JPH01122597A - Lamp control circuit - Google Patents

Abstract

PURPOSE:To reduce an amount of rush current and extend the lifetime of a lamp by providing a zero-cross detecting circuit for detecting the zero-cross point of an AC power supply and an ON/OFF control switching elements operating on an input signal connected to the lamp. CONSTITUTION:The circuit in the title is a lamp control circuit having a soft start function 24 for lowering voltage applied to a lamp 13 at the time of turning on a power supply. There are provided a zero-cross detecting circuit 20 for detecting the zero-cross point of an AC power supply and a switching element Q9 connected to the lamp 13 and making ON/OFF control with an input signal. The zero-cross point of a voltage waveform from the power supply is detected with the zero-cross detecting circuit 20 and power is supplied from the zero-cross point to the lamp 13, thereby forming a soft start system. As a result, rush current is reduced and the voltage applied to the lamp 13 rises even in a single AC cycle. In addition, the temperature of the filament of the lamp 13 rises, thereby giving higher resistance and a current value drops, thereby extending the lifetime of the lamp 13.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention is applied to lamps in rotary cameras, etc., and is particularly suitable for soft-starting lamps such as tungsten lamps and halogen lamps that flow a large current when the power is turned on. The present invention relates to a lamp control circuit for a lamp.

(Prior Art) Conventionally, one of the functions of lamp control is a function called soft start. This is a tungsten lamp,
Like a halogen lamp, its resistance value is very small at room temperature, so when the power is turned on, a large current called rush current flows as shown in FIG. This large current not only adversely affects the control element, but also has a significant impact on the life of the lamp. Therefore, the voltage applied to the lamp when the power is turned on is reduced by the soft start function described in Section 2.

That is, there is a soft start circuit as a conventional lamp control circuit as shown in FIG. In Figure 4,
The alternating current power supplies Act and AC2 are applied simultaneously in the same phase. The applied AC power supply Act is rectified by the diode bridge DBI (waveform in Fig. 5(a)), and is clipped by the constant voltage diode D1 and resistor R1 (Fig. 5('b)).
waveform).

This voltage gradually charges the capacitor C2 through the resistor R3 (waveform in FIG. 5(C)). Here, UJTQI
When the charging voltage of capacitor C1 exceeds this threshold, it becomes conductive, discharging capacitor C1 and triggering triac Q2, causing current to flow through lamp L, resulting in a voltage waveform as shown in Figure 5(d). Become. That is, when the power is turned on, the voltage of capacitor C2 is Ov, the charging current of capacitor C1 is small, it takes time for the voltage of capacitor C1 to exceed the UJTQI threshold, and the lighting voltage is low.
When the voltage of the capacitor C2 becomes higher, the charging time of the capacitor CI becomes shorter and the lighting voltage also becomes higher. When the voltage charged by the capacitor C2 and the resistor R3 becomes stable, the light can be dimmed by adjusting the charging time of the capacitor C1 by the resistor R5. Further, T1 is a pulse transformer.

(Problem to be solved by the invention) However, in such a conventional example, since the voltage value of the lamp L is always a finite value at the beginning of the current flow, the inrush current to the lamp becomes quite large. There is a problem that the lamp life is shortened. In addition, if the inrush current described in 2. is made sufficiently small, it takes too much time for the temperature of the filament of the lamp L to become high enough, resulting in a problem that the time required for soft start becomes longer. .

Therefore, the present invention has been devised to solve the above-mentioned problems of the conventional example.The purpose of the present invention is to reduce the inrush current to extend the life of the lamp, and to reduce the time required for soft start. The object of the present invention is to provide a lamp control circuit that can be shortened.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a lamp control circuit equipped with a soft start function that reduces the voltage applied to the lamp when the power is turned on. It is constructed by providing a zero-crossing detection circuit that detects the zero-crossing point of the AC power source, and a switching element that is connected to the lamp and controlled on and off by an input signal.

(Function) In the present invention having the above configuration, the zero-crossing point of the voltage waveform of the power supply is detected by the zero-crossing detection circuit,
By performing a soft start in which the lamp is energized and lit from the zero-crossing point, a large current does not flow through the lamp when the power is turned on, and the time required for the soft start is shortened.

(Example) The present invention will be explained below based on the illustrated example. Third
The figure is a schematic configuration diagram of a rotary camera to which a lamp control circuit according to an embodiment of the present invention is applied. In the figure, reference numeral 1 denotes a document table, on which a document 4 such as a check or document as an object is loaded. There is. The document 4 is fed by a feeding roller 2 as a feeding means.
and separation roller 3 are rotated in the directions of arrows by driving means (not shown), thereby separating and feeding the sheets one by one.

Then, the document 4 passes through the guide plate 5 and the document feed roller 6
, glass flat plates 9, 10 by a pair of feed rollers 8, 8.
It is sent at a constant speed to the shooting position in between. At the photographing position, the document 4 is irradiated by the exposure lamp 13.13 to perform slit exposure, and the document 4 is exposed to the photographing section 16 by an optical path (not shown).
After being reduced and recorded on a microfilm at , the document is discharged onto a document discharge tray 12 by a pair of discharge rollers 11, 11. Reference numeral 7 denotes a reflection type secessor as a document detecting means. Further, 14 and 15 are guide rollers.

By the way, tungsten lamps, halogen lamps, etc. are used as the exposure lamps 13.13, and since these have extremely low resistance values at room temperature, an inrush current flows when the current is turned on, which may shorten the life of the lamp or damage the control elements. have a negative impact. To prevent this, on the Kinomi flow side,
A lamp control circuit as shown in FIG. 1 is provided inside the device.

In FIG. 1, when an alternating current is applied from an alternating current fiAc, it passes through a transformer T1 and is connected to a diode bridge DB2.
The aftereffect is rectified (waveform in FIG. 2(a)), and then the rectified zero-crossing point is detected by the zero-crossing detection circuit 20 consisting of a resistor R1, a transistor Q1, and a resistor R2 (FIG. 2(b)). waveform). Further, a sawtooth wave (shown in FIG. 2(c)) is generated by the sawtooth wave generation circuit 22 in synchronization with the zero-cross signal detected by the zero-cross detection circuit 20, and the sawtooth wave generation circuit 22
consists of an integrating circuit consisting of a resistor R3, a transistor Q2, a resistor R4, and a capacitor C1. The current of the sawtooth wave generation circuit 22 is controlled by the soft start control circuit 24.
The signal is input to the comparator Q5 in the internal circuit, and is also input to the comparator Q6.

In the soft start control circuit 24, the power supply voltage ■. 0 is charged into the capacitor C2 through the resistor R5, and when this charging voltage exceeds a predetermined voltage, the transistor Q4 is turned on to accelerate the charging time of the capacitor C2 through the resistor R9. This is to eliminate unnecessary soft start time. Then, the diode D1 discharges the capacitor C2 when the power supply voltage vcc is off (waveform in FIG. 2(d)). Further, the resistor R7 is connected to the resistor R8 which is connected to the base of the transistor Q4, and is also connected to the collector of the transistor Q3. A Zener diode D2. is connected to the base of the transistor Q3. It is connected to capacitor C2 through resistor R6. However, the voltage from the sawtooth wave generating circuit 22 and the charging voltage of the capacitor C2 are compared by the comparator Q5, and when the charging voltage of the capacitor C2 becomes very high and decreases by 1, the voltage shown in FIG.
) is generated. That is, comparator Q
When the output of the switching circuit 26 is "old gh", the transistor Q7 is turned on through the resistor R11, and the transistor Q8 of the switching circuit 26 is turned off. Also, the comparator Q6 has a dimming voltage ■. By comparing the voltage from the ONT and the sawtooth wave generation circuit 22, the voltage for dimming vco is higher than the sawtooth wave.
When wr is higher, the output of comparator Q6 is “old gh
11, and the transistor Q of the switching circuit 26
8 is turned on and current flows through the lamp 13. In this way, when the voltage of the dimming voltage vCONT is high, the lamp 13
becomes brighter, and becomes darker when it is lower.

Here, the signal of the soft start control circuit 24 (Fig. 2 (
e)), the current flowing through the transistor Q8 becomes as shown in FIG. 2(g), and the current as shown in FIG. 2(D) flows through the lamp 13, resulting in a soft start.

The switching circuit 26 has a photocoupler 27, and one end of the photodiode 27a is connected to a resistor R12, and the other end is connected to the collector of a transistor Q8. The base of this transistor Q8 has a resistor R
IO is connected. Also, the phototransistor 27b
The emitter of is connected to the resistor R13 and to the gate terminal of a MOS FET Q9 as a switching element. Therefore, when transistor Q8 is on, MOS FET Q9 is on, and current flows through lamp 13.

On the other hand, 28 is a control power supply circuit for MOS FET Q9, which smooths the rectified waveform of the current from the AC power supply AC through the diode bridge DBI and converts it into M
It is for sending to OS FET Q9,
Zener diode D3. Capacitor C3 and resistor R1
Consists of 4.

As mentioned above, in this embodiment, since a soft start is adopted in which electricity is supplied from the zero cross point, the inrush current becomes small, and the voltage applied to the lamp 13 increases even in one AC cycle, and the temperature of the filament of the lamp 13 increases. The current value increases, the resistance increases, and the current value decreases, extending the life of the lamp 13. Furthermore, since the soft start ON time within one AC cycle can be longer than that of the conventional example, the soft start time can be shortened.

Incidentally, in the above embodiment, an example in which the present invention is used as a light source of a rotary camera is described, but it is also applicable to other devices. Further, in the above embodiment, a MOS FET is used as a switching element, but the switching element is not limited to this, and a bipolar transistor or the like may be used. Further, in the above embodiment, the energization time for one soft start cycle was gradually increased, but substantially the same effect can be obtained even if the energization time is constant.

(Effects of the Invention) The lamp control circuit according to the present invention has the above-described configuration and operation, and the inrush current is reduced, the life of the lamp is extended, and noise generation is also reduced. This also has the effect of shortening the time required for soft start.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing one embodiment of the lamp control circuit according to the present invention, and Figures 2 (a), (b), (c), (d), (e
). (f) and (g) are waveform diagrams of various parts in FIG. 1, FIG. 3 is a schematic configuration diagram of a rotary camera to which the present invention is applied, FIG. 4 is a circuit diagram showing a conventional lamp control circuit, and FIG. Figure (a),
(b), (c), and (d) are waveform diagrams of each part in FIG. 4, and FIG. 6 is a waveform diagram of rush current. Explanation of symbols 13...Exposure lamp 20...Zero cross detection circuit 22...Sawtooth wave generation circuit 24...Soft start control circuit 26...Switching circuit C2...Capacitor DB2...Diode bridge

Claims (1)

[Claims] In a lamp control circuit equipped with a soft start function that reduces the voltage applied to the lamp when the power is turned on, a zero cross detection circuit that detects the zero cross point of the AC power supply;
A lamp control circuit comprising: a switching element connected to the lamp and controlled on and off by an input signal.