JPS6130774A - Zero volt detection circuit - Google Patents

Abstract

PURPOSE:To reduce the pulse width and variations therein, by arranging a detection circuit to be made up of two light emitting diodes connected oppositely in parallel and two phototransistors optically coupled separately thereto to minimize deviation in the pulse exchange threshold and the phase. CONSTITUTION:A zero volt detecting circuit is made up of two light emitting diodes 20 and 21 connected oppositely in parallel to an AC power source 1, two phototransistors 22 and 23 optically coupled separately thereto and resistances 24 and 25. The threshold 1D (about 0.7V) is set for starting the energization of the light emitting diodes 20 and 21. Then, when the AC power source 1 is within + or -1D, the light emitting diodes 20 and 21 both fail to energized and the phototransistors 22 and 23 are turned OFF. As a result, the input I2 of a microcomputer 7 moves to Hi and also is given Hi near the AC power source zero volt. Otherwise, the zero volt pulse of Lo is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a zero port detection circuit that detects zero voltage/L/ ) of an alternating current power source and supplies a periodic signal to a circuit that operates periodically on the alternating current power source.

Conventional configurations and their problems In recent years, microcomputers (hereinafter referred to as microcomputers) have been rapidly applied to electrical equipment. Under these circumstances, demands for peripheral circuit technology for microcontrollers are also increasing. In particular, for control devices that control loads operated by AC power supplies in synchronization with the AC power supply, and devices with built-in timers that operate in synchronization with the AC power supply, it is important to know how to extract the synchronization signal of the AC power supply. It becomes a problem. Generally, in order to isolate the AC power supply and the control circuit, the AC synchronization signal is obtained by using a transformer and a Prinzi diode for full-wave rectification and a Schmitt circuit.

Hereinafter, the conventional zero void detection circuit as described above will be explained with reference to the drawings. FIG. 1 shows a conventional heater control circuit including a zero port detection circuit.

1 is an AC power supply, 2 is a transformer, 3 is a diode bridge circuit, and 4 is a regulator, which together with capacitors 5 and 6 constitute a power supply circuit of the control circuit. The Schmint circuit surrounded by the dotted line, the transformer 2, and the diode bridge circuit 3 constitute a zero-volt detection circuit, which supplies a zero-volt pulse synchronized with the AC power source to the input I2 of the microcomputer 7.

Reference numeral 8 denotes a comparator, which receives a reference potential obtained from a circuit constituted by a resistor 9 and 10, and a temperature signal obtained from a sensor 12 that detects the temperature of the heated object heated by the heater 11 and a temperature setting volume 13. Compare and send the results to microcontroller 7
is sent to input 11 of

The microcomputer 7 outputs a pulse to ol depending on the states of the inputs 11 and I2, and pulses the bidirectional switch element 16 via the buffer 14 and transformer 15.

FIG. 2 is a flowchart of a program built into the microcomputer 7 shown in FIG.

The operation of the conventional circuit configured as described above will be described below.

First, an AC voltage is transformed by a transformer 2, full-wave rectified by a diode bridge circuit 3, and a constant DC voltage is created by a regulator 4 and a capacitor 5.6.

A full-wave rectified waveform generated by the transformer 2 and the diode bridge circuit 3 is applied to the base of the transistor 17, and the waveform is shaped by VBE (base-emitter voltage) to generate a zero-volt pulse. Diode 18 prevents the full wave rectified waveform from being smoothed by blocking backflow from capacitor 5. However, in the vicinity where the voltage of the AC power supply 1 is 0 points/V), the voltage necessary to turn on the transistor 17 (approximately 0.7V) is not generated at the base of the transistor 17, so when the transistor 17 is turned off, the microcomputer 7 Hi is applied to the input I2, but when the voltage of the AC power supply 1 is not near O port, the transistor 17 is turned on, and the input I2 of the microcomputer 7 is turned on.
is applied. That is, a pulse synchronized with the zero point /&) of the AC power supply 1 is applied to the microcomputer 70 input I2.

Furthermore, regarding the temperature detection circuit which is composed of the temperature sensor 12, temperature setting volume 13, comparator 8, etc., the temperature of the heated object is first detected by the temperature sensor 12, and for example, when the temperature of the heated object becomes low, If the resistance value of the temperature sensor 12 is large and the potential of the inverting input (-input terminal) of the comparator 8 is lower than the reference potential obtained by the resistor 9.10, the output of the comparator 8 will be Becomes Hi. On the other hand, when the temperature of the object to be heated increases, the resistance value of the temperature selector 12 decreases, the potential of the inverting input of the comparator 8 increases, and the output of the comparator 8 becomes LO. Tip 9: When the temperature of the heated object is higher than the set temperature, the output of the comparator 8 becomes Hi when LO1 is lower. When the resistance value of the temperature setting volume 13 is decreased, the potential of the inverting input of the comparator 8 decreases, and the temperature sensor 12
Unless the resistance becomes smaller, it will not become higher than the reference potential obtained by the resistor 9.10, and therefore the temperature of the heated object will increase, causing the output of the comparator 8 to invert from Hi to LO1Lo to Hi. When the resistance value of the temperature setting volume 13 is decreased, the set temperature increases, and when it is increased, the set temperature decreases.

Here, the operation of the microcomputer 7 will be explained with reference to FIG. First, check input 11 with Sl.

(Lo and 0 and Hi and 1 correspond), it is determined that the temperature of the heated object is higher than the set temperature, and the output is 01 in S2.
Set to LO. When input 11 is Hl in S1, it is determined that the temperature of the heated object is lower than the set temperature, and first, in S3, input I
2, wait for the pulse to enter, S4,
At S5 and S6, a pulse of 700 μSea is output from the output Q1.

Returning to FIG. 1, the pulse output from 01 of the microcomputer 7 is transmitted via the buffer 14 to the gate circuit of the bidirectional switching element 16 by the transformer 15, and the bidirectional switching element 16 is pulse-ignited. Therefore, the heater 11 is controlled so that the heated object reaches the temperature set by the temperature setting volume 13.

However, in the above configuration, since the transformer 2 is shared with the DC constant voltage power supply circuit, the voltage is often relatively low, and the pulse width of the obtained zero volt pulse is also wide. Further, when the control circuit operates, the circuit current also fluctuates, and the secondary voltage fluctuates due to the regulation characteristics of the transformer 2, which affects the pulse width of the zero volt pulse.

In a microcomputer program, the pulse phase and pulse width to be output are generally determined based on the leading edge or trailing edge of the zero-volt pulse. In this embodiment, the tip of the zero volt pulse is used as a reference. However, the true AC power zero volt is almost at the center of the zero volt pulse, and if the pulse width is wide, the zero volt of the AC power source of the tool, the zero volt obtained from the zero volt pulse, and the tip of the zero volt pulse are only half the pulse width. If the pulse width changes further, the output o of the microcomputer 7 will change by that amount.
Unless the width of the pulse output from 1 is also widened, the subsequent effective pulse width cannot be obtained from the true zero volt required to fire the bidirectional switch element 16. For example, to fire a bidirectional switch element, an effective pulse width of 300μ
Suppose that Sea is necessary. The secondary voltage of transformer 2 is 12V~
When it fluctuates up to 15V, the parnu width halo of zero po μdopa/L'nu is 130 μSec of 60 μsec to 530 μSec.
It has a deviation width of c. As in this conventional example, when the tip of the zero volt pulse is used as a reference, it takes 330 μSec from the tip of the zero volt pulse to the true zero volt, and then 300 μSec of the effective pulse width, which means a total of 630 μ86C%, or twice the pulse width. It becomes necessary.

This means that the pulse current for igniting the bidirectional Nuinochi element 16 is doubled, which is very disadvantageous in terms of the design of the DC constant voltage power supply. This is particularly disadvantageous when multiple loads are controlled by a microcomputer. Note that if the firing pulse is issued after the zero volt PALNU, the pulse width can be narrowed, but the bidirectional Nuinoch element 16 will be fired after the true zero volt, and zero volt switching will not be possible. This is disadvantageous in terms of noise generation.

FIG. 3 shows how the pulse width of the Schizeroport pulse changes due to fluctuations in the secondary voltage of the transformer 2. (1)
is the secondary waveform of transformer 2, and two waveforms with different voltages are shown by a solid line and a broken line. It can be seen that (2) is the output waveform of diode bridge circuit 3, (3) is the zero volt pulse when the voltage is high (solid line), and (4) is the zero volt parnu width when the voltage is low (broken line). .

Next, FIG. 4 shows another conventional example in which a dedicated transformer 19 and a diode bridge circuit 20 are provided in the zero volt detection circuit. Note that the same components as in FIG. 1 are denoted by the same numbers. In this conventional example, since a dedicated transformer 19 is provided, the secondary voltage can also be raised, the secondary voltage does not change even if the circuit current of the control circuit changes, and the pulse width is appropriately narrow (50 μSea) as a zero volt pulse. degree) A product with little variation in parnu width can be obtained. However, transformer 1
The influence of a phase shift occurring between the primary and secondary components of 9 cannot be avoided. Furthermore, there are many disadvantages in terms of the number of parts, mounting, and cost.

Purpose of the Invention In view of the above-mentioned problems, the present invention provides a pulse width that is appropriately narrow,
Further, it is an object to easily provide a zero volt detection circuit that can generate a zero volt pulse with little pulse width variation.

Arrangement of the Invention To achieve this objective, the zero volt detection circuit of the present invention comprises two light emitting diodes connected in parallel in opposite directions, two phototransistors optically coupled to each, and a load resistor. It is configured. Light-emitting diodes connected in opposite directions to the AC power supply through load resistors detect zero-holt, turn on and off the optically coupled phototransistors, and connect the two phototransistors in parallel to generate a zero-volt pulse. get a

In the conventional example, including the diode bridge circuit, the Parnu conversion threshold was 3D (about 2.1V), but according to the present invention, it can be reduced to 1 diode (about 0.7V), and the pulse width can be reduced. This is very advantageous in narrowing the area. or,
Since optical coupling is used, the input and output are electrically isolated, and there is no phase shift as in the conventional example, so the pulse width is narrow, there is little fluctuation, and there is no phase shift. No zero volt pulse can be easily obtained.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 5 is a circuit diagram of an embodiment of the present invention, in which the same components as in the conventional example are designated by the same numbers. Further, the program built into the microcomputer 7 is the same as that shown in FIG.

The part surrounded by dotted line A in Figure 5 is this zero volt detection circuit,
It consists of two light emitting diodes, two phototransistors, and two photocouplers. The operation of the zero voltage/V) detection circuit configured as above will be explained below. First, the light emitting diode 20 is forwardly connected to I
When a voltage of D (approximately 0.7V) or more is applied, current begins to flow, and the phototransistor 22 also turns on.
Then, a Lo signal is input to input 2 of the microcomputer 7. Also, when a voltage higher than ID (approximately 0.7 V) is applied to the light emitting diode 21 in the forward direction, current begins to flow, and accordingly the phototransistor 23 turns on, and a Lo signal is also input to the input 2 of the microcomputer 7. . light emitting diode 20.2
1 is connected in the opposite direction to AC power supply 1, so when AC power supply 1 is within ±ID (approximately ±0.7 V),
Since both the light emitting diodes 20 and 21 are not energized and both the phototransistors 22 and 23 are turned off, the input I2 of the microcomputer 7 becomes Hi.

Therefore, a zero volt pulse is obtained that is Hi near zero port of the AC power supply and LO at other times.

As described above, according to this embodiment, since the threshold value at which the light emitting diode starts energizing is ID (approximately 0.7 V), a zero volt pulse with a narrow pulseless width can be obtained.

In addition, since the input is directly from the AC power supply, the pulse width does not fluctuate due to the influence of the control circuit as in the first conventional example, and the microcontroller can obtain the highest quality zero volt pulse. I can do it. Furthermore, if a photocoupler or the like is used as in this embodiment, the number of parts can be reduced and the circuit can be constructed with a simple structure.Compared to the second conventional example, it can be realized in a smaller volume, which has great advantages in terms of packaging. Due to the nature of semiconductor components, it can be said that there are great cost advantages, including future prospects.

If you want to widen the width of the zero-volt pulse due to microcomputer software, you can easily do so by inserting a constant voltage element such as a diode in series with the light emitting diode.

Also, if you connect this zero voltage/l/) detection circuit to both ends of the switch or load of the AC power supply, the switch will turn off.
It is possible to detect whether the load is turned on or off, or whether the load is energized or not.

Effects of the Invention As described above, the present invention can obtain the following effects by connecting two light emitting diodes to an AC power source in parallel with their polarities reversed, and turning on and off the optically coupled phototransistor. .

(1) A zero volt pulse with a narrow pulse width can be obtained, and the difference between the edge of the pulse and the true zero volt timing is small.

(2) The pulse width of the zero volt pulse is less affected by the control circuit.

0) The circuit can be configured simply, which has great advantages in terms of implementation.

(4) Since it is a semiconductor component, we can expect great cost benefits in the future.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of the first conventional example, Fig. 2 is a flowchart of a program built into the microcomputer used in the conventional example and the embodiment of the present invention, and Fig. 3 is a zero port detection circuit of the conventional example. This is a time chart of each part of the waveform, showing the relationship between the secondary voltage fluctuation of the transformer and the pulse peak. Fourth
The figure is a circuit diagram of a second conventional example. 1 line between j and f light - actual loss side 10 supply town ゛be 1...°... AC power supply, 2...
・Transformer, 3...Diode bridge circuit,
4...Regulator, 5, 6...Capacitor, 20, 21...Light emitting diode, 22,
23. River... phototransistor, 24, 25...
·resistance. Name of agent: Patent attorney Toshio Nakao and 1 other person 2nd
Figure 3

Claims (1)

[Claims] a first light emitting diode and a second light emitting diode connected in parallel with the first light emitting diode with opposite polarity;
A first resistor connected in series to the first light emitting diode and the second light emitting diode is connected in parallel to the detected part, and a first resistor is optically coupled to the first light emitting diode. a second phototransistor optically coupled to the second light emitting diode; a second resistor connected in series to the first phototransistor and the second phototransistor; A zero volt detection circuit comprised of a DC power source that supplies power to a first phototransistor, a second phototransistor, and a second resistor.