JPH0210905B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a signal detection circuit, and more particularly to an AC voltage signal detection circuit improved so that the detection level is not affected by temperature fluctuations of rectifying elements and DC voltage components of input signals.

FIG. 1 is a wiring diagram showing a conventional AC voltage signal detection circuit. An output signal 2 from an operational amplifier (hereinafter referred to as an operational amplifier) 1 for signal amplification is sent to a rectifier 3.
The signal is inputted to one input terminal 5 of the comparator 4 via. A resistor 6 and a capacitor 7 for smoothing AC signals are connected between the input terminal 5 and ground. A comparison voltage source 9 is connected between the other input terminal 8 of the comparator 4 and ground, and the detection signal 10 is taken out as the output signal of the comparator 4.

The output signal 2 is a voltage signal to be compared by the signal detection circuit, and is rectified into a half-wave voltage in the positive direction with respect to the signal ground potential by passing through the rectifying element 3.

Furthermore, this half-wave voltage is converted into a positive DC voltage with respect to the signal ground potential by a resistor 6 and a capacitor 7 that constitute a smoothing circuit. Output signal 2 and
The direct current voltage obtained as described above has a unique relationship according to the forward voltage of the rectifying element 3 and the rectifying efficiency determined by the time constant of the resistor 6 and capacitor 7 that constitute the smoothing circuit, so it is difficult to compare. By appropriately selecting the voltage value of the voltage source 9, it is possible to identify whether the output signal 2 is above or below a specific level and extract it as the detection signal 10.

However, in such a conventional circuit, since the forward voltage of the rectifying element 3 varies depending on the temperature, the level of the DC voltage to be applied to the input terminal 5 varies accordingly. Also, output voltage 2
The level of the DC voltage changes similarly when the voltage contains a DC voltage component due to the DC offset voltage of the operational amplifier 1. As a result, even if the AC signal voltages are the same, the detection levels of the detection signals 10 are not necessarily the same.

SUMMARY OF THE INVENTION An object of the present invention is to provide an improved AC voltage signal detection circuit that is not affected by the temperature characteristics of a rectifying element and does not cause fluctuations in detection level even due to DC voltage superimposed on an AC voltage signal. be.

In this invention, in order to prevent the forward voltage of the rectifying element from directly appearing in the DC voltage, another rectifying element having the same characteristics as the rectifying element is added, so that the DC voltage is equal to the forward voltage of these two rectifying elements. The above objective was achieved by making it appear as a difference between

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 2 is a wiring diagram showing the first embodiment of the present invention, in which a bipolar transistor is used as the rectifying element.

An output signal 12 from the operational amplifier 11 is connected to the base of a transistor 13, which is a first rectifier, and its emitter is connected via a resistor 14 to the emitter of a transistor 15, which is a second rectifier. The base of the transistor 15 is grounded, and the emitter terminal is connected to the negative power supply 1 through a resistor 16.
7 is connected. On the other hand two transistors 1
The collectors of 3 and 15 are commonly connected to the positive power supply 1.
8 is connected.

As a result, the transistor 13 and the resistor 14, and the transistor 15 and the resistor 16 respectively constitute an emitter follower circuit. The half-wave rectified voltage taken out from the emitter of the transistor 13 is converted into a DC voltage by a smoothing circuit composed of a resistor 20 and a capacitor 21, and is connected to one input terminal 22 of a comparator 23. On the other hand, the reference line 19 connected to the emitter of the transistor 15 is connected to the other input terminal 24 of the comparator 23 via a comparison voltage source 25. With such a connection, the comparator 23
A detection signal 26 is obtained as an output.

Next, the operation of this circuit will be explained.

The DC potential of the reference line 19 is the same as that of the transistor 1.
If the forward voltage between the base and emitter of No. 5 is V _F1 , it becomes -V _F1 , and it has a low output resistance.
On the other hand, at the emitter of the transistor 13, a voltage signal that is obtained by subtracting the forward voltage V _F2 between the base and emitter of the transistor 13 from the positive half-wave voltage signal with respect to the potential of the reference line 19 appears. Therefore, the voltage across the resistor 14 becomes υ+(V _F1 -V _F2 ), where υ is the half-wave voltage of the output signal 12 that is at a positive potential with respect to the reference line 19. Both ends of the resistor 14 are connected to the output of the emitter follower circuit, so it has a low driving resistance.
It can be regarded as a voltage source of υ+(V _F1 −V _F2 ). This voltage source of υ+(V _F1 −V _F2 ) is connected to the resistor 20 and capacitor 21 that constitute the smoothing circuit, so that the input terminal 22 of the comparator 23 has a potential in the positive direction with respect to the reference line 19. A DC voltage appears, and by appropriately selecting the magnitude of the comparison voltage source 25, it is possible to detect whether the AC voltage signal level is above or below a specific level as the output signal of the comparator 23.

FIG. 3 is a wiring diagram showing a second embodiment of the present invention. The same parts as in Fig. 2 are indicated by the same symbols,
Descriptions of parts that perform the same operations will be omitted. In the first embodiment, the base of the transistor 15 is grounded, but in this embodiment, a resistor 27 and a capacitor 28
The operational amplifier 11 is created by an RC circuit consisting of
The DC voltage component of the output signal 12 of is applied. Therefore, since the DC voltage components applied to the bases of the transistors 13 and 14 constituting the two emitter follower circuits are equal, this DC voltage component does not appear in the voltage appearing across the resistor 14.

Note that the time constant determined by the resistor 27 and the capacitor 28 needs to be set to a sufficiently large value compared to the AC voltage signal.

In the first embodiment, the base-emitter forward voltage of the transistor 13 does not directly appear as the differential input voltage of the comparator 23;
It appears as a difference between the base-emitter forward voltage of transistors 13 and 1 due to temperature fluctuations.
There is an advantage that the influence of fluctuations in the base-emitter forward voltage of No. 5 on the signal detection level can be made very small.

Furthermore, in the second embodiment, even if there is a DC voltage due to the DC offset voltage of the operational amplifier 11 in the output signal 12, the signal ground potential of the detection circuit is shifted by that DC voltage, so that the influence of the DC voltage is reduced. It has the advantage of not being accepted.

In each of the embodiments of the present invention, a single bipolar transistor is used as the rectifying element, but the present invention can be similarly applied to a case in which a diode or a rectifier is configured by combining a plurality of transistors. In order to further enhance the effects of the present invention, it is preferable to use a pair of rectifiers with similar characteristics. It can be realized more easily by configuring it as an integrated circuit. Furthermore, when configuring smoothing circuits and RC circuits, a large time constant can be obtained by using switched capacitor technology, which functions equivalently as a resistor.

According to the present invention, since the potential of the reference line is configured to be shifted in accordance with the DC voltage signal superimposed on the AC voltage signal and the forward voltage of the rectifier, it is not affected by temperature fluctuations or DC voltage components. A signal detection circuit can be realized.

[Brief explanation of drawings]

Fig. 1 is a wiring diagram showing a conventional AC voltage signal detection circuit, Fig. 2 is a wiring diagram showing a first embodiment of the present invention, and Fig. 3 is a wiring diagram showing a second embodiment. . 13, 15...transistor (rectifier), 19
... Reference line, 23 ... Comparator, 25 ... Comparison voltage source, 26 ... Detection signal.

Claims (1)

[Claims] 1. In a signal detection circuit that rectifies an AC voltage signal to a DC voltage via a rectifier and obtains a detection signal by comparing the DC voltage and a predetermined comparison voltage with a comparator, the comparator a signal line for transmitting the AC voltage signal to the comparator; a reference line for adding a specific fixed potential level to the comparison voltage; and a line connected to the signal line for rectifying the AC voltage signal. a second rectifier connected between a fixed level point that provides the specific fixed potential level and the reference line; a first input of the comparator, and the reference line is connected to a second input of the comparator via the predetermined comparison voltage. 2. The signal detection circuit according to claim 1, wherein the specific fixed potential level is a ground potential. 3. The signal detection circuit according to claim 1, wherein the specific fixed potential level is a level indicated by a DC voltage component superimposed on the AC voltage signal.