JPH0354310B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a voltage comparison circuit.

Voltage comparison circuits are commonly constructed using operational amplifiers. However, highly integrated operational amplifiers have problems in terms of reliability. Also, operational amplifiers require a power source to operate them.

The voltage comparator circuit of the present invention is constructed of components such as resistors and diodes that are relatively less likely to fail, and is of course simpler and much more reliable than a circuit constructed using an operational amplifier.
A power source is also not required. The present invention will be explained below using the drawings.

FIG. 1 is a diagram showing an embodiment of a voltage comparison circuit according to the present invention. In FIG. 1, Es indicates a reference voltage and Ex indicates a detected voltage.The voltage comparison circuit of the present invention compares this detected voltage Ex with the reference voltage Es, and detects when the difference exceeds a predetermined value. It outputs a signal. Ess is a power supply circuit that outputs a constant current I, and D1 to D4 are diodes. O1 and O2 are signal detection terminals, and terminal 01
is connected to the constant current output power supply circuit Ess, and terminal 0
2 is grounded. C1 and C2 are voltage comparison terminals, the terminal C1 is connected to the reference voltage source Es, and the terminal C2 is connected to the detected voltage source Ex. The diodes D1 and D2 and the diodes D3 and D4 are connected in series between the detection terminals O1 and O2, respectively, in a forward direction with respect to the output I of the constant current output power supply circuit Ess. The connection point between diodes D1 and D2 is connected to comparison terminal C1, and the connection point between diodes D3 and D4 is connected to comparison terminal C2. The operation of such a circuit will be explained as follows. In the following description, the forward voltage drops of the diodes D1 to D4 are assumed to be Vd1 to Vd4, respectively.

Assuming that the values of Vd1 to Vd4 are equal to each other, the constant current I supplied from the constant current output power supply circuit Ess flows equally through the series circuit consisting of diodes D1 and D2 and the series circuit consisting of diodes D3 and D4,
The current generates voltages at the detection terminals O1 and O2, respectively. If the voltage generated at the detection terminal O1 is E1, and the voltage generated at the detection terminal O2 is E2, then
The voltages E1 and E2 change as follows depending on the value of the detected voltage Ex with respect to the reference voltage Es.

(1) When Ex=Es Since Ex and Es are equal, diodes D1 to D
4 are all conductive. In this case, the voltage E1 is higher than the reference voltage Es by the forward voltage drop of the diode D1, and the voltage E2 is lower than the reference voltage source Es by the forward voltage drop of the diode D2. When such E1 and E2 are expressed numerically, the following equations (1) and (2) are obtained.

E1=Es+Vd1...(1) E2=Es-Vd2...(2) Also, this can be expressed as a(E1) and b in Figure 2 in the graph.
(E2) point, and there is 2Vd between E1 and E2.
There is a difference between In FIG. 2, the horizontal axis represents the magnitude of the detected voltage Ex, and the vertical axis represents the forward voltage drop Vd of the diode.

(2) When Ex>Es When the detected voltage source Ex becomes larger than the reference voltage source Es, diodes D2 and D3 are cut off. As a result, the voltage E1 of the detection terminal O1 is fixed to the voltage obtained by adding the forward voltage drop of the diode D1 to the reference voltage Es. Further, the voltage E2 at the detection terminal O2 increases as the detected voltage Ex increases. These relationships can be expressed mathematically as shown in equations (3) and (4) below.
1, b1.

E1=Es+Vd1...(3) E2=Ex-Vd4...(4) At this time, if the detection signals obtained from the detection terminals O1 and O2 are EO, then EO=E1-E2=Es-Ex+Vd1+Vd4...(5) becomes.

(3) When Ex<Es When the detected voltage source Ex becomes smaller than the reference voltage source Es, the diodes D1 and D4 are cut off.
As a result, the voltage E1 becomes lower as the detected voltage Ex decreases. On the other hand, the voltage E2 at the detection terminal O2 is fixed at a voltage obtained by subtracting the forward voltage drop of the diode D2 from the reference voltage Es. Therefore, these can be expressed by the following formulas (3) and (4), and in the graph, a in Figure 2.
2, b2.

E1=Ex+Vd3...(6) E2=Es-Vd2...(7) At this time, the detection signal Eo obtained from the detection terminals O1 and O2 becomes Eo=E1-E2=Ex-Es+Vd2+Vd3...(8). Here, from equation (5), Ex=Es+Vd1+Vd4 and Eo=0...(9), and from equation (8), Ex=Es-Vd2-Vd3 and Eo=0...(10). Equation (9) is represented by point P in FIG. 2, and equation (10) is represented by point Q. Therefore, equation (9) and
As is clear from equation (10), the signal Eo obtained from the detection terminals O1 and O2 causes 4Vd(Vd1+Vd2+Vd3
The detected voltage Ex can be detected in the +VD4) window.

There are various methods for detecting the signal Eo. FIG. 3 shows an embodiment of the detection means for the signal Eo.
Figure A shows a configuration in which a photodiode PD is connected in series to a resistor element R1. One end of the resistor element R1 is connected to the detection terminal O1 shown in Figure 1, and the cathode of the photodiode PD is connected to the detection terminal O2. Connected. If the forward voltage drop of the photodiode PD is Vd, the detection means of this configuration is the second
As shown in the figure, changes in the detected voltage Ex can be detected within a 2Vd window. for example,
If Vd is 0.6V and the reference voltage Es is 5V, the photodiode will
The PD emits light, and when it exceeds this range, the PD stops emitting light. Therefore, this change in the light emission state can be used as an alarm signal. Figure 3B shows a transistor Tr1 used to detect Eo.The emitter electrode of the transistor Tr1 is connected to the detection terminal O1 shown in Figure 1, and the base electrode is connected to the detection terminal O1 through the resistor R2. Connected to O2. Assuming that the Vbe of the transistor Tr1 is equal to the forward voltage drop Vd of the diode, the circuit of this figure B is similar to that of the figure A from the collector electrode CE.
Alarm signal can be detected in 2Vd window. FIG. 3C shows still another detection means, which is composed of a shotgun diode Ds and a transistor Tr2. In this circuit, the anode electrode of the shotgun diode Ds is connected to the detection terminal O1 shown in FIG. 1, and the base electrode of the transistor Tr2 is connected to the detection terminal O2 through the resistance element R3.
The alarm signal is taken out from the collector electrode CE of the transistor Tr2. In such a circuit, since the forward voltage drop of the Schottky diode Ds is small, fluctuations in the voltage to be detected Ex can be detected within a small window.

As described above, the voltage comparator circuit of the present invention is composed of components such as resistors and diodes that are relatively unlikely to fail, so it is simpler and far more reliable than the conventional circuit constructed using operational amplifiers. . Furthermore, if the power supply for obtaining the reference voltage Es is used as the power supply circuit Ess, there is no need for a special power supply to operate the circuit, and in addition, it can be easily made into a semiconductor, which is extremely effective in practical use. It is something.

The voltage comparator circuit of the present invention as described above is extremely suitable for a power supply alarm circuit that generates an alarm when the power supply voltage exceeds a reference value, particularly for generating an alarm in a power supply circuit having multiple outputs.

Figure 4 shows the voltage comparator circuit according to the present invention with multiple outputs as described above (the power supply voltage Ex to be detected is ±5V,
15V, ±30V) shows a circuit diagram of an embodiment when used to generate an alarm in a power supply circuit. Fourth
In the figure, Ess is the power supply circuit, Dz is the Zener diode that creates the 5V reference voltage + Es, D1, D2
are diodes corresponding to diodes D1 and D2 shown in Fig. 1, D3 and D4 are diodes corresponding to diodes D3 and D4 shown in Fig. 1, and the connection point of diodes D1 and D3 is connected to the detection terminal O1. . The output of the power supply circuit Ess is applied to this connection point as a constant current through the resistive element R4. A comparison terminal C1, which is a connection point between diodes D1 and D2, is connected to a reference voltage source Es, and a detection terminal O2, which is a connection point between diodes D2 and D4, is connected to a common COM via a resistance element R5. A detected voltage Ex of 5V with positive polarity is applied to the comparison terminal C2, which is the connection point between the diodes D3 and D4. D31, D41, D32, and D42 are diodes, and the diodes D31 and D41 are directly connected, and the diodes D32 and D42 are connected in series, and each series circuit is connected between the detection terminals O1 and O2. Diodes D31 and D41 together with diodes D1 and D2 form a voltage comparison circuit for +15V, and diodes D32 and D42 together with diodes D1 and D2 form a voltage comparison circuit for +30V. That is, when the output of the constant current output power supply circuit Ess is +15V, the voltage of 15V is applied to the resistive elements R6 and R7.
The voltage is divided to 5V by diodes D31 and D4.
The detected voltage Ex is applied to the comparison terminal C21, which is composed of one connection point. Also, if the power supply voltage applied to terminal T is +30V, diode D3
Comparison terminal C22 consisting of the connection point of 2 and D42
Then, the 30V voltage is divided into 5V by resistive elements R8 and R9 and applied as the detected voltage Ex. The above is a positive polarity voltage comparison circuit, but the lower half is a negative polarity voltage comparison circuit. That is, Dz' is a Zener diode that produces the reference voltage -Es, and D
1' and D2' are the diodes D1 and D2 shown in Figure 1.
The diodes D3' and D4' corresponding to are diodes for the detected voltage Ex of -5V. D31′,
D41' is a diode for detection voltage Ex of -15V, D32' and D42' are for detection voltage Ex of -30V.
These diodes are connected in the same way as on the + side.

DTC is a detection means, and the detection transistor Tr
3, Tr4, photodiode Do, resistance element R1
0 to R12, Zener diode Dz1 and protection diode d1 of transistors Tr3 and Tr4,
Consists of d2. The base electrode of the transistor Tr3 is connected to the + side detection terminal O2 via the resistance element R10, and the emitter electrode is also connected to the + side detection terminal O2.
Connected to 1. The base electrode of the transistor Tr4 is connected to the negative detection terminal O2' via the resistance element R11, and the emitter electrode is also connected to the negative detection terminal O1'. Transistor Tr
A series circuit consisting of a Zener diode Dz1, a resistance element R12, and a photodiode Do is connected between the collector electrodes of Tr3 and Tr4. The series circuit of the Zener diode Dz1 and the resistance element R12 is provided for voltage absorption, and is unnecessary in principle.

In such a multi-output power supply alarm circuit shown in FIG. 4, the detection transistors Tr3 and Tr4
It is possible to detect a change in the voltage to be detected Ex at a level of Vbe that is twice that of Vbe. That is, the transistor Tr
3. Assuming that Vbe of Tr4 is 0.6V, when the power supply voltage Ex to be detected is 5V, if it changes by 5V±0.6V or more, the photodiode Do becomes conductive, and this becomes an alarm signal. Also, the detected voltage Ex is
The photodiode Do conducts at 15V±1.8V for 15V and 30±3V for 30V.

In this way, when the voltage comparator circuit according to the present invention is used for a multi-output power supply alarm, it is constructed from components with relatively few failures as explained in Fig. 1, so it is highly reliable and does not require a power supply. A multi-output power supply alarm generation circuit with a simple configuration can be obtained.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an embodiment of the voltage comparison circuit according to the present invention, FIG. 2 is a diagram for explaining the operating characteristics of the circuit of FIG. 1, and FIG. 3 is a diagram of the detection means used in the circuit of FIG. 1. Circuit Diagram of Embodiment FIG. 4 is a circuit diagram of an embodiment in which the voltage comparison circuit according to the present invention is used in a multi-output power supply alarm circuit. D1 to D4...Diode, C1, C2...Comparison terminal, O1, O2...Detection terminal, Es...Reference voltage, Ex...Voltage to be detected.

Claims (1)

[Claims] 1 A pair of detection terminals, first and second diodes and third and fourth diodes connected in series between both detection terminals with the same polarity, and a forward direction to each diode through both detection terminals. a power supply circuit that supplies a constant current; a first comparison terminal that is connected to the connection point between the first and second diodes and to which a reference voltage is applied; and a detection terminal that is connected to the connection point between the third and fourth diodes. A voltage comparison circuit comprising a second comparison terminal to which a voltage is applied, and signal detection means for detecting a signal generated between the two detection terminals.