JPH08203677A - Power control circuit - Google Patents

Abstract

PURPOSE: To prevent the excessive supply of a power to a load in a steady state while the load is operable just after power feeding and provide ideal soft starting characteristic. CONSTITUTION: A resistor T1 is connected in parallel to a thermistor TH, a trigger element TG is laid in ON state (a TRIAC TR is in continued state) from just after the input of a power source AC, and an incandescent lamp LP is operated from just after the input of the power source AC. A resistor R2 is connected in series to the thermistor TH, the ON-period of the trigger element TG is shortened in the steady state, and a power is also prevented from being excessively supplied to the incandescent lamp LP. The time constant is regulated by a capacitor C2 and a resistor R3, and the ON-period of the trigger element TG is gently increased to provide ideal soft starting characteristic.

Description

Detailed Description of the Invention

[0001]

[Industrial application] This application is an incandescent light bulb soft-star.
The present invention relates to a power control circuit used for a power supply device, an inrush current prevention device, and the like.

[0002]

2. Description of the Related Art FIG. 3 is an electric circuit diagram showing a power control circuit previously filed by the applicant of the present application (Japanese Patent Application No. 5-57669).

TR is a triac (bidirectional thyristor) for controlling electric power, which is connected in series to an incandescent light bulb LP which is an object of electric power control. TH is a thermistor whose resistance decreases as temperature rises, C1 is a capacitor, and the thermistor TH and the capacitor C1 are connected in series at point P. The other end of the thermistor TH is connected to the triac terminal T2, and the other end of the capacitor C1 is connected to the triac terminal T1. TG is a trigger element (a diac, a trigger diode, etc.) for controlling the triac TR, one end of which is connected to the gate G of the triac TR, and the other end is at a connection point P between the thermistor TH and the capacitor C1. It is connected. AC is an AC power supply.

Next, the operation of the power control circuit shown in FIG. 3 will be described with reference to FIGS. 4 and 5.

FIG. 4 shows timing charts in a transient state in which a small amount of time has not elapsed after power-on, and FIG. 5 shows timing charts in a steady state in which a sufficient time has elapsed after power-on. VL is the voltage across the incandescent bulb LP, V
C1 indicates the voltage across the capacitor C1.

Immediately after turning on the power supply AC, the thermistor TH
Has a high resistance value, VC1 is lower than the switching voltage VB0 of the trigger element TG. Therefore, the triac TR remains off and the incandescent bulb LP does not light. However, although a slight amount of current flows through the thermistor TH, the temperature of the thermistor TH gradually increases due to self-heating over time, and its resistance value gradually decreases. As a result, the voltage of VC1 gradually rises, and finally a timing of exceeding the switching voltage VB0 of the trigger element TG occurs.

FIG. 4 shows a state in which the voltage of VC1 exceeds the switching voltage VB0 of the trigger element TG.
Since VC1> VB0 at time t1, the trigger element TG makes the triac TR conductive. Then, the conduction state is maintained until the polarities of the voltages at the terminals T1 and T2 of the triac TR are reversed (until time t2). Similarly, the triac TR becomes conductive between t3 and t4. In the upper timing chart of FIG. 4, the dotted line represents the waveform of the power supply AC, and the solid line represents the actual voltage VL applied to the incandescent lamp LP. In this state, since the triac TR has a short conduction period, the incandescent light bulb LP is dimly lit. Also, in the timing chart in the lower part of FIG. 4, the dotted line represents the voltage VC1 across the capacitor C1 assuming that one end of the trigger element TG is not connected to the point P. The applied voltages VAC and VC1 are out of phase by a time Δt determined by the resistance value of the thermistor TH and the capacitance value of the capacitor C1. As the time further elapses, the temperature of the thermistor TH further rises and its resistance value further lowers, so that the voltage VC0 further increases and the phase difference Δt between VAC and VC1 decreases, and the conduction period of the triac TR decreases. Becomes longer.

FIG. 5 shows that the thermistor T
The resistance value of H becomes sufficiently low, and the phase difference Δ between VAC and VC1
The state when t becomes almost 0 is shown. In this state, the conduction period of the triac TR becomes long, so that the incandescent lamp LP illuminates brightly.

As explained above, after the power is turned on, the resistance of the thermistor TH gradually decreases due to self-heating, and as a result, the conduction period of the triac TR can be gradually lengthened. It can be lit gradually brightly.

[0010]

However, in the above-mentioned conventional example, since the thermistor TH has a high resistance value immediately after the power source AC is turned on, VC1 is lower than the switching voltage VB0 of the trigger element TG, and the triac TR is It remains off for a period of time. Therefore, as shown in a range a in FIG. 6, there is a problem that the incandescent bulb LP does not light for a certain period after the power source AC is turned on.

Further, in the above-mentioned conventional example, since the resistance value of the thermistor TH is sufficiently low in a steady state in which a sufficient time has passed after the power is turned on, as shown in FIG. TG is turned on (triac TR is conductive). Therefore, incandescent light bulb LP
However, there is a problem that the illuminance becomes excessively large, and the electric power is excessively supplied to the incandescent light bulb LP.

Further, in the above-mentioned conventional example, the ON period of the trigger element TG (conduction period of the triac TR) is rapidly increased due to the temperature characteristic of the thermistor in which the resistance value sharply decreases as the temperature rises. Then, as shown in the range b of FIG. 6, the illuminance of the incandescent lamp LP rapidly increases. Therefore, there is a problem that it is difficult to obtain an ideal soft start characteristic that the brightness is gradually increased after lighting.

Although each of the above problems has been described by taking an incandescent light bulb as a load, similar problems generally occur with other loads such as a motor.

A first object of the invention according to the present application is to provide a power control circuit in which a load can operate immediately after the power is turned on.

A second object of the invention according to the present application is to provide a power control circuit capable of preventing an excessive supply of power to a load in a steady state in which a sufficient time has elapsed after power-on. Is.

A third object of the invention according to the present application is to provide a power control circuit capable of obtaining an ideal soft start characteristic.

[0017]

A power control circuit according to the present application includes a first circuit having a thermistor, a second circuit having a first capacitor and connected in series to the first circuit, and the second circuit. A triac connected in parallel to a series circuit composed of one circuit and the second circuit, and connected between a connection point between the first circuit and the second circuit and the gate of the triac. In a power control circuit having a trigger element, (1) the first circuit includes a thermistor and a first resistor connected in parallel with the thermistor,
(2) The first circuit is composed of a thermistor and a second resistor connected in series with the thermistor. (3) The power control circuit is further connected in parallel with the second circuit. A third circuit connected to a connection point between the first circuit and the second circuit and the trigger element, and the third circuit in series with the third circuit. Second connected
And a capacitor.

[0018]

1 is an electric circuit diagram showing a power control circuit according to an embodiment.

LP is an incandescent lamp as a load, and a capacitor C5 for preventing inrush current is connected to the incandescent lamp LP. AC is an AC power source that serves as a power source,
A fuse FU is connected to the AC power supply AC, and a capacitor C3, a varistor VR, and a resistor R5 are connected to prevent an inrush current.

TR is a triac, and a capacitor C4 and a resistor R4 are connected to the triac TR for preventing malfunction. TG is a trigger element (a diac, a trigger diode, etc.), and one end thereof is connected to the gate of the triac TR.

TH is a thermistor, and resistors R1 and R2 are connected to the thermistor TH. The resistor R1 is connected in parallel with the thermistor TH, and the resistor R1
1, the trigger element TG is activated immediately after the power source AC is turned on.
It is possible to turn on the incandescent lamp LP immediately after the power source AC is turned on by turning on (turning on the triac TR). The resistor R2 is connected in series with the thermistor TH, and the resistor R2 limits the current flowing through the thermistor TH so that the trigger element TG has an ON period (triac TR It is possible to prevent the illuminance of the incandescent lamp LP from becoming excessively large (the electric power is excessively supplied to the incandescent lamp LP).

A capacitor C2 and a resistor R3 are connected to the capacitor C1. The capacitor C2 and the resistor R3 are for adjusting the time constant, and are for increasing the brightness gently after the incandescent lamp LP is turned on to obtain an ideal soft start characteristic.

Next, the operation of the power control circuit shown in FIG. 1 will be described with reference to FIG. 2 (a diagram showing a change in illuminance of the incandescent lamp LP with the lapse of time after the power source AC is turned on). .

First, the operation in the period immediately after the power source AC is turned on (mainly in the range of a in FIG. 2) will be described. Immediately after the power supply AC is turned on, the resistance value of the thermistor TH is high, so that almost no current flows through the thermistor TH. However, at this time point, the resistance value of the resistor R1 is sufficiently smaller than the resistance value of the thermistor TH, so that the current flowing through the resistor R1 supplies the current to the trigger element TG through the resistor R3. Therefore, immediately after the power supply AC is turned on, the trigger element TG is turned on (the triac TR is in a conductive state), and the incandescent light bulb LP is lit darkly.

Next, the ON period of the trigger element TG (conduction period of the triac TR) gradually increases, and the illuminance of the incandescent lamp gradually increases (mainly b in FIG. 2).
The range of) will be described. The resistance value of the thermistor TH gradually decreases with time due to self-heating. The current supplied to the trigger element TG through the resistor R3 gradually becomes dominant as the current flowing through the thermistor TH. Here, the resistor R3 and the trigger element T
Since the capacitor C2 is connected to the connection point with G, there is a time delay due to the time constant determined by the capacitor C2 and the resistor R3. As a result, the ON period of the trigger element TG (conduction period of the triac TR) gradually increases, and the illuminance of the incandescent lamp LP also gently increases. That is,
It is possible to obtain ideal soft start characteristics. The capacitance value of the capacitor C2 and the resistance R3
It is also possible to obtain a desired soft start characteristic by appropriately adjusting the resistance value of.

Next, the ON period of the trigger element TG (conduction period of the triac TR) is saturated, and the illuminance of the incandescent lamp is in a saturated state (steady state) (mainly c in FIG. 2).
The operation within the range will be described. In the conventional example, as described above (see FIG. 5), the trigger element TG is in the ON state (the triac TR is in the conducting state) for almost the entire period of one AC cycle, so that the illuminance of the incandescent lamp LP is excessively large. May be. In this embodiment, the server
Since the resistance T2 is connected in series to the mister TH (the resistance value of the thermistor TH is smaller than the resistance value of the resistance T2 in the range c), the current supplied to the trigger element TG is limited accordingly. Accordingly, the ON period of the trigger element TG (conduction period of the triac TR) becomes shorter than that in the case where the resistor T2 is not provided. Therefore, by appropriately selecting the resistance value of the resistor T2, the illuminance of the incandescent lamp LP can be set to a desired value.

Although the incandescent lamp has been described as an example of the load in the above embodiment, it can be similarly applied to other loads such as a motor.

[0028]

According to the invention of claim 1 of the present application,
The first circuit, in which a resistor is connected in parallel to the thermistor, allows the trigger element to be turned on (triac is in a conductive state) immediately after the power is turned on, and the load can be operated immediately after the power is turned on. Becomes

According to the second aspect of the present invention, by the first circuit in which the thermistor is connected in series with the resistor, the ON period of the trigger element (triac It is possible to shorten the conduction period) and prevent excessive supply of electric power to the load.

According to the invention of claim 3 of the present application, since the time constant can be adjusted by the third circuit including the capacitor and the resistor, the ON period of the trigger element (triac conduction period) is moderate. It is possible to increase the number, and it is possible to obtain an ideal soft start characteristic.

[Brief description of drawings]

FIG. 1 is an electric circuit diagram showing a power control circuit according to an embodiment.

FIG. 2 is a diagram for explaining the operation of FIG.

FIG. 3 is an electric circuit diagram showing a conventional example.

FIG. 4 is a diagram for explaining the operation of FIG.

FIG. 5 is a diagram for explaining the operation of FIG.

FIG. 6 is a diagram for explaining the operation of FIG.

[Explanation of symbols]

 TR ... Triac TG ... Trigger element TH ... Thermistor (first circuit) R1 ... First resistance (first circuit) R2 ... Second resistance (first circuit) C1 ... First capacitor (first) 2 circuits) C2: second capacitor (third circuit) R3: third resistor (third circuit)

Claims (3)

[Claims] 1. A first circuit having a thermistor, a second circuit having a first capacitor connected in series to the first circuit, a first circuit and a second circuit. A power control circuit having a triac connected in parallel to a series circuit, and a trigger element connected between a connection point between the first circuit and the second circuit and a gate of the triac, A power control circuit, wherein one circuit is composed of a thermistor and a first resistor connected in parallel to the thermistor. 2. A first circuit having a thermistor, a second circuit having a first capacitor connected in series to the first circuit, a first circuit and a second circuit. A power control circuit having a triac connected in parallel to a series circuit, and a trigger element connected between a connection point between the first circuit and the second circuit and a gate of the triac, A power control circuit characterized in that one circuit is composed of a thermistor and a second resistor connected in series to the thermistor. 3. A first circuit having a thermistor, a second circuit having a first capacitor connected in series to the first circuit, a first circuit and a second circuit. A power control circuit having a triac connected in parallel to a series circuit, a trigger element connected between a connection point between the first circuit and the second circuit, and a gate of the triac, The control circuit further includes a third circuit connected in parallel to the second circuit, the third circuit being connected between a connection point between the first circuit and the second circuit and the trigger element. A power control circuit having a third resistor and a second capacitor connected in series to the third resistor.