JP2000353596A - Method and device for controlling lamp - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avoid increasing the size of a smoothing capacitor, to reduce the cost, and to obtain a lamp light intensity early enough in a lamp control device providing a lamp lighting voltage through the smoothing capacitor. SOLUTION: After an input voltage Vin is rectified by a diode bridge DB1, and is smoothed by a smoothing capacitor C1, a lamp lighting voltage is supplied for a lamp 1 through a step-down type chopper circuit. A constant voltage circuit 4 controls an output voltage Vo to be constant by detecting the output voltage Vo. In this process, an input voltage to the copper circuit is detected, and if the detected value is low, a PWM control circuit 8 controls a drive of FETQ1 which is a switching element for the chopper circuit to restrict the output voltage Vo to the lamp 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device and a control method for a lamp used in an electrophotographic copying machine or the like.

[0002]

2. Description of the Related Art FIG. 6 is a diagram showing a circuit configuration of a DC voltage lamp lighting device generally used in a copying machine or the like.
This circuit has a configuration using a step-down chopper circuit, and includes a starting / power supply circuit 2 for driving a lamp 1 and a PWM for switching and driving an FET Q as a switching element.
A (pulse width modulation) control circuit 3 and an output constant voltage control circuit 4 are provided.

The starting and power supply circuit 2 includes a secondary winding N21 of a choke coil L1, a diode D1 and a capacitor C3 for rectifying and smoothing the voltage, a diode D2 for supplying a power supply voltage PVcc to a PWM control circuit 3, A capacitor C2 and resistors R1 and R2 are provided.

The PWM control circuit 3 comprises a triangular wave oscillating circuit 5 and a DTC (dead time control) circuit 6 and a comparator IC1 for comparing their outputs, and a constant voltage control circuit 4 comprises a differential circuit having an operational amplifier IC2. Amplifying circuit 7, its amplified output and reference voltage Vr of reference voltage source E1
It comprises an operational amplifier IC3 to which et1 is input.

In the configuration shown in FIG. 6, L1 is a choke coil having two windings. A step-down type chopper circuit is constituted by a primary winding N11, an FET Q1, a flywheel diode D6 and a smoothing capacitor C4. Is configured. The DC voltage Vs of the capacitor C1 is switched at a high frequency by the FET Q1, and the primary winding N11, the capacitor C4, and the diode D6 are switched.
Rectifying and smoothing.

[0006] Here, the FET Q
The desired output voltage Vo is controlled by controlling the on / off time ratio of 1. Further, a differential amplifier circuit 7 is used to detect the output voltage, and the error voltage is compared with a reference voltage Vref1 by an error amplifier circuit 8 to detect an error.
The on / off time ratio of the FET Q1 is controlled by using the PWM control circuit 3 so that the error voltage becomes zero.
Thus, constant voltage control is performed.

FIG. 7 shows the output waveform of each part of the above circuit. The input voltage Vin at point A and the DC voltage V at point B are shown in FIG.
s, output current Io, and power supply voltage PV of the PWM control circuit 3
The state of time (t) change of cc is shown. In the figure,
VH represents the starting voltage of the PWM control circuit 3, Vx represents the voltage at point C, and VL represents the operation stop voltage of the PWM control circuit 3.

[0008]

However, in the lamp control device using the above-mentioned chopper circuit, the following problems arise when trying to stabilize the lamp light amount to a desired light amount at a high speed. There was a point.

That is, the electric characteristics of a lamp generally have a very small impedance (〜Ω) at low temperature and normal temperature before lighting, and a relatively high impedance (〜１０Ω) at high temperature when the light emission of the lamp is stable. become.
The light emission amount of the lamp is stabilized when the temperature of the lamp reaches a predetermined temperature, the impedance of the lamp is stabilized, and the lamp current is stabilized.

Therefore, when the impedance of the lamp before lighting is low, an inrush current flows. At this time, since (rush current)> (current for charging the smoothing capacitor by the commercial power supply), the capacitor voltage Vs gradually decreases. When the lamp is extremely cold or when the input voltage from the commercial power supply is low for some reason (line drop, instantaneous voltage drop, etc.), the capacitor voltage becomes too low and the lamp cannot be turned on normally. There is.

As a countermeasure, (1) make the capacitance of the smoothing capacitor sufficiently large to reduce the voltage drop of the capacitor voltage due to (rush current)> (current for charging the smoothing capacitor by the commercial power supply), or (2) a predetermined period of rise so as to limit the maximum value of the inrush current;
Methods such as applying a soft start are taken. However, in the case of (1), the size of the smoothing capacitor becomes large, which is disadvantageous in both cost and size. In the case of (2), the time until the lamp reaches a predetermined brightness is delayed. There is a problem.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and a lamp control apparatus and a lamp control apparatus capable of obtaining a sufficiently fast light rising at low cost without increasing the size of a smoothing capacitor. It is intended to provide a way.

[0013]

A lamp control device and a lamp control method according to the present invention are configured as follows.

(1) A lamp control device for outputting a lighting voltage to a lamp through a smoothing capacitor, wherein an output voltage to the lamp is limited according to an input voltage of the smoothing capacitor.

(2) In the configuration of (1), a DC voltage obtained by rectifying an AC voltage from a commercial AC power supply is used as an input voltage of the smoothing capacitor.

(3) In the above configuration (1) or (2), the output voltage is limited by changing the upper limit of the maximum pulse width of the output control signal.

(4) In the above configuration (1) or (2), the output voltage is limited by changing the set value of the voltage control circuit for controlling the output voltage.

(5) A lamp control method for outputting a lighting voltage to a lamp through a smoothing capacitor, wherein the output voltage to the lamp is limited according to the input voltage of the smoothing capacitor.

(6) In the configuration of (5), a DC voltage obtained by rectifying an AC voltage from a commercial AC power supply is used as an input voltage of the smoothing capacitor.

(7) In the configuration of (5) or (6), the output voltage is limited by changing the upper limit of the maximum pulse width of the output control signal.

(8) In the configuration of (5) or (6), the output voltage is limited by changing the set value of a voltage control circuit for controlling the output voltage.

[0022]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a lamp control device according to an embodiment of the present invention.

(Embodiment 1) FIG. 1 is a diagram showing a circuit configuration of Embodiment 1 of the present invention. 6, the same reference numerals as those in FIG. 6 denote the same components, and redundant detailed description will be omitted.

The improvement of this embodiment over the circuit of FIG.
This is to limit the output voltage Vo to the lamp 1 according to the input voltage of the chopper circuit. That is, FIG.
The voltage Vx at the point C of the startup / power supply circuit 2
(Equivalently, the DC voltage Vs at the point B) is detected, and if the value is low, the output (DT) of the DTC circuit 6 in the PWM control circuit 3 is detected.
C signal) to reduce the switching element FET
The on / off ratio of Q1 is reduced. Therefore, C
The point voltage Vx is input to the DTC circuit 6. Other configurations are the same as those of the circuit of FIG.

FIG. 2 is a diagram showing a specific internal configuration of the DCT circuit 6. In the figure, R11, R12, R13 are resistors for dividing the reference voltage Vret2 of the reference voltage source E2,
Q11 is a transistor connected in parallel with the resistor R13,
ZD11 is a Zener diode connected to the base.

FIG. 3 is a diagram showing output waveforms of various parts of the circuit of FIG. 1. The solid line shows the case of the present invention, and the dotted line shows the case of the conventional example.

In the circuit of FIG. 1, the positive terminal of the DC voltage Vs obtained by rectifying and smoothing the input voltage Vin from the commercial power supply is connected to the cathode of the diode D6, the capacitor C4 and the lamp 1, and The end is connected to the other end of the capacitor C4 and the primary winding N11 of the choke coil L1. Primary winding N11 of choke coil L1
Is connected to the anode of the diode D6 and the drain of the FET Q1, and the source of the FET Q1 is connected to the negative terminal (return line) of the DC voltage Vs.

In this manner, a step-down chopper circuit is formed by the FET Q1, the diode D6, the choke coil L1, and the capacitor C4, and the input voltage Vs is reduced to a desired lamp voltage Vo. Further, the voltage between both ends of the lamp is detected by the differential amplifier circuit 7, the detected value is compared with the reference voltage Vref1 of the reference voltage source E1 by the error amplifier circuit 8, and the PWM control circuit 3 sets the difference to zero. F
The on / off time ratio of the ETQ1 is controlled, thereby controlling the lamp voltage Vo to a constant voltage.

The diode D of the starting / power supply circuit 2
1, D2, capacitors C2, C3 and choke coil L
1, the power supply voltage P of the PWM control circuit 3 at the secondary winding N21.
Vcc. The resistor R1 is a starting resistor for supplying the starting power of the lamp control device to the capacitor C2.

As shown in FIG. 7, when a commercial power supply (for example, AC 100 V) is supplied at time TO, the circuit operation of the lamp control device at the time of starting the lamp is as follows. And the voltage Vs at the point B is charged and rises. At the same time, the power supply PVcc of the PWM control circuit 3 is supplied with the capacitor C through the starting resistor R1 by the voltage Vs.
2 is charged and rises.

Then, at time T1, the power supply voltage PVcc
Reaches the starting voltage VH of the PWM control circuit 3, the PWM
The control circuit 3 starts operation, turns on / off the FET Q1 at a high frequency to generate a pulse voltage, smoothes the voltage with the choke coil L1, the capacitor C4, and the diode D6, and applies the DC voltage Vo to the lamp 1. . Meanwhile, PW
The power supply voltage PVcc of the M control circuit 3 decreases while discharging the charge stored in the capacitor C2.

On the other hand, when the switching of the FET Q1 is started, the voltage Vx obtained by rectifying and smoothing the voltage induced in the secondary winding N21 of the choke coil L1 by the diode D1 and the capacitor C3 increases. The power supply voltage PVcc becomes higher than the voltage Vx.
Up to the stable voltage. After that, the power supply voltage PVcc becomes
The lamp lighting device is stabilized at a constant value (a value determined by the voltage Vs and the windings N11 and N22), and the lamp lighting device continues the steady operation.
Note that the “valley” occurs in the voltage Vx in FIG. 7 because the voltage Vs is temporarily reduced.

By the way, when the lamp 1 is very cold (morning in a cold region, immediately after the heating device is operated, etc.),
The inrush current at the start of the lamp is very large, much larger than the current supplied from the commercial power supply. Then, the voltage Vs of the capacitor C1 drops sufficiently compared with the second and subsequent lamp lighting, the voltage Vx at the point C does not increase, the power supply voltage PVcc continues to decrease, and the operation stop voltage of the PWM control circuit 3 is stopped. VL, the PWM control circuit 3 stops, and the lighting of the lamp 1 may fail.

The dotted line in FIG. 3 shows this state. When the PWM control circuit 3 starts operating at time T1, the power supply voltage PVcc decreases while discharging the charge of the capacitor C2. On the other hand, (lamp inrush current)> (capacitor C
(1 charging current), the voltage Vs at the point B decreases, and the voltage Vx at the point C cannot sufficiently increase. And
Eventually, the voltage PVcc falls below a certain voltage VL at time T14, and the PWM control circuit 3 stops.

For this reason, in order to perform the "first lamp lighting in the morning" once, the capacitance of the capacitor C1 is increased to increase the cost or to perform "soft start" when the lamp is turned on. The time until the lamp 1 reaches a predetermined brightness is delayed. "

However, in the present embodiment, the voltage Vs of the capacitor C1 is detected and "when the lamp is completely cooled".
And FE only when the input voltage Vin from the commercial power supply is low
The ON / OFF ratio of TQ1 is reduced, and the time until the brightness of lamp 1 reaches a predetermined value is delayed only at that time. Thus, when the lamp is turned on for the second time or later, or when the commercial power supply voltage is at a steady value, the brightness of the lamp can be quickly raised to a predetermined value.

Hereinafter, the operation of this embodiment will be specifically described.

At time T0 in FIG. 3, a commercial power supply (for example, A
When C100V is supplied to the lamp lighting device, it is rectified and smoothed by the diode bridge DB1 and the capacitor C1, and the DC voltage Vs at the point B rises by charging the capacitor C1. At the same time, the power supply PVcc of the PWM control circuit 3
, The capacitor C2 is charged by the above-described voltage Vs through the starting resistor R1 and rises.

At time T1, the voltage PVcc becomes P
When the starting voltage VH of the WM control circuit 3 is reached, the PWM control circuit 3 starts operation, turns on / off the FET Q1 at a high frequency to generate a pulse voltage, and supplies the voltage to the choke coil L1, the capacitor C4, and the diode D6. And smooth
A DC voltage Vo is applied to the lamp 1. Meanwhile, the voltage PV
cc decreases while discharging the charge stored in the capacitor C2.

On the other hand, when the switching of the FET Q1 is started, a voltage Vx obtained by rectifying and smoothing the voltage induced in the secondary winding N21 of the choke coil L1 by the diode D1 and the capacitor C3 becomes a voltage similar to the voltage Vs. Indicates that
When the rush current flows through the lamp 1 and the voltage Vs decreases, the voltage Vx also decreases.

At this time, the voltage Vx is input to the cathode of the Zener diode ZD11 (the Zener voltage is Vz) as shown in FIG. And T1 to T1
During the period of 1, Vx> Vz, the transistor Q11 is on, and the DTC output is the reference voltage Vref2.
Is divided by resistors R11 and R12 to obtain a value V (DTC1), which is input to the negative terminal of the comparator IC1 in the PWM control circuit 3 and is determined by the magnitude relationship between the voltage and the triangular wave input to the positive terminal of the comparator IC1. For example, FET Q1
Is limited to 50%.

When Vx <Vz at time T11, the transistor Q11 is turned off, and the reference voltage Vref2 is set to R11, (R12 + R13) as the DTC output.
V (DTC2), which is input to the negative terminal of the comparator IC1 in the PWM control circuit 3 and, for example, the maximum on-duty of the FET Q1, Is limited to 20%.

Immediately after the start of lighting of the lamp 1 at the time T1, (rush current into the lamp 1)> (current for charging the capacitor C1 from the commercial power supply), the voltage Vs continues to decrease. During that period, the voltage PVcc continues to decrease,
When PVcc <Vz at time T11, the above DTC
Since the maximum on-duty of the FET Q1 is limited to 20% by the operation of the circuit 6, the rush current to the lamp 1 is limited, and the decrease of the voltage Vs is suppressed. Then, when the lamp 1 warms and its impedance increases to reduce the inrush current, (inrush current to the lamp 1) <(current for charging the capacitor C1 by the commercial power supply), and the voltage Vs
Starts rising, and at the same time, the voltage Vx also rises.

At time T12, when Vx = PVcc, the voltage PVcc is thereafter charged with the voltage Vx, and rises toward the voltage Vs and the values determined by the windings N11 and N21, at time T15. Stabilized. On the way, at time T13, PVcc> Vz, and the operation of the DTC circuit 6 returns to the state where the maximum on-duty of the FET Q1 is limited to 50%.

As described above, when "lamp 1 is cold", (lamp inrush current) >> (capacitor C1
Charging current) and the time is long, the voltage Vs of the capacitor C1 decreases. However, the voltage Vs is detected to limit the lamp inrush current, and "the lamp 1 warms and its impedance increases". And the current limit to the lamp 1 is released after the voltage Vs is sufficiently charged, without increasing the capacitance of the capacitor C1 and impairing the lamp lighting speed after the second time. And a lamp control device without the need for such a lamp control device.

(Embodiment 2) FIG. 4 is a diagram showing a circuit configuration of Embodiment 2 of the present invention, and the same reference numerals as in FIG. 1 denote the same components.

In the first embodiment, the upper limit value of the maximum pulse width of the control signal for controlling the FET Q1 which is the switching element of the chopper circuit is set by the DTC circuit 6 of the PWM control circuit 3.
In this embodiment, the output voltage Vo is limited by varying the set value of the constant voltage control circuit 4 that controls the output voltage Vo. .

That is, the difference between the second embodiment and the first embodiment is that the voltage Vx at the point C (the voltage Vs at the point B is equivalently detected) is detected, and the error is detected by the variable reference voltage circuit 9 if the value is low. This means that the reference voltage Vref1 input to the amplifier circuit 8 is temporarily changed to a lower value.

FIG. 5 is a diagram showing a specific internal configuration of the variable reference voltage circuit 9. In the figure, R21, R2
2, R23 is a resistor for dividing the reference voltage Vref2 of the reference voltage source E2, Q21 is a transistor connected in parallel with the resistor 23, Q22 is a transistor connected between the base and the emitter of the transistor Q21, and ZD21 is a base of the transistor Q22. Is connected to the Zener diode.

In the circuit shown in FIG. 4, while the voltage Vs at the point B obtained by rectifying and smoothing the commercial power supply is falling, the lamp lighting voltage value is temporarily reduced to "lamp warms up".
Wait for the impedance to increase. Thereafter, when the value of the voltage Vs returns to the predetermined value, the reference voltage Vref1 of the error amplifier circuit 8 is returned to the original value.

With such a configuration, even if the output voltage Vo to the lamp 1 is limited in accordance with the input voltage Vs of the chopper circuit, the same operation and effect as those of the first embodiment can be obtained.

[0052]

As described above, according to the present invention,
It is possible to obtain a sufficiently fast rise of the lamp light amount at a low cost without increasing the size of the smoothing capacitor.

In other words, the lamp can be turned on when the lamp is completely cooled without increasing the capacity of the smoothing capacitor, without impairing the lamp rising speed after the second time.

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram of a first embodiment of the present invention.

FIG. 2 is an internal configuration diagram of the DTC circuit according to the first embodiment;

FIG. 3 is an output waveform diagram of each unit according to the first embodiment.

FIG. 4 is a circuit configuration diagram according to a second embodiment of the present invention.

FIG. 5 is an internal configuration diagram of a reference variable voltage circuit according to a second embodiment.

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

FIG. 7 is an output waveform diagram of each section of the conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Lamp 2 Start-up / power supply circuit 3 PWM control circuit 4 Constant voltage control circuit 5 Triangular wave oscillation circuit 6 DTC circuit 7 Differential amplification circuit 8 Error amplification circuit 9 Variable reference voltage circuit C1 Smoothing capacitor D6 Flywheel diode DB1 Diode bridge E1 Reference voltage Source E2 Reference voltage source IC1 Comparator IC2 Operational amplifier IC3 Operational amplifier L1 Choke coil N11 Primary winding N21 Secondary winding Q1 FET (switching element)

Claims (8)

[Claims] 1. A lamp control device for outputting a lighting voltage to a lamp through a smoothing capacitor, wherein the output voltage to the lamp is limited according to an input voltage of the smoothing capacitor. 2. The lamp control device according to claim 1, wherein a DC voltage obtained by rectifying an AC voltage from a commercial AC power supply is used as an input voltage of the smoothing capacitor. 3. The lamp control device according to claim 1, wherein the output voltage is limited by changing an upper limit value of a maximum pulse width of the output control signal. 4. The lamp control device according to claim 1, wherein the output voltage is limited by changing a set value of a voltage control circuit for controlling the output voltage. 5. A lamp control method for outputting a lighting voltage to a lamp through a smoothing capacitor, wherein the output voltage to the lamp is limited according to an input voltage of the smoothing capacitor. . 6. The lamp control method according to claim 5, wherein a DC voltage obtained by rectifying an AC voltage from a commercial AC power supply is used as an input voltage of the smoothing capacitor. 7. The lamp control method according to claim 5, wherein the output voltage is limited by changing an upper limit value of a maximum pulse width of the output control signal. 8. The lamp control method according to claim 5, wherein the output voltage is limited by changing a set value of a voltage control circuit for controlling the output voltage.