JP3852399B2 - Power switching circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a power supply switching circuit belonging to a semiconductor integrated circuit, and can be applied to various portable electronic devices that need to increase the voltage utilization efficiency by switching the power supply circuit according to the operating state of the system. [0002] circuit
[Prior art]
The cited document here is Japanese Patent No. 2970363, “Switch Circuit”. FIG. 3 shows the conventional switch circuit proposed above. The voltage of the input terminal 301 is monitored by a voltage detector 307 as voltage detection means for the input voltage. A switching transistor 309 controlled by the output of the voltage control circuit 316 is provided between the input terminal 301 and the output terminal 305, and a switching transistor 306 is provided between the input terminal 302 and the output terminal 305.
[0003]
The voltage control circuit 316 functions as a control means for conducting one of the transistors 306 and 309 as well as a function of controlling the output voltage to be constant. That is, when the output of the voltage detector 307 is at a high voltage level, the transistor 306 is turned off to operate the voltage control circuit 316 as a voltage regulator. On the other hand, when the output of the voltage detector 307 is at a low voltage level, the transistor 309 is turned off. The transistor 306 is turned on. In this figure, the voltage detector 307 monitors the voltage at the input terminal 301, but the input terminal 302 may be monitored depending on circumstances.
[0004]
In FIG. 3, 303 is an error amplifier, 304 is a reference power supply, 314 is a transistor, 315 is a resistor group, 316 is a voltage control circuit, and 317 and 318 are diodes.
[0005]
The cited document here is “DC power supply device” described in Japanese Patent Application No. 2002-216929 and drawings. The power supply device in the document is shown in FIG.
The output terminal 403 of the power supply circuit 406 and the output terminal 404 of the power supply circuit 407 with control input are connected in common, and the power supply circuit 407 is provided according to the state of the control signal applied to the control input. Switch to active or inactive. The power supply circuit 407 is configured so as to be able to supply a predetermined voltage to the common output terminal when operating, and not to generate a voltage when not operating. The power supply circuit 406 is configured not to send an output voltage when the power supply circuit 407 generates a voltage at the common output terminal, and to send an output voltage when the power supply circuit 407 does not generate a voltage. [0006]
In the specification and drawings of Japanese Patent Application No. 2002-216929, as a specific implementation method of voltage transmission / non-transmission of the power supply circuit 406, a series regulator is used for the power supply circuit 406, and its output voltage is set from the set voltage of the power supply circuit 407. A method of lowering or a method of inserting a diode as a control element between the power supply circuit 406 (the output terminal 403 thereof) and the common output terminal 405 has been proposed. However, in any of the above methods, it is necessary to set the voltage output to the output terminal 403 at a position slightly lower than the set value of the power supply circuit 407.
[0007]
In the present power supply device, a load is gradually applied to the power supply circuit 406 in accordance with the voltage drop of the power supply circuit 407. Normally, it is considered that the falling speed of the power supply circuit 407 is sufficiently slower than the response speed of the power supply circuit 406, so that undershoot does not occur at the common output terminal 405.
[0008]
However, in this power supply device, it is necessary to set the output voltage of the power supply circuit 406 slightly lower than the output voltage of the power supply circuit 407, which causes inconvenience when the guaranteed voltage range of the CPU connected as a load is narrow. Also, when a diode is connected, it is necessary to set the output voltage of the power supply circuit 406 in anticipation of the fluctuation, which is a design difficulty.
[0009]
In FIG. 4, 401 is an input terminal, 402 is an input terminal, 405 is a common output terminal, 408 is a control input, 409 is a control signal, 410 is a power supply BAT, 411 is a resistor R1, 412 is a resistor R2, and 413 is a capacitor C2. 414 is a load, 415 is a MOS transistor M1, and 416 is a power supply Vref.
[0010]
[Patent Document 1]
Japanese Patent No. 2970363 [0011]
[Problems to be solved by the invention]
In portable electronic devices such as video cameras that are driven by a battery, a switching regulator is used when the power consumption of the CPU is large to increase the voltage utilization efficiency when the voltage is applied to the CPU by stepping down from the battery. In a small standby state, a method of using a series regulator is often used.
[0012]
When the above system is assumed, use of the switch circuit described in Patent Document 1 can be considered. That is, in FIG. 3, if the voltage from the battery is input to the input terminal 301, the voltage from the switching regulator is input to the input terminal 302, and the detection voltage 307 is configured to monitor the voltage of the input terminal 302, the switching regulator In the state in which is operated, voltage is supplied from the input terminal 302 to the output terminal 305, and power supply from the battery to the output terminal 305 is cut off by controlling the transistor 309 to be turned off.
[0013]
On the other hand, when the switching regulator enters a non-operating state and the voltage at the input terminal 302 drops, the voltage detector 307 detects this state and outputs a high voltage level. The transistor 306 is turned off, the gate of the transistor 309 is controlled by the voltage control circuit 316, and functions as a series regulator that outputs a constant voltage from the battery.
[0014]
However, in this switch circuit, when the output of the voltage detector 307 is at a low voltage level, the series regulator composed of the voltage control circuit 316 and the transistor 309 does not function, and the value output from the error amplifier 303 is the input terminal 302. Is obtained by comparing the divided voltage component of the voltage output to the output terminal 305 via the transistor 306 with the reference voltage, so that it does not match the output when the load is applied to the series regulator. It is reasonable to think.
[0015]
When the voltage detector 307 is inverted from such a state, 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 303, the output The voltage output to the terminal 305 momentarily overshoots or undershoots. At this time, when a CPU or the like is mainly assumed as a load connected to the output terminal 305, overshoot or undershoot becomes a serious problem.
[0016]
The object of the present invention has been made in view of such a problem, and in a steady operation state while sufficiently suppressing output voltage overshoot and undershoot at the time of power supply switching, it is constant regardless of the selection of the power supply. To provide a power supply switching circuit capable of supplying an output voltage.
[0017]
[Means for Solving the Problems]
In the power supply switching circuit according to the present invention, the power supply switching circuit includes two input terminals to which power is input and an output terminal to which the two input terminals are connected, and the power supply of any of the input terminals is switched to the output terminal. A power supply switching circuit for supplying power at least by connecting a constant voltage circuit between one of the input terminals and the output terminal, and supplying power from one input terminal to the other input terminal. At the time of switching, the output voltage of the constant voltage circuit is controlled to a value lower than the power supply voltage input from the other input terminal .
[0018]
Specifically, it has an output terminal in which a plurality of input terminals and an output node of at least one constant voltage circuit are directly connected, and selects from which input voltage the voltage is output according to the voltage condition of the input terminal. It is configured like this.
[0019]
The present invention relates to a power supply switching circuit, which has first and second input terminals and one output terminal, and is a series in the configuration of a constant voltage circuit directly interposed between the first input terminal and the output terminal. It has a regulator, and it has switch means which can control a conduction state between the 2nd input terminal and an output terminal, It is characterized by the above-mentioned.
[0020]
In the above power supply switching 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, and the power supply of the first input terminal is selected. When set, it is possible to return to any set voltage higher than the low set voltage.
[0021]
In the power supply switching circuit, a diode, a MOS transistor, or a second series regulator is used as means instead of the switch means between the second input terminal and the output terminal.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail based on examples shown in the drawings.
[0023]
A first embodiment of the present invention is shown in FIG. The input terminal 101 and the output terminal 105 form an input terminal and an output terminal of a constant voltage circuit 110 which is a series regulator. On the other hand, a switch means 106 capable of controlling the conduction state is connected between the output terminal 105 and the input terminal 102. Yes. In FIG. 1, 103 is an error amplifier, 104 is a reference voltage, 107 is a voltage detector, 108 and 109 are transistors, 111 is a resistor R1, 112 is a resistor R2, and 113 is a resistor R3.
[0024]
The constant voltage circuit 110 includes an error amplifier 103, a reference voltage 104, a transistor 109 serving as an output driver, an output terminal 105, resistors R1-111, R2-112, R3-113, and a transistor 108 connected in series between the ground and an error. The amplifier 103 compares the divided component of the voltage at the output terminal 105 with the reference voltage 104 and controls the gate of the transistor 109 serving as a driver to output a stable constant voltage to the output terminal 105. Here, the constant voltage circuit 110 has a transistor 108 between the connection point of R2-112 and R3-113 and the ground. When the transistor 108 is turned off, the output voltage of the constant voltage circuit 110 is changed according to the change in resistance ratio. Can be lowered.
[0025]
Further, a voltage detector 107 for detecting the voltage level of the input terminal 102 for power supply switching is provided, and the conduction state of the switch means 106 and the output voltage of the constant voltage circuit 110 are controlled by the output of the voltage detector 107. Here, in FIG. 1, a transistor is used as the switch means 106, but any means that can control the conduction state of the input terminal 102 and the output terminal 105 can be used. In some cases, the anode is connected to the input terminal 102. A diode having a cathode connected to the output terminal 105 may be used. Further, when the output of the voltage detector 107 is a low voltage, the constant voltage circuit 110 is set to output a voltage lower than the steady output state, but the detection level of the voltage detector 107 is a lower value. Is set to
[0026]
With the configuration as described above, the voltage from the battery is supplied to the input terminal 101 and the voltage from the switching regulator is supplied to the input terminal 102.
[0027]
First, when there is no voltage supply from the switching regulator, the voltage detector 107 outputs a high voltage level, turns off the switching means 106, turns on the transistor 108, and outputs a stable constant voltage of 3 V, for example, to the output terminal 105. However, it functions as a series regulator based on the supply voltage from the input terminal 101.
[0028]
Next, when the switching regulator operates to increase the voltage at the input terminal 102, for example, to the set voltage 2.85 V of the voltage detector 107, the switching means 106 is turned on and the transistor 108 is turned off at the same time. Operates as a 2.9V output series regulator. At this time, as a result, the output of the switching regulator is charged to 2.9V, and further rises to a normal output, for example, 3V, and becomes stable. During this time, the constant voltage circuit 110 continues to operate as a 2.9V output series regulator.
[0029]
On the other hand, when the switching regulator shifts from the operating state to the non-operating state, the following operation is performed. First, when the voltage at the input terminal 102 drops to 2.9 V, a load is also applied to the series regulator (that is, the constant voltage circuit 110) by the supply voltage from the input terminal 101 from that moment. It comes to output. If the terminal voltage of the input terminal 102 further drops to 2.85 V in this state, the output of the voltage detector 107 is inverted to a high voltage level at that moment, and at the same time the output voltage of the constant voltage circuit 110 returns to 3 V. The switching means 106 is turned off. The conduction state between the input terminal 102 and the output terminal 105 is interrupted.
[0030]
As described above, in the circuit according to the present invention, the constant voltage circuit 110 is operated as a low voltage output series regulator while the voltage from the input terminal 102 is supplied, and the output operation is performed using both power sources when the power source is switched. Thus, the voltage fluctuation of the output terminal 105 is moderated, and the occurrence of a transient undershoot is avoided. When a simple diode is used as the switching means, assuming that the forward voltage of the diode is 0.6V, the detection voltage of the voltage detector 107 is, for example, 3.45V (2.85V + 0.6V). You can get the same effect.
[0031]
A second embodiment of the present invention is shown in FIG. 2, 201 is an input terminal, 202 is an input terminal, 203 is an error amplifier, 204 is a reference power supply, 205 is an output terminal, 206 is a transistor, 207 is a voltage detector, 208 is a transistor, 209 is a transistor, and 210 is A constant voltage circuit, 211 is an error amplifier, 212 is a reference power supply, 213 is a constant voltage circuit, 214 is a resistor R1, 215 is a resistor R2, 216 is a resistor R3, 217 is a resistor R4, and 218 is a resistor R5.
[0032]
The operations of the series regulator, the switching regulator, etc. in FIG. 2 are basically the same as those in FIG. 1, and the above-described switch means 106 is replaced with a constant voltage circuit 213. These two are the same functional elements, but the constant voltage circuit 213 controls the output of the error amplifier 211 therein to turn the constant voltage circuit 213 on and off. In other words, the circuit of FIG. 2 has a function of controlling a conduction state between the input terminal 202 and the output terminal 205 and a function of a constant voltage circuit, so that the ripple and variation of the switching regulator can be suppressed. Yes.
[0033]
According to the present invention, since the switching means 106 in the first embodiment is replaced by the constant voltage circuit 213, for example, the output of the switching regulator can be output from the second input terminal 202 without changing the operational effects of the first embodiment. Even when a voltage is supplied, a more stable output voltage can be supplied. In addition, a stable voltage can be supplied to a wider range of input voltages at the second input terminal 202.
[0034]
【The invention's effect】
As described above, according to the present invention, at least one constant voltage circuit is always operated, and a state in which the output terminal is supplied with the voltage of both input terminals when the power source is switched is more stable with respect to the load such as the CPU. A power supply switching circuit having transient characteristics can be provided.
[0035]
According to the present invention, since the voltage output in the steady state is configured to return to the normal set voltage, a suitable output voltage for the load can be selected.
[0036]
By using a simple diode as the switching means, the control wiring can be omitted. Similarly, by using a MOS transistor, the voltage can be set more accurately when switching the power supply.
[0037]
In addition, according to the present invention, a more stable voltage can be supplied even when an output voltage is supplied with a supply voltage from the second input terminal.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of a power supply switching circuit according to a first embodiment of the present invention (claims 1, 2, and 4).
FIG. 2 is a circuit diagram of a power supply switching circuit according to a second embodiment (claim 5) of the present invention.
FIG. 3 is a circuit diagram of a conventional switch circuit (Japanese Patent Application No. 2002-216929 and drawings).
FIG. 4 is a diagram of a conventional power supply device (described in Japanese Patent Application No. 2002-216929 and drawings).
[Explanation of symbols]
101 Input terminal 102 Input terminal 103 Error amplifier 104 Reference power supply 105 Output terminal 106 Transistor 107 Voltage detector 108 Transistor 109 Transistor 110 Constant voltage circuit 111 Resistance R1
112 Resistance R2
113 resistor R3
201 input terminal 202 input terminal 203 error amplifier 204 reference power supply 205 output terminal 206 transistor 207 voltage detector 208 transistor 209 transistor 210 constant voltage circuit 211 error amplifier 212 reference power supply 213 constant voltage circuit 214 resistor R1
215 resistor R2
216 resistor R3
217 resistor R4
218 resistor R5
301 Input Terminal 302 Input Terminal 303 Error Amplifier 304 Reference Power Supply 305 Output Terminal 306 Transistor 307 Voltage Detector 309 Transistor 314 Transistor 315 Resistor Group 316 Voltage Control Circuit 317 Diode 318 Diode 401 Input Terminal 402 Input Terminal 403 Output Terminal 404 Output Terminal 405 Common Output terminal 406 Power supply circuit 407 Power supply circuit 408 Control input 409 Control signal 410 Power supply BAT
411 resistor R1
412 Resistor R2
413 Capacitor C2
414 Load 415 MOS transistor 416 Power supply Vref

Claims (5)

Two input terminals to which power is input;
An output terminal to which the two input terminals are connected;
A power supply switching circuit for switching and supplying any power of the input terminal to the output terminal,
At least a constant voltage circuit is connected between the one input terminal and the output terminal,
A power supply characterized by controlling the output voltage of the constant voltage circuit to a value lower than the power supply voltage input from the other input terminal when switching the power supply from one input terminal to the other input terminal. Switching circuit.   The power supply switching circuit according to claim 1, wherein the input terminal and the output terminal have first and second input terminals and one output terminal, and are directly interposed between the first input terminal and the output terminal. A series regulator that constitutes a constant voltage circuit, a switch means that can control a conduction state between the second input terminal and the output terminal, and the power source of the second input terminal is selected; The regulator set voltage is operated at a low set voltage lower than the voltage of the output terminal, and when the power source of the first input terminal is selected, it returns to an arbitrary set voltage higher than the low set voltage. Power supply switching circuit.   3. The power supply switching circuit according to claim 2, wherein a diode is used as a switch means between the second input terminal and the output terminal.   3. The power supply switching circuit according to claim 2, wherein a MOS transistor is used as a switch means between the second input terminal and the output terminal.   3. The power supply switching circuit according to claim 2, wherein a second series regulator is inserted in place of the switch means between the second input terminal and the output terminal.

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