JPH08241133A - Constant current, constant-voltage direct-current power source for incandescent lamp - Google Patents

Abstract

PURPOSE: To provide the power source for the incandescent lamp which can suppress a rush current and prevent a flicker due to variation in source voltage. CONSTITUTION: A switching means 4, which is provided between a rectifying circuit 1 and the lamp 2 and turns on and off and outputs a DC voltage with input pulses of specific frequency for control to the lamp 2, is provided with a voltage detecting circuit 5 which detects the voltage impressed to the lamp 2 and a current detecting means 6 which detects a current flowing to the lamp 2, so that the rush current and the voltage impressed to the lamp 2 can be detected. A control means 8 compares the detected voltages of the detecting means 5 and 6 with a reference voltage for constant current setting, set for the rated current of the lamp 2, and a reference voltage for constant voltage setting, set for the rated voltage of the lamp 2, that a reference signal generating means 7 generates, and controls the pulse width of input pulses for control outputted to the switching means 4 so as to eliminates the differences. Consequently, the rush current when the lamp 2 is turned on is suppressed to prolong its life, and the flicker due to variation in source voltage can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power source for an incandescent light bulb (hereinafter, lamp) used as a light source for an OHP (over head projector), a slide projector, a projector, and the like.

[0002]

2. Description of the Related Art Incandescent light bulbs (hereinafter referred to as "over head projector" (OHP), slide projector, projector, etc.
In a device using a lamp as a light source, the resistance value of a cold lamp before lighting is extremely small, and when a rated voltage is applied to the lamp before lighting, a very large inrush current flows as shown in FIG. The inrush current shortens the life of the lamp, and at the same time, a large current flows through the equipment,
Conventionally, for example, the lighting circuit shown in FIG. 6 has been used because it has a problem of damaging the contacts of parts such as switches constituting the device.

This circuit is called a soft start circuit. When the power is turned on, the capacitor C1 is charged through the diode D6 and the resistor R1, and the charging voltage is UJT at the end of the half cycle of the AC input voltage. Is discharged by and the triac T1 is triggered. At this time, the trigger cycle of the triac T1 is as follows: as the charging voltage of the capacitor C1 increases,
The charging time is fast and the discharge time of UJT is shortened and shortened, and the time when the triac T1 is turned ON is gradually increased. For this reason, the effective load voltage applied to the lamp 2 gradually increases, and the voltage does not suddenly increase when the power is turned on.

[0004]

However, in the above lighting circuit, although there is a certain effect in suppressing the inrush current, the triac becomes conductive during steady lighting after lighting, and the lamp and the AC input are turned on. Since the and are directly connected to each other, for example, if the power supply voltage fluctuates in the power system, the lamp flickers and the amount of light cannot be kept constant.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a power supply circuit capable of suppressing the inrush current, extending the lamp life, and preventing the flicker due to the fluctuation of the power supply voltage.

[0006]

In order to solve the above problems, the present invention is provided between a rectifier circuit and an incandescent lamp, and turns on / off the DC voltage of the rectifier circuit by a control input pulse having a predetermined frequency. Output pulse voltage, and the output voltage to the incandescent light bulb through a ripple filter that converts the output pulse voltage to a DC voltage, and a switching means,
Voltage detection means for detecting the voltage applied to the incandescent bulb, current detection means for detecting the current flowing in the incandescent bulb, constant current setting reference voltage for setting the current flowing in the incandescent bulb, incandescent Reference signal generating means for generating a constant voltage setting reference voltage for setting the voltage applied to the light bulb, and constant current setting reference voltage generated by the reference signal generating means and the detection output of the current detecting means are compared. In addition, the constant voltage setting reference voltage generated by the reference signal generating means and the detection output of the voltage detecting means are compared, and the pulse width of the control input pulse output to the switch means so as to eliminate the difference between them. That is, a structure including a control means for controlling the is adopted.

[0007]

In the constant-current constant-voltage DC power supply for an incandescent light bulb configured as described above, the switching means provided between the rectifier circuit and the lamp turns on the rectified DC voltage of the rectifier circuit by the control input pulse of a predetermined frequency. By turning on / off, the pulse voltage is output to the ripple filter. The output pulse voltage is rectified by the ripple filter, converted into a DC voltage according to the duty ratio of the pulse, and applied to the lamp. In addition, a load voltage corresponding to the voltage value is passed through the lamp. At this time, the voltage applied to the lamp and the current flowing through the lamp are detected by the voltage detection means and the current detection means, respectively, and input to the control means. The control means to which the detection output is inputted from these detecting means compares the detection output inputted from the voltage detecting means with the reference voltage for constant voltage setting inputted from the reference voltage setting means, and at the same time inputs from the current detecting means. The detected output is compared with the constant current setting reference voltage, and the width of the control input pulse output to the switch means is controlled so as to eliminate the difference between the compared results.

That is, when the detection output of the voltage detecting means exceeds the constant voltage setting reference voltage, the pulse width is reduced and the duty ratio of the pulse is reduced to reduce the output voltage.
On the contrary, when the voltage falls below the constant voltage setting reference voltage, the pulse width is increased, the pulse duty ratio is increased, and the output voltage is increased.

For this reason, if the reference voltage for constant voltage setting is set to the rated voltage value of the lamp by this constant voltage operation, for example, the voltage of a constant rating is always maintained regardless of the fluctuation of the input voltage. Can be applied to the lamp.

Similarly, when the detected output of the current detecting means exceeds the constant current setting reference voltage, for example, the pulse width is made small and the duty ratio of the pulse is made small so that the output voltage is lowered and the current flowing through the lamp is reduced. To reduce. vice versa,
If it falls below the reference voltage for constant current setting, the pulse width will increase,
The output voltage is increased by increasing the pulse duty ratio and the current flowing through the lamp is increased.

Therefore, if the constant current setting reference voltage is set to the rated current value of the lamp by the constant current operation, for example, when the resistance value of the lamp during lighting is small, the current is limited. By doing so, it is possible to prevent the current from flowing excessively than the rated current.

[0012]

Embodiments of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, the constant-current constant-voltage DC power supply for an incandescent light bulb of this embodiment comprises a rectifying circuit 1, a switching means 4, a voltage detecting means 5, a current detecting means 6, a reference signal generating means 7 and a control. It is a forward converter type switching regulator composed of means 8 and is capable of achieving high efficiency and miniaturization.

The rectifier circuit 1 includes an AC input capacitor C.
1, a line filter 10 including C9 and a common mode choke coil L1, and a rectifying diode bridge D3
And a voltage doubler circuit 11 in which two smoothing capacitors C3 and C10 connected in series are connected to the output of the diode bridge D3, and A input to the rectifier circuit 1 is formed.
The voltage of the C power source is almost doubled and input to the switching means 4.

The switching means 4 comprises a transformer T, a switching element composed of an FET transistor Q1 provided on the primary side of the transformer T, and a flywheel diode D1, and is rectified by a control input pulse applied to the gate of the FET Q1. The DC input voltage from the circuit 1 is turned on / off to output the pulse voltage to the ripple filter 3 connected to the secondary side of the transformer T.

The ripple filter 3 is composed of rectifying diodes D4 and D4 ', a choke coil L2 and an output smoothing capacitor C2. When the FET Q1 is turned on, the pulse voltage changes from the primary winding of the transformer T to the secondary winding of the transformer T. When it is added to the winding, the rectifying diode D4 becomes conductive, and power is supplied to the choke coil L2 and the load. In addition, FET
When Q1 is turned off, the diode D4 is turned off, and the energy stored in the choke coil L2 passes through the diode D4 ′ to supply power to the load.

The voltage detecting means 5 includes resistors R10, R21,
R15 is connected in series, one end of the resistor R10 of the series circuit is connected to the output end of the ripple filter 3, the other end of the resistor R15 of the series circuit is connected to the ground, and the resistors R10 and R10 are connected.
The connection point of 21 is connected to the control means 8, and the resistance R10
The detection voltage divided by the resistors R21 and R15 is input to the + input of the second error amplifier of the control means 8 which will be described later. The connection point between the resistors R21 and R15 is pulled out and connected to the Hi / Low switch 12, and the switch 12 is operated to change the voltage division ratio and change the feedback amount to change the output voltage in two steps. You can do it.

The current detecting means 6 is a load current detecting resistor R6 inserted in series with the output of the ripple filter 3,
The voltage generated in the resistor R6 by the load current is passed through the resistor R9 connected to the transformer T side to the first of the control means 8 which will be described later.
It is designed to be input to the-input of the error amplifier of.

The reference signal generating means 7 includes a current setting circuit 13 for generating a reference voltage for setting a constant current for setting a current flowing to the lamp 2, and a constant voltage setting for setting a voltage applied to the lamp 2. Voltage setting circuit 1 for generating reference voltage
4, the current setting circuit 13 connects one end of the series circuit in which the resistor R19 and the volume VR2 are connected in series to the reference regulator of the terminal number 14 of the control means 8 described later, and the other end of the resistor R9. By connecting to the-input terminal of the first error amplifier having the terminal number 2 of the control means 8 to be inputted, the reference voltage for constant current setting is inputted. On the other hand, the voltage setting circuit 14 includes a resistor R12.
Similarly to the current setting circuit 13, one end of a series circuit in which the control unit 8 and the volume VR1 are connected in series is connected to a reference regulator of the terminal number 14 of the control unit 8 described later, and the other end is connected to the reference number of the terminal number 15 of the control unit 8. The reference voltage for setting the constant voltage is input to the control means 8 by inputting it to the negative input of the error amplification unit 2 of the volume VR1.
And VR2 can be adjusted to set their respective values.

The control means 8 is a control IC for a general-purpose PWM type switching regulator shown in FIG.
It has a PWM comparator, an oscillator for generating a triangular wave connected to the comparator, and two error amplifiers additionally connected to the PWM comparator. In the embodiment, as described above, among these two error amplifiers, The reference voltage for constant voltage setting of the voltage setting circuit 14 is input to the-input of the second error amplifier (error amplifier 2 in FIG. 2), and the terminal voltage of the resistor R10 of the voltage detecting means 5 is input to the + input of the second error amplifier.
The output of the second error amplifier is − of the PWM comparator.
Input has been entered. In addition, the first error amplifier (see FIG.
Then, to the-input of the error amplifier 1), the detection voltage of the resistor R6 of the current detecting means 6 is input via the resistor R9, and the reference voltage for constant current setting of the current setting circuit 13 is additionally input to input +. Is connected to the ground via a bias resistor R20, and the output of the first error amplifier is added to the negative input of the PWM comparator.

On the other hand, the output of the oscillator is input to the + input of this PWM comparator, and the PWM comparator compares the addition output of the first and second error amplifiers with the level of the triangular wave, and the triangular wave is obtained by the comparison. As shown in FIGS. 3A and 3B by slicing, the output pulse width is changed according to the level of the input signal.

This output pulse corresponds to 1 of the control IC.
It is applied to the gate circuit of the FET Q1 for switching through the driving transistor Q2 connected to the 0th and 11th terminals and drives it.

Here, a parallel circuit including resistors R4 and R3 and a capacitor C8 provided between the feedback terminal FB of the terminal number 3 of the control IC of FIG. 1, the current setting circuit 13 and the voltage setting circuit 14 and the resistors R13 and R14. The parallel circuit including the capacitor C4 is a feedback circuit for determining the gain and the phase characteristic of the first and second error amplifiers, and the resistor R16 and the capacitor C6 connected between the terminal numbers 5 and 6 of the control IC. Is a CR element for setting the oscillation frequency of the oscillator for generating a triangular wave, and is determined by experience or experiments so that the oscillation frequency becomes the most efficient predetermined oscillation frequency.

The photocoupler PC connected to the terminal No. 4 of the control IC is operated by the lamp switch 15 connected in parallel with the LED of the coupler PC.
The output of the PWM comparator of FIG. 2 is changed from enable to enable.
Turn on / off this power supply by starting and stopping 1
You can do it.

This embodiment is constructed as described above. When the lamp 2 is connected to the output terminal and the AC power source is connected to the input of the line filter 10 of the rectifier circuit 1, the control means 8 is connected.
Oscillator starts oscillating. Next, the voltage V of the voltage setting circuit 14 and the current setting circuit 13 of the reference signal generating means 7
R1 and VR2 set a predetermined voltage that may be applied to the lamp 2 as a constant voltage setting reference voltage and a predetermined current that may be applied to the lamp 2 as a constant current setting reference voltage. After that, when the lamp switch 15 is activated,
The output of the control IC is enabled by the photocoupler PC, the control pulse signal is output, and the FET
Q1 turns on / off the DC voltage of the rectifier circuit 1, and the output pulse voltage is rectified into a DC voltage by the ripple filter 3 and applied to the lamp 2.

At this time, since the lamp 2 is cold before being lit, its resistance value is extremely small and an inrush current tends to flow. However, the increase in the current is caused by the resistance R6 of the current detecting means 6 as a voltage change. The detected reference voltage for setting the constant current is added and input to the first error amplifier of the control means 8. Therefore, in the first error amplifier, the output obtained by adding the detection voltage and the constant current setting reference voltage is input to the PWM comparator. In the PWM comparator to which the addition output is input, depending on the level of the input addition output,
The triangular wave output from the oscillator is sliced, and the width of the output pulse is changed according to the magnitude of the detected current. That is, when the detection output of the current detection means 6 exceeds the constant current setting reference voltage due to the inrush current, the pulse width is reduced and the duty ratio is reduced. Therefore, the ON time of the FET Q1 is shortened, the output voltage is lowered, and the inrush current to the lamp 2 can be limited. After this, the lamp 2
Filament temperature rises and the resistance value rises, conversely,
When the voltage falls below the constant current setting reference voltage, the pulse width is widened and the duty ratio is increased. Therefore, FET
The ON time of Q1 becomes long and the output voltage becomes high.
It is possible to keep the current constant by increasing the current flowing through.

Therefore, if the constant current setting reference voltage is set to the rated current value by the constant current operation, for example, when the resistance value of the lamp 2 is small, the current flows too much than the rated current. By preventing this, the current can be limited.

At this time, at the same time, the voltage applied to the lamp 2 is detected by the detection resistor R10 of the voltage detection means 5 and is input to the + input of the second error amplifier. The detected voltage and the second The constant voltage setting reference voltage input to the negative input of the error amplifier is compared, and the difference is input to the PWM comparator. Therefore, in the PWM comparator, the slice level of the triangular wave of the oscillator is determined by this input level. For example, if the detection voltage may fall below the constant voltage setting reference voltage, the slice level of the triangular wave by the PWM comparator will decrease. The width of the output pulse is wide, the duty ratio is large, the ON time of the FET Q1 is long, and the voltage applied to the lamp 2 is high. On the contrary, when the applied voltage to the lamp 2 rises and the detected voltage exceeds the reference voltage for constant voltage setting, P
The slice level for the triangular wave by the WM comparator rises, the width of the output pulse becomes narrow, the duty ratio becomes small, the ON time of the FET Q1 becomes short, and the voltage applied to the lamp 2 becomes low. Therefore, if the constant voltage setting reference voltage is set to the rated voltage by the constant voltage operation, for example, even if the power supply voltage fluctuates during the lighting of the lamp 2, the influence thereof is suppressed and the lamp is suppressed. The flicker of 2 can be prevented.

As described above, in this constant-current constant-voltage power supply for incandescent bulbs, the constant-current operation and the constant-voltage operation are simultaneously performed to suppress the inrush current when the lamp 2 is turned on, and to prevent fluctuations in the power supply voltage. The lamp 2 can be prevented from flickering and the amount of light can be kept constant.

If the Hi / Low selector switch 12 is switched while the lamp 2 is on, the resistor R15 is inserted into the series circuit of the voltage detecting means 5 and short-circuited, so that the voltage applied to the lamp 2 is high. It can be switched to low two steps.

That is, the detection voltage to be compared with the constant voltage setting reference voltage is changed by inserting and shorting the resistor R15, the slice level for the triangular wave is adjusted by the PWM comparator, and the voltage applied to the lamp 2 is switched.

Looking at the lamp power, current, and voltage immediately after the incandescent lamp lit by the constant current / constant voltage DC power supply in this way, as shown in FIG. 4, when the filament resistance is low, Due to the constant current characteristics, the power and voltage of the lamp are kept lower than that of the rated value, and if the filament resistance reaches the rated value due to the heat generated by the lamp itself, all of the power, voltage and current will be It will be lit at the rated value.

[0033]

The present invention is configured as described above, detects the lamp current and the lamp voltage, and determines the detected lamp current and lamp voltage as the constant current setting reference voltage generated by the reference signal generating means. The voltage applied to the incandescent light bulb is controlled by comparing with the reference voltage for voltage setting and controlling the pulse width of the control input pulse output to the switch means so as to eliminate the respective differences. Therefore, it is possible to extend the life of the incandescent light bulb by suppressing the inrush current when the incandescent light bulb is turned on. Further, a constant voltage and current are always applied to the incandescent lamp even when the power supply voltage fluctuates, so that it is possible to prevent the incandescent lamp from flickering due to fluctuations in the power system and keep the light amount constant.

As described above, since the incandescent light bulb can be stably lit and the switching power supply is used, the efficiency and size of the device can be improved, and thus the OHP (over head projector) and the slide projector can be achieved. Ideal for powering incandescent light bulbs such as projectors.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment.

FIG. 2 is a block diagram of control means according to the embodiment.

FIG. 3 is an operation diagram for explaining pulse width control of a control means.

FIG. 4 is a diagram showing the lamp power / current / voltage characteristics of the embodiment.

FIG. 5 is a diagram showing a waveform when the lamp is turned on.

FIG. 6 is a circuit diagram of a conventional lighting circuit.

[Explanation of symbols]

 1 Rectifier circuit 2 Lamp (incandescent light bulb) 3 Ripple filter 4 Switching means 5 Voltage detection means 6 Current detection means 7 Reference voltage signal generation means 8 Control means

Claims (1)

[Claims] 1. A rectifier circuit and an incandescent light bulb, which are provided between the rectifier circuit and the incandescent lamp, which output a pulse voltage by turning on / off the DC voltage of the rectifier circuit by a control input pulse of a predetermined frequency, and convert the output pulse voltage to a DC voltage Switching means for outputting to the incandescent light bulb through a ripple filter, a voltage detecting means for detecting a voltage applied to the incandescent light bulb, a current detecting means for detecting a current flowing through the incandescent light bulb, and a flow for the incandescent light bulb. A constant current setting reference voltage for setting a current, and a reference signal generating means for generating a constant voltage setting reference voltage for setting the voltage applied to the incandescent lamp, and a constant signal generated by the reference signal generating means. The reference voltage for current setting is compared with the detection output of the current detecting means, and the reference voltage for constant voltage setting generated by the reference signal generating means and the detection by the voltage detecting means. It compares the power control means and the constant-current constant-voltage DC power supply incandescent lamp consisting of controlling the pulse width of the control input pulses to be outputted to the switching means so as to eliminate the difference that each comparison.