JPH0834667B2 - Power supply status detector - Google Patents

Description

Description: (a) Field of Industrial Application The present invention relates to a power supply state detection device for detecting a power supply state in an electronic device or the like that uses a commercial power source as a power source.

(B) Conventional Technology Generally, in an electronic device using a commercial power source as a power source,
The power supply circuit provided therein has a property that the output voltage rises after a fixed time has passed since the commercial power supply was turned on, and the output voltage drops after a fixed time has passed since the power supply was cut off. Such a delay in the rise of the power source is caused by a delay in the rise of the DC converter or a delay due to the smoothing or charging time of the capacitor for preventing instantaneous power failure, and the delay in the fall of the power source is caused by the discharging time of the capacitor.

In electronic devices such as computers and their peripherals that are composed of digital circuits, the operating margin is set so that they can operate normally, and if they are not operated only when the power supply voltage is within this operating margin, they may cause malfunctions. Becomes Therefore, it is configured to detect the state where the power supply voltage is within the operation margin in consideration of the delay of the rise and fall of the power supply as described above, and operate only for that time.

FIG. 4 shows a circuit of a power supply state detecting device provided with a circuit for detecting such a power supply state. In the figure, AC is a commercial power supply, SW is its power switch, 1 is a noise filter, D1 to D4 are diode bridges, C7 is a smoothing capacitor, and 2 is a DC-DC converter. When the power switch SW is turned on, the diode bridge
The DC voltage is rectified by D1 to D4, smoothed by C7, a DC voltage is obtained, and a DC power source of a predetermined voltage stabilized by the DC-DC converter 2 is obtained, which is supplied to the load circuit 3. Reference numeral 6 denotes a voltage detection circuit, which is composed of a diode bridge composed of diodes D5 to D8, a current limiting resistor R8, and a light emitting diode LED of the photocoupler 4. Reference numeral 5 represents a circuit for detecting the supply state of power by the signal input from the phototransistor PT of the photocoupler.
When the power switch SW is turned on, a current flows through the LED via R8 and the diode bridges D5 to D8, and the state is detected by the state detection circuit 5 via the phototransistor PT. The state detection circuit 5 activates the signal indicating the supply state of the power source after a lapse of a certain time after detecting the power-on.
By providing such a time delay, the load circuit 3
The operation can be started when the power supply voltage supplied to is stable. Provided to the voltage detection circuit 6 when the power switch SW is turned off or when a power failure occurs
The LED is turned off, and the state detection circuit 5 immediately detects the cutoff state of the power source through the phototransistor PT and puts the signal indicating the supply state of the power source into the inactive state. As a result, the load circuit performs the necessary processing for the end of operation or power failure.

(C) Problems to be Solved by the Invention However, in such a conventional power supply state detecting device, the power supply voltage actually supplied to the load circuit drops after detecting the off state or the power failure state of the power switch. There was a problem that I could not get enough time to do.
FIG. 5 is a diagram showing timings and waveforms of the circuit shown in FIG. In the figure, (1) represents the supply state of the commercial power supply, that is, the ON / OFF state of the power switch or the energization / power failure state, (2) represents the supply voltage supplied to the load circuit 3, and (3) represents the supply state of the power supply. Represents the voltage signal detected by the state detection circuit 5, and (4) represents the output signal of the state detection circuit 5. now,
When the supply of commercial power is started at t ₀ , the load supply voltage (2) rises with a certain time delay. The detection voltage (3) also gradually rises after the power is turned on, and the power supply state signal (4) becomes active when it reaches a certain threshold voltage. After that, if the commercial power supply is cut off at the timing of t ₂ , the detection voltage (3) is lowered, and when it is lower than t _3, that is, the threshold voltage, the power supply state signal (4) is set to the inactive state. However, even if the supply of commercial power is cut off, the charges charged in the capacitors C1 to C4 provided in the noise filter 1 shown in FIG.
Since D is turned on, the status signal cannot be made inactive immediately even when the power is cut off, and the delay time is delayed by the capacitance of the noise filter capacitor and the time constant of R8. The time between t3 and t4 in Fig. 5 is short. There was a problem of becoming. If a relay is used as the voltage detection circuit, the above problem can be solved, but the problem remains in terms of reliability and the like.

An object of the present invention is to provide a power supply state detecting device capable of detecting the state immediately after the commercial power supply is cut off and allowing sufficient time for the power supply voltage actually supplied to the load to fall below an operating margin. It is in.

(D) Means for Solving Problems The power supply state detecting device of the present invention includes a noise filter including a capacitor between the input lines of the commercial power supply, and a photocoupler between the power input lines in parallel with the noise filter. A voltage detection circuit including a light emitting diode is connected, and in a power supply state detection device having a detection circuit for detecting the power supply state based on the output signal of the photocoupler, the voltage detection circuit, It is characterized in that a capacitor having a capacity sufficiently smaller than that of the capacitor of the noise filter is connected in series to the light emitting diode.

(E) Function In the power supply state detecting device of the present invention, since at least the capacitor is connected in series to the light emitting diode of the photocoupler as the voltage detecting circuit, the current flowing in the light emitting diode is limited by the impedance of the capacitor, and the light emitting diode emits light. The diode emits a light amount according to the voltage of the commercial power supply. In other words, the capacitor connected in series with the light emitting diode of the photo coupler has a low capacitance. Further, since the forward impedance of the light emitting diode is smaller than the impedance of the capacitor, the voltage across the capacitor is substantially equal to the power supply voltage. Therefore, the charging voltage of the capacitor provided as a noise filter and the charging voltage of the capacitor connected in series to the light emitting diode are almost the same regardless of the timing of the sine wave of the commercial power supply. equal. Therefore, almost no current flows from the capacitor of the noise filter to the light emitting diode of the photocoupler when the power is cut off. A current flows from a capacitor connected in series to the light emitting diode, but since the capacitor has a low capacity and the discharge time becomes equal to that of the noise filter capacitor (the discharge time is long), this current causes the light emitting diode to flow. Does not light.
That is, the light emitting diode turns off immediately after the power is cut off.

(F) Embodiment FIG. 1 is a circuit diagram of a power supply state detecting device according to an embodiment of the present invention, and FIG. 2 is a diagram showing timings and waveforms of respective parts thereof. In the figure, AC is a commercial power supply and SW is a power switch. Noise filter 1 is placed between the power input lines.
Is provided. In the noise filter 1, two capacitors C1 and C2 are connected in series between the input lines of the power supply, and the middle point is connected to the ground to remove common mode noise. The capacitors C3 and C4 absorb noise generated between the power input lines together with the toroidal coils L1 and L2. In the voltage detection circuit 6, D5 to D8 represent diode bridges, the resistor R1 and the light emitting diode LED of the photocoupler are connected in series to the diode bridge, and the capacitor C5 is connected in series to the diode bridge. Therefore, the current rectified by the diode bridges D5 to D8 flows to the LED via the capacitor C5. Here, the capacitor C5 has a low capacitance in order to limit the current flowing through the LED. The capacitor C6 provided in the voltage detection circuit 6 represents a capacitor having a lower capacity than the capacitor C5 for removing high frequency noise. The state detection circuit 5 that detects the supply state of the power supply outputs a signal indicating the supply state of the power supply to the load circuit 3 based on the signal input from the phototransistor PT of the photocoupler 4.

In the state detection circuit 5, R3 and C8 are circuits that generate a time constant at the rise of the power supply and smooth the flicker output of the phototransistor PT, and ZD is a zener diode that is energized when the charging voltage Va of C8 reaches a constant voltage. Yes,
When Va reaches the Zener voltage, the transistor Q1 is turned on, whereby the transistor Q2 is turned on and the "H" level is output.

Next, the operation will be described. First, when the power switch SW is turned on, rectification is performed by the diode bridges D1 to D4 and smoothed by C7. As a result, the input voltage of the DC-DC converter 2 rises, starts operating when reaching a certain voltage, and supplies the voltage to the load circuit 3. Meanwhile, LED
Is turned on at about the same time the power switch SW is turned on and starts lighting.

By supplying the output voltage of the DC-DC converter 2 and increasing the light amount of the LED, the collector current of the phototransistor PT increases and the charging voltage Va of the capacitor C8 rises. When this voltage reaches the Zener voltage of the Zener diode ZD, a base current flows in Q1, which lowers the base potential of Q2 and turns on Q2. As a result, the "H" level is output to the load circuit 3 as a signal indicating the power supply state (t _{0 to} t _{1 in} FIG. 2).

Next, when the power switch SW is turned off or a power failure occurs, the charging voltage of the capacitor C5 varies depending on the timing of the cutoff. However, the charging voltage and voltage of each capacitor provided in the noise filter 1 The charging voltage of C5 formed in the detection circuit 6 is substantially equal. Therefore, the charge of each capacitor of the noise filter 1 is
The LED is immediately turned off without being discharged to the LED via C5. Therefore, in the state detection circuit 5, the capacitor
Since the charge of C8 is discharged quickly through ZD, R4, Q1 and R3, Va drops below the Zener voltage and Q1 and Q2
Turn off. As a result, "L" level is output to the load circuit 3. As shown in FIG. ₂ , since the power supply state signal (4) quickly becomes “L” level at t ₃ after the commercial power is cut off at t ₂ , the load supply voltage falls below the operating margin from this t _3. It can take a long time until t ₄ .

When the commercial power supply is cut off, the electric charge charged in the capacitor C6 flows as a discharge current to the LED via the diode bridges D5 to D8 and R1, but the capacity and charge voltage of the capacitor C6 are low, and the commercial power supply is cut off. Since it is discharged immediately afterwards, there is no delay in turning off the LED. After the capacitor C6 has been discharged, the charge stored in the capacitor C5 flows to the LED as a discharge current, but the capacitor C5 has a small capacity to limit the current flowing to the LED. C
Since the discharge times of 3 and C4 are the same, the current flowing through the LED due to the discharge of the capacitor C5 is minute. Therefore, the LED does not light up due to the discharge of the capacitor C5.

The embodiment is an example in which a rectifier circuit using a diode bridge and a single LED are used for the voltage detection circuit, but by connecting two light emitting diodes LED1 and LED2 in parallel in opposite polarities as shown in FIG. It can be used similarly.

(G) Effect of the Invention As described above, according to the present invention, even in the case where the noise filter including the capacitor is provided between the input lines of the commercial power source, the cutoff state of the commercial power source can be detected within the end time. Therefore, it is possible to secure a long time until the output voltage of the power supply circuit falls below the operation margin voltage of the load circuit, and during that time, it is possible to perform a series of processes necessary for the end of operation or power failure.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a power supply state detecting device according to an embodiment of the present invention, FIG. 2 is a diagram showing timings and waveforms of respective parts shown in FIG. 1, and FIG. 3 is a circuit according to another embodiment. FIG. 4 is a circuit diagram of a conventional power supply state detecting device, and FIG. 5 is a diagram showing timings and waveforms of respective parts in FIG. 1-noise filter, 4-photo coupler, 5-state detection circuit, 6-voltage detection circuit, C1-C4-noise filter capacitor, C5-capacitor, LED-light emitting diode.

Claims (1)

[Claims] 1. A noise filter including a capacitor is provided between input lines of a commercial power supply, and a voltage detection circuit including a light emitting diode of a photocoupler is connected in parallel with the noise filter between the power supply input lines. In a power supply state detection device including a detection circuit that detects a power supply state based on an output signal, the voltage detection circuit includes a light emitting diode of the photocoupler with a capacitance sufficiently smaller than at least a capacitor of the noise filter. A power supply state detection device characterized in that capacitors are connected in series.