JPS59212926A - Detector for voltage drop of power supply - Google Patents

Abstract

PURPOSE:To detect preeviously and accurately a voltage drop of the power supply to the allowance level or lower by detecting the input/output voltage difference of a constant voltage circuit with use of a voltage drop detecting transistor and a constant voltage diode. CONSTITUTION:A voltage dividing circuit consisting of a resistance 4, a reverse current preventing diode D6 and a resistance 5 is connected to the output side of a constant voltage circuit 1 provided between a source power supply 2 and a load 3. The input side point (a) of the circuit 1 and the junction (b) between the diode D6 and a resistance 5 are connected to the emitter and the base of a voltage drop detecting transistor TR7 respectively. Then a constant voltage diode D8 is connected between the collector and the earth of the TR7. The voltage applied between the base and the emitter of the TR7 is equal to the sum of the potential difference Ea between the input and the output of the circuit 1 and the voltage drop amount Eb of the point (b). The base-emitter bias can be set at an optional level by increasing or decreasing the voltage of the Eb. The fluctuation of the collector potential of the TR7 is set at a fixed level by the diode D8. Then the D8 detects that the collector potential drops suddenly down to 0 when the TR7 is turned on.

Description

[Detailed Description of the Invention] The present invention is a power supply circuit equipped with a DC voltage stabilizing circuit (hereinafter referred to as a constant voltage circuit), which detects a drop in the power supply voltage before the power supply voltage drops below a permissible value. The purpose of this invention is to prevent equipment malfunction due to a drop in power supply voltage, and is particularly useful for power supply devices using batteries.

In general, in analog circuits, when the power supply voltage decreases, the dyne and undistorted output gradually decreases, so it is possible to predict the decrease in power supply voltage, but in digital circuits, they operate normally above the critical voltage, but It is almost impossible to predict a voltage drop based on operation, as malfunctions or operation stop suddenly occur below this voltage.In particular, advanced integrated circuits and memory circuits are affected by a drop in power supply voltage, so important circuits are The system is equipped with a separate backup power source and can be switched.
Although it is equipped with an automatic production switching device, in order to use it, a means for detecting a drop in the power supply voltage is required, and the present invention provides an extremely effective circuit that can be used for such a purpose. It provides:

FIG. 1 shows an example of a basic circuit of the present invention, and its configuration and operation will be explained. The circuit shown in the figure is a circuit that supplies a constant voltage (1) to a load 3 through a constant voltage circuit 1 using the voltage Vcc of the original power source 2. Generally, vcc>vL, and in order to keep vL constant, the voltage difference from vcc is consumed in the constant voltage circuit 1 to obtain a constant output voltage. Therefore, a change in vcc results in a potential difference between input A and output B of the constant voltage circuit 1, and in order to ensure constant voltage operation, at least 0.
A potential difference of 2-0.5 V is required. The present invention focuses on the fact that vI is constant when the potential difference of the constant voltage circuit exceeds a predetermined value, and uses the initial bias voltage between the pace emitter of the transistor as a detection standard to achieve clear detection with a relatively simple configuration. It is possible.

The lowest effective potential difference in the constant voltage circuit is 0.2~
Although it is set to 0.5V, in order to widen the effective operating range in small power circuits powered by batteries, this potential difference is configured to be as small as possible, and it is usually around 0.2 to 0.3V. . On the other hand, since the initial bias between the pace and emitter of a normal transistor is approximately 0.6V, the potential difference in the constant voltage circuit may be simply added between the pace and emitter of the transistor and detected at the conduction point between the collector and emitter. The difference between 0.3 and 0.4 V results in a disadvantageous range of invalid operation. Therefore, in the present invention, a series circuit consisting of a resistor 4 and a resistor 5 for voltage division is provided in parallel with the load 3 on the output side B of the voltage stabilizing circuit 1, and the base of the voltage drop detection transistor 70 is connected to the junction point of the resistor 4 and the resistor 5 to provide a constant voltage. The emitter is connected to the input side a of the circuit 1, and a diode 6 for backflow prevention is connected in series to the high potential side resistor 4 of the series resistors, and the collector of the voltage drop detection transistor 7 and the power supply return path ( A circuit is constructed by inserting a constant voltage diode 8 between (ground) and a change in the terminal voltage, that is, the collector potential of the voltage drop detection transistor 7, to detect and predict a drop in the power supply voltage in advance. The bias voltage applied to the pace emitter of the voltage drop detection transistor is the sum of the potential difference Ea between the input and output of the constant voltage circuit 1 and the voltage drop Eb of the load side voltage dividing resistor 4 and diode 6. Of these, Ea is 0.2 to 0.3 as mentioned above.
Therefore, by adjusting the voltage value of Eb, it is possible to set the level of the pace-emitter bias voltage to any value greater than or equal to Ea (however, the maximum value is the power supply voltage vcc). Therefore, a very wide range of settings can be made. In reality, considering the purpose of use of this circuit, when the source voltage Vco drops to a value extremely close to the load side voltage VL, the voltage drop detection transistor's pace
By crossing the initial bias (threshold) point between the emitters, a large change occurs in the internal resistance value between the collector and emitter. Therefore, E is usually about 0.5 to 1 .

In this circuit, the backflow prevention diode 6 is not particularly necessary during normal operation, but when an abnormality occurs in the constant voltage circuit 1 or the detection transistor 7, the potential at point b becomes higher than the potential at point B. , can be effective in preventing current from flowing backward through the resistor 4.

In addition, the collector potential of the detection transistor 7 is
When the bias voltage between the emitter is below the initial (threshold) voltage, the internal resistance between the collector and emitter is extremely large and is in a cut-off state. Therefore, if a slight resistance is inserted between the collector and ground, the collector potential is almost zero, but when the voltage between the pace emitter exceeds the initial (threshold) voltage, the collector internal resistance is suddenly reduced and the collector potential is raised, so the collector voltage increases. By monitoring in this way, it is possible to know very clearly whether the potential difference E& of the stabilizing circuit has exceeded the detection set value.

However, since the collector voltage when the transistor 7 is in a conductive (ON) state fluctuates within a considerable range, this may cause some inconvenience depending on the collector potential detection method. By placing a constant voltage (zener) diode between (ground) and the collector potential is displayed as either O or the zener voltage, the display is extremely stable and clear, or the trigger of the automatic control circuit. However, it has the advantage that there is little risk of malfunction.

Figure 1 shows the basic circuit of the present invention, and although it is possible to operate as is, in order to operate more stably, a resistor must be connected between the pace and emitter of the detection transistor 7 and in parallel with the Zener diode of the collector. Additions such as inserting a resistor in series with the electrode to prevent parasitic vibration may be made as appropriate depending on design and operational requirements.

Next, an example of a circuit implementing the present invention is shown in FIG. 2, and actual measured values of its operation are shown in FIG. In the figure, the same symbols as in FIG. 1 indicate the same parts. Resistance values are written for the other resistors used; a PNP type silicon transistor 2SA1121 was used as the voltage drop detection transistor, 182837 was used as the backflow prevention diode, and H27B3 was used as the Zener diode. These are mass-produced parts that are currently on the market. The difference between the basic circuit in Figure 2 and the basic circuit in Figure 1 is that there are resistors between the transistor's pace and emitter, between the emitter and power supply, and between the collector and ground. It is used to reduce variations in the characteristics of semiconductors during mass production and fluctuations in characteristics due to temperature.

In Figure 3, the horizontal axis represents the source voltage ■. . The B output vL of the constant voltage circuit when changing from 2V to 15V is shown by the dashed line at the end.When vce is 5.3V or more, ■1 is a constant voltage characteristic of 5V constant, and below that, it is a constant voltage characteristic of the power supply voltage. 0, which is gradually decreasing almost in parallel with the decrease in 0. Also, the C output of the collector potential of the detection transistor ■o is shown by the solid line ■. .

Zena I (Z7 B
According to the constant voltage characteristics of 3, the voltage is constant at approximately 5V, but it drops rapidly below that, so if the L level required for detection is set to IV and the H level to 4■, the L level will be set to V.
When cc is 5V, the H level is ■. . It can be seen that the 5.5V diameter is detected. Also, the load voltage vL at that time is 4
．． They are about 7v and 5v. Therefore, when using the C output as a detection source, the load voltage VL will change from the rated 5V to 4V.
．． Until it drops to 7■, the source voltage ■c.

By predicting a drop in power supply voltage or automatically switching to a backup power supply, it is possible to reliably prevent malfunctions due to a drop in power supply voltage. In a normal detection circuit based on a decrease in B output, the detection H level is reached only when vL decreases by 4Vt, and it gradually decreases to the L level IV-, so it depends on how many V VCC has decreased. It is clear how superior the detection operation of the inventive circuit is compared to the fact that the detection is very uncertain.

[Brief explanation of drawings]

FIG. 1 is a basic circuit diagram of the present invention, FIG. 2 is an example of an applied circuit of the present invention, and FIG. 3 is an example of actual measurement of the operating characteristics of the circuit shown in FIG. l... Constant voltage circuit, 2... Original power supply, 3... Load,
4゜5... Resistor, 6... Diode, 7... Transistor, 8... Constant voltage diode. Patent applicant Yaesu Musen Co., Ltd.

Claims (1)

[Claims] In a DC power supply circuit that has a DC voltage stabilization circuit installed between the source power source and the load, a voltage drop detection transistor is connected to the junction point of two series resistors that divide the load side voltage by one voltage, and the voltage stabilization circuit is connected to the voltage drop detection transistor. In addition to connecting the emitter to the input side, a diode for backflow prevention is connected in series to the high potential side resistor of the series resistors, and a voltage regulator diode is connected between the collector of the transistor and the power return path to complete the circuit. What is claimed is: 1. A power supply voltage drop detection circuit comprising: a power supply voltage drop detection circuit configured to perform detection using a change in terminal voltage of the constant voltage diode.