JPH08280142A - Power supply switch circuit - Google Patents

Abstract

PURPOSE: To use a power supply of high priority (for instance, external power supply), even when a power supply of high voltage such as a lithium-ion secondary cell is used as a power supply of low priority (for instance, internal power supply). CONSTITUTION: A device has external/internal power supply input terminals ϕ1, ϕ2 respectively connected external/internal power supplies P1, P2, a comparator circuit 3 for comparing the voltage of the input terminal ϕ1 with reference voltage Vref and a connection switching means for selectively connecting the external/internal power supplies P1, P2 to a load based on the comparison result sent from this comparator circuit 3. The connection switch means can be constituted of the first switch circuit 1 connected between the input terminal ϕ1 and the load and performing on-action by a high level output from the comparator circuit 3 and the second switch circuit 2 connected between the input terminal ϕ2 and the load and performing on-action by a low level output from the comparator circuit 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply switching circuit for selectively switching between two power supplies, and is particularly applied to portable electronic equipment (for example, portable video cameras and camera-integrated VTRs). And a suitable power supply switching circuit.

[0002]

2. Description of the Related Art Generally, in a portable video camera, a camera-integrated VTR, etc., the size and weight of the device itself have been reduced in consideration of portability and operability, and a new image quality correction process has been made. Many technologies have been proposed and put to practical use.

Furthermore, a technique has been developed for compressing and recording and transmitting image information so that a large amount of image information can be handled, for example, a large amount of information can be recorded on a recording medium such as a magnetic tape or an optical disk. , Has been put to practical use.

Such signal processing requires a large-scale circuit configuration, but with the advent of LSI such as DSP (digital signal processor), the circuit configuration has become very simple and the device It contributes to downsizing and weight reduction.

Since such a portable electronic device is used outdoors where commercial power supply cannot be expected, it is necessary to prolong the power supply of the battery that is detachably incorporated in the device itself. In order to make the power supply of the battery last longer, it is easy to increase the capacity of the battery itself, but in this case, the structure of the battery itself becomes large, which hinders the reduction in size and weight of the portable electronic device.

Therefore, it is conceivable to reduce the size and weight of the battery without reducing the current capacity of the battery, that is, to adopt a structure in which the battery itself has a long-lasting power supply, but its development involves difficulties. Therefore, at present, when the circuit configuration of the signal processing system is designed to reduce power consumption, or a power supply switching circuit is provided between the power supply and the load (signal processing system) to connect an external power supply. To
The external power supply is used preferentially to save the battery power supply.

Now, a conventional power supply switching circuit will be described with reference to FIG. This power supply switching circuit has a structure in which two systems of power supplies are connected. Specifically, the external power supply P
1 is connected to an external power supply input terminal φ1, a battery (internal power supply) P2 is connected to an internal power supply input terminal φ2, and one output terminal φout connected to a load (DC / DC circuit or signal processing circuit system) in the subsequent stage. Have. This power supply switching circuit has an external power supply input terminal φ1 and an output terminal φou.
The mechanical switch 51 is inserted and connected in the middle path of the power supply line L wired between t, and the internal power input terminal φ
A power supply switching transistor Q is connected between 2 and the power supply line L.

The mechanical switch 51 is, for example,
First fixed contact 51 connected to external power supply input terminal φ1
a, the second fixed contact 51b connected to the internal power supply input terminal φ2, and the movable contact 5 connected to the power supply line L.
1c, and the contact piece S connected to the movable contact 51c is selectively fixed to the first fixed contact 51a or the second fixed contact 51b by the mechanical reciprocating motion of the operation piece 52 described later.
Is configured to be connected to.

The operation piece 52 is an external power source input terminal φ1.
Of the receiving side connector (not shown) (for example, a known 4-pin connector) from which the plug-in side connector (not shown) extending from the external power source P1 is connected, from the facing surface by, for example, a coil spring. When the insertion-side connector is inserted, the insertion-side connector is inserted into the receiving-side connector against the bias of the coil spring by the pressing force of the facing surface of the insertion-side connector. It is configured so as to retract toward you.

The mechanical switch 51 is
When the receiving side connector is not inserted into the receiving side connector and the receiving side connector is a free end, the contact piece S of the mechanical switch 51 causes the second fixed contact by the outward protrusion of the operation piece 52. When the power supply line L and the internal power supply P2 are electrically connected by contacting 51b and the plug-in connector is inserted to connect the external power supply P1 to the external power supply input terminal φ1, the operation piece 52 is The contact piece S of the mechanical switch 51 is forcibly brought into contact with the first fixed contact 51a by being pulled inward, so that the power supply line L and the external power supply P1 are electrically connected.

The power switching transistor Q is formed of, for example, an npn transistor, its emitter terminal E is connected to the power supply line L, its collector terminal C is connected to the internal power input terminal φ2 side, and its base terminal B. Is connected to the internal power supply input terminal φ2 side via the bias resistor R. Therefore, when the voltage of the internal power supply input terminal φ2 becomes higher than the voltage of the power supply line L, the power supply switching transistor Q is turned on, whereby the internal power supply connected to the internal power supply input terminal φ2. P2 will be connected to the load through the output terminal φout.

Next, the operation of the power source switching circuit will be described. First, when the external power source P1 is not connected to the external power source input terminal φ1, that is, the insertion side connector connected to the external power source P1 is the power source switching circuit. When not connected to the receiving side connector, the operation piece 52 projects outward,
The contact piece S of the mechanical switch 51 is the second fixed contact 5
It comes into contact with 1b. As a result, the internal power source P2 connected to the internal power source input terminal φ2 receives the mechanical switch 51, the power source supply line L, and the output terminal φout.
Will be electrically connected to the load through the path A consisting of

After that, when the external power source P1 is connected to the external power source input terminal φ1, that is, when the insertion side connector connected to the external power source P1 is connected to the receiving side connector of the power source switching circuit, the operating piece 52 is inserted. It is pressed inward by the facing surface of the connector, so that the contact piece S of the mechanical switch 51 comes into contact with the first fixed contact 51a. In this case, external power input terminal φ1
The external power source P1 connected to is electrically connected to the load through the path B including the mechanical switch 51, the power supply line L and the output terminal φout.

When the power source voltage V1 of the external power source P1 connected to the external power source input terminal φ1 is lower than the power source voltage V2 of the internal power source P2 by about 0.6 V or more, the power source switching transistor Q is turned on. Then, this time the internal power supply P
2 is connected to the load through the path C formed by the power supply switching transistor Q, the power supply line L, and the output terminal φout.

After that, when the power supply voltage V1 of the external power supply P1 is restored by cutting off from the load, the power supply switching transistor Q is turned off, so that the external power supply P1 is connected to the load through the path B again. .

As described above, in the power source switching circuit, when the external power source P1 is connected to the external power source input terminal φ1, the mechanical switch 51 forcibly connects the external power source P1 to the load. The external power source P1 is handled with priority over the internal power source P2.

[0017]

However, the conventional power supply switching circuit has a mechanism of monitoring the voltage difference between the power supplies of two systems and selecting the higher one, which is the external power supply P1 and the internal power supply. This is effective when the power supply voltages V1 and V2 of P2 are substantially the same, and when the power supply voltage V1 of the external power supply P1 that is higher than the power supply voltage V1 of the external power supply P2 is used, the internal power supply P1 with the lower priority is first There was a problem of consumption.

For example, a power supply voltage V2 is used as the internal power supply P2.
When a high-performance lithium-ion secondary battery (battery) is used, the power supply voltage V1 of the external power supply P1 is 13.5 V, and the power supply voltage V2 of the internal power supply P2 is 16 to 17 V, and the voltage difference is 2.5 Since the voltage is up to 3.5 V, the power switch transistor Q is rendered conductive by the voltage difference even though the contact piece S of the mechanical switch 51 is in contact with the first fixed contact 51a, and as a result, the internal power supply is turned on. P2
Will be connected to the load through the path C, and the internal power supply P2 having a low priority will be consumed first.

Further, in this case, since the power supply line L and the external power supply P1 are electrically connected to each other via the mechanical switch 51, the internal power supply P2 supplied to the power supply line L from the path C is connected to the internal power supply P2. There is a risk that the current will flow into the external power source P1 and cause an abnormality in the external power source P1.

Further, in the path C, since it passes through the power source switching transistor Q, there is a problem that the power consumption in the transistor Q becomes large due to the voltage drop in the internal resistance of the transistor Q.

As a method for solving the above-mentioned problem, when the internal power source P2 having a high power source voltage V2 is connected, the contact piece S of the mechanical switch 51 is forcibly forced to the second power source by the second force.
When the structure is such that the fixed contact 51b is switched to, or the voltage difference between the external power source P1 connected to the external power source input terminal φ1 and the internal power source P2 is detected and the voltage difference is larger than a predetermined value, for example, A structure is conceivable in which the contact piece S of the mechanical switch 51 is forcibly switched to the second fixed contact 51b side by a relay switch such as a solenoid.

However, in the case of the above structure, it is necessary to separately provide a switch having a complicated structure in addition to the mechanical switch 51, which complicates the structure of the power supply switching circuit, and consequently various portable devices equipped with the power supply switching circuit. The structure of the electronic device may increase in size.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a power source having a high power source voltage such as a lithium ion secondary battery (battery) with a low priority (eg, a power source having a low power source voltage). An object of the present invention is to provide a power supply switching circuit that can be surely consumed from a power supply with a high priority (eg, external power supply) even when used as an internal power supply.

Further, in addition to the above effects, another object of the present invention is that it is not necessary to use a mechanical switch for the switching operation of the power source, and all the switching operations of the power source can be performed by electrical processing. Another object of the present invention is to provide a power supply switching circuit that can achieve higher reliability.

[0025]

A power supply switching circuit according to the present invention includes a first power supply input terminal and a second power supply input terminal to which a first power supply and a second power supply are respectively connected, The comparison means for comparing the voltage of the first power supply input terminal with the reference voltage, and based on the comparison result from the comparison means, selectively switches between the first power supply and the second power supply to connect to the load. Connection switching means is provided to configure.

In this case, the connection switching means is connected between the first power source input terminal and the load, and is turned on by the first attribute from the comparison means, and by the second attribute. It is connected between the first switching circuit that performs an off operation, the second power supply input terminal and the load, and performs the on operation by the second attribute from the comparison means, and turns off by the first attribute. It can be configured to have a second switching circuit that operates.

[0027]

In the power supply switching circuit according to the present invention, the comparison means compares the voltage of the first power supply input terminal with the reference voltage. Then, based on the comparison result, the first power source and the second power source are selectively switched and connected to the load.

In this case, the voltage of the second power supply input terminal is irrelevant to the comparison target in the comparison means, and therefore even if the voltage of the first power supply input terminal is lower than the voltage of the second power supply input terminal. Therefore, the second power supply is not forcibly connected to the load.

Therefore, when a lithium-ion secondary battery (battery) having a power supply voltage of, for example, 16 to 17 V is used as the second power supply, the second power supply is forcibly connected to the load. Instead, the internal power supply is connected to the load only when the power supply voltage of the first power supply drops below the reference voltage, and the first power supply can always be handled with priority over the internal power supply.

In particular, the connection switching means is connected between the first power supply input terminal and the load, and is turned on by the first attribute from the comparison means, and turned off by the second attribute. It is connected between the first switching circuit that operates and the second power supply input terminal and the load, and performs the ON operation by the second attribute from the comparison means and the OFF operation by the first attribute. When the second switching circuit for performing the above is included, the following operation is performed.

First, when the first power source is not connected to the first power source input terminal, the voltage of the first power source input terminal is 0 V, so that the second attribute from the comparing means causes The first switching circuit is turned off and the second switching circuit is turned on. As a result, the second
The second power source connected to the power source input terminal of is electrically connected to the load.

Next, when the first power source is connected to the first power source input terminal, the voltage of the first power source input terminal becomes higher than the reference voltage, so the comparison result from the comparing means is the first. Will have attributes. As a result, the first switching circuit turns on and the second switching circuit turns off, and the first power supply connected to the first power supply input terminal is electrically connected to the load. become.

Then, by the consumption of the first power source,
When the voltage of the first power supply input terminal becomes lower than the reference voltage, the voltage of the first power supply input terminal becomes lower than the reference voltage this time. Therefore, the comparison result from the comparing means has the second attribute. Will have. As a result, the first switching circuit is turned off again and the second switching circuit is turned on, so that the supply of the first power source to the load is interrupted and the second power source input terminal is connected instead. The second
Will be electrically connected to the load.

After that, when the voltage of the first power supply input terminal is restored, the comparison result from the comparison means has the first attribute, so that the supply of the second power supply to the load is interrupted and the first power is again supplied.
Will be connected to the load.

As described above, in the power supply switching circuit according to the present invention, the first power supply can always be preferentially handled over the second power supply, and the second switching circuit is turned on. When the second power supply and the load are connected, the first switching circuit is turned off and the first power supply and the load are electrically cut off.
The current from the second power source does not flow into the first power source side, and the first power source does not malfunction.

Moreover, it is not necessary to use a mechanical switch for the power source switching operation, and all the power source switching operations can be performed by electrical processing, and the reliability can be improved.

[0037]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Some embodiments in which the power supply switching circuit according to the present invention is applied to a portable electronic device such as a portable camera-integrated VTR will be described below with reference to FIGS.

First, the power supply switching circuit according to the first embodiment has a structure in which power supplies of two systems are connected as shown in FIG. 1. Specifically, the external power supply P1 is connected to the external power supply. It has an internal power supply input terminal φ2 to which the input terminal φ1 and the battery P2 are connected and one output terminal φout to be connected to a load (DC / DC circuit or signal processing circuit system) in the subsequent stage.

The power supply switching circuit includes a first switching circuit 1 inserted and connected in an intermediate path of a first power supply line L1 wired between an external power supply input terminal φ1 and an output terminal φout, and an internal power supply. The second switching circuit 2 inserted and connected in the middle path of the second power supply line L2 wired between the input terminal φ2 and the output terminal φout
And a comparison circuit 3 connected between the first power supply line L1 and GND.

The comparator circuit 3 can use a comparator 4. In the illustrated example, the non-inverting input terminal of the comparator 4 is connected to the external power supply input terminal φ1 through the resistor R1 and the first power supply line L1. A resistor R2 is connected between the non-inverting input terminal and the GND, and a reference voltage generator for generating a reference voltage (+ potential) Vref, for example, a DC power supply 5 is connected between the inverting input terminal and the GND. The comparison circuit 3 is configured. In the following description, the output signal Sc output from the comparison circuit 3 will be referred to as a comparison result signal.

The resistors R1 and R2 are for dividing the power source voltage V1 of the external power source P1. When the voltage of the external power source input terminal φ1 becomes, for example, 11 V, the resistors R1 and R2 are divided by the voltage dividing ratio of the resistors R1 and R2. Each resistance value is set so that the voltage Va of the non-inverting input terminal becomes, for example, 5V.

The power supply voltage (+ V and -V) of the comparator 4 is set to, for example, + 5V and -5V. Therefore, when the voltage Va of the non-inverting input terminal of the comparator 4 becomes higher than the voltage Vref of the inverting input terminal, a high level comparison result signal Sc of +5 V is output from the output terminal of the non-inverting input terminal. Voltage Va
Becomes lower than the voltage Vref of the inverting input terminal, the output terminal outputs the low level comparison result signal Sc of -5V.

The first switching circuit 1 has a switch SW1 which is turned on / off based on the comparison result signal Sc from the comparison circuit 3. Specifically, the comparison from the comparison circuit 3 is performed. It is configured to be turned on when the result signal Sc is at a high level.

The second switching circuit 2 comprises a switch SW2 which is inserted and connected to the second power supply line L2, and an inverter 6 which is inserted and connected after the comparison circuit 3. In particular, the switch SW2 is turned on / off.
The off-operation is controlled by an output signal / Sc from the inverter 6 (this signal is an inverted signal of the comparison result signal, and therefore will be referred to as a comparison result inversion signal for convenience in the following description). Specifically, it is configured to be turned on when the comparison result inversion signal / Sc from the inverter 6 is at a high level.

Next, the operation of the power supply switching circuit according to the first embodiment, for example, the reference voltage Vref in the comparison circuit 3 will be described.
Is set to 5 V (that is, the power supply voltage V1 of the external power supply P1
When the external power supply input terminal φ1 is not connected to the external power supply P1, the voltage of the external power supply input terminal φ1 is 0V, so the comparison circuit 3 outputs a low-level comparison result signal Sc, and the inverter 6 outputs a high-level comparison result inversion signal / Sc. As a result, the switch SW1 in the first switching circuit 1 is output.
Turns off, and the switch SW2 in the second switching circuit 2 turns on.

Therefore, in this case, the internal power supply input terminal φ2
The internal power supply P2, which is connected to, is electrically connected to the load through the path B including the second power supply line L2 and the output terminal φout.

Next, the power source voltage V is applied to the external power source input terminal φ1.
When 1 is connected to the external power supply P1 of 13.5V, for example, the voltage applied to the non-inverting input terminal of the comparison circuit 3 becomes higher than the reference voltage (5V), so that the comparison result of high level is obtained from the comparison circuit 3. The signal Sc is output and the inverter 6
Outputs a low-level comparison result inversion signal / Sc, and as a result, the switch SW1 in the first switching circuit 1 is turned on and the switch SW2 in the second switching circuit 2 is turned off.

Therefore, in this case, the external power supply input terminal φ1
The external power supply P1 connected to is electrically connected to the load through the path A formed of the first power supply line L1 and the output terminal φout.

When the power source voltage V1 of the external power source P1 drops below 11V due to the consumption of the external power source P1, this time, the voltage V of the inverting input terminal of the comparator circuit 3 is turned on.
Since ref becomes higher than the voltage Va of the non-inverting input terminal, the comparison result signal Sc of low level is output from the comparison circuit 3.
Is output, and the high level comparison result inversion signal / Sc is output from the inverter 6, and as a result, the first comparison result inversion signal / Sc is output.
The switch SW1 in the switching circuit 1 is turned off again, and the switch SW2 in the second switching circuit 2 is turned on.

Therefore, in this case, the supply of the external power supply P1 to the load is cut off, and instead the internal power supply P2 connected to the internal power supply input terminal φ2 is again supplied from the second power supply line L2 and the output terminal φout. It will be electrically connected to the load through the path B.

After that, when the power supply voltage V1 of the external power supply P1 is restored, each output S of the comparison circuit 3 and the inverter 6 is output.
Since c and / Sc become high level and low level, respectively, the supply of the internal power source P2 to the load is cut off, and the external power source P1 is again connected to the load through the path A.

As described above, in the power supply switching circuit according to the first embodiment, the comparison circuit 3 compares the voltage of the external power supply input terminal φ1 with the power supply voltage conversion voltage of the reference voltage Vref, and the comparison result is obtained. Accordingly, the external power source P1 and the internal power source P2 are selectively switched. Therefore, when a lithium ion secondary battery (battery) having a power source voltage V2 of 16 to 17 V is used as the internal power source P2, The power supply P2 is not forcibly connected to the load, and the internal power supply P2 is connected to the load only when the power supply voltage V1 of the external power supply P1 becomes lower than the power supply voltage conversion voltage of the reference voltage Vref. , The external power source P1 can always be preferentially handled over the internal power source P2.

When the switch SW2 in the second switching circuit 2 is turned on and the internal power source P2 and the load are connected, the switch SW1 in the first switching circuit 1 is turned off and electrically. External power supply P
1 and the load are cut off, the internal power supply P2
The current from the terminal does not flow into the external power supply P1 side, and the external power supply P1 does not become abnormal.

Next, a power supply switching circuit according to the second embodiment will be described with reference to FIG. The same reference numerals are given to those corresponding to FIG.

The power supply switching circuit according to the second embodiment is
As shown in FIG. 2, the switch SW1 and SW2 in the first and second switching circuits 1 and 2 have substantially the same configuration as the power supply switching circuit according to the first embodiment.
Are configured by n-channel type MOSFETs 11 and 12, respectively. In the following explanation,
N-channel type M corresponding to the first switching circuit 1
The OSFET 11 is referred to as a first FET 11 and corresponds to the second switching circuit 2 and is an n-channel MOSFET.
12 is referred to as a second FET 12.

In the power supply switching circuit according to the second embodiment, the source terminal S of the first FET 11 is on the external power supply input terminal φ1 side and the drain terminal D is the output terminal φ.
On the out side, the gate electrode G is connected to the output side of the comparison circuit 3, the source terminal S of the second FET 12 is on the internal power supply input terminal φ2 side, and the drain terminal D is the output terminal φou.
The gate electrode G is connected to the output side of the inverter 6 on the t side.

The source terminals S of the first and second FETs 11 and 12 are connected to the external power source P1 and the internal power source P2, respectively, in the n-channel MOSFET in which the source terminal S is the anode and the drain terminal D is the drain terminal D. This connection is based on the existence of parasitic diodes serving as cathodes, and this connection positively utilizes these parasitic diodes.

That is, in the first FET 11, the parasitic diode D1 whose forward direction is from the external power supply input terminal φ1 to the output terminal φout is connected, and the second F1 is connected.
In ET12, it is equivalent to connecting a parasitic diode D2 whose forward direction is from the internal power supply input terminal φ2 to the output terminal φout.

Normally, a reflected wave (reflected voltage, reflected current) arrives from the output side (for example, a DC / DC circuit or a signal processing circuit system) toward the power source side, which causes noise. By connecting the source terminals S of the second FETs 11 and 12 to the corresponding power sources P1 and P2, respectively, the parasitic diodes D1 and D2 present in the FETs 11 and 12 are connected in the direction in which the arrival of reflected waves is blocked. This makes it possible to prevent the occurrence of noise due to the arrival of the reflected wave.

Next, the operation of the power supply switching circuit according to the second embodiment will be described. First, when the external power supply P1 is not connected to the external power supply input terminal φ1, the voltage of the external power supply input terminal φ1 is 0V. Therefore, the comparison circuit 3 outputs the low-level comparison result signal Sc, and the inverter 6 outputs the high-level comparison result inversion signal / Sc. As a result, the first FET 11 is turned off and the second FET 12 is turned on, so that the internal power supply P2 connected to the internal power supply input terminal φ2 is connected to the second FET 12, the second power supply line L2, and the second power supply line L2. Output terminal φ
It will be electrically connected to the load through the path B consisting of out.

Next, the power supply voltage V is applied to the external power supply input terminal φ1.
When 1 is connected to the external power supply P1 of 13.5V, for example, the voltage Va applied to the non-inverting input terminal of the comparison circuit 3 becomes higher than the reference voltage Vref (5V), and therefore the comparison circuit 3 outputs a high level signal. The comparison result signal Sc is output,
From the inverter 6, a low level comparison result inversion signal / Sc
Will be output. As a result, the first FET 11
Turns on and the second FET 12 turns off,
External power supply P1 connected to external power supply input terminal φ1
Will be electrically connected to the load through the path A formed of the first FET 11, the first power supply line L1, and the output terminal φout.

When the power source voltage V1 of the external power source P1 drops below 11V due to the consumption of the external power source P1, the voltage Va at the non-inverting input terminal becomes lower than the reference voltage Vref (5V) this time. Therefore, the comparison circuit 3 outputs the low level comparison result signal Sc, and the inverter 6 outputs the high level comparison result inversion signal / Sc. As a result, the first FET 11 turns off again and the second FET 12 turns on,
The supply of the external power supply P1 to the load is cut off, and instead, the internal power supply P1 connected to the internal power supply input terminal φ2 is electrically connected to the load through the path B.

After that, when the power supply voltage V1 of the external power supply P1 is restored, each output S of the comparison circuit 3 and the inverter 6
Since c and / Sc become high level and low level, respectively, the supply of the internal power source P2 to the load is cut off, and the external power source P1 is again connected to the load through the path A.

As described above, in the power supply switching circuit according to the second embodiment, similarly to the power supply switching circuit according to the first embodiment, in the comparison circuit 3, the voltage of the external power supply input terminal φ1 and the reference voltage Vref. Since the external power source P1 and the internal power source P2 are selectively switched according to the comparison result, a lithium ion secondary battery (battery) having a power source voltage V2 of 16 to 17 V is used as the internal power source P2. ) Is not forcibly connected to the load, the internal power supply P2 is connected to the load only when the power supply voltage V1 of the external power supply P1 becomes lower than the reference voltage Vref. As a result, the external power source P1 can always be handled with priority over the internal power source P2.

When the second FET 12 is turned on and the internal power source P2 and the load are connected, the first F
Since the ET11 is turned off and the external power supply P1 and the load are electrically disconnected, the current from the internal power supply P2 does not flow into the external power supply P1 side and the external power supply P1 becomes abnormal. Disappears.

Particularly, in the power supply switching circuit according to the second embodiment, the power supply switching circuit is an n-channel type MOSFET.
Since it is configured by the (first and second FETs 11 and 12), it is not necessary to use a mechanical switch for the power switching operation, and all the power switching operations are performed by electrical processing. Therefore, the reliability can be improved.

Next, a power supply switching circuit according to the third embodiment will be described with reference to FIG. The same reference numerals are given to those corresponding to FIG.

The power supply switching circuit according to the third embodiment is
As shown in FIG. 3, the power supply switching circuit according to the second embodiment has almost the same configuration, but an n-channel type M is connected in series with the second FET 12 after the second FET 12.
The difference is that an OSFET (for convenience, referred to as a third FET) 13 is connected.

Specifically, the drain terminal D of the third FET 13 is the drain terminal D of the second FET 12.
, The source terminal S is connected to the output terminal φout side, and the gate electrode G is commonly connected to the gate electrode G of the second FET 12. Therefore, this third FET
The parasitic diode D3 in 13 has an output terminal φout.
The direction from the side toward the internal power supply P2 side is the forward direction.

The reason for connecting the third FET 13 is as follows.
For example, by turning on the first FET 11, the external power source P
This is because when 1 is preferentially used, a current may flow from the internal power supply P2 to the output terminal φout side through the parasitic diode D2 in the second FET 12. This phenomenon may occur remarkably when the lithium-ion secondary battery is used as the internal power supply P2 because the power supply voltage V2 is high.

Therefore, by connecting the third FET 13 to the subsequent stage of the second FET 12, the second FET 1
Internal power supply P2 based on the parasitic diode D2 existing in 2
Unnecessary current (parasitic current) from the third FET 13
It is possible to effectively prevent the parasitic diode D3 existing in the.

As described above, the power supply switching circuit according to the third embodiment has substantially the same effect as the power supply switching circuit according to the second embodiment, and the third FET 1 is also provided.
By connecting 3 in series with the second FET 12, it is possible to effectively prevent an unnecessary current (parasitic current) from flowing from the internal power supply P2 to the output side, which contributes to further improvement in reliability. You can

Next, a power supply switching circuit according to the fourth embodiment will be described with reference to FIG. Note that the same reference numerals are given to those corresponding to FIG.

The power supply switching circuit according to the fourth embodiment is
As shown in FIG. 4, it has substantially the same configuration as the power supply switching circuit according to the third embodiment, but differs in that a hysteresis means is added to the comparison circuit 3.

The hysteresis means is the comparator 4
Of the feedback resistor Rf connected between the non-inverting input terminal of the comparator 4.

Explaining the operation by this hysteresis means, first, when the external power source P1 of 13.5V is connected to the external power source input terminal φ1, the voltage Va of the non-inverting input terminal is caused by the voltage drop in the resistor R. For example, 5V
When the voltage is higher than the above, the comparator 4 outputs a high level comparison result signal Sc of + 5V,
As a result, the external power source P1 is connected to the load through the path A.

From this state, when the external power source P1 is consumed, the power source voltage V1 of the external power source P1 changes from 13.5V to 1V.
When it becomes lower than 1V, the voltage V of the non-inverting input terminal
Since a becomes a voltage lower than 5V, the comparator 4 outputs a low level comparison result signal Sc of -5V,
As a result, the internal power supply P2 is now connected to the load through the path B.

After that, when the power supply voltage V1 of the external power supply P1 becomes, for example, 11 V due to the interruption of the load, the voltage Va at the non-inverting input terminal normally becomes 5 V, which is the same as the reference voltage Vref, and the comparator 4 outputs Although 0V is output, in this fourth embodiment, since the feedback resistor Rf is connected to the non-inverting input terminal, the non-inverting input is caused by a voltage drop of, for example, 0.5V at the feedback resistor Rf. The terminal voltage Va becomes 4.5V. In this case, since the reference voltage Vref is still higher, the comparator 4 outputs the low-level comparison result signal Sc of -5V.

When the external power supply P1 gradually recovers and its power supply voltage V1 exceeds 12V, the voltage Va at the non-inverting input terminal is 5 of the reference voltage Vref.
Since it exceeds V, +5 from the comparator 4.
The high-level comparison result signal Sc of V is output, and the external power supply P1 is again connected to the load through the path A.

That is, the hysteresis means (feedback resistor R
When f) is not added, the internal power supply P2 is supplied when the power supply voltage V1 of the external power supply P1 becomes lower than 11V.
Is connected to the load, and when the external power supply P1 gradually returns from this state and becomes higher than 11V, the external power supply P1 is connected to the load this time.

In this case, when a battery is used as the external power source P1 in the actual circuit, the external power source P1
When the power supply voltage V1 of the external power supply P1 is reduced to switch to the internal power supply P2 due to consumption, the external power supply P1 is disconnected from the load, so that the power supply voltage V1 is gradually recovered and the external power supply P1 is restored again. The power supply voltage V1 is reduced by being connected to the load and the consumption thereof is started, and the internal power supply P2 is again connected to the load. A series of these operations are repeated, and as a result, the power supply voltage V1 of the external power supply P1 rises and falls near the power supply voltage conversion voltage of the reference voltage Vref, and the power supply switching operation is frequently performed.

However, in the fourth embodiment, since the hysteresis means (feedback resistor Rf) is added, the internal power supply P2 is turned on when the power supply voltage V1 of the external power supply P1 becomes lower than 11V. It is connected to a load, and the external power supply P1 gradually recovers from this state, and is not the above 11V but a voltage + α higher than the 11V, for example, 12V.
Since the external power supply P1 is connected to the load at a higher stage, it is possible to avoid the inconvenience of frequent power supply switching operation when a battery is used as the external power supply P1. it can.

As described above, the power source switching circuit according to the fourth embodiment has substantially the same effect as the power source switching circuit according to the third embodiment, and the power source switching circuit when the battery is used as the external power source P1. Inconvenience related to operation (inconvenience of frequent power switching operations)
Can be prevented in advance, and power can be stably supplied to the signal processing circuit system connected to the output terminal φout.

In each of the above-described embodiments, an example in which the present invention is applied to a portable electronic device such as a portable camera-integrated VTR is shown, but the present invention is not limited to this, and an electronic device in which two power sources are switched and used. Applicable to all devices.

[0085]

As described above, according to the power supply switching circuit of the present invention, the first power supply input terminal and the second power supply input terminal to which the first power supply and the second power supply are connected, respectively. A comparing means for comparing the voltage of the first power supply input terminal with a reference voltage; and a load for selectively switching the first power supply and the second power supply based on the comparison result from the comparing means. Since a connection switching means for connecting to the power supply is provided, even if a power supply with a high power supply voltage such as a lithium-ion secondary battery (battery) is used as a power supply with a low priority (for example, internal power supply), it will be given priority. It can be consumed from a high frequency power source (for example, an external power source).

Further, according to the power supply switching circuit of the present invention, in the above structure, the connection switching means is connected between the first power supply input terminal and the load, and the connection switching means is connected to the first power supply input terminal and the load. A first switching circuit which performs an ON operation according to the attribute 1 and an OFF operation according to the second attribute, is connected between the second power supply input terminal and the load, and is connected to the second switching circuit. Since the second switching circuit is configured to perform the ON operation according to the attribute of and the OFF operation according to the first attribute, a mechanical switch is used for the switching operation of the power source in addition to the above effect. There is no need, and all power source switching operations can be performed by electrical processing, and reliability can be improved.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of a power supply switching circuit according to a first embodiment among embodiments in which a power supply switching circuit according to the present invention is applied to a portable electronic device such as a portable camera-integrated VTR. is there.

FIG. 2 is a circuit diagram showing a configuration of a power supply switching circuit according to a second embodiment.

FIG. 3 is a circuit diagram showing a configuration of a power supply switching circuit according to a third embodiment.

FIG. 4 is a circuit diagram showing a configuration of a power supply switching circuit according to a fourth embodiment.

FIG. 5 is a circuit diagram showing a configuration of a power supply switching circuit according to a conventional example.

[Explanation of reference symbols] P1 external power supply P2 internal power supply φ1 external power supply input terminal φ2 internal power supply input terminal φout output terminal L1 first power supply line L2 second power supply line 1 first switching circuit 2 second switching circuit 3 Comparison Circuit 4 Comparator 5 Reference Voltage Generator (DC Power Supply) 6 Inverter 11 First FET 12 Second FET 13 Third FET Rf Feedback Resistance

Claims (7)

[Claims] 1. A first power source input terminal and a second power source input terminal to which a first power source and a second power source are respectively connected, and a voltage of the first power source input terminal and a reference voltage are compared. Switching means for selectively switching between the first power source and the second power source to connect to the load based on the comparison result from the comparing means. circuit. 2. The voltage of the first power input terminal is V1,
When the reference voltage is Vref, the connection switching means switches and connects the second power supply and the load when the comparison result from the comparison means indicates V1 ≦ Vref. The power supply switching circuit according to item 1. 3. The connection switching means is connected between the first power supply input terminal and the load, and turns on according to the first attribute from the comparing means and turns off according to the second attribute. Is connected between the first switching circuit for performing the above, the second power supply input terminal and the load,
The ON operation is performed by the second attribute from the comparison means,
The power supply switching circuit according to claim 1, further comprising a second switching circuit that performs an off operation according to the first attribute. 4. The FET of the first switching circuit, wherein the source terminal is connected to the first power supply input terminal, the drain terminal is connected to the load, and the gate electrode is connected to the output side of the comparison means. In the second switching circuit, the source terminal is connected to the second power supply input terminal, the drain terminal is connected to the load, and the gate electrode is connected to the output side of the comparison means via the inverting circuit. The power supply switching circuit according to claim 3, wherein the power supply switching circuit is configured by an FET. 5. The power supply switching circuit according to claim 4, wherein a parasitic current cutoff element is connected to a stage subsequent to the FET constituting the second switching circuit. 6. The parasitic current cutoff element has a drain terminal commonly connected to a drain terminal of an FET constituting the second switching circuit, a source terminal connected to a load, and a gate electrode connected to the gate electrode of the FET. The power supply switching circuit according to claim 5, wherein the power supply switching circuit is configured by commonly connected FETs. 7. The comparison means includes a voltage value of the first power supply input terminal with respect to the reference voltage at which the comparison result changes from the first attribute to the second attribute, and the comparison result is the second value. 4. The power supply switching circuit according to claim 3, further comprising hysteresis means for making a difference between the reference voltage changing from the attribute to the first attribute and the voltage value of the first power input terminal with respect to the reference voltage.