JPH0717013Y2 - Voltage detection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a voltage detection circuit for detecting a decrease in power supply voltage of a device that operates on a battery or the like.

[Prior Art] FIG. 3 is a block diagram showing a conventional voltage detection circuit, and FIG. 4 is an operation time chart of the circuit of FIG. 3, in which (V ₀₀ ) is a power supply voltage (detected voltage), R ₁ and R ₂ ) are resistance voltage divider circuits, (a) is the voltage at the voltage dividing point, and (1) is voltage detection I
C and (b) are detection outputs.

Next, the operation will be described. This voltage detection IC (1) has the threshold values (U) and (L) of hysteresis, and once the voltage (a) at the voltage dividing point exceeds the threshold (U) level, the voltage detection IC (1) is detected. Threshold changes to (L) level,
Once the voltage falls below the threshold (L) level, the threshold of the voltage detection IC (1) changes to the (U) level. Therefore, for example, when the voltage (a) at the voltage dividing point drops in a spike shape due to the load change as shown in FIG. 4, the detection output (b) of the voltage detection IC (1) is the voltage at the voltage dividing point ( The voltage detection IC (1) changes to the threshold (U) level even if the voltage (a) at the voltage dividing point immediately returns to the LOW level when the voltage (a) once falls below the threshold (L) level. Detection output (b)
Will remain at the LOW level, and will erroneously detect a drop in the power supply voltage.

[Problems to be Solved by the Invention] Since the conventional voltage detection circuit as described above is configured and operates as described above, it malfunctions in response to a momentary drop in the power supply voltage due to a load change, and the power supply voltage There is a problem that the detection output does not recover even if it is substantially constant.

The present invention has been made in order to solve such a problem, and an object thereof is to obtain a voltage detection circuit for surely discriminating and detecting a decrease in the power supply voltage itself.

[Means for Solving the Problems] A voltage detection circuit according to the present invention is a resistance circuit for dividing a voltage to be detected, an integrating circuit connected to the voltage division point, and the voltage detection circuit for the voltage division point at a constant cycle. It is decided to include a switch circuit for connecting to and disconnecting from the circuit and a comparison circuit for comparing the voltage at the voltage dividing point at a constant timing after the circuit is cut off with a predetermined threshold value.

[Operation] In the voltage detection circuit of the present invention, the high-frequency component of the voltage at the voltage dividing point is absorbed by the integrating circuit, and the voltage at the voltage dividing point is connected to the power supply voltage at a constant cycle to be cut off to provide a threshold value with hysteresis. Is reset to the threshold value on the side where the power supply voltage is to be detected every time, and the voltage at the voltage dividing point at a constant timing after interruption is compared with the above-mentioned constant threshold value. If the power supply voltage does not recover immediately, it is determined that the power supply voltage has dropped.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings. First
FIG. 2 is a diagram showing an embodiment of the present invention, and FIG. 2 is an operation time chart of the circuit shown in FIG. 1. In the diagrams, the same reference numerals as those in FIGS. ) Is a switch circuit, (3) is a timing circuit, (4) is a detection circuit, and (5) is a capacitor.

Next, the operation will be described. The timing circuit (3) generates a switch signal (c) having a predetermined cycle T and a sampling signal (d) which is delayed from this switch signal (c) by a fixed time (t). ) Is LO
At the W level, the switch circuit (2) is closed and the power supply (e) at the voltage dividing point is rapidly charged up to the power supply voltage (V ₀₀ ), and when the switch signal (c) returns to the HIGH level, The voltage (e) at the voltage dividing point when the switch circuit (2) opens
Is exponentially discharged toward the divided voltage determined by the resistance voltage divider circuit (R ₁ , R ₂ ).

Therefore, if the cycle (T) of the switch signal (c) is appropriately selected, the voltage (e) at the voltage dividing point is determined by the resistance voltage dividing circuit (R ₁ , R ₂ ) within this cycle (T) every time. Discharge to the divided voltage, and if this is detected each time at the timing of the sampling signal (d) after a sufficient time (t) has passed, the voltage at the voltage dividing point according to the transition of the power supply voltage (V ₀₀ ). (E) can be detected.

In this way, if the power supply voltage (V ₀₀ ) continues to be detected, and if the power supply voltage (V ₀₀ ) drops in a spike shape due to a sudden load change, as shown in the timing diagram of (t ₁ ), in this example, Since the power source (e) at the pressure point is charged up to the power source voltage (V ₀₀ ) before the voltage drop, the effect of the spike does not appear.

Moreover, since the power supply voltage (V ₀₀ ) is immediately restored, it does not affect the subsequent detection. Eventually, the power supply voltage (V ₀₀ ) begins to gradually drop, and for example, at the timing of (t ₂ ), the power supply (e) at the voltage dividing point falls below the threshold (L) and the voltage detection IC
Although the output signal (f) of (1) becomes LOW level, the detection circuit (4) does not detect that the power supply voltage (V ₀₀ ) has dropped because the sampling signal (d) has already ended.

Then, at the next switch signal (c), the voltage at the voltage dividing point (e)
Is charged up to the power supply voltage (V ₀₀ ), the output signal (f) of the voltage detection IC (1) is forcibly forced by this.
It is set to HIGH level, and the threshold value of the voltage detection IC (1) is returned to (L) level.

Therefore, if the power supply voltage (V ₀₀ ) is restored at the next time point, the detection circuit (4) will not detect the decrease in the power supply voltage (V ₀₀ ).

However, at the timing when the power supply voltage (V ₀₀ ) further drops (t ₃ ) as in this example, the amount (V _R1 ) of charging up the capacitor (5) also becomes small, and the resistance voltage dividing circuit (R ₁ , R ₂ ) also lowers the divided voltage, so the voltage (e) at the voltage dividing point falls below the threshold (L) level faster than in the case of (t ₂ ) and the voltage detection IC (1) The output signal (f) becomes LOW level early, and the detection circuit (4) detects the voltage detection IC by the subsequent sampling signal (d).
Latch output signal (f) of (1) and supply voltage (V ₀₀ )
LOW level detection output (g) is detected.

[Effects of the Invention] As described above, the present invention connects the voltage dividing point to the integrating circuit, connects the voltage at the voltage dividing point to the detected voltage at a constant cycle, and shuts off the threshold voltage having hysteresis every time. The voltage is restored to one of the thresholds that you want to detect, and the voltage at the voltage dividing point at a fixed timing after this interruption is compared with the constant threshold every time, so the high-frequency component of power supply fluctuation is absorbed, and the power is restored by each time the threshold is restored. When the fluctuation returns immediately, it is not judged that the power supply voltage has dropped, and therefore, there is an effect that the drop of the power supply voltage itself can be reliably discriminated and detected.

[Brief description of drawings]

1 is a diagram showing an embodiment of the present invention, FIG. 2 is an operation time chart of the circuit shown in FIG. 1, FIG. 3 is a block diagram showing a conventional power supply detection circuit, and FIG. 4 is FIG. 3 is an operation time chart of the circuit shown in FIG. In the figure, (R ₁ , R ₂ ) is a resistance voltage divider circuit, (1) is a voltage detection IC, (2) is a switch circuit, (3) is a timing circuit, (4) is a detection circuit, and (5) is a capacitor. Show.

Claims (1)

[Scope of utility model registration request] 1. A resistance circuit for dividing a voltage to be detected and a ground voltage, an integrating circuit connected between the voltage dividing point of the resistance circuit and the ground voltage, and a voltage dividing point of the resistance circuit at a constant cycle. A voltage detection circuit including a switch circuit that connects to a detected voltage and cuts it off, and a comparison circuit that compares the voltage at a voltage dividing point at a certain timing after the cutoff with a predetermined threshold.