JP2003009515A - Power system - Google Patents

Abstract

(57) [Problem] To provide a stable power supply output with low ripple while maintaining high conversion efficiency even at low load current operation. A device that uses a battery as a power source, such as a PDA or a portable terminal, performs high-efficiency voltage conversion by switching and using a low dropout regulator 1 and a DC / DC converter 16 according to a load current. When switching between the low dropout regulator 1 and the DC / DC converter 16, the DC / DC converter 1
By operating the low dropout regulator 1 and the DC / DC converter 16 at the same time, the voltage fluctuation at the time of switching is reduced, and a power supply having a constantly stable output voltage is provided.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a PDA (Personal).
The present invention relates to a power supply system used for a device that uses a battery as a power source, such as a Digital Assistant, a personal digital assistant), a mobile terminal (for example, a mobile phone), and the like. In particular, for example, a series regulator such as a low dropout regulator (so-called LDO) and a switching regulator such as a DC / DC converter are switched and used according to the magnitude of the load current to perform voltage conversion with high efficiency. , A series regulator and a switching regulator are the main components of the power supply system.

[0002]

2. Description of the Related Art FIG. 3 shows a power supply system (voltage conversion system) using a conventional asynchronous DC / DC converter. In FIG. 3, 20 is a pulse width modulation circuit (PW
M), 21 is a P-channel field effect transistor, 22 is a Schottky diode, 23 is a coil, 24 is a capacitor, 25 and 26 are resistors serving as feedback means for voltage setting, 27 is a power supply output terminal, and 28 is a power supply. A voltage input terminal from the battery BAT, 29 is a reference voltage terminal for inputting a reference voltage for setting a load voltage, and 30 is an error amplifier. “DCDC CTL” is a pulse width modulation circuit 20
Control signal.

In a device such as a PDA or a mobile terminal which uses a battery as a power source, in order to keep the battery long, there are states such as a sleep mode and a standby mode in which the current consumption is extremely reduced to the order of μA or less.
However, in a normal power supply system using a DC / DC converter, current consumption in the DC / DC converter itself is as large as about mA order or less, so that the voltage conversion efficiency becomes extremely low during such a low load current operation. In order to avoid this, in the conventional example, at the time of low load current operation, P
The conversion efficiency is increased by switching from the WM system to the intermittent operation PFM system.

FIG. 4 shows a PWM (pulse width modulation) method and a PF.
FIG. 3 is a diagram showing an M (pulse frequency modulation) type power supply output voltage waveform. 4, (b) is the gate control voltage (PWM output or PFM output) of the P-channel field effect transistor 21 of FIG. 3, (a) is the corresponding power supply output voltage, and the first part is the PWM method. Of the PFM method, and the subsequent part shows the operation of the PFM method.

[0005]

As in the conventional example, the PF
In the configuration in which the voltage control is performed by the M method, it is possible to increase the conversion efficiency during the low load current operation such as the sleep mode and the standby mode. However, the power supply output voltage at that time has many voltage fluctuations, and it is very difficult to output a stable voltage with a small ripple.

Therefore, an object of the present invention is to provide a power supply system capable of outputting a stable power supply output voltage with a small ripple while maintaining a high conversion efficiency even at a low load current operation.

[0007]

SUMMARY OF THE INVENTION A power supply system of the present invention is a power supply system for supplying power to a load, which includes a series regulator and a switching regulator for controlling a power supply output voltage at a constant level. Is selectively operated, and the switching regulator is selectively operated when the load current is large.

According to this structure, since the series regulator that consumes less circuit current is used when the load current is small, high conversion efficiency can be realized in the region where the load current is small. Moreover, by using the series regulator, it is possible to output a stable power supply output voltage with less ripple compared to the PFM type switching regulator. Therefore, in the entire load current region, it is possible to output a stable power supply output voltage having high conversion efficiency and little ripple.

In the above structure, it is preferable to provide a simultaneous operation period of the series regulator and the switching regulator when switching the operations of the series regulator and the switching regulator. With such a configuration, it is possible to reduce voltage fluctuations at the time of switching, and it is possible to provide a power supply system that always has a stable output voltage.

A low dropout regulator is used as the series regulator, and a DC / DC converter is used as the switching regulator. The DC / DC converter is switchable between a synchronous system operation and an asynchronous system operation, performs a synchronous system operation when operating independently, and performs an asynchronous system operation when operating simultaneously with a low dropout regulator. By doing so, it is possible to prevent a shoot-through current passing through the low dropout regulator and the DC / DC converter during simultaneous operation, and to prevent destruction of the low dropout regulator or the DC / DC converter.

The above-mentioned low dropout regulator is, for example, a differential amplifier having two inputs of a reference voltage and an output voltage of a feedback means for detecting the power supply output voltage, one end of which is connected to the power supply and the other end of which is the power supply. It consists of a transistor connected to the output terminal and to which the output of the differential amplifier is applied to the control terminal.

The DC / DC converter is, for example,
An error amplifier that amplifies the difference between the reference voltage and the output voltage of the feedback means, a pulse width modulation circuit that changes the pulse width according to the output of this error amplifier, and one end of the pulse width modulation circuit whose one end is connected to the power supply. For a first switching element whose output is applied to the control terminal and for a synchronous operation in which one end is connected to the other end of the first switching element and the other end is grounded and the other output of the pulse width modulation circuit is applied to the control terminal Second switching element, a diode for asynchronous operation provided in parallel with the second switching element, and an LC provided between the connection point of the first and second switching elements and the power supply output terminal. It consists of a circuit.

As described above, the power supply system of the present invention switches the low dropout regulator and the DC / DC converter depending on the magnitude of the load current in a device such as a PDA or a mobile terminal which uses a battery as a power supply. By using it, it performs highly efficient voltage conversion in the entire load current range, and when switching between the low dropout regulator and the DC / DC converter, the low dropout regulator and the asynchronous DC
By simultaneously operating the / DC converters, it is possible to reduce the voltage fluctuations at the time of switching and provide a power supply having a stable output voltage.

[0014]

DETAILED DESCRIPTION OF THE INVENTION A power supply system according to an embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 is a circuit diagram showing an embodiment of a power supply system of the present invention. As shown in FIG. 1, this power supply system supplies power to a load, and includes a low dropout regulator 1 as a series regulator and a DC / DC converter 16 as a switching regulator.
have. These low dropout regulator 1 and DC / DC converter 16 have a power output terminal 1
The output voltage of the power supply appearing in FIG. 3 is controlled to be constant regardless of the magnitude of the load current. The common reference voltage Vr is used as an input and the output voltage Vs of the common feedback circuit 21 is used as an input. The output terminals 13 are commonly connected.

In the above power supply system, the low dropout regulator 1 is selectively operated when the load current is small, and the DC / DC converter 1 is operated when the load current is large.
6 is selectively operated. At the time of switching the operations of the low dropout regulator 1 and the DC / DC converter 16, the low dropout regulator 1 and the DC / D are switched.
It is preferable to provide a simultaneous operation period of the C converter 16.

The operation of the low dropout regulator 1 and the DC / DC converter 16 is switched by applying a control signal from the outside or by comparing the magnitude of the load current with a predetermined threshold value, When the load current is larger than the above threshold value, the low dropout regulator 1 is operated when the load current is smaller than the above threshold value.
This is possible by providing an automatic discrimination control circuit that operates the C converter 16. At this time, by adding a delay time to the switching operation, simultaneous operations at the time of switching become possible.

Further, in the above power supply system, there is an inconvenience when the simultaneous operation period of the low dropout regulator 1 and the DC / DC converter 16 is provided, that is, the output portion of the low dropout regulator 1 outputs the DC / DC converter 16. The DC / DC converter 16 is capable of switching between a synchronous system operation and an asynchronous system operation in order to prevent a through current from flowing to the section. This DC / D
The C converter 16 performs a synchronous operation when operating independently, and an asynchronous operation when operating simultaneously with the low dropout regulator 1. Note that the DC / DC converter 16 may be configured to perform an asynchronous operation even in a single operation.

In the above DC / DC converter 16,
The synchronous method is an operation method in which the P-channel field effect transistor 8 and the N-channel field effect transistor 9 are alternately turned on, and the asynchronous method is
This is an operation method in which the N-channel field effect transistor 9 is always off and a current flows from the Schottky diode 10 to the coil 11.

Here, when the DC / DC converter 16 operates independently, the synchronous system operation has the following advantages over the asynchronous system operation. When the P-channel field effect transistor 8 is on, the voltage input terminal 15
A current I flows to the coil 11 via the channel field effect transistor 8. This current I tends to continue flowing even if the P-channel field effect transistor 8 is turned off. In this case, if the path through which the current I flows is the synchronous type, it becomes the N-channel field effect transistor 9, and if it is the asynchronous type, it becomes the Schottky diode 10. Normally, the drain-source voltage of the N-channel field effect transistor 9 is smaller than the forward voltage of the Schottky diode 10. Therefore, the synchronous type has less power loss.

Low Dropout Regulator 1 Above
Is a differential amplifier 2 and a P-channel field effect transistor 3
Consists of. The differential amplifier 2 compares the reference voltage Vr given to the reference voltage terminal 14 and the output voltage Vs of the feedback circuit 21 for detecting the power supply output voltage as two inputs and compares them, and according to the comparison result, a low dropout regulator. Adjust the output voltage of 1.

The P-channel field effect transistor 3 has a voltage input terminal 15 to which a battery BAT as a power source is connected.
Is connected to the source (one end), the drain (the other end) is connected to the power supply output terminal 13, and the output of the differential amplifier 2 is applied to the gate (control terminal). That is, the gate potential is controlled by the differential amplifier 2 to keep the output voltage constant. Reference numeral 17 is a control signal “LDO CT for the differential amplifier 2.
L ″, and the control signal 17 controls the operation / non-operation of the low dropout regulator 1.

The feedback circuit 21 comprises a series circuit of resistors 4 and 5 for voltage division connected between the power output terminal 13 and the ground (ground), and outputs the voltage Vs from the connection point of the resistors 4 and 5. To do.

The DC / DC converter 16 includes an error amplifier 6, a pulse width modulation circuit 7, a P-channel field effect transistor 8 as a switching element, an N-channel field effect transistor 9 for synchronous operation, and a Schottky. It is composed of a diode 10 and an LC circuit 22.

The error amplifier 6 amplifies the difference between the reference voltage Vr applied to the reference voltage terminal 14 and the output voltage Vs of the feedback circuit 21. That is, this error amplifier 6
Is for adjusting the voltage of the DC / DC converter 16, compares the reference voltage Vr with the feedback voltage, that is, the output voltage Vs of the feedback circuit 22, and adjusts the pulse width of the output of the pulse width modulation circuit 7. .

The pulse width modulation circuit 7 changes the pulse width according to the output of the error amplifier 6. That is, the gate potentials of the P-channel field effect transistor 8 and the N-channel field effect transistor 9 are controlled according to the output voltage of the error amplifier 6 to control ON / OFF of the P-channel field effect transistor 8 and the N-channel field effect transistor 9. .

The P-channel field effect transistor 8 which is the first switching element is a battery BAT which is a power source.
The source (one end) is connected to the voltage input terminal 15 to which is connected, one output of the pulse width modulation circuit 7 is added to the gate (control terminal), and the pulse width modulation circuit 7 is turned on / off according to one output level. .

In the N-channel field effect transistor (second switching element) 9 for synchronous operation, the drain (one end) is connected to the drain (the other end) of the P channel field effect transistor 8 and the source (the other end) is grounded. The other output of the pulse width modulation circuit 7 is applied to the gate (control terminal) and turned on / off according to the level of the other output of the pulse width modulation circuit 7.

The asynchronous Schottky diode 10 is provided in parallel with the N-channel field effect transistor 9. This Schottky diode 10
It substitutes for the N-channel field effect transistor 9 when operating in an asynchronous manner.

The LC circuit 22 comprises a coil 11 and a capacitor 12, and has a P-channel field effect transistor 8
It is provided between the connection point of the N-channel field effect transistor 9 and the power output terminal 13. A load (not shown) is connected to the power output terminal 13.

Reference numeral 18 is a control signal "DCDC CTL" for the pulse width modulation circuit 7, and the control signal 18 causes the pulse width modulation circuit 7 to operate / not operate, that is,
The operation / non-operation of the DC / DC converter 16 is switched. The pulse width modulation circuit 18 operates when the control signal 18 is at high level and does not operate when it is at low level. Further, 19 is a control signal "synchronous / asynchronous switching CTL" of the pulse width modulation circuit 7, and the control signal 19 causes the pulse width modulation circuit 7 to selectively execute a synchronous system operation or an asynchronous system operation.

FIG. 2 is a signal waveform diagram of each part of the power supply system of FIG. In FIG. 2, (a) is the power supply output voltage of the power supply system. (B) is a DC / DC converter 16
The pulse width modulation circuit 7 is off and does not operate at the low level. Further, at the high level, the pulse width modulation circuit 7 is turned on, and the DC / DC converter 16
Control to keep the power supply output voltage constant. (C) is a control signal 17 for the low dropout regulator 1. The low dropout regulator 1 is turned off at a low level, the low dropout regulator 1 is turned on at a high level, and the low dropout regulator 6 is controlled. Keep the output voltage constant. (D) is a synchronous / asynchronous switching control signal for the DC / DC converter 16, which is synchronous at the low level and asynchronous at the high level.
Works. (E) has shown the partial expanded waveform of the same figure (a).

In the same waveform diagram, a period A shows a single operation period of the low dropout regulator 1, a period B shows a simultaneous operation period of the low dropout regulator 1 and the DC / DC converter 16, and a period C shows DC / DC. A single operation period of the converter 16 is shown, and the period D is DC / D.
The asynchronous operation period of the C converter 16 in the independent operation period is shown, and the period E shows the synchronous operation period of the DC / DC converter 16. Part X is asynchronous DC
/ DC converter operating region (abbreviated as asynchronous DC / DC region), part Y is operating region of low dropout regulator (abbreviated as LDO region), part Z is synchronous DC / D
Operating area of C converter (abbreviated as synchronous DC / DC area)
Is shown.

The operation of this power supply system will be described below.

Low Dropout Regulator 1 of FIG.
Since the low dropout regulator itself can operate with a circuit current consumption of about several μA, its conversion efficiency can be approximated by efficiency (%) = output voltage / input voltage × 100 and is not significantly affected by load current. It is almost determined only by the input / output potential difference. Therefore, in particular, the DC / DC converter 16
The conversion efficiency at low load is higher than that of
Compared with the FM type DC / DC converter, a stable voltage with less voltage fluctuation can be supplied. Therefore, it is mainly in charge of power supply operation at low load.

Further, the DC / DC converter 16 can realize a conversion efficiency of about 90% at the time of a high load, and therefore takes charge of power supply operation in a load current range having a higher conversion efficiency than the low dropout regulator 1.

As a result, high conversion efficiency can be realized in the entire load current range.

Further, the low dropout regulator 1 and the DC / DC converter 16 have the same feedback system, and when switching, as shown in FIG.
The converter 16 is set to the asynchronous system, and in this state, it is operated simultaneously with the low dropout regulator 1.

Normally, when the low dropout regulator and the synchronous DC / DC converter are simultaneously operated, the low dropout regulator 1 in FIG.
DC / DC from the P-channel field effect transistor 3 of
A through current flows through the N-channel field effect transistor 9 of the converter 16, and in the worst case, the power supply is destroyed. However, in the present invention, the N-channel field effect transistor 9 is maintained in the off state, and the asynchronous DC / DC converter operation by the P-channel field effect transistor 8 and the Schottky diode 10 is performed.
By operating the converter 16 and the low dropout regulator 1 at the same time, a shoot-through current from the low dropout regulator 1 to the DC / DC converter 16 can be prevented, and further, the voltage fluctuation at the time of switching can be reduced to the minimum. it can.

[0040]

As described above, according to the present invention, a series regulator such as a low dropout regulator that consumes less circuit current is used at a low load, and a switching regulator such as a DC / DC converter having a high conversion efficiency at a high load. By switching and operating, high conversion efficiency can be realized in the entire load current range. Moreover, when switching between the series regulator and the switching regulator, the series regulator and the asynchronous switching regulator are operated simultaneously for a predetermined period of time, so voltage fluctuations at the time of switching can be reduced and stable switching can be performed. A power supply system having an output voltage can be provided.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of an embodiment of a power supply system of the present invention.

FIG. 2 is a waveform diagram of each part in the power supply system of the same embodiment.

FIG. 3 is a circuit diagram showing a configuration of a conventional power supply system using a conventional asynchronous DC / DC converter.

FIG. 4 is a power supply output voltage waveform diagram of a PWM (pulse width modulation) system and a PFM (pulse frequency modulation) system.

[Explanation of symbols]

1 Low dropout regulator 2 differential amplifier 3 P-channel field effect transistor 4,5 resistance 6 Error amplifier 7 Pulse width modulation circuit 8 P-channel field effect transistor 9 N-channel field effect transistor 10 Schottky diode 11 coils 12 capacitors 13 Power output terminal 14 Reference voltage terminal 15 Voltage input terminal 16 DC / DC converter 17 Control signal 18 Control signal 19 Control signal 20 pulse width modulation circuit 21 P-channel field effect transistor 22 Schottky diode 23 coils 24 capacitors 25,26 resistance 27 Power output terminal 28 Voltage input terminal 29 Reference voltage terminal 30 Error amplifier 31 Feedback circuit 32 LC circuit

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 5G065 AA01 DA01 DA02 DA07 EA02                       GA07 HA04 KA02 KA05 LA01                       MA10 NA01 NA03 NA04 NA06                 5H430 BB01 BB09 BB11 BB13 BB20                       EE04 EE09 EE12 EE13 FF04                       FF13 GG08 GG17 HH03 KK16                 5H730 AA14 AA16 AS01 AS23 BB13                       BB57 BB96 BB98 DD04 EE08                       EE13 EE53 EE60 FD01 FF01                       FG05 FG22 FV05 XC20

Claims (5)

[Claims] 1. A power supply system for supplying power to a load, comprising:
A series regulator and a switching regulator that control the power supply output voltage to be constant are provided, and the series regulator is selectively operated when the load current is small, and the switching regulator is selectively operated when the load current is large. Power supply system characterized by 2. The power supply system according to claim 1, wherein a simultaneous operation period of the series regulator and the switching regulator is provided when the operations of the series regulator and the switching regulator are switched. 3. The series regulator is a low dropout regulator and the switching regulator is D
The power supply system according to claim 1, which is a C / DC converter. 4. A DC / DC converter capable of switching between a synchronous operation and an asynchronous operation, performing a synchronous operation when operating independently and performing an asynchronous operation when operating simultaneously with a low dropout regulator. The power supply system according to item 3. 5. A low dropout regulator, a differential amplifier having two inputs of a reference voltage and an output voltage of a feedback means for detecting a power supply output voltage, one end of which is connected to a power supply, and the other end of which is a power supply output terminal. A DC / DC converter that amplifies the difference between the reference voltage and the output voltage of the feedback means, and is connected to the output terminal of the differential amplifier.
A pulse width modulation circuit that changes the pulse width according to the output of the error amplifier; a first switching element whose one end is connected to a power supply and one output of the pulse width modulation circuit is applied to a control terminal; A second switching element for synchronous system operation, one end of which is connected to the other end of the switching element, the other end of which is grounded, and the other output of the pulse width modulation circuit is applied to a control terminal; The power supply system according to claim 4, comprising an asynchronous operation diode provided in parallel, and an LC circuit provided between a connection point of the first and second switching elements and the power supply output terminal.