JPS61187662A - Power source voltage detection circuit - Google Patents

Abstract

PURPOSE:To prevent erroneous operation, by allowing a pair of transistors for detecting both positive and negative polarity voltages to perform the judgement of the presence of AC voltage and performing the determination of the delay time from the OFF-time of AC voltage by a condenser, a constant current circuit and a voltage comparator. CONSTITUTION:When AC voltage is turned ON, a Tr(transistor)4 for detecting positive voltage is turned On and the voltage of a condenser 5 is held to saturat ed voltage of Tr4. Next, when AC voltage changes from positive to negative, Tr4 is cut off whereas Tr3 for detecting negative voltage is turned ON. At this time, the voltage of the condenser 5 is held to the saturated voltage of Tr3. As mentioned above, a pair of Tr3, 4 for detecting both positive and nega tive polarity voltages are alternately and repeatedly turned ON and OFF. Next, when AC voltage is turned OFF, both of Tr3, 4 are cut off. Therefore, the voltage of the condenser 5 begins to receive charging by a constant current circuit 7. The state of output terminal 10 of a voltage comparator is held from this time until reaching the threshold value voltage 9 of the voltage comparator and this time is set as a delay time and, thereafter, reversal holding is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a power supply voltage detection circuit for detecting the presence or absence of an alternating current power supply voltage.

2. Description of the Related Art In recent years, power supply voltage detection circuits have been used in various forms in electronic circuits used in commercial power supplies.

An example of the above-mentioned conventional power supply voltage detection circuit will be described below with reference to the drawings. FIG. 3 shows an example of a conventional power supply voltage detection circuit.

In FIG. 3, 1 is an AC voltage input terminal, 3 is a negative voltage detection transistor, 13 is a diode for negative voltage rectification, 1
4 is a diode for positive voltage commutation, 15° and 16 are resistors for dividing the AC voltage, 17 is a rectifier height, 18 is a resistor for discharging the electric charge, and 19 is a resistor for limiting the base current of transistor 3 for negative voltage detection. , 2o is a negative voltage detection transistor output terminal.

The operation of the power supply voltage detection circuit configured as described above will be described below.

First, when an AC voltage is turned on at the AC voltage input terminal 1, its peak voltage is set to an appropriate value by resistors 15 and 16.

When the alternating current voltage is positive, it is bypassed by the commutating diode 14, and when the AC voltage is negative, a negative voltage is generated in the tip/su 17 through the rectifying diode 13. As a result, the negative voltage detection transistor 3 becomes saturated with the negative voltage of the tip 7 and the base current set by the resistor 19. Next, when the AC voltage is turned off, the charge accumulated in the capacitor 17 is discharged through the resistor 18. At this time, the delay time after turning off is mainly determined by the capacitor voltage, the capacitance of the capacitor 17, and the resistance value of the resistor 18. The pace potential of the discharged negative voltage detection transistor 3 is approximately 0.
．． When the voltage drops beyond the threshold of 6V, a shut-off state occurs.

Problems to be Solved by the Invention However, with the above configuration, there is a problem that the delay time after turning off changes proportionally to changes in AC voltage and frequency as the capacitor voltage changes. In view of the above problems, the present invention has the following points:
An object of the present invention is to provide a power supply voltage detection circuit whose OFF time delay time does not change at all due to alternating current power supply voltage fluctuations or frequency fluctuations.

Means for Solving the Problems In order to solve the above problems, the power supply voltage detection circuit of the present invention includes a pair of transistors for detecting positive and negative polarity voltages to determine the presence or absence of an AC power supply voltage, and a delay when turned off. The present invention is equipped with a configuration including a capacitor, a constant current circuit, and a voltage comparator that determine time. By limiting the judgment to binary judgment of the presence or absence of the OFF state, the influence can be eliminated, and by operating the circuit with a DC power supply, the influence can be eliminated. The detection circuit will be explained with reference to the drawings.

FIG. 1 shows a basic circuit of a power supply voltage detection circuit in one embodiment of the present invention. In FIG. 1, 1 is an AC voltage input terminal, 2 is a resistor, 3 is a negative voltage detection transistor, 4 is a positive voltage detection transistor, 5 is a capacitor, and 6
is the output terminal of a pair of transistors for detecting positive and negative polarity voltages, 7 is a constant current circuit, 8 is a voltage comparator, 9 is the threshold voltage of the voltage comparator, 1o is the output terminal of the voltage comparator, 11 is DC It is a power source.

The operation of the power supply voltage detection circuit configured as described above will be described below with reference to FIGS. 1 and 2. First, Fig. 2 shows the voltage waveforms of each part in Fig. 1, and shows the state when an AC voltage as shown in Fig. 2 (a) is input to the AC voltage input terminal 1 and turned OFF. FIG. 2(b) shows the voltage waveform at the output end 6 of a pair of transistors for detecting positive and negative polarity voltages. Figure 2 (C
) is the voltage waveform at the voltage comparator output terminal 1o. First, when the AC voltage is turned ON, the positive voltage detection transistor 4 is turned OFF.
N, and the voltage of the capacitor 6 is held at the saturation voltage vP of the transistor 4. Next, when the AC voltage changes from positive to negative, the positive voltage detection transistor 4 is cut off, and the negative voltage detection transistor 3 is turned on instead.

At this time, the voltage of the capacitor 5 is maintained at the saturation voltage of the transistor 3N. In this way, a pair of transistors for detecting voltages of both positive and negative polarities are alternately turned ON and OFF. At this time, the output terminal of the voltage comparator maintains the condition 1. Next, when the AC voltage is turned off, the negative voltage detection transistor 3
Both transistors of the positive voltage detection transistor 4 are cut off. Therefore, the voltage of the capacitor 6 is changed to the constant current circuit 7.
From this time when charging is started at 0, the voltage comparator output terminal 1° maintains state 1 until the voltage vT of the voltage comparator threshold voltage 9 is reached. This time becomes a delay time, and then the state is inverted and held in state 2.

As described above, according to this embodiment, by providing a pair of transistors for detecting positive and negative polarity voltages to determine the presence or absence of AC voltage, it is not affected by AC voltage fluctuations or AC frequency fluctuations. The delay time at the time of OFF can be accurately set by supplying the constant current circuit and voltage comparator from the DC power supply.

In the above embodiment, a pair of transistors for detecting positive and negative polarity voltages was constructed from a PNP transistor.
chMO3 and NPN) U/Jista and NchMO8) U/
Effects of the Invention As described above, the present invention allows a pair of transistors for detecting positive and negative polarity voltages to determine the presence or absence of an alternating current voltage, and determines the delay time from when the alternating current voltage is turned off. By using a constant current circuit and a voltage comparator, it is possible to perform power supply voltage detection that is not affected by AC voltage fluctuations or frequency fluctuations and is unlikely to cause malfunctions, and is extremely useful in practice. .

[Brief explanation of drawings]

Fig. 1 is a basic circuit diagram of a power supply voltage detection circuit according to a first embodiment of the present invention, Fig. 2 is a voltage waveform diagram of each part of Fig. 1 showing the operation of the same embodiment, and Fig. 3 is a diagram of a conventional power supply. FIG. 2 is a basic circuit diagram of a voltage detection circuit. DESCRIPTION OF SYMBOLS 1... AC voltage input terminal, 3... Transistor for negative voltage detection, 4... Transistor for positive voltage detection, 6... Capacitor, 7...・・・・・・
Constant current circuit, 8... Voltage comparator. Name of agent: Patent attorney Toshio Nakao and 1 other person11
．． , AC input terminal 3-AT, transistor for street moxibustion No. 1 Figure 4...
・Transistor 5 for positive T Figure 3

Claims (1)

[Claims] an AC voltage input terminal, a pair of transistors for detecting positive and negative polarity voltages connected to the AC voltage input terminal, and a capacitor connected in parallel to the output terminal of the pair of transistors for detecting positive and negative voltages; , a power supply voltage detection circuit comprising a constant current circuit and a voltage comparator, one end of which is connected to the output terminals of the pair of transistors for detecting the positive and negative polarity voltages.