JP2000324718A - Power circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce cost and eliminate the limitation of a using circuit, by arranging the constitution such that it includes a power failure detecting circuit to turn off a transistor at power failure of the main power source and a backup power source connected to the second power source. SOLUTION: For this power circuit, the main power source 53 is composed of a constant voltage circuit 52 and an AC adaptor 51, and at normality, specified DC voltage is supplied to the first and second power systems from the main power source 53, but the second power system 56 is supplied with power voltage through a transistor 55. On the other hand, when the main power source 53 fails, the supply of power voltage to the first power system 54 stops, but the second power system 56 is supplied with power voltage from a backup power source 57, and a power failure detecting circuit 59 detects the power failure of the main power source 53, and positive voltage is generated, whereby the transistor 55 is turned off. As a result, a standard constant voltage circuit can be used, the limitation of a using circuit can be eliminated, and also since an interposed element is only one, the cost can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a power supply circuit used for a telephone or the like.

[0002]

2. Description of the Related Art In a power supply circuit of a telephone, a power supply system connected to an RF module or a compander IC in the telephone and supplied with a power supply voltage only when energized is provided.
There are two types of power supply systems that are connected to the U or the like and require backup at the time of power failure. FIG. 4 shows a conventional power supply circuit including these two power supply systems. In this figure, 71 is AC
The adapter converts the commercial AC power supply voltage to a predetermined DC voltage. A constant voltage circuit 72 is connected to the output of the AC adapter 71 and provided in the telephone. The constant voltage circuit 72 and the AC adapter 71 constitute a main power supply 73. The output of the constant voltage circuit 72 is a voltage adjusting diode 7
4, it is connected to a first power supply system 75 which only needs to be supplied with a power supply voltage during energization. The output of the constant voltage circuit 72 is connected via a reverse current preventing diode 76 to a second power supply system 77 requiring backup, and a backup power supply 78 is connected to the second power supply system 77. .

In the power supply circuit configured as described above, normally, a predetermined DC power supply voltage is supplied from the main power supply 73 via the diodes 74 and 76 to the first and second power supply systems 75 and 77.
Supplied to On the other hand, when the main power supply 73 fails, the supply of the power supply voltage to the first power supply system 75 is stopped, but the power supply voltage is supplied from the backup power supply 78 to the second power supply system 77 that requires backup. . At this time, since the reverse current prevention diode 76 is turned off, the backflow of the current from the backup power supply 78 to the first power supply system 75 is prevented.

As described above, in the conventional power supply circuit, the reverse current is prevented by the reverse current preventing diode 76 during a power failure. When the diode 76 is inserted, the voltage drops from the output voltage of the constant voltage circuit 72 by the voltage between the anode and the cathode of the diode, and the power supply voltage is supplied to the second power supply system 77. Therefore, in order to obtain a predetermined power supply voltage in the second power supply system 77, the output voltage of the constant voltage circuit 72 must be increased from the predetermined power supply voltage by the voltage between the anode and the cathode of the diode. However, if the output voltage of the constant voltage circuit 72 is set as described above and there is no voltage adjusting diode 74, the power supply voltage higher than the predetermined power supply voltage by the voltage between the anode and the cathode of the diode is applied to the first power supply system. 75. Therefore, a predetermined power supply voltage is also supplied to the first power supply system 75 by inserting the diode 74 on the first power supply system 75 side and reducing the voltage by the voltage between the anode and the cathode of the diode.

[0005]

However, in the above-described conventional power supply circuit, a voltage adjusting diode 74 is required in addition to the reverse current preventing diode 76, and two diodes are required. There was a problem that caused an increase in cost. Further, since the output voltage of the constant voltage circuit 72 must take into account the voltage drop due to the diode, there is a problem that a constant voltage circuit of a standard output voltage cannot be used, and the circuit to be used is limited. .

[0006] The present invention has been made in view of the above points,
It is an object of the present invention to provide a power supply circuit which can reduce the cost, can use a constant voltage circuit having a standard output voltage, and can release the restriction on the circuit to be used.

[0007]

A power supply circuit according to the present invention includes a main power supply for outputting a power supply voltage, a first power supply system to which the power supply voltage is supplied from the main power supply, and a power supply voltage supplied from the main power supply. A second power supply system, an output section of the main power supply, and the first power supply system.
A power supply system or a transistor connected between the second power supply systems, a power failure detection circuit for turning off the transistors when the main power supply fails, and a backup power supply connected to the second power supply system. Features. here,
The main power supply can be constituted by a conversion circuit for converting a commercial AC power supply voltage into a predetermined DC voltage, and a constant voltage circuit connected to the output thereof. The conversion circuit is specifically an AC adapter.
Further, the backup power supply can be constituted by a capacitor.
The first power supply system is a voice processing (DSP) circuit, an LCD display unit, a radio frequency (RF) circuit, a speech network circuit, a power amplifier circuit, or the like. The second power supply system is a control unit (CPU), a dialer circuit, a data storage unit, or the like.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of a power supply circuit according to the present invention will be described in detail with reference to the accompanying drawings. FIG. 3 shows a base unit of a cordless telephone using the power supply circuit according to the embodiment of the present invention.

The master unit 10 shown in FIG. 3 has a CPU 11 for controlling the entire master unit. A dialer IC 25, an LCD display unit 13, and a hook switch 16 are connected to the CPU 11. The dialer IC 25 has a DP / DTMF transmission function and is connected to the key matrix 12.
Here, the key matrix 12 has an absence key, a play key, a hands-free key, a registration key, a numeric keypad, and the like.
Enter various information. The LCD display unit 13 displays various information such as the received caller's telephone number. Hook switch 16 determines whether or not the receiver is installed on base unit 10.

Reference numeral 17 denotes a line terminal to which an incoming call detecting circuit 18 for detecting a ringer signal is connected, and an output of the incoming call detecting circuit 18 is connected to the CPU 11. 19 is a rectifier circuit for preventing the inversion of the voltage polarity of the line terminal 17 from affecting the inside of the telephone, 20 is a DP sending circuit for connecting / disconnecting the line, and 21 is a speech network IC for performing 2-wire to 4-wire conversion. The line terminal 17 is connected to the CP via these circuits.
Connected to U11. Also, a speech network IC
21 includes a receiver 22, a microphone 23, a speaker 24, D
The SPIC 15 is connected, has a recording / reproducing, hands-free, TONE / VOX detection, caller ID receiving function, and is also connected to the CPU 11 and the ROM 14 for storing information. The ROM 14 stores various information such as the telephone number of the received sender, and also stores voice data such as a memory function as a telephone directory, a response message in the answering machine mode, and a received message from the sender. Further, the speech network IC 21 and the CPU 11 are connected to an RF module 27 via a compander IC 26 for performing wireless communication with the slave unit, and an antenna 28 is connected to the RF module 27. Further, base unit 10 has a power supply circuit 29, and a power supply voltage is supplied from power supply circuit 29 to each of the above units.

FIG. 1 is a specific example of the power supply circuit 29 of the master unit 10 and shows a power supply circuit according to a first embodiment of the present invention. In this figure, reference numeral 51 denotes an AC adapter as a conversion circuit, which converts a commercial AC power supply voltage into a predetermined DC voltage. 52 is a constant voltage circuit connected to the output of the AC adapter 51 and provided in the telephone.
2 and the AC adapter 51 constitute a main power supply 53.
The output of the constant voltage circuit 52 is directly connected to the first power supply system 54.
The first power supply system 54 is a power supply system which only needs to supply a power supply voltage when power is supplied.
No. 0 RF module 27 and compander IC 26 are connected. The output of the constant voltage circuit 52 is connected to a second power supply system 56 via a transistor 55. Second
The power supply system 56 is a power supply system requiring a backup, and includes the CPU 11 and the dialer IC 2 of the base unit 10.
5 are connected. Therefore, a backup power supply 57 is connected to the second power supply system 56. The backup power supply 57 is, for example, 0.22
It is composed of an F capacitor 58. The transistor 55 is a PNP transistor, having an emitter connected to the output of the constant voltage circuit 52, a collector connected to the second power supply system 56, and connected between the constant voltage circuit 52 and the second power supply system 56. The output of the power failure detection circuit 59 is connected to the base of the transistor 55 via the resistor 60. The power failure detection circuit 59 detects the power failure of the main power supply 53 and generates a positive voltage at the output, thereby turning off the transistor 55 at the time of the power failure of the main power supply 53.

In the power supply circuit configured as described above, a predetermined DC power supply voltage is normally supplied from the main power supply 53 to the first and second power supply systems 54 and 56. At this time, the transistor 55 is on, and the power supply voltage is supplied to the second power supply system 56 via the transistor 55. On the other hand, when the main power supply 53 loses power, the supply of the power supply voltage to the first power supply system 54 is stopped, but the power supply voltage is supplied from the backup power supply 57 to the second power supply system 56 that requires backup. At this time, a power failure of the main power supply 53 is detected by the power failure detection circuit 59, and a positive voltage is generated at its output, so that the transistor 55 is turned off. Therefore, when the transistor 55 is turned off, a current is prevented from flowing backward from the backup power supply 57 toward the first power supply system 54.

Here, it can be considered that there is almost no potential difference between the emitter and the collector of the transistor 55. Therefore, when the backflow of current is prevented by the transistor 55 as described above, there is no voltage drop due to the current backflow prevention element, and the output voltage of the constant voltage circuit 52 and the voltage of the second power supply system 56 become the same. If the power supply voltage of the two-power supply system 56 is set to a predetermined voltage, the output voltage of the constant voltage circuit 52 may be set to the same predetermined voltage. A voltage constant voltage circuit can be used, and the restriction on the circuit used is released. Further, if the output voltage of the constant voltage circuit 52 can be made the same as the predetermined voltage supplied to the power supply system, the first power supply system 54 does not require a voltage adjusting diode for reducing the voltage to the predetermined voltage. The output of the constant voltage circuit 52 can be directly connected. As a result, only one transistor 55 is interposed between the constant voltage circuit and the power supply system, and the cost can be reduced.

FIG. 2 shows a second example (second embodiment of the present invention) of the power supply circuit 29 of FIG. In the second example, the transistor 55 for preventing current backflow is connected to the constant voltage circuit 5.
2 and the first power supply system 54. Even in this case, when the main power supply 53 fails, the power supply voltage can be supplied to the second power supply system 56 by the backup power supply 57, and at the same time, the reverse flow of the current from the backup power supply 57 to the first power supply system 54 ). Further, also in this case, the voltages of the first and second power supply systems 53 and 56 and the output voltage of the constant voltage circuit 52 become the same, and the output voltage of the constant voltage circuit 52 does not need to consider the voltage drop. A constant voltage circuit with a standard output voltage can be used, the restriction on the circuit to be used is released, and the cost can be reduced by using only one transistor 55 as the element interposed between the constant voltage circuit and the power supply system. it can.

In the above embodiment, the case where the power supply circuit of the present invention is used for a cordless telephone has been described. However, the power supply circuit of the present invention can be widely used for other similar electronic devices.

[0016]

As described above in detail, according to the present invention, a power supply system which only needs to supply a power supply voltage when energized,
In a power supply circuit having a power supply system that requires a backup at the time of a power failure, cost can be reduced, and a constant voltage circuit with a standard output voltage can be used, and the restriction on the circuit used can be released.

[Brief description of the drawings]

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

FIG. 2 is a circuit diagram showing a power supply circuit according to a second embodiment of the present invention.

FIG. 3 is a circuit diagram of a base unit of the cordless telephone.

FIG. 4 is a circuit diagram of a conventional power supply circuit.

[Explanation of symbols]

 Reference Signs List 51 AC adapter 52 Constant voltage circuit 53 Main power supply 54 First power supply system 55 Transistor 56 Second power supply system 57 Backup power supply 58 Capacitor 59 Power failure detection circuit 60 Resistance

Claims (6)

[Claims] A main power supply that outputs a power supply voltage; a first power supply system to which a power supply voltage is supplied from the main power supply; a second power supply system to which a power supply voltage is supplied from the main power supply; An output unit and the first power supply system or the second power supply system
A power supply circuit comprising: a transistor connected between power supply systems; a power failure detection circuit that turns off the transistor when the main power supply fails, and a backup power supply connected to the second power supply system. 2. The power supply circuit according to claim 1, wherein the main power supply comprises a conversion circuit for converting a commercial AC power supply voltage into a predetermined DC voltage, and a constant voltage circuit connected to an output of the conversion circuit. 3. The power supply circuit according to claim 2, wherein the conversion circuit is an AC adapter. 4. The power supply circuit according to claim 1, wherein the backup power supply comprises a capacitor. 5. The power supply according to claim 1, wherein the first power supply system is a voice processing (DSP) circuit, an LCD display, a radio frequency (RF) circuit, a speech network circuit, a power amplifier circuit, or the like. circuit. 6. The power supply circuit according to claim 1, wherein the second power supply system is a control unit (CPU), a dialer circuit, a data storage unit, or the like.