JPS61198953A - Power supply circuit for telephone set - Google Patents

Abstract

PURPOSE:To block surely generation of malfunction or power supply interruption during operation by interrupting the supply of an output voltage of a voltage converter when it is discriminated that an output voltage of the voltage converter is less than the minimum operating voltage of a telephone set main body. CONSTITUTION:A pseudo load circuit 10 to flow a current corresponding to a current flowed from the voltage converter when a load of a telephone set main body is maximum is provided, an output voltage of the voltage converter fed to the circuit 10 is detected by a voltage discriminating means 5 and whether or not the detected voltage is less than the minimum operating voltage is discriminated and when it is discriminated that the output voltage of the voltage converter is less than the minimum operating voltage of the telephone set main body, a power supply control switch 4 is opened to interrupt the supply of the output voltage of the voltage converter to the telephone set main body 2.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a power supply for a telephone device that converts a power supply voltage supplied from an external power supply into a predetermined DC voltage using a voltage converter and supplies it to the telephone device main body for operation. Regarding circuit improvement.

[Technical background of the invention and its problems]

Conventionally, the following circuits are known as this type of circuit. FIG. 6 shows its configuration, with reference numeral 1 indicating an AC adapter and reference numeral 2 indicating the main body of the telephone device. The AC adapter 1 converts the output voltage of a commercial power source (not shown) as an external power source into a predetermined DC voltage, and applies this converted DC voltage (adapter voltage) to the power switch 3 and the power supply control switch 4, respectively. It is supplied to the telephone device main body 2 through the telephone device main body 2. In addition, a voltage detector 5 is connected to the output side of the power switch 3.
and a control circuit 6 are provided. This voltage detector 5 is
It monitors the level of the adapter voltage and outputs a voltage drop detection signal when this level becomes less than a predetermined monitoring level Eo. In addition, the voltage drop monitoring level E mentioned above.

is set to a level slightly higher than the required minimum voltage level at which the telephone device body 2 can operate. The control circuit 6 includes, for example, a microcomputer, and performs on/off control of the power supply control switch 4 according to the detection result of the voltage detector 5, and emits light when adapter voltage is supplied to each telephone device 2. This is notified by lighting the element 7.

With this configuration, when the power switch 3S is turned on, the output voltage of the adapter 1 is supplied to the voltage detector 5 to determine the level, and if this level is equal to or higher than the voltage drop monitoring level Eo, the control circuit 6 An on control signal is output from the power supply control switch 4 to turn on the power supply control switch 4, and as a result, the adapter voltage is supplied to the telephone device main body 2, and the telephone device main body 2 becomes ready for operation. At this time, the control circuit 6 outputs a drive signal to the light emitting element 7 to turn it on, thereby notifying the telephone device body 2 that the power supply voltage has been supplied. On the other hand, when the adapter voltage drops due to a failure of the adapter 1 or a voltage drop in the commercial power supply, for example, and the voltage level reaches the voltage drop monitoring level Eo, an OFF control signal is generated from the control circuit 6 and the power supply control switch 4 is turned off. is turned off, and as a result, the supply of adapter voltage to the telephone device main body 2 is cut off, and the telephone device main body 2 becomes inactive. Also,
At this time, for example, a blinking drive signal is outputted from the control circuit 6 to the light emitting element 7 to notify that a power supply abnormality has occurred. Therefore, according to such a power supply circuit, it is possible to always supply an adapter voltage higher than the required minimum voltage to the telephone device body 2, and the user can be clearly informed of the power supply status.

However, since the AC adapter 1 generally has an internal resistance r, the output voltage of the adapter changes depending on the operation of the telephone device body 2 due to the influence of this internal resistance r. For example, when the power switch 3 is turned on while the power is off, current is supplied to the telephone device body 2, so the adapter voltage, which was El when the power was off, drops to <E2 as shown in FIG.

When the hook switch of the telephone device main body 2 is turned on in this state, the telephone device main body 2 performs an outgoing call operation.
The adapter voltage drops to E3 as shown in Figure 7, and if the dial is operated in this state, a large current is consumed in the dial sending circuit, so the adapter voltage decreases to E3 (amount of change Vo) in Figure 7. As shown, it decreases further. For this reason, in a conventional power supply circuit in which the voltage drop monitoring level Eo of the voltage detector 5 is fixed, even if the adapter voltage is sufficient to operate at power-on or transmission operation, the dial signal cannot be adjusted. Required minimum operating voltage E of the telephone device main body 2 when transitioning to transmission operation.

and enters the inoperable area A of the telephone device main body 2,
As a result, supply interruption or interruption of the adapter voltage may occur. If the power supply is cut off or interrupted during the transmission of dial signals in this way, it will cause erroneous connections or disconnections in the exchange, which is very undesirable.

On the other hand, as a circuit to eliminate such problems, conventionally,
It has been considered to provide a voltage detector that has hysteresis characteristics in its voltage determination characteristics.

With this kind of circuit, power will not be supplied unless the adapter voltage when the power is turned on is higher than the required minimum operating voltage Eo of the telephone device body 2 by a certain voltage or more, so malfunctions during call operation can be avoided. will be prevented in advance.

However, in this type of conventional circuit, the hysteresis voltage is fixed and set in advance, so this hysteresis voltage is set to a somewhat large value in consideration of variations in the internal resistance r of the AC adapter 1, changes over time, etc. There is a need. For this reason, it is necessary to increase the output voltage of the AC adapter 1, or it is necessary to use circuit elements with a low minimum operating voltage value in the main body of the telephone device, resulting in the disadvantage that the device becomes expensive. Furthermore, even if the internal resistance r of the battery can be used up to a value close to the minimum operating voltage of the telephone device body 2,
Since the hysteresis voltage is set to a large voltage value assuming the maximum value of the internal resistance r, it cannot be used, resulting in a decrease in the efficiency of use of the power supply and being uneconomical.

[Purpose of the invention]

The present invention reliably prevents power outages and malfunctions during operation, and also makes it possible to set hysteresis characteristics according to the internal resistance r of the voltage converter, thereby making it possible to use the power supply without wasting it. It is an object of the present invention to provide a power supply circuit for a telephone device that can improve power usage efficiency and reduce the cost of the device.

(Summary of the Invention) In order to achieve the above object, the present invention provides a pseudo load circuit for flowing a current corresponding to the current flowing out from the voltage converter when the load on the telephone device main body is maximum, and After the output voltage of the voltage converter starts to be supplied to the main body, the output voltage of the voltage converter is supplied to the pseudo load circuit, the output voltage value of the voltage converter at this time is detected by the voltage determination means, and the detected voltage value is determined. is less than the minimum operating voltage of the telephone device main body, and if it is determined that the output voltage of the voltage converter is higher than the minimum operating voltage of the telephone device main body, voltage conversion for the telephone device main body is performed. The output voltage of the converter continues to be supplied to the telephone device main body to perform the prescribed operation, and - if it is determined that the output voltage of the voltage converter is less than the minimum operating voltage of the telephone device main body, The output voltage of the voltage converter is cut off from being supplied to the main body.

[Embodiments of the invention]

FIG. 1 shows the configuration of a power supply circuit according to an embodiment of the present invention, and the same parts as in FIG. 6 are given the same reference numerals and detailed explanation will be omitted.

A power-on detection circuit 8 is provided on the output side of the power switch 3 at the output ends 1a and Ib of the AC adapter 1. This power-on detection circuit 8 consists of a resistor 8a and an integrating circuit 8.
b, and supplies the control circuit 9 with a voltage that increases according to the time constant of the integrating circuit 8b from the time the power switch 3 is turned on. - Connection terminal 2 of Manraiwa device main body 2
A pseudo load circuit 10 is connected between a and 2b in parallel with the telephone device body 2. This pseudo load circuit 10 consists of a semiconductor switch 10a and a resistor 10b.
The semiconductor switch 10 is activated for a certain period of time by a control signal from
When resistor 10b is turned on, resistor 10b is connected to AC adapter 1, thereby pseudo-generating a large current corresponding to the adapter current that flows during dial signal transmission operation of telephone device body 2. That is, by generating this pseudo-large current, a voltage drop V of the adapter voltage corresponding to the product of this current and the internal resistance r of the AC adapter 1 is pseudo-generated.

In such a configuration, when the power switch 3 is turned on to make a call, for example, the output voltage of the AC adapter 1 is supplied to the voltage detector 5 via the power switch 3.
If the adapter voltage at this time is necessarily higher than the voltage drop monitoring level Eo, the control circuit 9 outputs an on control signal according to the output of the voltage detector 5, turning on the power supply control switch 4, and as a result, the telephone device main body 2 Adapter voltage is supplied. When the power switch 3 is turned on, the control circuit 10 outputs an ON control signal for a short period of time defined by the integral time constant of the power-on detection circuit 8, and this causes the switch 10a of the pseudo load circuit 10 to It is turned on only for a short time that does not adversely affect the transmission operation of 2. Note that if the voltage detection circuit 5 determines that the output voltage of the AC adapter 1 has decreased below the voltage drop monitoring level Eo, the power supply control switch 4 will not turn on, and as a result, the power supply control switch 4 will not turn on. No adapter voltage is supplied.

Now, the power supply control switch 6 and the pseudo load circuit 10
When the switch 10b is turned on, the output voltage of the AC adapter 1 is supplied to the telephone device main body 2 and the resistor 10b of the pseudo load circuit 10, thereby causing a large current corresponding to the current flowing during the dial signal transmission operation of the telephone device main body 2. flows to AC adapter 1. Therefore, at this time, the output voltage of the AC adapter 1 is a voltage drop V)7 corresponding to the product of the output current of the adapter and the internal resistance r of the adapter 1.
decreases by the same amount. In other words, a voltage drop equivalent to the adapter voltage drop Vo that occurs when the telephone device body 2 performs a dial signal transmission operation is created. Then, the output voltage of the AC adapter 1 at this time is compared with the voltage drop monitoring level Eo by the voltage detector 5, and the voltage drop monitoring level Eo is compared with the voltage drop monitoring level Eo.
If the voltage is equal to or higher than o, the control circuit 9 determines that the voltage is sufficient for the telephone device body 2 to operate, and causes the power supply control switch 4 to remain on. On the other hand, if the adapter voltage at the above voltage drop V) (is necessarily lower than the voltage drop monitoring level Eo), it is determined that the adapter voltage is insufficient to perform the dial sending operation, and the power supply control switch 4 is turned off. After that, the supply of adapter voltage to the telephone device main body 2 is cut off.

For example, if the output voltage of the AC adapter 1 is sufficiently higher than the voltage drop monitoring level Eo as shown in FIG. When a falling VH is generated,
Since the voltage Ec exceeds the voltage drop monitoring level Eo as shown in the figure, the power supply control switch 4 maintains the on state. Therefore, the telephone device body 2 continues to perform the predetermined calling operation and dial signal transmission operation.

On the other hand, if the adapter voltage drops as shown in FIG. When a voltage drop VH occurs, the adapter voltage Ec' becomes less than the voltage drop monitoring level Eo of the voltage detector 5 as shown in the figure, so the power supply control switch 4 is turned off and the subsequent telephone device body 2
The supply of adapter voltage to is cut off. Therefore, the telephone device main body 2 enters a non-operating state before sending out a dial signal. Incidentally, FIG. 3 shows the recovery locus of the adapter voltage at this time.

In this way, in the power supply circuit of this embodiment, the pseudo load circuit 10
The voltage drop VH determined by the product of the output current of the adapter and the internal resistance r of the AC adapter 1 when it is connected to the AC adapter 1 is defined as the hysteresis voltage, and the output voltage of the AC adapter 1 is the minimum required operation of the telephone device body 2. The adapter voltage is supplied to the telephone device main body 2 only when the voltage is larger than the voltage drop monitoring level EO set for the voltage by at least the hysteresis voltage VH. Therefore, the problem that the adapter voltage supply is turned off when a dial signal is sent out, causing the telephone device main body 2 to stop operating or malfunction, is prevented, and as a result, the telephone device main body 2 always operates stably.

Incidentally, the internal resistance r of the AC adapter 1 generally has variations, and even if the adapter voltage decreases, if this internal resistance r is small, the adapter voltage decreases relatively little when sending a dial signal. Therefore, in this case, the hysteresis voltage VH may be small, and setting the hysteresis voltage large is not preferable because the power usage efficiency will decrease accordingly. However, in the circuit of this embodiment, as described above, the hysteresis voltage is set by the product of the adapter's output current when the pseudo load circuit [0] is connected and the internal resistance r at that time. It changes each time depending on the value of the internal resistance r of the AC adapter 1. Therefore, when the internal resistance r is relatively small, the hysteresis voltage V
H also becomes a small value Ecn, for example, as shown at the beginning of FIG. 4, and as a result, the voltage detector 5 does not determine that the adapter voltage has decreased, and the telephone device 1*2 becomes operable.

By the way, when the hysteresis voltage is fixedly set in advance as in the conventional case, this hysteresis voltage is set to a relatively large value taking into account the variation in the internal resistance r of the AC adapter 1. As shown in the figure, even if the internal resistance is actually small and the drop in adapter voltage when sending the dial signal is relatively small as shown in E in the figure, the hysteresis voltage is set as large as Vu@2, so the voltage decreases. The detector 5 and the control circuit 9 determine that the AC adapter 1 is unusable, and the AC adapter 1 becomes unusable, resulting in a decrease in the power usage efficiency. In this example, A
When the internal resistance r of the C adapter 1 is large, the hysteresis voltage is also set large according to this internal resistance value r, as shown in FIG. After the determination is made, the supply of adapter voltage to the telephone device body 2 is immediately stopped.

As described above, in this embodiment, by providing a hysteresis characteristic to the adapter voltage drop determination, the adapter voltage is lower than the voltage drop monitoring level Eo while the telephone device body 2 is in operation (for example, while sending a dial signal). If there is a possibility that this may occur, the supply of adapter voltage can be cut off before operation, so that the supply of adapter voltage is cut off while the telephone device main body 2 is in operation, and the telephone device main body 2 Problems such as malfunctions can be prevented before they occur.Moreover, the hysteresis voltage VH is set by the product of the output current of the AC adapter 1 when the pseudo load circuit 10 is connected to the adapter 2 and the internal resistance r of the AC adapter 1. Therefore, it is possible to set the optimum hysteresis voltage for each AC adapter according to the variation in the internal resistance r of the AC adapter 1, and thereby the AV adapter 1 can be used without waste, improving the efficiency of power usage. In addition, the output voltage value of the AC adapter 1 can be set lower than before, and the circuit elements of the telephone device body 2 can be used even if they have a high minimum operating voltage. be able to.

Note that the present invention is not limited to the above embodiments. For example, in the above embodiment, when the power switch 3 is turned on, the voltage drop is determined using the pseudo load circuit 10. However, when the power switch 3 is always turned on, the calling operation 7! -11 may be performed every time. In this case, it is sufficient to detect the on operation of the hook switch. Further, the level determination of the adapter voltage using the pseudo load circuit 10 may be periodically performed, for example, by driving a timer. Further, the resistor 11b of the pseudo load circuit may be shared with a DC resistance circuit provided for another purpose. In this way, the circuit configuration can be further simplified. Furthermore, the switch 10a of the pseudo load circuit 10 is not only turned on for a short period of time specified by the integral time constant of the power-on detection circuit 8, but also has a timing function, and this timing function allows a predetermined time to be set from the time of startup. It may be configured so that it is turned on only for a certain amount of time. Further, as a means for detecting the turning on of the power switch, a switch interlocked with the power switch 3 may be provided instead of the power turning on detection circuit, and the output signal of the switch 1 may be supplied to the control circuit. In this case, the driving time of the pseudo load circuit may be set by operating a timer using the control circuit. In addition, various modifications may be made to the type of external power supply (a DC power supply may be used), the configuration of the pseudo load circuit and power-on detection circuit, the configuration of the control circuit, the control procedure, the control content, etc. without departing from the gist of the present invention. It can be implemented by

(Effects of the Invention) As described in detail above, the present invention provides a pseudo load circuit for flowing a current corresponding to the output current of the voltage converter when the load on the telephone device main body is maximum, and the voltage applied to the telephone device main body is After the output voltage of the converter starts to be supplied, the output voltage of the voltage converter is supplied to the pseudo load circuit, the output voltage value of the voltage converter at this time is detected by the voltage detection means, and this detected voltage value is detected by the telephone device. It is determined whether the output voltage of the voltage converter is lower than the minimum operating voltage of the main unit, and if it is determined that the output voltage of the voltage converter is equal to or higher than the minimum operating voltage of the main unit of the telephone device, the output voltage of the voltage converter to the main unit of the telephone device is The voltage is continued to be supplied and the telephone device main body performs the prescribed operation, and - if it is determined that the output voltage of the voltage converter is less than the minimum operating voltage of the telephone device main body, the output of the voltage converter is The voltage supply is cut off.

Therefore, according to the present invention, it is possible to reliably prevent the occurrence of power failure or malfunction during operation, and furthermore, the hysteresis characteristic can be set according to the internal resistance of the voltage converter, so that the power supply can be used without wasting it. As a result, it is possible to provide a power supply circuit for a telephone device that can improve the power usage efficiency and reduce the cost of the device.

[Brief explanation of drawings]

Figures 1 to 5 are for explaining a power supply circuit according to an embodiment of the present invention. Figure 1 is a circuit block diagram showing the configuration of the circuit, and Figures 2 to 5 are operational diagrams, respectively. Figure 6 is a circuit block diagram showing the configuration of a conventional power supply circuit, and Figure 7 is a diagram showing changes in adapter voltage used to explain the disadvantages of the circuit. Ru. ]...AC adapter, 2...telephone device body, 3...
- Power switch, 4... Power supply control switch 5... Voltage detector, 7... Light emitting element, 8... Power on detection circuit, 8b... Integrating circuit, 9... Control circuit, 10・・・
・Pseudo load circuit, 10a...switch, 10b...
Resistance, VH...Voltage drop in battery voltage (hysteresis voltage) when the pseudo load circuit is connected to the AC adapter, V
D: Voltage drop in battery voltage during dial signal transmission operation. Applicant's Representative Patent Attorney Takehiko Suzue Figure 3 A Figure 4 Department Figure 5 A Figure 6 Figure 7 I

Claims (1)

[Claims] In a power supply circuit of a telephone device that includes a voltage converter and converts an output voltage supplied from an external power supply into a predetermined DC voltage by the voltage converter and supplies the converted DC voltage to a telephone device main body for operation, the operating load of the telephone device main body is a pseudo load circuit having a resistance for equivalently flowing the output current of the voltage converter when the voltage is at a maximum; means for supplying the output voltage of the voltage converter to the pseudo load circuit, and detecting the output voltage value of the voltage converter while supplying the output voltage of the voltage converter to the pseudo load circuit, and detecting the output voltage value below the minimum operating voltage of the main body of the telephone device. a voltage determining means for determining whether the output voltage is lower than the minimum operating voltage of the telephone device body; A power supply circuit for a telephone device, characterized in that it is equipped with a switch means for disconnecting the power.