JP4259999B2 - Power supply switching circuit - Google Patents

Description

  The present invention relates to a power supply switching circuit composed of a semiconductor integrated circuit, and more particularly to a power supply switching circuit in various portable electronic devices that need to increase the power utilization efficiency by switching the power supply circuit according to the operating state of the system. .

As a conventional proposal of a power supply switching circuit, for example, there is a switch circuit described in Japanese Patent No. 2970363.
FIG. 7 is a block diagram of the proposed switch circuit.
The voltage of the input terminal 1 is monitored by a voltage detector 7 as voltage detection means for the input voltage. A switching transistor 9 controlled by the output of the voltage control circuit 17 is provided between the input terminal 1 and the output terminal 5, and a switching transistor 6 is provided between the input terminal 2 and the output terminal 5. The voltage control circuit 17 functions as a selection unit for conducting either one of the transistor 6 and the transistor 9 as well as a function of controlling the output voltage to be constant. That is, when the output of the voltage detector 7 is at a high voltage level, the transistor 6 is turned off to operate the voltage control circuit 17 as a voltage regulator. On the other hand, when the output of the voltage detector 7 is at a low voltage level, the transistor 9 is turned off. Thus, the transistor 6 is turned on. In FIG. 7, the voltage detector 7 monitors the voltage at the input terminal 1, but the voltage at the input terminal 2 may be monitored in some cases.

Further, for example, there is a power supply system described in Japanese Patent Application Laid-Open No. 2003-9515.
FIG. 8 is a diagram showing a configuration of the power supply system.
A low dropout regulator 10 and a DC / DC converter 32 are connected in parallel to the output terminal. When the load is low, a series regulator is used as the low dropout regulator 10 with low circuit current consumption. When the load is high, the switching regulator is switched to a switching regulator such as the DC / DC converter 32 having a high conversion efficiency. As a result, the power use efficiency is improved, and the series regulator and the switching regulator are simultaneously operated for a predetermined period, thereby reducing the voltage fluctuation at the time of switching and enabling stable switching.

Japanese Patent No. 2970363 JP 2003-9515 A

  In portable electronic devices such as a video camera driven by a battery, a switching regulator is used when the power consumption of the CPU is large in order to increase the power utilization efficiency when applying voltage to the CPU by stepping down from the battery. In a small standby state, a method of using a series regulator is often used. When configuring the system as described above, the switch circuit described in Japanese Patent No. 2970363 and the power supply system described in Japanese Patent Application Laid-Open No. 2003-9515 can be considered.

  That is, in the former case, if the voltage from the battery is input to the input terminal 1, the voltage from the switching regulator is input to the input terminal 2, and the detection voltage 7 is configured to monitor the voltage of the input terminal 2, the switching is performed. In a state where the regulator is operating, power is supplied from the input terminal 2 to the output terminal 5, and the constant voltage output from the battery to the output terminal 5 is cut off by controlling the transistor 9 to be turned off. On the other hand, when the switching regulator enters a non-operating state and the voltage at the input terminal 2 drops, the voltage detector 7 detects this state and outputs a high voltage level. The transistor 6 is turned off, the gate of the transistor 9 is controlled by the voltage control circuit 17, and functions as a series regulator that outputs a constant voltage from the battery.

  However, in the switch circuit described in Japanese Patent No. 2970363, when the output of the voltage detector 7 is at a low voltage level, the series regulator composed of the voltage control circuit 17 and the transistor 9 does not function and an error occurs. Since the value output from the amplifier 3 is obtained by comparing the divided component of the voltage output from the input terminal 2 to the output terminal 5 via the transistor 6 with the reference voltage, a load is applied to the series regulator. It is reasonable to think that the output does not match the output. From this state, when the voltage detector 7 is inverted, the series regulator starts to function from that moment, but since there is a considerable delay before the output corresponding to the load state is obtained from the error amplifier 3, the output The voltage output to the terminal 5 momentarily overshoots or undershoots.

  With respect to this problem, the power supply system described in Japanese Patent Application Laid-Open No. 2003-9515 proposes to reduce voltage fluctuation at the time of switching by providing a simultaneous operation period of the series regulator and the switching regulator. However, strictly speaking, for the reasons described above, this proposal may not function effectively unless the output voltages of the two regulators are not exactly the same. That is, if the output voltages do not match, the constant voltage circuit that outputs one of the lower voltages is not sufficiently loaded, and as a result, the load is suddenly applied after the simultaneous operation period ends. As a result, the occurrence of undershoot cannot be avoided. In this case, since a CPU or the like is mainly assumed as the system load, the occurrence of undershoot becomes a serious problem.

In response to such a problem, the present inventor has previously proposed a power supply switching circuit.
9 and 10 are configuration diagrams of the power supply switching circuit proposed by the inventor.
FIG. 11 is a characteristic diagram at the time of power supply switching operation using the circuit shown in FIG.
FIG. 11 is a waveform diagram for explaining the power source switching operation when the direct voltage from the battery is input to the input terminal 1 and the voltage stepped down from the battery by the DC / DC converter is input to the input terminal 2. ing. In a state where power is supplied to the input terminal 2, that is, in a state where a switching regulator such as a DC / DC converter is operating, by intentionally lowering the output voltage of the first series regulator 10 via the input terminal 1, In the state where the output is cut off and no power is supplied to the input terminal 2, the output voltage of the first series regulator 10 is restored to the original set value, whereby a stable constant voltage output from the input terminal 2 or from the input terminal 2 is restored. It is possible to supply the power.

In addition, by setting the detection voltage at the time of switching to a value slightly lower than the low setting voltage of the first series regulator 10, a state in which power is supplied by the power sources of both input terminals at the time of switching is provided, and the load fluctuations applied to the series regulator To prevent the output voltage from overshooting or undershooting.
Strictly speaking, in this method, the current flows backward from the first series regulator 10 to the input terminal 2 in the portion indicated by B in FIG. 11, and in particular in the process where the power supply of the input terminal 2 falls, the current is connected to the input terminal 2. The current is drawn by the external load being applied, so that the first series regulator 10 is gently loaded, and the voltage detector is operated to realize the switching operation.
However, this method has a problem that it cannot be applied, for example, when there is no external load at the input terminal 2, or due to the difference between the detection voltage and the low set voltage and the variation in the voltage drop at the switch means 6 during reverse flow. There is a problem that the backflow current required for the switching operation increases or decreases, and in the worst case, there is a risk that the switching operation itself is not completed and the current continues to flow back.

(the purpose)
In order to overcome the above-described problems, the object of the present invention is to enable switching operation without being affected by manufacturing variations and fluctuations in the external environment. The object is to provide a more reliable power supply switching circuit.

A power supply switching circuit according to the present invention is a power supply switching circuit configured to have a plurality of input terminals and a single output terminal, and to control which power is supplied from the plurality of input terminals. At least one constant voltage circuit connected to one of the plurality of input terminals, at least one conducting means connected to the other one of the plurality of input terminals, and a detection level of the constant voltage circuit A voltage detector configured to detect another voltage level of the plurality of input terminals set to a voltage higher than a normal setting voltage , and the voltage at the time of switching operation of the power source connected to the plurality of input terminals; The output voltage of the constant voltage circuit is changed based on the output of the detector, and the delay is activated only when the conduction means is cut off .
The first and second input terminals, one output terminal , the first input terminal and a constant voltage circuit constituting a series regulator interposed between the output terminal , the second input terminal and the output terminal And a voltage detector for detecting the voltage level of the second input terminal, the detection level of which is set to a voltage higher than the normal setting voltage of the constant voltage circuit. When the power supply of the second input terminal is selected, the set voltage of the series regulator is operated at a low set voltage lower than the voltage of the output terminal based on the output of the voltage detector, and the first input terminal with when the power is selected to return to the high arbitrary set voltage than the low set voltage, and wherein only the delay is configured to act when the switch means is cut off.

Further, the above-described series regulator is characterized in that it is configured so that it gradually shifts when returning to a low set voltage and quickly when returning.
Further, the above-described series regulator is characterized in that it is configured such that when the voltage is shifted to a low setting voltage, the voltage is shifted in a stepwise manner when the voltage is restored.
The power supply switching circuit is characterized in that a MOS transistor is used as a switch means between the second input terminal and the output terminal.
The power supply switching circuit is characterized in that a second series regulator is inserted as a switch means between the second input terminal and the output terminal.
In the power supply switching circuit, the switching operation is controlled by the voltage state of the input terminal.
Further, the power supply switching circuit is characterized in that the switching operation is controlled by an external input signal.

According to the present invention, the following effects can be obtained.
(1) At least one constant voltage circuit is always operated to create a state in which power is supplied from the power sources of both input terminals when the power is switched, and the output voltage of the constant voltage circuit and the conduction state of the switch means are temporally controlled. As a result, the operation is more reliable regardless of manufacturing variations and input terminal states.
(2) Since the output voltage of the series regulator as a constant voltage circuit can be output with the normal setting voltage and low setting voltage, it is possible to select a more optimal output voltage for the load, and against transient undershoot. However, the level can be limited by a low set voltage.
(3) Since the transition of the series regulator to a low setting voltage has been relaxed, the output voltage when the power source is switched can be kept stable.
(4) Since the series regulator is gradually shifted to a low setting voltage, it is possible to reduce output fluctuations when the power source is switched.
(5) All the components of the power supply switching circuit can be integrated in a space-saving manner using an existing CMOS process.
(6) Since the second series regulator is added, it is possible to realize a more stable constant voltage output even when power is supplied from the power source from the second input terminal.
(7) Since the power switching operation is performed by detecting the voltage level of the input terminal, it is not necessary to input a control signal input terminal or a control signal.
(8) Since the operation of switching the power supply is performed by the control signal, the voltage detector is unnecessary, and the circuit configuration can be simplified.

(First embodiment)
FIG. 1 is a configuration diagram of a power supply switching circuit showing a first embodiment of the present invention.
The input terminal 1 and the output terminal 5 constitute an input terminal and an output terminal of the constant voltage circuit 10, and a switch means 6 capable of controlling the conduction state is connected between the output terminal 5 and the input terminal 2.
The constant voltage circuit 10 functions as a series regulator including the error amplifier 3, the reference voltage 4, the Pch transistor 9 serving as an output driver, resistors R1, R2, R3 connected in series between the output terminal and the ground, and the Nch transistor 8. The error amplifier 3 compares the divided component of the voltage at the output terminal 5 with the reference voltage, controls the gate of the Pch transistor 9 serving as a driver, and outputs a constant voltage to the output terminal 5. Here, in the constant voltage circuit 10, there is an Nch transistor 8 between the connection point of the resistors R2 and R3 and the ground, and when this transistor 8 is turned off, the output of the constant voltage circuit 10 is changed according to the change in the resistance ratio. Thus, the normal set voltage can be lowered to the low set voltage.

  On the other hand, a voltage detector 7 for detecting the voltage level of the input terminal 2, a delay circuit 11, a NOR circuit 12 and an inverter circuit 13 are provided. The output signal of the voltage detector 7 and the delay circuit 11, the NOR circuit 12 and the inverter circuit are provided. 13 controls the conduction state of the switch means 6 and the output voltage of the constant voltage circuit 10. Here, the detection level of the voltage detector 7 is set to a voltage somewhat higher than the normal set voltage of the constant voltage circuit 10, unlike the power supply switching circuit of FIGS. 9 and 10, and the switch means 6 is cut off. It is configured so that the delay works only when

  Using the power supply switching circuit as described above, for example, when a direct voltage from the battery is input to the input terminal 1 and a voltage from the switching regulator is input to the input terminal 2, respectively, after the voltage of the switching regulator starts to drop, Since the switch means 6 is shut off at a time interval, a load is gently applied to the constant voltage circuit 10 during this time, and then the switch means 6 is shut off. In the circuit of the present embodiment, since the current drawing from the constant voltage circuit 10 to the input terminal 2 is not necessarily required during the switching operation as described above, the problem that has been a concern in the power supply switching circuit of FIGS. 9 and 10 is overcome. Is possible. On the other hand, when the switching regulator rises, the load of the output terminal is instantaneously applied to the input terminal 2 by raising the detection level of the voltage detector 7, so the output of the switching regulator may drop. Since the voltage drop at the output terminal 5 is limited by the low set voltage of the constant voltage circuit 10 that was loaded until just before that, the occurrence of a fatal undershoot can be avoided.

(Second embodiment)
FIG. 2 is a configuration diagram of a power supply switching circuit showing a second embodiment of the present invention.
In FIG. 2, the components of FIG. 1 are left as they are, a parallel circuit of a resistor R4 and a diode D1 is connected between the inverter circuit 13 and the Nch transistor 8, and further, between the connection point of the Nch transistor 8 and the resistor R4 and the ground. A capacitor C1 was connected to With these newly added circuits, the constant voltage circuit 10 shifts slowly when shifting from a normal set voltage to a low set voltage and quickly when returning. That is, when shifting to the low setting voltage, the parallel circuit of the resistor R4 and the diode D1 serves as a delay circuit, so that the transistor 8 is gradually switched from on to off by gradually decreasing the gate voltage of the transistor 8. . When returning to the normal set voltage, the capacitor C1 is rapidly charged with the charge through the diode D1, thereby rapidly increasing the gate voltage of the transistor 8 and instantaneously switching from off to on.
Thus, for example, when the power source is switched from the input terminal 1 to the input terminal 2, it is possible to loosen the load connection to the input terminal 2 and further stabilize the voltage fluctuation of the output terminal 5. Of course, any configuration may be used as long as the output of the constant voltage circuit 10 can be similarly controlled.

(Third embodiment)
FIG. 3 is a configuration diagram of a power supply switching circuit showing a third embodiment of the present invention.
In FIG. 3, the components of FIG. 1 are left as they are, the resistor R3 is divided, and an Nch transistor 82 is added between the midpoint and the ground. At the same time, the inverter 14 is connected to the gate of the transistor 82. The gate of the transistor 82 is controlled by inverting the output of the delay circuit 11 by the inverter circuit 14. The newly connected circuits 82 and 14 allow the constant voltage circuit 10 to shift stepwise when shifting from a normal set voltage to a low set voltage and directly shift when returning. That is, when shifting to the low setting voltage, a low voltage is applied to the gate of the transistor 81 via the inverter circuit 13 bypassing the delay circuit 11, the transistor 81 is suddenly turned off, and then the delay circuit 11. By applying a low voltage to the gate of the transistor 82 via the inverter circuit 14 via the circuit, the gate of the transistor 82 is gradually turned from on to off, and is gradually shifted to a low set voltage. On the other hand, when returning from the low set voltage, a high voltage is applied to the gate of the transistor 81 via the inverter circuit 13 bypassing the delay circuit 11 to turn the transistor 81 abruptly from off to on, and the delay circuit 11 By applying a high voltage to the gate of the transistor 82 via the inverter circuit 14 via the transistor 82, the transistor 82 is also turned on from off.
With these newly added circuits, the constant voltage circuit 10 shifts stepwise when shifting from a normal set voltage to a low set voltage and directly when returning.
As a result, for example, when the power source is switched from the input terminal 1 to the input terminal 2, the load connection to the input terminal 2 can be stepwise to reduce the voltage fluctuation of the output terminal 5.

(Fourth embodiment)
FIG. 4 is a configuration diagram of a power supply switching circuit showing a fourth embodiment of the present invention.
FIG. 5 shows a case where, for example, a direct voltage from a battery is input to the input terminal 1 and a voltage from a DC / DC converter as a switching regulator is input to the input terminal 2 using the power supply switching circuit of FIG. It is a wave form diagram explaining switching operation.
In this embodiment, the switching means 6 in the second embodiment is replaced with a second series regulator as the constant voltage circuit 20.
In a state where power is supplied to the input terminal 2, that is, a switching regulator such as a DC / DC converter is operating, the output voltage of the first series regulator 10 via the input terminal 1 is intentionally lowered to In the state where the output is cut off and no power is supplied to the input terminal 2, the output voltage of the first series regulator 10 is restored to the original set value, so that a stable constant voltage output from the input terminal 2 or from the input terminal 2 can be obtained. Make power available.

In the fourth embodiment, as in the second embodiment, a parallel circuit of a resistor R4 and a diode D1 is provided between the inverter 13 and the Nch transistor 8, and a connection point between the transistor 8 and the resistor R4 and the ground. A capacitor C1 is provided between the two. As a result, when the first series regulator 10 is shifted to the low setting voltage, the transistor 8 is gradually turned from on to off, and is gradually shifted to the low setting voltage, and when returning, the transistor 8 is suddenly turned from off to on. To change to the original set voltage instantly.
Further, by providing the second series regulator 20 including the error amplifier 23, the reference voltage 24, and the voltage dividing resistors R21 and R22 in the previous stage of the Pch transistor 6, a control voltage for suppressing voltage fluctuation is applied to the gate of the transistor 6. Therefore, a stable voltage can be output to the output terminal 5.
With such a configuration, a more stable voltage can be output even when, for example, a constant voltage is output from the input terminal 2 as the output of the switching regulator, while maintaining the operational effects of the second embodiment.

  In FIG. 5, A is a period during which a load is applied to the first series regulator, that is, a period during which the terminal voltage of the input terminal 2 begins to drop, and B is a delay time by the delay circuit 11, that is, the DC / DC converter output drops. For the first time, the voltage detector 7 detects it and transmits it to the first series regulator 10 via the inverter 13 so that the output of the first series regulator 10 is switched from the low level to the high level. This is the period up to the time when the terminal voltage starts dropping. C is a period during which the first series regulator 10 shifts from a normal output voltage to a low set voltage, that is, the output of the DC / DC converter begins to rise, and the voltage detector 7 detects it and This is a period of shifting to the low set voltage by transmitting to the Nch transistor 8 of the 1 series regulator 10.

(Fifth embodiment)
FIG. 6 is a configuration diagram of a power supply switching circuit showing a fifth embodiment of the present invention.
FIG. 6 shows a case where the control signal input terminal 15 is provided instead of the voltage detector 7 connected in the first to fourth embodiments, and the power supply switching operation is performed by the control signal.
When the switching regulator for supplying power to the input terminal 2 is provided with a control terminal for controlling the operation state, the operation effect of the first to fourth embodiments can be obtained by using the circuit of the present embodiment. The circuit configuration can be simplified while leaving it as it is. That is, since the voltage detector 7 becomes unnecessary, the circuit configuration is simple and the operation is also simple.

1 is a configuration diagram of a power supply switching circuit showing a first embodiment (corresponding to claims 1, 2, 5, and 7) of the present invention. It is a block diagram of the power supply switching circuit which shows the 2nd Example (corresponding to Claim 3) of this invention. It is a block diagram of the power supply switching circuit which shows the 3rd Example (corresponding to Claim 4) of this invention. It is a block diagram of the power supply switching circuit which shows the 4th Example (corresponding to Claim 6) of this invention. It is a wave form diagram for demonstrating the switching operation | movement in FIG. It is a block diagram of the power supply switching circuit which shows the 5th Example (corresponding to Claim 8) of this invention. It is a block diagram of the power supply switching circuit of the 1st prior art example. It is a block diagram of the power supply switching circuit of the 2nd prior art example. It is a block diagram of the conventional power supply switching circuit (the 1) which this inventor proposed. It is a block diagram of the conventional power supply switching circuit (the 2) which this inventor proposed. It is a wave form diagram for demonstrating operation | movement of the power supply switching circuit in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Input terminal, 2 ... Input terminal, 3 ... Error amplifier, 4 ... Reference voltage, 5 ... Output terminal,
6 ... switch means (Pch transistor), 7 ... voltage detector, 8 ... Nch transistor,
9: Switch means (Pch transistor), 10 ... Constant voltage circuit, 11 ... Delay circuit,
12 ... NOR circuit, 13 ... inverter circuit, 14 ... second inverter circuit,
15 ... control signal input terminal, 20 ... second constant voltage circuit, 23 ... second error amplifier,
24 ... reference voltage, 82 ... Nch transistor,
R1, R2, R3 ... resistors, R21, R22 ... resistors, R32 ... resistors, C1 ... capacitors,
D1 is a diode.

Claims (8)

A power supply switching circuit having a plurality of input terminals and one output terminal, and configured to control which power of the plurality of input terminals supplies power,
At least one constant voltage circuit connected to one of the plurality of input terminals;
At least one conducting means connected to another one of the plurality of input terminals ;
A voltage detector configured to detect another voltage level of the plurality of input terminals, the detection level of which is set to a voltage higher than a normal setting voltage of the constant voltage circuit ;
At the time of switching operation of the power source connected to the plurality of input terminals, the output voltage of the constant voltage circuit is changed based on the output of the voltage detector , and the delay works only when the conduction means is cut off. A power supply switching circuit characterized by being configured . A first and second input terminals; one output terminal; a constant voltage circuit interposed between the first input terminal and the output terminal and constituting a series regulator; the second input terminal; Switch means capable of controlling the conduction state between the output terminals, and a voltage detector for detecting the voltage level of the second input terminal, the detection level of which is set to a voltage higher than the normal setting voltage of the constant voltage circuit A voltage detector ,
When the power supply of the second input terminal is selected, the set voltage of the series regulator is operated at a low set voltage lower than the voltage of the output terminal based on the output of the voltage detector , and the first input when the power of the terminal is selected, the power supply switching circuit, characterized in that said with returning to any set voltage higher than the low set voltage, configured to only the delay acts when the switch means is cut off . In the power supply switching circuit according to claim 2,
A power supply switching circuit characterized in that when the series regulator shifts to a low set voltage, the series regulator shifts slowly, and when returning from the low set voltage to the original voltage, shifts quickly. In the power supply switching circuit according to claim 2,
When the series regulator shifts to a low setting voltage, the power supply switching circuit is configured to shift in a stepwise manner and to shift directly when returning from the low setting voltage to the original voltage. . In the power supply switching circuit according to claim 2,
A power supply switching circuit, wherein a MOS transistor is used as a switch means between the second input terminal and the output terminal. In the power supply switching circuit according to claim 2 or 5,
A power supply switching circuit, wherein a second series regulator is disposed as a switch means between the second input terminal and the output terminal. In the power supply switching circuit according to any one of claims 2 to 6,
The power supply switching circuit, wherein the switching operation is controlled according to a voltage state of the input terminal. In the power supply switching circuit according to any one of claims 2 to 6,
A power supply switching circuit, wherein the switching operation is controlled by an external input signal.

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