JPH05142271A - Power source monitoring circuit - Google Patents

Abstract

PURPOSE:To prevent errorneous detection due to abnormal current when an electronic device is used together with a coffee maker or a hair dryer. CONSTITUTION:Light in response to current supplied to an electronic device 1 is generated by the use of light emitting diodes 16a1, 16a2 of a photocoupler 16. Change of the light quantity is detected by the use of a pototransistor 16b and is converted into a voltage by the use of a resistor 17 and output from capacitance 18. The other capacitance 23 is connected to the light emitting diodes 16a1, 16a2 in series.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply monitoring circuit for monitoring the supply of power to electronic equipment such as video tape recorders and video disc players.

[0002]

2. Description of the Related Art FIG. 3 shows an example of the configuration of a conventional power supply monitoring circuit. In the figure, necessary electric power is supplied to the electronic device 1 through the power line 3 through the plug 2. The power supply line 3 is provided with a power supply monitoring circuit 4. The power supply monitoring circuit 4 is connected in parallel to the power supply line 3, a diode 12 connected in reverse direction to the diode 11 and in parallel, and connected in parallel to the diodes 11 and 12. A voltage detection resistor 13, a series circuit of a resistor 14 and a capacitor 15 connected to both ends of the resistor 13, a light emitting diode 16a and a phototransistor 16b connected in parallel with the capacitor 15.
16 and a phototransistor 16
It is composed of a resistor 17 connected to the emitter of b and a capacitor 18 connected in parallel to the resistor 17.

The AC voltage supplied from the plug 2 is supplied to the electronic device 1 via the power supply line 3. Since the capacitors 11 and 12 connected in opposite directions to each other are inserted in the power supply line 3 in series, forward and backward currents can flow in the electronic device 1. The voltage generated across the resistor 13 charges the capacitor 15 via the resistor 14. Then, the light emitting diode 16a forming the photocoupler 16 corresponding to the charging voltage of the capacitor 15
Emits light. The amount of light generated by the light emitting diode 16 a is proportional to the current supplied to the electronic device 1 via the power supply line 3. The phototransistor 16b conducts when light is incident from the light emitting diode 16a, and the phototransistor 16b becomes conductive.
An electric current will flow through. As a result, the voltage corresponding to the voltage drop generated in the resistor 17 is charged in the capacitor 18 via the resistor 19, and the terminal voltage of the capacitor 18 is supplied as a detection voltage to a circuit (not shown).

When the electronic device 1 is used alone,
The voltage of the power supply line 3 is vertically symmetrical as shown in FIG. The voltage generated across the resistor 13 at this time is as shown in FIG.

On the other hand, when a coffee maker, a hair dryer, etc. are used for other than the electronic device 1, for example, the voltage waveform supplied from the power line 3 to the electronic device 1 is shown in FIG.
It will be distorted as shown in FIG. As a result, resistance 1
The voltage generated at both ends of 3 changes as shown in FIG. That is, in the figure, the level indicated by the arrowed portion is higher than that in the case shown in FIG. Therefore, the terminal voltage of the capacitor 18 is the electronic device 1
When used alone, the voltage V ₁ shown in FIG. 4A becomes a voltage V ₂ (V ₂ > V ₁ ) as shown in FIG. 4B.

That is, as shown in FIG. 5 (b), the current flowing corresponding to the voltage having the crushed waveform (in this example, the negative voltage) hardly changes, but the waveform having the crushed waveform is not changed. The current flowing corresponding to the voltage (in this example, a positive voltage) increases, and when combined, the current greatly increases. As a result, the detected voltage greatly changes from V ₁ to V ₂ .

[0007]

When the conventional power supply monitoring circuit is used together with other electronic equipment as described above, the voltage supplied to the electronic equipment is irrespective of whether the electronic equipment itself has no abnormality. do is erroneously detected as becomes abnormal, or if not be erroneously detected, changes tend to be erroneously detected state had (voltage greatly changes from V ₁ to V ₂₎ challenge.

The present invention has been made in view of such a situation, and reduces the risk of erroneous detection.

[0009]

A power supply monitoring circuit of the present invention is connected in the middle of a power supply line 3 for supplying power to an electronic device 1, and monitors the supply state of power to the electronic device 1. It is characterized by including a photocoupler 16 as a detection element connected in series to the power supply line 3 and a capacitor 23 connected in series to the photocoupler 16.

[0010]

In the power supply monitoring circuit having the above structure, the DC component is suppressed by the capacitor 23 and it becomes difficult for the DC component to pass through the photocoupler 16. Therefore, the risk of erroneous detection is reduced.

[0011]

1 is a block diagram showing the configuration of an embodiment of a power supply monitoring circuit of the present invention, in which parts corresponding to those in FIG. 3 are designated by the same reference numerals. In this embodiment, the power supply monitoring circuit 4 is connected to the power supply line 3 in series as in the case of FIG. 3, but the internal configuration is slightly different from that in FIG. That is, in this embodiment, the thermistor 21 is connected to the resistor 14.
Are connected in parallel. Further, a parallel circuit of a resistor 22 and a capacitor 23 is connected between the capacitor 15 and the resistor 13. The resistance 22 is set to a value that is, for example, about twice that of the sensitivity adjustment resistance 14. Further, the photocoupler 16 is provided with two light emitting diodes, that is, the light emitting diodes 16a1 and 16a2. Other configurations are similar to those in FIG.

That is, in this embodiment, the forward and reverse currents are supplied to the electronic device 1 via the diodes 11 and 12. Then, the resistor 13 generates a voltage corresponding to the current flowing through the electronic device 1. This voltage causes the parallel circuit of the resistor 14 and the thermistor 21 and the resistor 2
2 through the parallel circuit of the capacitor 23 and the capacitor 15
Will be applied to both ends of. And capacitor 15
The voltage between both ends of is applied to the light emitting diodes 16a1 and 16a2. Therefore, the amount of light generated by these light emitting diodes changes according to the current supplied to the electronic device 1, and the conductivity of the phototransistor 16b changes corresponding to this amount of light. As a result, the voltage drop generated in the resistor 17 is integrated by the resistor 19 and the capacitor 18 and output.

When the electronic device 1 is used alone, the voltage generated across the resistor 13 is as shown in FIG. 2 (a). Therefore, in this case, the terminal voltage of the capacitor 18 is V ₁ . This voltage V ₁ increases as the supply current to the electronic device 1 increases, and therefore an abnormality of the electronic device 1 can be detected by comparing this voltage V ₁ with a predetermined reference voltage.

When the electronic device 1 is used with a coffee maker or a hair dryer, the terminal voltage of the resistor 13 becomes as shown in FIG. 2 (b). That is, the level indicated by the arrow in the figure is higher than that in the case shown in FIG. However, in this embodiment, since the capacitor 23 is connected in series with the light emitting diodes 16a1 and 16a2, the direct current component is suppressed. As a result, the terminal voltage of the capacitor 18 is shown in FIG.
The voltage V ₂ is shown in FIG. 2B, and a slight change from the voltage V ₁ in FIG. Therefore, when the presence or absence of abnormality of the electronic device 1 is detected by comparing the terminal voltage of the capacitor 18 with a predetermined reference voltage, the coffee maker or As a result of being used together with the hair dryer, there is less risk of erroneous detection that an abnormality has occurred in the electronic device 1.

However, depending on the electronic device 1, when the voltage of the power supply line 3 is distorted as shown in FIG. 5B, the current corresponding to the collapsed voltage (negative voltage in this example) is generated. Although it decreases, the current corresponding to the voltage that does not collapse (a positive voltage in this example) increases, and the current may not increase on average. In this embodiment, two light emitting diodes of the photocoupler 16 are provided so that light is generated by current in both forward and reverse directions in order to prevent erroneous detection of abnormalities even in such a case. As a result, the phototransistor 16b receives light corresponding to the average current, and even if the current increases in only one polarity, the detection voltage does not increase unless the average current increases, and this is detected as an abnormality. Is prevented. In this embodiment, the resistor 22 is connected in parallel with the capacitor 23 in order to detect this DC component as well. However, the resistor 22 may be omitted if the control target to be connected is known in advance.

The thermistor 21 includes a diode 11,
This is for compensating for the change in the characteristics of No. 12 due to the change in temperature.

[0017]

As described above, according to the power supply monitoring circuit of the present invention, since the capacitor is connected in series to the detection element, it is possible to erroneously detect that there is an abnormality although there is no abnormality. Less fear.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of an embodiment of a power supply monitoring circuit of the present invention.

FIG. 2 is a waveform diagram illustrating the operation of the embodiment of FIG.

FIG. 3 is a circuit diagram showing a configuration of an example of a conventional power supply monitoring circuit.

FIG. 4 is a waveform diagram illustrating the operation of the example of FIG.

FIG. 5 is a diagram illustrating a voltage change of a power supply line.

[Explanation of symbols]

 1 Electronic Equipment 2 Plug 3 Power Supply Line 4 Power Supply Monitoring Circuit 16 Photocoupler 21 Thermistor 22 Resistor 23 Capacitor

Claims (1)

[Claims] 1. A power supply monitoring circuit that is connected in the middle of a power supply line for supplying electric power to an electronic device and monitors a supply state of electric power to the electronic device, the detection being connected in series to the power supply line. A power supply monitoring circuit comprising an element and a capacitor connected in series to the detection element.