JPS62157922A - Phase control circuit - Google Patents

Abstract

PURPOSE:To prevent the inductive load of a transformer, etc., from burning by constituting a phase controller so that a thyristor is not turned on for a specific time in a phase deviation section between the voltage and current of a power source. CONSTITUTION:The phase controller consists of the AC power source 1, transformer (inductive load) T2, respective diodes D1-D4, resistances R0-R10, capacitors C1-C3, an operational amplifier Q1, and IC Q2, a PNP type transistor (TR) Q3, and an LED 7 so that the thyristor is not turned on for the specific time in the phase deviation section between the source voltage and current. Thus, the thyristor is not turned on for the specific time after the zero crossing of the voltage is detected, so an overcurrent is prevented from flowing through the inductive load, which is protected from burning, etc.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a power control circuit using bidirectional transistors, and in particular to a phase control circuit thereof. 3-terminal thyristor) is conventionally
For example, this type of power control circuit is used in a power control circuit for controlling the brightness of a lamp, etc. FIG. 2 shows an example of this type of power control circuit. 1 is an AC power supply, 2 is a lamp, and 3 is a triac. Lamp 2 and triac 3 are connected in series to power supply 1, and resistor 4 and diode bridge 5
The phototransistor 6 is configured to turn on when it receives light from a light emitting diode (LED) 7. As in this example, the load of the triac 3 is In the case of a resistive load like lamp 2, as shown in the voltage/current waveform diagram in Figure 3, there is no phase shift (time shift) between the voltage waveform V and the current waveform I, and the voltage/current waveform is displayed normally. [Problem to be Solved by the Invention] However, as shown in the second example of the power control circuit shown in FIG. In the case of a static load (components that are the same or equivalent to those in Figure 2 are indicated by the same symbols), the current waveform 1 is higher than the voltage waveform V, as shown in the voltage/current waveform diagram of this second example in Figure 5. While the phase is delayed, the triax 8 itself is
It is an element that turns off by itself when the current reaches zero. For an element with such characteristics, when firing a triac based on the voltage waveform, the element turns off before the current reaches zero. If the transformer 8 arcs, an excessive current flows through the transformer 8, generating heat, and there is a possibility of damage due to overheating.

The present invention has been made in view of the problems of the conventional methods as described above, and prevents the possibility of burnout of inductive loads such as transformers even in ignition circuits based on the component waveform of the power supply. [Means for solving the problem] Therefore, in the present invention, when the load of a power control device using a thyristor is an inductive load, the power supply city 7
The above object is achieved by configuring the phase 'TljlJ control device so as not to fire the thyristor during the phase difference period between voltage and current and the required time.

[Effect]

With the above configuration, the thyristor is prevented from firing for a predetermined period of time after the zero crossing of the voltage is detected, so that excessive current is prevented from flowing through the inductive load, and the load is protected from burnout and the like.

〔Example〕

The present invention will be explained below based on examples. In Figure 1,
0 showing one embodiment of the phase control circuit according to the present invention (Structure) 1 is an AC power supply, T2 is a transformer, and Dl.

C2, . . . , C4 are diodes, each forming a diode bridge D. R.O.

R1, RIM: each resistance, CI, C2, C3 (d each = +
In addition, QL is an operational amplifier that functions as a comparator, and C2 is an IC for configuring a timer. For example, HA17555 (manufactured by Hitachi), NE555 (
OQ3 (manufactured by Signetakes) is a PNP type transistor, and 1 is an LED.

(motion) In FIG. 6, each position shown in FIG.

A timing chart of each signal waveform in (2) is shown, and the operation will be explained in comparison with FIGS. 1 and 4.

In Fig. 1, the voltage of the AC power ill is the transformer T2
A waveform as shown in FIG. This waveform is used by the operational amplifier Q1 to form an AC zero-cross detection signal as the waveform shown in (2). This signal is input to the timer 555 to form a one-shot waveform as shown in FIG. This shot time width T11 is determined by the time constant formed by the resistor R7 and capacitor C2 in FIG. During this period, the output terminal of the timer 555 is at a high V level, so the transistor Q3 is turned off and the LEI)7 does not emit light. Therefore, during this period, the triac 3 in FIG. 4 does not fire.

Next, when the timing of time T1 ends, timer 5
The output of 55 becomes low level, transistor Q3 becomes conductive, and as shown in FIG. 6 (5), current also flows through LEl) 7, the LED emits light, and the phototransistor 6 of FIG. 4 becomes conductive. The triac 6 as shown in Figure 6 (O)
fires.

As described above, since the timer is controlled so as not to fire during the protection time T+, even if the current is turned off after the phase shift time To than the voltage, the next firing time (T1
Since there is a margin of If it is a load, there is no phase difference between voltage/current (
(Fig. 3), the corresponding waveform of Fig. 6 (■) according to this embodiment is:
0 as shown in FIG. 7 [Effects of the Invention] As described above based on the embodiments, according to the present invention, when the load of this type of power control circuit is an inductive load; However, since the thyristor does not fire for a predetermined period of time after the voltage zero cross is detected, there is no longer any risk of damage to the load due to excessive current.

4. Detailed explanation of the invention FIG. 1 shows a second embodiment of the phase control circuit according to the present invention.
2 and 4 respectively, and FIG. 3 and FIG.
Figure 6 is a timing chart of the signal waveforms of each part in Figure 1, and Figure 7 is an example of the voltage/current waveforms of this implementation tlJ. ... AC & power supply 2 ... Lamp (resistive load) 3 ...
...Triac (bidirectional three-terminal triac) 6...Phototransistor 7...
...LED 8...Transformer (inductive load) To
...Voltage/current phase shift time TI ...
・・Protection time Fig. 2 Voltage/current waveform diagram of Fig. 2 Voltage/current waveform diagram

Claims (1)

[Claims] In the phase control circuit using bidirectional transistors, when the load is inductive, the bidirectional transistors are configured not to fire for a predetermined period of time during a phase shift period between the power supply voltage and current. Phase control circuit.