JPH02309410A - Lighting circuit - Google Patents

Abstract

PURPOSE:To reduce a rush current under stable output control by providing a lighting circuit with a switch circuit for returning a connecting angle gradually increased to a regulated connecting angle at the time of energizing a bidirectional thyristor. CONSTITUTION:The bidirectional thyristor 16 is connected to an AC power supply connected to terminals A, B in series with a current restricting coil 15, a phase-controlled voltage is fully rectified by a diode bridge 17 and its output is supplied to a lamp load 18 and a capacitor 19. To prevent the generation of a rush current at the time of starting lighting, an output setting time constant determined by a triangular wave generating circuit 34, a resistor 20, a control circuit 33, capacitors 19, 25, 26, and so on. The connecting angle of a feedback voltage for determining a lamp load feeding voltage can be gradually expanded in accordance with a lighting start signal (trigger ON). Consequently, the lighting circuit capable of preventing the generation of malfunction at the time of lighting and reducing the rush circuit at the time of starting lamp lighting can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a lighting circuit for a lamp or the like used in a copying machine.

2. Description of the Related Art Conventionally, this type of lighting circuit has had a configuration as shown in FIG. 3, for example. In FIG. 3, a lamp 3 is connected to an AC power source connected to A and B via a current limiting coil 1 and a bidirectional thyristor 2 connected in series, and a current is applied to the lamp 3. A trigger pulse is output from the control circuit 5, and a pulse is applied to the gate of the bidirectional thyristor 2 through the pulse transformer 4 so that the effective value of the voltage has a linear relationship with the DC output voltage setting value Vs. The brightness of the lamp load 3 is controlled by controlling the phase of the thyristor 2.

In recent years, with the increase in speed and quality of copying machines, there has been a demand for a reduction in the optical ripple of lamps. Since voltage application using alternating current phase control is affected by its frequency, a method of supplying direct current voltage to the lamp has been considered.

FIG. 4 shows a direct current version of the circuit shown in FIG. 3.

In FIG. 4, the input from the AC power supply connected to A and B is full-wave rectified by a current limiting coil 6 and a diode bridge circuit 7 connected in series. The phase of the full-wave rectified waveform is controlled by a thyristor 8 and applied to a lamp load 9 and a capacitor 10. Capacitor 10 is used to smooth the voltage applied to lamp load 9.

The voltage applied to the lamp load 9 is set at a set voltage Vs. The control circuit 11 generates a trigger pulse for operating the thyristor 8 so that the applied voltage becomes a set voltage, and the trigger pulse is supplied to the gate of the thyristor 8 through the pulse transformer 12. The trigger pulse is determined by the output of the triangular wave generating circuit in the control circuit 11, the time constants of the feedback resistor 13, the timing adjustment capacitor 14, etc., and influences the magnitude of the rush current.

Problems to be Solved by the Invention In such a conventional configuration, the output cannot be controlled due to problems such as the possibility of erroneous firing of the thyristor and the large inrush current into the lamp due to difficulty in soft start timing. There were problems in that the lamp would burn out due to the rush current and the lamp life would be shortened.

The present invention is intended to solve these problems, and aims to reduce inrush current under stable output control.

Means for Solving the Problem In order to solve this problem, the present invention provides a bidirectional thyristor for controlling the phase of an AC input voltage, a current limiting coil connected in series with the bidirectional thyristor, and a phase control coil for controlling the current. It consists of a diode bridge circuit that full-wave rectifies the controlled voltage, a lamp load and a capacitor connected in parallel with the output side of this diode bridge circuit, and a control circuit that provides a trigger pulse to the bidirectional thyristor. A switch circuit is provided which applies an output start signal from the circuit to the bidirectional thyristor, gradually increases the conduction angle when the bidirectional thyristor conducts, and then sets the conduction angle to a specified conduction angle.

Effect With this configuration, the lamp lighting start signal can be used as the conventional one.
The thyristor's inrush current can be reduced by adjusting the time constant so that turn-on and turn-off can be performed more reliably and malfunctions can be prevented, and the conduction angle can be gradually increased than when using the method.

Embodiment FIG. 1 shows the primary side, 2, of a lighting circuit according to an embodiment of the present invention.
Showing the next side. A bidirectional thyristor 16 is connected in series with the current limiting coil 15 to the AC power supply connected to A and B, and the phase-controlled voltage is applied to the diode bridge 1.
7 performs full-wave rectification, and its output is supplied to a lamp load 18 and a capacitor 19. 20-24 is resistance, 25-2
7 is a capacitor, 28 to 30 are phototransistors, 2
8a to 30a are light emitting diodes, and the output transistor 31 is used in the control circuit to switch lighting signals. 32 is a pulse transformer, 33 is a control circuit that determines the output voltage to the lamp, 34 is a triangular wave generating circuit which is a part of the control circuit 33, 35 is a Zener diode, and 36 is a transistor. Vcc is an internal power supply voltage for operating the control circuit.

According to this embodiment, erroneous firing of the bidirectional thyristor 16 can be prevented by first controlling the phase of the alternating current and then performing full-wave rectification. In other words, controlling the phase of a full-wave rectified AC waveform requires timing adjustment with the turn-off time of the thyristor; it requires an extremely delicate circuit configuration, variable set voltage, consideration of temperature characteristics, etc. Considering these points, it was extremely difficult to construct such a W control circuit, but this circuit adopted a method of gold wave rectification after phase control to solve the problem.

Second, in order to prevent an inrush current at the start of lighting, the time constant of the output setting determined by the triangular wave generating circuit 34, the resistor 20, the control circuit 33, the capacitors 19, 25, 26, etc. is varied. That is, when the trigger is off, no current flows through the phototransistor 31 in the isolated secondary circuit, and the capacitor 26 is connected in the primary circuit due to the conduction of the phototransistors 28 and 29, and the charge is discharged. It has been accumulated. When the trigger is turned on, the phototransistor 31 becomes conductive and the phototransistors 28 and 29 are turned off.

However, a time delay occurs in the secondary circuit due to the capacitor 27 and the resistor 24. Therefore, the time constant of the feedback voltage Vo that determines the voltage supplied to the lamp is delayed by the capacitance of the capacitor 26. On the other hand, when the output is varied while the trigger is on, the response of the output is delayed. However, in this circuit, after a certain period of time, the capacitor 26
is disconnected from the circuit by turning off the phototransistors 29 and 30, and the resistor 20, capacitor 19,
, 25, the control circuit 33, etc., there is no influence.

Figure 2 shows the input and output waveforms. With the lighting start signal (trigger-on), the feedback voltage Vo that determines the lamp load supply voltage becomes V2, and its conduction angle can be gradually widened. vl in Figure 2 (B), Figure 2 (C
) shows the waveform in the conventional case.

In FIG. 1, the pulse transformer 32 is used to provide a trigger pulse to the bidirectional thyristor 16, but a phototriac may be used instead. Also,
Although a phototransistor was used to switch the capacitance, switching using a relay or the like is also possible.

Effects of the Invention As described above, according to the present invention, it is possible to obtain a lighting circuit that can prevent malfunctions during lighting and can reduce rush current when starting lamp lighting.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a lighting circuit according to an embodiment of the present invention, FIG. 2 is a waveform diagram showing main waveforms in the lighting circuit, and FIGS. 3 and 4 are circuit diagrams showing lamp lighting circuits according to conventional technology. It is a diagram. 15...Current control coil, 16...
Bidirectional thyristor, 17... diode bridge, 18... lamp load, 19.26...
... Capacitor, 28.29.30 ... Phototransistor, 33 ... Control circuit. Name of agent: Patent attorney Shigetaka Awano and one other person (1')

Claims (1)

[Claims] A bidirectional thyristor that controls the phase of an AC input voltage, a current limiting coil connected in series with the bidirectional thyristor, a diode bridge circuit that full-wave rectifies the phase-controlled voltage, and a diode bridge circuit that performs full-wave rectification of the phase-controlled voltage. It consists of a lamp load and a capacitor connected in parallel with the output side, and a control circuit that gives a trigger pulse to the bidirectional thyristor. A lighting circuit equipped with a switch circuit that gradually increases the conduction angle at which conduction begins and then returns to the specified conduction angle.