JP2534308Y2 - Power supply circuit for electronic equipment - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply circuit of an electronic device which can be switched to two or more power supplies.

[0002]

2. Description of the Related Art Conventionally, when power is supplied to an electronic circuit that executes data input / output processing and arithmetic processing in accordance with a predetermined program such as a microcomputer, an internal power supply and an external power supply are used to carry the electronic equipment and to prevent power failure. Switching to two or more power supplies.

In general, switching from an internal power supply to an external power supply by moving a contact by attaching an external power supply plug to a connector provided in an electronic device, and removing the external power supply plug from the external power supply to an internal power supply again. A switching power supply circuit is used.

[0004] However, in such a power supply circuit, the power supply voltage applied to the electronic circuit may fluctuate at the time of power supply switching or may be momentarily interrupted, resulting in unstable operation of the electronic circuit. In particular, in an electronic circuit using a microcomputer, data stored before the power supply is changed after the power supply is changed, so that the microcomputer does not execute according to a predetermined program, so-called runaway state, May not enter a signal input state, that is, a so-called latch state may occur.

Therefore, in order to surely return the electronic circuit to the initial state at the time of power supply switching, it is necessary to add a reset circuit which detects a change in power supply voltage applied to the electronic circuit or a momentary interruption and generates a reset signal. Many.

[0006]

However, the above-mentioned reset circuit comprises a power supply voltage measuring means, a discrimination level generating means, a comparing means for comparing outputs from these means, and a predetermined time based on the output of the comparing means. Since it is composed of pulse generating means for generating a pulse having a width, the number of parts increases naturally, and the occupied space of the electronic device increases, and the product cost and power consumption of the electronic device increase.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems, to surely return an electronic circuit to an initial state at the time of power supply switching, and to reduce power consumption and reduce the number of parts during normal operation. An object of the present invention is to provide a power supply circuit of an electronic device that can be realized.

[0008]

According to the present invention, there is provided a power supply circuit of an electronic device for supplying power to an electronic circuit having a pair of power input terminals and a reset input terminal, the plug having a first electrode and a second electrode. A first DC power supply connected to the first electrode and the second electrode; a first terminal, a second terminal, and a third terminal detachably attached to the second terminal. A connector to which the second terminal is connected, the third terminal and the second electrode are connected, and the second terminal and the third terminal are detached, and the first terminal is connected to one of the power input terminals; A third terminal is connected to the other of the power input terminals, a second DC power supply is connected between the first terminal and the second terminal, and a second terminal is connected between the second terminal and the reset input terminal. Controlled by the potential difference between the other of the power input terminals It is a power source circuit of an electronic device, characterized in that the switching element is inserted.

[0009]

According to the present invention, the plug connected to the first DC power supply is used when the power supply of the electronic circuit is switched from the second DC power supply to the first DC power supply, or when the electronic circuit is switched from the first DC power supply to the second DC power supply. The power supply can be switched by attaching / detaching the plug, and when the plug is attached / detached, the second terminal of the connector does not come into contact with any of the third terminal of the connector and the second electrode of the plug. The power supply causes a predetermined potential difference between the second terminal and the other of the power supply input terminals, and the switching element is turned on, whereby the reset input terminal and the second terminal of the electronic circuit are turned on, and the electronic circuit is turned off. Can be returned to the initial state.

[0010]

1 is a circuit diagram showing a power supply circuit of an electronic apparatus according to an embodiment of the present invention. The electronic device 20 includes an electronic circuit 11 having a pair of power input terminals V, G and a reset input terminal R, and a first terminal 7, a second terminal 8, and a third terminal 9 detachable from the second terminal 8. Connector 6, a second DC power supply 10 connected between the first terminal 7 and the second terminal 8, and a switching element 13 interposed between the second terminal 8 and the reset input terminal R. The first
The terminal 7 is connected to the power input terminal V, and the second terminal 8 is connected to the power input terminal G. Note that a current flows between the second DC power supply 10 and the first terminal 7.
It is preferable to insert a backflow prevention diode 14 so that the current does not flow toward the first terminal 7.

The electronic circuit 11 includes a read only memory (ROM) and a random access memory (RAM) for storing predetermined programs and data, and a central processing unit (CPU) for executing data input / output processing and arithmetic processing according to the programs. ), Etc., and when a voltage equal to or higher than a predetermined value is applied to the power input terminals V and G,
When the operation starts and a low-level (L) signal close to the voltage of the power supply input terminal G is input to the reset input terminal R, the operation returns to the initial state and the predetermined operation is restarted.

As shown in the sectional view, the connector 6 has a first terminal 7 having a columnar shape and conductivity, a second terminal 8 having a plate shape and conductivity, and a flexible and conductivity type. A third terminal 9 realized by a metal leaf spring or the like, and a holder 15 for holding these terminals in an insulated state. When the plug 2 is not attached to the connector 6, the second terminal 8 is formed. Third
Although the terminals 9 are in contact and conducting, when the plug 2 is attached to the connector 6, the third terminals 9 are deformed to separate the second terminals 8 and 9.

The switching element 13 can be realized by an NPN transistor, and the emitter is the second terminal 8
, The collector is connected to the reset input terminal R, and the base is connected to the power supply input terminal G via the resistor 12.

On the other hand, when the power supply for supplying power to the electronic circuit 11 is switched from the second DC power supply 10 to the first DC power supply 1, as shown in the cross-sectional view, the first conductive electrode 3 and the cylindrical electrode 3 are electrically connected to each other. A plug 2 composed of a second electrode 5 and a holding member 4 for holding these electrodes in an insulated state,
It is attached to the connector 6. Note that the first electrode 3 and the second electrode
The electrode 5 is connected to the first DC power supply 1 and the plug 2 is attached to the connector 6 so that the second terminal 8 and the third terminal 9 are connected.
In order to prevent the third terminal 9 from coming into contact with the second electrode 5 immediately after the plug 2 is detached, the tip of the plug 2 is attached to the holding member 4.
Covered with.

Next, the operation of such a power supply circuit will be described. When the second DC power supply 10 supplies power to the electronic circuit 11, that is, when the plug 2 is not attached to the connector 6, the second terminal 8 and the third terminal 9 of the connector 6 are in contact with each other and are in a conductive state. , One output of the second DC power supply 10 is connected to the power supply input terminal V of the electronic circuit 11,
The other output of DC power supply 10 is connected to power input terminal G via second terminal 8 and third terminal 9.

The switching element 13 has a high resistance state between the emitter and the collector because the base and the emitter have the same potential due to the contact between the second terminal 8 and the third terminal 9 and no base current flows. .

On the other hand, when the first DC power supply 1 supplies power to the electronic circuit 11, the plug 2 is attached to the connector 6. After the plug 2 moves inside the connector 6 and the holding member 4 comes into contact with the third terminal 9, the plug 2 further moves, thereby deforming the third terminal 9 and making contact with the second terminal 9. Disappears. Then, the switching element 13 has the base and the emitter no longer at the same potential, and the second DC power supply 10
Power supply input terminal V, electronic circuit 11, power supply input terminal G, resistor 12, base and emitter of switching element 13, second
A circuit loop of the DC power supply is formed, and a base current determined by the output voltage of the second DC power supply 10, the forward voltage between the emitter and the base, the circuit impedance of the electronic circuit 11, and the resistor 12 flows.

If the resistance value of the resistor 12 is set so that a predetermined base current flows, when the above-described circuit loop is formed, the collector and the emitter of the switching element 13 become conductive, and the reset input terminal R Is supplied with the potential of the second terminal 8, and the electronic circuit is reset.

Further, the plug 2 moves in the connector 6 and the third terminal 9 of the connector 6 and the second electrode 5 of the plug 2
Makes contact and conducts, so that one output of the first DC power supply 1 is connected to the power supply input terminal V of the electronic circuit via the first electrode 3, the first terminal 7 and the backflow prevention diode 14, and , The other output of the first DC power supply 1
The electrode 5 is connected to the power input terminal G via the third terminal 8. At this time, the switching element 13 has a base
The terminal has the same potential as that of the terminal 9, and the emitter supplies the forward voltage of the reverse current prevention diode 14 and the output voltage of the second DC power supply 10 from the output voltage of the first DC power supply 1 to the potential of the third terminal 9. The subtracted voltage is applied. Therefore, if the output voltage of the first DC power supply 1 is equal to or higher than the output voltage of the second DC power supply 10, no base current flows through the switching element 13, and the high resistance state is established again between the connector and the emitter.

Conversely, when the power supply for supplying power to the electronic circuit 11 is switched from the first DC power supply 1 to the second DC power supply 10, the plug 2 moves outward from the connector 6 and the third terminal 9 When the contact target moves from the second electrode to the holding member 4, the contact between the second terminal 8 and the third terminal 9 is eliminated, so that a base current flows through the switching element 13 to be in a conductive state, and the reset input terminal A low-level signal is input to R. When the plug 2 is completely detached from the connector 6, the second terminal 8 and the third terminal 9 come into contact again, the second DC power supply 10 starts supplying power to the electronic circuit 11, and the switching element 13 Becomes the high resistance state again.

In this way, switching between the two power supplies can be realized by plugging and unplugging, and a reset signal can be reliably generated in the process of plugging and unplugging. Therefore, even if a runaway or latch state of the CPU occurs due to the power supply switching, the reset can be reliably performed.

In the above embodiment, an example has been described in which the switching element 13 is realized by an NPN transistor. However, the same can be realized by using a field effect transistor (FET).

In the above embodiment, the electronic circuit 1
Reference numeral 1 describes an example in which a reset operation is performed when the reset signal goes low, that is, a so-called low active state. However, when the reset signal goes high, a reset operation is performed.
Each of the DC power supplies 1 and 2 is a PNP transistor.
This can be realized by connecting the polarity of the reverse current prevention diode 10 and the reverse current prevention diode 14 and exchanging the connection of the electronic circuit 11 to the power input terminals V and G.

In the above embodiment, the first DC power supply 1 and the second DC power supply 10 are represented by a symbol of a battery. However, a power supply that converts AC or DC to a predetermined DC voltage is similarly applied. .

[0025]

[Effects of the Invention] As described in detail above, according to the present invention,
The switching of the power supply of the electronic circuit can be easily performed by plugging and unplugging, and the reset signal can be securely generated at the time of plugging and unplugging. Therefore, the unstable operation of the electronic circuit due to the power supply switching can be eliminated. . In addition, according to the present invention, during normal operation without power supply switching, there is almost no power consumption, so that the load on each DC power supply can be reduced. Further, since the present invention can be realized with a small number of parts, it is possible to contribute to a reduction in size and weight of an electronic device and to suppress an increase in product cost.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a power supply circuit of an electronic device according to an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st DC power supply 2 Plug 6 Connector 10 2nd DC power supply 11 Electronic circuit 13 Switching element 20 Electronic equipment

Claims (1)

(57) [Scope of request for utility model registration] 1. A power supply circuit of an electronic device for supplying power to an electronic circuit having a pair of power input terminals and a reset input terminal, wherein a plug having a first electrode and a second electrode, a first electrode and a second electrode are provided. A first DC power supply connected to the electrode, a first terminal, a second terminal, and a third terminal detachably attached to the second terminal;
A first electrode and a second terminal are connected by mounting the plug, a third terminal is connected to the second electrode, and a second
A terminal and a connector from which the third terminal is detached, wherein the first terminal is connected to one of the power input terminals, and the third terminal is connected to the third terminal.
A second DC power supply is connected between a first terminal and a second terminal, and a second terminal and the power supply are connected between a second terminal and the reset input terminal. A power supply circuit for an electronic device, wherein a switching element controlled by a potential difference between the input terminal and the other input terminal is interposed.