JPH0649110Y2 - Zero volt signal generation circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a zero volt signal generating circuit.

(B) Conventional technology Conventionally, as a method for controlling an AC load, a switching element such as an SCR or a triac is used and ON / OFF control is performed by a phase control circuit. At this time, if switching control is performed within a half cycle of the AC signal, high-frequency noise is generated when the switching element is turned on and off, which causes noise interference to the radio, etc.Therefore, in general, zero volt control for switching control at the zero point of the AC signal is used. It has been adopted (see, for example, JP-A-52-147756 [58H172]).

(C) Problems to be solved by the invention However, as shown in FIG. 3, the zero volt signal generated by the conventional zero volt signal generating circuit is a pulse having a predetermined width centered on the zero point of the AC signal. Since it is a signal and switching control is performed at a position slightly deviated from the zero point, there is a problem that noise generation cannot be completely prevented.

(D) Means for solving the problem The present invention is a clamp means for clamping an alternating current signal to produce a square wave signal, and an amplifier for amplifying the clamped signal,
It is configured by a differentiating circuit that differentiates the output of the amplifier, a comparator that compares the differential output with the ground level, and a logical sum circuit that takes the logical sum of the comparator outputs.

(E) Operation The present invention, which is configured as described above, can generate a rising zero volt signal at the zero point of an alternating current signal, can perfectly match the switching time of the switching element with the zero point of the alternating current signal, and It is possible to reliably prevent the occurrence of.

(F) Embodiment An embodiment of the present invention will be described below with reference to the drawings.

(1) is a power supply transformer to which an AC power supply is connected, and outputs an AC signal of a predetermined voltage from the secondary side. (2) is a clamp circuit composed of resistors (3) and (4) and diodes (5) and (6) connected to the secondary side of the power transformer (1) and clamps an AC signal to output a square wave signal. (7) (8)
Square wave signal is input to the positive input terminal and the negative input terminal, respectively, and the other negative input terminal and the positive input terminal are grounded,
The first and second operational amplifiers functioning as amplifiers, and the amplified signal obtained by inverting the output of the first operational amplifier (7) is output from the second operational amplifier (8). (9) and (10) are differentiating circuits that differentiate the outputs of the operational amplifiers (7) and (8), and the third and fourth operational amplifiers (11) whose differential outputs act as comparators.
It is supplied to (12) and compared with the ground level. (13)
(14) and (15) are a diode and a resistor that form an OR circuit (16). The above-mentioned four operational amplifiers (7) (8)
(11) and (12) are integrated and composed of one IC, ± 5V
It is powered by.

Next, the operation of the present invention having such a configuration will be described with reference to the waveform chart of FIG.

First, when an AC signal as shown in FIG. 2 (a) is supplied, about 0.7 as shown in FIG. 2 (b) based on the forward voltage of the diodes (5) and (6) of the clamp circuit (2). It is clamped to the voltage of V, converted into a square wave signal, and supplied to the first and second operational amplifiers (7) and (8). Then, the square wave signal inputted by the operational amplifiers (7) and (8) is amplified. However, since the power supply voltage of the operational amplifiers (7) and (8) is ± 5 V, and the amplifier operates as an infinite amplifier, From the operational amplifiers (7) and (8), see FIG. 2 (c) and (f).
The amplified signal output shown in is obtained. The operational amplifier (8) outputs an amplified signal obtained by inverting the input square wave signal. Then, the output signals of the operational amplifiers (7) and (8) are
Each is differentiated by the differentiating circuit (9) (10), but since the differentiating circuit (9) (10) is pulled down to the -5V power supply,
A differential waveform output as shown in FIGS. 2 (d) and (g) centered on 5 V is obtained. This differential waveform output is supplied to the third and fourth operational amplifiers (11) and (12) which function as comparators,
By comparing with the ground level, the portion of the differential waveform above the grad level is output, and FIG. 2 (e) (h)
Opamp as pulse signal as shown in (11) (12)
Will be output. The outputs of the operational amplifiers (11) and (12) are supplied to the logical sum circuit (16), but are pulled down to the ground level by the resistor (15).
As shown in, an output pulse lower than the forward voltage of the diodes (13) and (14) is generated. This output pulse is a zero volt pulse signal that rises at the zero point of the input AC signal.By supplying this pulse signal to a switching element (not shown), the AC load can be reliably turned on and off at the zero point.
It can be controlled.

(G) Effect of the Invention As described above, the zero volt signal generating circuit of the present invention can generate a zero volt signal rising at the zero point of an AC signal by a simple circuit configuration such as a clamp circuit, an operational amplifier and a differentiating circuit. Since the switching control is performed when the AC signal supplied to the switching element becomes completely zero during the ON / OFF control of the AC load, it is possible to completely prevent the generation of noise accompanying the switching.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of a zero volt signal generating circuit of the present invention, FIG. 2 is a waveform diagram of an essential part of FIG. 1, and FIG. 3 is a waveform diagram showing a conventional zero volt signal. (2) ... Clamp circuit, (7) (8) (11) (12) ... Operational amplifier, (9) (10) ... Differentiation circuit, (16) ... OR circuit.

Claims (1)

[Scope of utility model registration request] 1. A clamp circuit which clamps an AC signal and outputs a square wave, a first operational amplifier whose positive input is supplied with the output of the clamp circuit and whose negative input is grounded, and a negative input which is connected to the output of the clamp circuit. A second operational amplifier which is supplied and whose positive input is grounded; a differential circuit which differentiates the outputs of the first and second operational amplifiers; and third and fourth operational amplifiers which compare the outputs of the differential circuit with the ground level, respectively. A zero-volt signal generation circuit comprising a logical sum circuit that outputs a logical sum of the outputs of the third and fourth operational amplifiers.