JPH0687432B2 - Power control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a light control device for adjusting the amount of light of a lighting fixture or the like.

(B) Conventional Technology For example, a power control device that controls power steplessly, such as a light amount control of a lighting fixture, has conventionally been composed of a circuit that controls a phase angle of a switching element. The most typical circuit of such a conventional power control device is to configure a CR phase adjustment circuit with a variable resistor and a capacitor, and to provide a trigger element between the gate of the thyristor (triac etc.) and the phase control circuit. The resistance value controls the phase at which the trigger element breaks over, thereby determining the conduction angle of the thyristor. As a result, the voltage shown in FIG. 3 is applied to the load such as the lamp.

(C) Problem to be Solved by the Invention However, in the conventional dimmer that controls the conduction angle of the thyristor in phase, the voltage waveform applied to the load is a non-continuous signal for each half cycle of the commercial AC power supply voltage waveform. Since there is a conduction angle, it has a characteristic that relatively low-order harmonic components are superposed on the power system at a high content rate. For this reason, there has been a problem of increasing the power loss in the transformer and the phase adjusting circuit connected to the power system.

The above-mentioned problems are becoming more serious due to the heavy use of power control devices using phase control in recent years, and standards and regulations have been proposed for limiting the content rate of harmonic components superposed on a power system by devices.

In the conventional power control device using phase control, hysteresis occurs due to the difference in the initial condition of the phase adjustment capacitor, the characteristics change due to the difference in the commercial AC power supply frequency, and the conduction angle also changes due to the fluctuation of the power supply voltage. There was also a problem that the supplied power greatly fluctuated.

An object of the present invention is to provide a power control device that reduces the influence of harmonics on a power system and solves the above problems.

(D) Means for Solving the Problems A power control device according to the present invention is a device that is connected in series to a load that uses a commercial AC power source as a power source, and a diode bridge that rectifies a current flowing between input terminals, Between the output of the diode bridge, a smoothing circuit that smoothes the output of this diode bridge to generate a DC voltage, an astable multivibrator that oscillates at high frequency using the DC voltage as a power supply, and includes a variable resistor for controlling the duty ratio. The switching transistor is connected and is turned on / off by the output of the astable multivibrator.

(E) Function In the light control device of the present invention, the diode bridge rectifies the voltage and current applied to the load, and the smoothing circuit smooths the output to generate a DC voltage. The non-stable multivibrator operates by using the DC voltage as a power source and generates a pulse having a duty ratio determined by the state of the variable resistance. Then, the switching transistor is turned on / off by the output of the astable multivibrator so as to connect / disconnect between the output terminals of the diode bridge. Since the repetition cycle of the unstable multivibrator is sufficiently shorter than the cycle of the commercial alternating-current power supply, the current flowing through the load is interrupted multiple times within one cycle of the alternating-current power supply according to the rectangular wave signal generated by the unstable multivibrator. The load supply power is determined by the on-duty ratio of the switching transistor, and the load supply power can be adjusted by adjusting the duty ratio control variable resistor of the unstable multivibrator.

In this way, the load supply current is not interrupted continuously during the half cycle of the commercial AC power supply voltage, and the load supply current is interrupted at a constant duty ratio over the entire cycle. The content of harmonic components is low. Of course, the frequency component corresponding to the on / off cycle of the switching transistor occurs as a high-order harmonic component, but this harmonic component is attenuated by the inductance component of the power system and can be easily filtered by a coil with a relatively low inductance. The power system and other devices connected to the power system are not adversely affected.

(F) Embodiment FIG. 1 shows a circuit of a light control device according to an embodiment of the present invention. In FIG. 1, L is a lamp as a load, and the commercial AC power supply AC is also connected to the lamp L via terminals T1 and T2.
The circuit connected in series with is a dimming circuit. Capacitor C
3, the choke coil CH, the resistor R5, and the capacitor C4 form a filter circuit that removes harmonic components (particularly, the oscillation frequency of an unstable multivibrator described later). D3, D4,
D5 and D6 form a diode bridge that rectifies the current flowing between the input terminals T1 and T2 via the filter. Q5 is a FET that connects / disconnects between the output terminals of the diode bridge
Is a switching transistor. D7 is a backflow prevention diode. Resistor R6, capacitor C5, resistor R7,
Transistor Q6, Zener diode ZD, capacitor C6
Constitutes a DC voltage stabilizing circuit. Transistor Q1, Q
2. The capacitors C1 and C2, the resistors R1 and R2, the variable resistor VR, the transistors Q3 and Q4, the resistors R3 and R4, and the diodes D1 and D2 form an astable multivibrator (hereinafter simply referred to as a multivibrator). The output signal of this multivibrator is given to the gate of the switching transistor Q5 via the resistor R8 and the speed-up capacitor C7. The diode D8 keeps the 0 level of the gate of the switching transistor Q5 at the ground potential. Resistors R9, R10, Capacitors C8, C9
And the trigger element SBS constitutes a trigger circuit for giving a trica pulse to the multivibrator.

The operation of the circuit shown in FIG. 1 is as follows. First, when the commercial AC power supply AC is supplied, a rectified voltage appears at the outputs of the diode bridges D3 to D6, and the voltage is smoothed by R6 and C5. And Q6 outputs the stabilized DC voltage which is almost equal to the Zener voltage of ZD + the base-emitter voltage of Q6.
C6 smoothes that voltage. R6, C5 and C6 correspond to the smoothing circuit according to the present invention.

When the power supply voltage is applied to the multivibrator and the trigger circuit in this manner, a charging current flows through C9 via R9 and a charging current flows through C9 through R10. When the voltage applied to the trigger element SBS rises with the charging of C9 and the voltage exceeds the breakover voltage, the path of C8 → SBS → R10
Negative trigger pulse is applied to Q2. This turns off Q2. After SBS breakover, SBS remains on. When Q2 turns off, the base potential of Q4 rises, Q4 turns on, and the base current flows to Q1 through the path of Q4 → C2 → Q1 and Q1 turns on. Then, the charging current flows to C1 along the route of VR → R1 → C1 → D1 → Q1. At this time, the gate potential of the switching transistor Q5 becomes a low potential almost equal to the forward voltage drop of D1.
Q5 turns off. As a result, the load current to the lamp L is cut off.

After that, the base voltage of Q2 rises due to the increase of the charging voltage of C1.
When V _BE is exceeded, Q2 turns on and the charging current flows to C2 through the route of VR → R2 → C2 → D2 → Q2. At the same time, the base potential of Q1 becomes negative and Q1 is turned off. This raises the base potential of Q3 and turns on Q3. Therefore, the gate potential of Q5 becomes high via Q3 and Q5 turns on. As a result, a load current flows through the lamp L via the diode bridges D3 to D6 and the switching transistor Q5.

The base potential of Q1 rises with the charging of C2, and when the base potential of Q1 exceeds V _BE , Q1 turns on. As a result, Q3 turns off, the gate potential of Q5 becomes low, and Q5 turns off again. As is clear from the above operation, Q3 and Q4 are provided to accelerate the turn-off of Q2 and Q1.

By repeating the above operation, the multivibrator oscillates and the switching transistor Q5 interrupts the load current. FIG. 2 shows an example of the waveform of the voltage / current supplied to the lamp L.

The on-time of the switching transistor Q5 is equal to the on-time of Q2, which is determined by the time constants of VR, R2 and C2. On the contrary, the off time of Q2 (= the on time of Q1) is determined by the time constants of VR, R1, and C1. Therefore, both ON time and OFF time of Q2 change depending on the position of VR. If C1 = C2, the ON time + OFF time of Q2 is constant, and the Q2 on-duty ratio, that is, the on-duty ratio of the switching transistor Q5 is determined by the position of VR.

As described above, it is possible to control the supply electric power by controlling the on-duty ratio of the lamp L by adjusting the VR by connecting and disconnecting the lamp L by the oscillation operation of the multivibrator.

(G) Effect of the Invention According to the present invention, since the load supply current is interrupted at a frequency higher than the commercial AC power supply frequency and the on-duty ratio thereof is made variable, relatively low-order harmonic components are suppressed, and the power system is suppressed. It is possible to prevent adverse effects.
Further, since the method is not based on the phase control, it is possible to obtain a power control device having stable characteristics with no problem due to a hysteresis phenomenon, a characteristic change due to a commercial AC power source frequency, and further, a variation in the power source voltage.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a light control device according to an embodiment of the present invention, FIG. 2 is a load supply voltage / current waveform diagram of the device, and FIG. 3 is a load supply voltage / power supply device of a conventional phase control power control device. It is a current waveform diagram. D3, D4, D5, D6 …… Diode bridge, R6, C5, C6 …… Smoothing circuit, Q5 …… Switching transistor.

Claims (1)

[Claims] 1. A device connected in series to a load using a commercial AC power source as a power source, the diode bridge rectifying a current flowing between input terminals, and a DC voltage generated by smoothing the output of the diode bridge. Connected between the output circuit of the diode bridge and the astable multi-vibrator that oscillates at high frequency using the DC voltage as a power source and has a variable resistor for controlling the duty ratio, and is turned on / off by the output of the astable multi-vibrator. A power control device including a switching transistor that is turned off.