JPH0212617Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a voltage detection circuit that can detect bipolar voltages at low potential. The present invention relates to a bipolar voltage detection circuit that can be used.

For example, Japanese Patent Publication No. 52-25110 is known as a detection circuit that detects bipolar voltages (currents).
This detection circuit consists of two transistors whose bases and emitters are connected in opposite polarities between input terminals, and a series circuit of two impedance elements, which are connected in parallel between the collectors of the two transistors. According to this circuit, one pole of the power supply and one of the input terminals are connected between the load resistor and the common connection point of the impedance elements connected in series. Since an impedance element is interposed between the input terminal and the terminal, the potential on the power supply side differs from the potential on the input terminal (signal source) side due to the voltage drop in this element. Therefore, when this detection circuit is applied to a measuring instrument or the like, there is a drawback that the power supply of this circuit cannot be shared as a power supply for other circuits in the measuring instrument.

Also, Utility Model No. 53-79072 (Utility Model No. 51-161716)
For example, a center point detection circuit for detecting the center point of a signal level output from an audio amplifier is disclosed in No. According to this, the detection circuit has two transistors of opposite polarity whose bases are commonly connected to the input terminal, that is, one is a PNP type transistor and the other is an NPN type transistor, and for example, the input signal level is PNP on the negative side of the center point
The transistor is on, and the NPN transistor is on on the positive side. However, in this prior example, the input terminal and the base of each transistor are connected to the ground line via a C/R time constant circuit, which causes them to be electrically floating, resulting in unstable operation. . Another drawback is that it cannot be detected if the center point of the input signal level is below the ground line potential.

The present invention has been made in order to eliminate the drawbacks of the conventional example described above, and embodiments of the present invention will be described below with reference to the accompanying drawings.

As shown in FIG. 1, this bipolar voltage detection circuit has a pair of input terminals 1 and 2 and a battery 3.
In this case, one input terminal 2 and the negative electrode of the battery 3 are connected to each other by a common power supply line 4. Two NPN transistors 5 and 6 are connected between the input terminals 1 and 2 so that their base-emitter polarities are opposite to each other. That is, the base of the first transistor 5 is connected to the input terminal 1 and its emitter is connected to the power supply line 4, while the base of the second transistor 6 is connected to the power supply line 4 and its emitter is connected to the input terminal 1. Connected to terminal 1. The collector of the first transistor 5 is connected to the base of a switching PNP transistor 7 via a resistor _R1 . This transistor 7 connects the battery 3 and an indicator lamp 8, which is a detector, via its emitter-collector. The collector of the second transistor 6 is a switching PNP transistor 9.
connected to the base of. In this case, the emitter of transistor 9 is connected to a connection point between the collector of transistor 5 and the base of transistor 7, and the collector is connected to power supply line 4.

During voltage detection, when the voltage appearing at the input terminal 1 is positive, the first transistor 5 is turned on.
As a result, the base current of the transistor 7 flows through its collector-emitter, and the transistor 7 is turned on, so that the circuit including the battery 3, the emitter-collector of the transistor 7, and the indicator lamp 8 is closed, and the indicator lamp 8 lights up. On the other hand,
When the voltage appearing at the input terminal 1 is negative, the second transistor 6 is turned on. As a result, the base current of transistor 9 flows through its collector-emitter, turning on transistor 9. Along with this, the base current of transistor 7 flows through its emitter-collector, turning transistor 7 on. become. Therefore, the indicator lamp 8 is lit in the same manner as described above. Regarding the transistor 9, its emitter-collector may be connected in parallel with the emitter-collector of the transistor 7 between the battery 3 and the display lamp 8 as shown in FIG. According to this, when transistor 6 is on, its output turns on transistor 9, and battery current is supplied from battery 3 to indicator lamp 8 through the emitter-collector of transistor 9.

FIG. 3 shows an embodiment in which the voltage detection circuit shown in FIG. 1 is applied to an indicator protection circuit of a circuit meter. In the figure, 10 and 11 are input terminals of a circuit meter, and a circuit breaking relay contact 12S, a protective resistor 13, and an indicator 14 are connected in series between these terminals. The voltage detection circuit connects the indicating instrument 1 via its input terminals 1 and 2.
4, but in this example,
A relay coil 12 for driving a relay contact 12S is connected in place of the indicator lamp 8, and a diode 15 and a resistor are connected between the collector of the transistor 7 and the base of the second transistor 6.
A series circuit consisting of R ₂ is added, and
A resistor R ₃ is connected between the base of the transistor 6 and the earth line 4.

In this configuration, input terminals 10, 1 of the circuit meter
When an excessive input is applied to the indicator 14 via the first transistor 5, the first transistor 5
Alternatively, since the second transistor 6 is turned on, the transistor 7 is turned on. As a result, the relay coil 12 is energized by the current from the battery 3, and the relay contact 12S is opened. in this case,
Since the collector potential of transistor 7 becomes high,
Diode 15 and resistor from this collector side
A current is supplied to the base-emitter of transistor 6 via _R2 , keeping transistor 6 in the on state. Therefore, transistor 7 is also kept in an on state, and as a result, relay coil 12 is self-maintained by the current from battery 3. In this way, the indicator 14 is protected against excessive input. Further, as shown in this embodiment, since the battery 3 of the current detection circuit and one input terminal 11 of the circuit meter are connected via the common power supply line 4, this battery 3 can be connected to the circuit meter. Other circuits,
For example, it can be used as a power source for a resistance measuring circuit.

As described above, according to the present invention, bipolar voltages can be reliably detected at low potential with a simple circuit configuration, and the battery and input terminal (signal source) can be connected via a common power line. Since it can be connected, the battery of this voltage detection circuit can also be used as a power source for other measurement circuits, especially in circuit meters and the like.

[Brief explanation of drawings]

Figure 1 is a circuit diagram of a voltage detection circuit according to the present invention.
FIG. 2 is a circuit diagram showing a modified embodiment of FIG. 1, and FIG. 3 is a circuit diagram of an embodiment in which this voltage detection circuit is applied to an indicator protection circuit of a circuit meter. In the figure, 1 and 2 are input terminals, 3 is a battery, 4 is a common power supply line, 5, 7, and 9 are transistors, and 8 is a display lamp.

Claims (1)

[Scope of utility model registration request] a pair of input terminals; first and second transistors, both of which are NPN type transistors, connected so that their respective base-emitters have opposite polarities with respect to the pair of input terminals;
a DC power supply connected to one of the input terminals via a common power supply line; a switch circuit including a third transistor operated by the outputs of the first and second transistors; A bipolar voltage detection circuit comprising: a detector connected to a DC power supply.