF and operation stop signal are supplied to a plurality of control systems. In such a power supply control device, in the first embodiment of the present invention, an oscillation circuit provided in the device is shared by each control system, and a reference waveform signal (triangular wave voltage) having the same frequency is output from the oscillation circuit. Supply to each control system. A frequency dividing circuit is provided in at least one of the plurality of control systems (a control system that controls a synchronous rectification type switching power supply circuit), and a switching frequency of a pulse output signal output from the control system is controlled by another control system. The pulse output signal has a low frequency (1 / n) of the switching frequency.

A low frequency pulse output signal of a control system provided with a frequency dividing circuit is supplied to a synchronous rectification type switching power supply circuit, and a high frequency pulse output signal of another control system is supplied to a normal rectification type switching power supply circuit. Supply to The frequency dividing circuit is provided at the output terminal of the comparator or the input terminal for the reference waveform signal of the comparator in the control system. Further, in the second embodiment of the present invention, a frequency dividing means is added to an oscillation circuit provided in the control device to obtain a high-frequency reference waveform signal and a low-frequency reference waveform signal. By supplying each reference waveform signal to each control system, a control system that outputs a high-frequency pulse output signal and a control system that outputs a low-frequency pulse output signal are formed. A low frequency pulse output signal is supplied to a synchronous rectification type switching power supply circuit, and a high frequency pulse output signal is supplied to a normal rectification type switching power supply circuit.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A plurality of switching power supply circuits having different characteristics such as a normal rectification system and a synchronous rectification system can be driven independently under switching conditions suitable for each of them.
FIG. 1 schematically shows a first embodiment of a power supply control device according to the present invention. In FIG. 1, the same components as those shown in FIG. 4 are denoted by the same reference numerals. The power supply control device CD shown in FIG. 1 has a control system 1 and a control system 2 therein.
a, and further includes an oscillation circuit 3, a reference voltage source 4, and an accessory circuit 5 shared by the respective control systems. The control system 1 includes an error amplifier Err1, a comparator Comp1, and an output buffer Buf1, but the control system 2a includes a frequency divider div1 in addition to the error amplifier Err2, a comparator Comp2, and an output buffer Buf2. It has a configuration.

Here, the frequency dividing circuit div1 is provided with a comparator Com.
p2, which is connected to the output terminal of p2, divides the switching frequency of the pulse output signal (PO2) generated by the comparator Comp2, and outputs the pulse output signal (PO
The switching frequency is lower than the switching frequency of 1). In such a control device CD, the control system 1 drives and controls the switching power supply circuit of the normal rectification system, and the control system 2a
If the synchronous rectification type switching power supply circuit is driven and controlled, the normal rectification type switching power supply circuit can be downsized by increasing the frequency, and the synchronous rectification type switching power supply circuit can be increased in efficiency by lowering the frequency. Since the operation timings of the two pulse output signals are almost the same, there is no need to worry about the occurrence of a switching beat.

Incidentally, the oscillation frequency of the triangular wave voltage output from the oscillation circuit is set to 400 [kHz], that is, the switching frequency is set to 400 [kHz], and a switching power supply circuit based on a certain synchronous rectification method has a predetermined specification (output voltage = (2.8 [V], output current = 200 [mA]), the efficiency of the switching power supply circuit is 60
[%]. On the other hand, under the condition equivalent to setting the oscillation frequency of the triangular wave voltage output from the oscillation circuit to 400 [kHz] and the frequency division ratio of the frequency dividing circuit to 2, that is, the switching frequency to 200 [kHz]. It has been confirmed that when the same switching power supply circuit is driven under the same specification conditions, the efficiency of the switching power supply circuit increases to 85%. Therefore, in a power supply device in which a switching power supply circuit of a normal rectification type and a synchronous rectification type are provided inside, the size of the power supply device is almost determined by the oscillation frequency of the triangular wave voltage output from the oscillation circuit. It is understood that the efficiency of the power supply is greatly improved by the frequency divider.

In the control device CD shown in FIG. 1, the pulse output signal (PO
To divide 2), the divider circuit div1 is connected to the comparator Com.
It is configured to be connected to the output terminal of p2.
The output terminal of omp2 is connected to the output buffer Buf2,
A configuration in which a frequency dividing circuit is connected to the output terminal of the output buffer Buf2 may be adopted.

FIG. 2 shows a second embodiment of the power supply control device according to the present invention. In the control system 2a of the control device (CD) shown in FIG. 1, the frequency divider circuit d is provided on the output side of the comparator Comp2 in order to lower the frequency of the pulse output signal of the control system 2a.
Although iv1 is connected, in the control system 2b of the control device (CD) in FIG. 2, the frequency divider div2 is connected to the input terminal of the comparator Comp2 that receives the triangular wave voltage. In this case, the frequency of the triangular wave voltage input to the comparator Comp2 is divided by the frequency dividing circuit div2.
Of course, the pulse output signal (PO2) generated at omp2 has a lower frequency than the pulse output signal (PO1) of the control system 1, and the control system 2b in FIG. 2 and the control system 2a in FIG. That is, if the control system 1 drives and controls the normal rectification type switching power supply circuit and the control system 2b drives and controls the synchronous rectification type switching power supply circuit, respectively, the downsizing and the high efficiency can be simultaneously performed without difficulty.

FIG. 3 shows a third embodiment of the power supply control device according to the present invention. In the control devices shown in FIGS. 1 and 2, the frequency dividing circuits (div1, div2) are individually provided for the respective control systems (2a, 2b). However, in the control device of FIG. Dividing means is added to the shared oscillation circuit 3a so that the oscillation circuit 3a can obtain two reference waveform signals of a high-frequency triangular wave voltage and a low-frequency triangular wave voltage. By inputting the high-frequency triangular-wave voltage to the comparator Comp1 of the control system 1 and the low-frequency triangular-wave voltage to the comparator Comp2 of the control system 2, the control device of FIGS. CD) can have the same function and effect. Although there are various circuit systems for an oscillation circuit that outputs a triangular wave, generally, a circuit that generates a rectangular wave voltage from a DC voltage and further converts the rectangular wave voltage into a triangular wave voltage is often used. The oscillation circuit 3a shown in the embodiment of FIG. 3 divides the frequency when a rectangular wave voltage is generated, and then performs a triangular wave conversion to obtain a high frequency triangular wave voltage and a low frequency triangular wave voltage, or a rectangular wave. There are two types of means for obtaining a high-frequency triangular wave voltage and a low-frequency triangular wave voltage by dividing the voltage after converting the voltage into a triangular wave, and either of them may be adopted.

In the description of the embodiment shown in FIGS. 1, 2 and 3, two control systems are used, one for driving control of a normal rectification type switching power supply circuit and the other for synchronous rectification type switching power supply circuit. However, the present invention is not limited to the embodiment, and it goes without saying that the present invention is also applicable to a control device having an unspecified number of control systems. Further, in a control device having an unspecified number of control systems, when there are a plurality of control systems provided with frequency dividing circuits as in the embodiment of FIGS. 1 and 2, the frequency dividing ratio of each frequency dividing circuit is There is no need to make them the same, and the frequency division ratio is set in accordance with the characteristics of the switching power supply circuit to be driven and controlled, so that a pulse output signal (PO) having several different frequencies can be obtained from one controller. Is also good. Further, in order to obtain pulse output signals having several different frequencies, the respective frequency dividing means shown in FIGS. 1, 2 and 3 may be combined and used in one control device.

[0021]

As described above, in the power supply control device according to the present invention, one oscillating means is shared by a plurality of control systems configured in the control device, and the frequency is divided by a predetermined control system or oscillating means. By providing the means, a plurality of pulse output signals having different frequencies can be obtained from one control device by synchronizing their operation timings.
As a result, a plurality of switching power supply circuits having different properties, such as a normal rectification method and a synchronous rectification method, can be simultaneously driven independently and under switching conditions suitable for each of them. The occurrence of switching beats in the device is prevented.
As a result, by applying the control device according to the present invention, it is possible to achieve a good balance between miniaturization and high efficiency of the power supply device without sacrificing one of miniaturization and high efficiency.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a first embodiment of a power supply control circuit according to the present invention.

FIG. 2 is a circuit diagram of a power supply control circuit according to a second embodiment of the present invention.

FIG. 3 is a circuit diagram of a power supply control circuit according to a third embodiment of the present invention.

FIG. 4 is a schematic diagram of a conventional power supply control circuit and a power supply device to which the control circuit is applied.

[Description of Signs] 1, 2 Control system 2a, 2b Control system provided with frequency dividing circuit 3 Oscillation circuit 3a Oscillating circuit with frequency dividing means 4 Reference voltage source 5 Accessory circuit CD control device PS1 Switching power supply circuit PS2 Switching power supply circuit

Claims (3)

(57) [Claims] A plurality of control systems for performing independent control on a plurality of power supply circuits, and oscillating means for the control systems are shared to synchronize pulse output signals of the respective control systems. In a power supply control device of a pulse width modulation system, a pulse frequency of a pulse output signal of at least one of the plurality of control systems is set to (1 / n) of a pulse frequency of another control system by a frequency dividing means. A control device for a power supply, characterized by having a low frequency. 2. A control system comprising: a plurality of control systems so that independent control can be performed on a plurality of power supply circuits; and oscillating means for the control systems is shared to synchronize pulse output signals of the respective control systems. In a pulse width modulation type power supply control device, a frequency dividing means is provided in at least one of the plurality of control systems, and a control system capable of obtaining a high frequency pulse output signal and a low frequency pulse output signal are provided. A control device for a power supply, wherein a control system is provided. 3. A plurality of control systems so that independent control can be performed on a plurality of power supply circuits, and oscillating means for the control systems are shared to synchronize pulse output signals of the respective control systems. In a pulse width modulation type power supply control device, a frequency dividing means is added to the oscillating means, and a control system which can obtain a high frequency pulse output signal according to a frequency of a reference waveform signal supplied from the oscillating means, and a low frequency A control device for a power supply, wherein a control system for obtaining a pulse output signal is formed.