JP2001284088A - Power supply circuit for lamp - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power supply circuit which can light a lamp in a stable manner both at light load mode and at constant power heavy load mode. SOLUTION: A switch element Q2 connected in series with a first winding line L01 of a transformer T1 of a converter circuit is put under an on-off control by a signal output or the like of RS flip-flop 123. A comparator 122 detects a current flowing to the switching element Q2 from a resistor RS, and outputs a reset signal to the RS flip-flop 123. A trigger pulse generating circuit 70 generates a trigger pulse using charging and discharging waveforms formed by the resistor RS and a capacitor CT and supply it to the comparator 122, so that the comparator 122 can output a reset signal in a stable manner even when a current flowing in the switching element Q2 is at a small light load mode.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lamp power supply circuit used for lighting a lamp load, and more particularly to a lamp power supply circuit which operates stably in both a light load mode and a constant power heavy load mode.

[0002]

2. Description of the Related Art FIG. 3 is a block diagram showing the overall configuration of a lamp power supply circuit. In FIG. 3, a bridge diode D0 for rectifying an AC voltage from the AC power supply 10, a capacitor C0, a choke coil L1, and a switch element S
1, a rectifier diode D1, a smoothing capacitor C1,
The resistor RS1 constitutes the rectifying / smoothing circuit 20, and actually operates as a boost factor chopper circuit type power factor correction circuit. The switch element S1 is turned on / off by the control circuit 11. The detection resistor RS1 is for detecting the rectified pulsating voltage VL. The operation of the rectifying / smoothing circuit 20 has been described in detail in Japanese Patent Application No. 11-219640, which is a prior application of the present applicant, and thus will not be described.

The DC voltage V0 generated by the rectifying and smoothing circuit 20
Is input to the primary winding L01 of the transformer T1. A switching element S2 and a resistor RS2 for detection are connected in series to the primary winding L01, and a series circuit including the primary winding L01 and the resistor RS2 is connected in parallel to the rectifying / smoothing circuit 20. The switch element S2 is turned on by the control circuit 12.
Turned off. For a specific configuration example of the control circuit 12,
It will be described later.

A series circuit of a rectifier diode D2 and a flywheel diode D3 is connected in parallel to a secondary winding L02 of the transformer T1, and a flywheel diode D3
, A series circuit of a choke coil L2 and a smoothing capacitor C3 is connected in parallel. The transformer T1, the rectifier diode D2, the flywheel diode D3, the choke coil L2, and the smoothing capacitor C3
, And is a current mode DC / DC converter of a primary peak current control method.

The converter circuit 30 includes a diode D4
And a series circuit of a resistor R1 and a capacitor C4 are connected in parallel. At the connection point between the diode D4 and the resistor R1,
The boost output circuit 40 is connected. A high-voltage pulse generation circuit 50 is connected in parallel to the resistor R1 and the capacitor C4, and a discharge lamp 60 is connected to the high-voltage pulse generation circuit 50. In order to turn on the discharge lamp 60, an ignition pulse is applied to the discharge lamp 60 by the high-voltage pulse generation circuit 50, thereby causing dielectric breakdown between the cathode and anode of the discharge lamp 60. When lighting the discharge lamp 60, a high voltage is required, so the boost output circuit 40 supplies a boost voltage to the high-voltage pulse generation circuit 50, whereby the high-voltage pulse generation circuit 50 generates a high voltage. To the discharge lamp 60. Since a large current is required to light the discharge lamp 60 and maintain the lighting, the converter circuit 30 supplies the discharge lamp 60 with a large current.

[0006] From the boost output circuit 40 to the diode D4
If the voltage supplied to the connection point between the resistor D1 and the resistor R1 is higher than the voltage from the converter circuit 30, the diode D4 becomes reverse-biased, so that the voltage and current are supplied from the converter circuit 30 to the high-voltage pulse generating circuit 50. Not done. When the discharge lamp 60 is turned on and the output voltage from the boost output circuit 40 decreases and falls below the output voltage from the converter circuit 30, the diode D4 becomes forward-biased. The voltage from the constant power output circuit 30 to the high voltage pulse generation circuit 50 is
Current will be supplied. Further, the lamp current detection circuit 13 detects the amount of lamp current flowing through the discharge lamp 60 by the detection resistor RS3, and controls an indicator (not shown) for displaying that the lamp is lit. I have.

FIG. 4 is a circuit diagram of a conventional example, and FIGS.
FIG. 5 is a waveform diagram for explaining the operation of FIG. 4 and will be described together. FIG. 4 shows a specific configuration of the control circuit 12 and its peripheral portion in FIG. In FIG. 4, a base of a transistor Q3 is connected to a connection point between a resistor RT and a capacitor CT, which are charge / discharge circuits. The power supply voltage Vcc1 is applied to the resistor RT. The power supply voltage Vcc1 is supplied to the collector of the transistor Q3, and the emitter is
FE, which is the switch element S2, via the resistors R4 and R5
It is connected to a connection point between a T (field effect transistor) Q2 and a detection resistor RS2.

The capacitor CT generates a sawtooth-shaped charge / discharge waveform as shown in FIG. This charge / discharge waveform is input to the oscillator 121. Oscillator 121
Generates a square wave pulse which becomes high during the discharge period of the charge / discharge waveform from the capacitor CT, as shown in FIG. 5 (B). This pulse is output from the RS flip-flop 123
Is input to one of the set (S) input terminals and one input terminal of the OR circuit 124. The non-inverting input terminal of the comparator 122 includes the voltage of the capacitor CT via the transistor Q3 and the resistor R4, the transformer T1 and the switch element S2.
A control voltage indicated by a solid line in FIG. 5C, in which the current flowing through (FET Q2) is mixed with the voltage detected by the resistor RS2.

It is not necessary to supply the voltage of the capacitor CT via the transistor Q3 and the resistor R4 to the non-inverting input terminal of the comparator 122 in principle, but for the purpose of compensating the slope of the control signal described later. Mixed. 5 is connected to the inverting input terminal of the comparator 122.
A reference voltage Vref indicated by a broken line is input to (C). Here, a waveform when the reference voltage Vref is changed is shown. The output of the comparator 122 is shown in FIG.
The pulse waveform shown in (D) is input to the reset (R) input terminal of the RS flip-flop 123. The output of the RS flip-flop 123 is input to the other input terminal of the OR circuit 124.

The output of the OR circuit 124 is a transistor Q5
And the inverted output of the OR circuit 124 is input to the base of the transistor Q4. The transistors Q4 and Q5 form an amplifier circuit, and this amplifier circuit uses the pulse waveform shown in FIG.
2 (switch element S2). Transistor Q4
Is applied with a power supply voltage Vcc2. Note that the signals input to the set input terminal and the reset input terminal of the RS flip-flop 123 are not limited to the present embodiment, and may be configured to be opposite to each other. The reference voltage Vref input to the inverting input terminal of the comparator 122
Is constant, the smaller the capacitance of the capacitor CT is,
The ON period of switch element S2 can be lengthened, and output voltage V0 of converter circuit 30 can be increased.

When the discharge lamp 60 is turned on, the discharge lamp 60 shifts from arc discharge to glow discharge.
The boost output circuit 40 generates a boost voltage so that the high voltage pulse generation circuit 50 generates a high voltage ignition pulse. During the period in which the high-voltage pulse generating circuit 50 is operated with this boost voltage, the converter circuit 30 is almost in a no-load state.
A sufficient voltage cannot be fed back to the non-inverting input terminal 22. Therefore, in order to prevent the reset pulse from the comparator 122 from being in the non-output state and the output voltage of the constant power output circuit 30 from becoming unstable, the transistor Q3
The slope compensation described later is performed in which the voltage of the capacitor CT is simultaneously fed back to the non-inverting input terminal of the comparator 122 through the comparator.

FIG. 6 shows that when the voltage input to the non-inverting input terminal of the comparator 122 and the reference voltage Vref change, in other words, when the switching current flowing through the switch element S2 (FET Q2) changes, the comparator 1
It shows how the phase of the reset pulse output from 22 changes according to the magnitude of the capacitance of the capacitor CT. The slope portion of the voltage waveform input to the non-inverting input terminal of the comparator 122 is generated from the slope of the switching current and the slope of the charging voltage characteristic of the capacitor CT via the transistor Q3. In FIG. 6A, a solid line is a composite voltage waveform input to the non-inverting input terminal of the comparator 122 when the capacitance of the capacitor CT is large, and a dashed line is a non-inverting input terminal of the comparator 122 when the capacitance of the capacitor CT is small. It is an input composite voltage waveform.

As shown in FIG. 6A, the reference voltage Vref
Is at the position a, the reset pulse output from the comparator 122 is at the position shown in FIG. When the reference voltage Vref drops to the position b (that is, when the switching current flowing through the switch element S2 increases),
If the capacitance of the capacitor CT is large, the reset pulse moves to the position shown in FIG. As a result, the on-period of the switch element S2 changes in a direction of shortening, and negative power is applied so as to suppress the switching current, thereby making the power constant.

If the capacitance of the capacitor CT is small, the slope of the voltage waveform of the control signal input to the non-inverting input terminal of the comparator 122 becomes gentle as shown by the broken line in FIG. , Greatly move to the position shown in FIG. As a result, similarly, the on-period of the switch element S2 changes in the direction of shortening, and negative power is applied so as to suppress the switching current, thereby making the power constant. The switching element S2 is controlled to be turned on and off at a fixed frequency, and is controlled so that the power output from the converter circuit 30 is constant.

The above description is based on the switching element S2 (FET
In the case where the duty cycle of the current flowing through Q2) is in a stable state of less than 50%, when a current mode converter of the primary side peak current control method is used as the converter circuit 30, as is well known, the switching element is used. 50% duty cycle of switching current flowing through S2
In the unstable state described above, oscillation may occur at a cycle that is an integral multiple of the switching frequency of the DC / DC converter circuit, and this is called subharmonic oscillation.

In FIG. 4 described above, Rt, Ct
Is superimposed on the rising slope Lu signal of the switching current when the switching current is insufficient and the RS flip-flop 123 is in the light load mode.
To avoid a reset input signal from being generated, or a problem such as sub-harmonic oscillation when the duty cycle is 50% or more.

[0017]

In the case of a lamp load, stable operation is required while having both extremes of a light load mode and a constant power heavy load mode. The light load mode is a transitional period to lamp breakdown, glow discharge, and arc discharge in the lamp lighting operation process. Light power is supplied to the lamp load via the boost output circuit. In the forward type current mode converter, the 1
Assuming that the number of secondary windings is Np and the number of secondary windings is Ns, the duty cycle of the switching current in the light load mode δ = Ns /
Np. For example, when Np: Ns = 5: 1,
Since the duty cycle δ = Ns / Np = 0.2, the RS flip-flop 12
During a period of 0.2 from the input of the set signal to 3, the reset input signal must be reliably present.

In order to increase the output power in a steady state, it is necessary to reduce the resistance RS2 for detection and increase the switching current Is. However, conversely, in the light load mode, since the switching current Is is small, the voltage generated at the resistor RS2 may not reach the threshold voltage at which the output of the comparator 122 can be generated. The conventional slope compensation is effective to some extent but is not perfect, and the required output voltage does not appear in the light load mode, and the discharge lamp does not light up, and other problems occur. SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem. By providing a new circuit for forcibly supplying a trigger pulse in a light load mode, a voltage generated in a resistor RS2 is generated by an output of a comparator 122. An object of the present invention is to provide a lamp power supply circuit that can stably turn on a lamp in both a light load mode and a constant power heavy load mode because the voltage reaches a possible threshold voltage.

[0019]

In order to achieve the above object, a rectifying / smoothing circuit for rectifying and smoothing an AC voltage from an AC power supply to generate a DC output voltage, and a discharge lamp for controlling the DC output voltage. And a high-voltage pulse generating circuit for generating a high-voltage pulse for starting the discharge lamp, wherein the converter circuit comprises a primary winding and a secondary winding. A primary winding, a transformer connected to the rectifying and smoothing circuit, a switch element connected to the primary winding,
A rectifier diode and a smoothing capacitor connected to the secondary winding; and a control circuit that controls on / off of the switch element so that power supplied to the discharge lamp is constant.The control circuit includes a resistor and A charge / discharge circuit comprising a capacitor, an oscillator for generating a square wave pulse using the charge / discharge waveform of the charge / discharge circuit, a reference voltage input to its inverting input terminal, and the primary winding to its non-inverting input terminal. A comparator for inputting a voltage obtained by detecting a current flowing through the line and a mixed voltage of a trigger pulse and outputting a reset pulse; and an RS flip-flop to which a square wave pulse output from the oscillator and the reset pulse are input. ,
An OR circuit to which a square wave pulse output from the oscillator and an output of the RS flip-flop are input;
An amplifier circuit for amplifying the output of the R circuit and driving the switch element; and generating the trigger pulse by using a charge / discharge waveform by the charge / discharge circuit, and supplying the trigger pulse to the comparator for reliably generating the reset pulse. And a trigger pulse generating circuit.

[0020]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a waveform diagram for explaining the operation of FIG. 1, which will be described together. The same parts as those in the conventional example shown in FIG. 4 are denoted by the same reference numerals, and description thereof will be omitted. In FIG.
The oscillator 121 receives the RT and CT charge / discharge voltages having the waveforms shown in FIG. 2 (A), generates a square wave pulse having the waveform shown in FIG. 2 (B), and sets (S) a terminal of the RS flip-flop 123. To supply. The switching current I flowing through the transformer T1 is connected to the non-inverting input terminal of the comparator 122.
The voltage of the waveform shown in FIG. 2C generated in the resistor RS2 for detecting s and the charge / discharge voltage of RT and CT for slope compensation are passed through an emitter follower circuit composed of a transistor Q3. The voltage to which the voltage is added is supplied.

On the other hand, the reference voltage Vref is supplied to the inverting input terminal of the comparator 122,
Generates an output pulse having the waveform shown in FIG. 2D and supplies it to the reset (R) terminal of the RS flip-flop 123. The output of the RS flip-flop 123 and the oscillator 12
The output of 1 is supplied to the OR circuit 124. FIG.
The output signal of the OR circuit 124 having the waveform shown in (E) is supplied to the gate of the switching element Q2 via the SEPP amplifying circuit composed of the transistors Q4 and Q5, and performs the switching operation.

Hereinafter, the operation of the trigger pulse generation circuit 70, which is the point of the present invention, will be described. The non-inverting input terminal of the comparator 126 is supplied with a voltage through the emitter follower circuit composed of the transistor Q3, and the charging and discharging voltage of RT and CT is supplied to the non-inverting input terminal.
And a reference voltage determined by R7. Note that the resistor R8 is a feedback resistor. The comparator 126 is shown in FIG.
An output pulse having the waveform shown in (F) is generated. This output pulse includes a capacitor C5, a resistor R9 and a diode D
The signal is supplied to the differentiating circuit composed of the trigger signal 5 and becomes a trigger pulse having the waveform shown in FIG.

The trigger pulse has a phase relationship so as not to affect the rise of the output signal of the OR circuit 124 having the waveform shown in FIG. 2 (E) and the rise of the output in the next cycle. It is supplied to the non-inverting input terminal of the comparator 122 via the diode D6. Assuming the number of primary windings Np and the number of secondary windings Ns of the transformer T1, the duty cycle δ of switching current in the light load mode is δ = Ns / Np. This trigger pulse must surely be present during the period of duty Ns / Np from the set signal input to the RS flip-flop 123. The diode D6 is provided by adding a circuit for generating a trigger pulse other than the comparator 126.
This is for keeping the operating conditions of the conventional circuit unchanged.

A switching element S3 is connected between the connection point of the resistor R10 and the diode D6 and the ground. The switch element S3 is turned on / off by the lamp current detection circuit 13 described in FIG. The lamp current detection circuit 13 detects the amount of the lamp current flowing through the discharge lamp 60 by the detection resistor RS3 in FIG. 3, and turns on the switch element S3 in the steady heavy load mode, thereby turning on the comparator. The supply of the trigger pulse to 122 is stopped. That is, the trigger pulse is supplied only in the light load mode.

According to the present invention, even when the ratio of the light load power to the steady heavy load power is large and the value of the resistor RS2 for detecting the switching current of the transformer T1 must be reduced, the trigger pulse must be generated in the light load mode. , The reset input signal to the RS flip-flop 123 can be generated, and the stable operation is performed in both the light load mode and the constant power heavy load mode.

[0026]

According to the lamp power supply circuit of the present invention, the voltage generated in the detection resistor RS2 generates the output of the comparator 122 by newly providing a circuit for forcibly supplying a trigger pulse in the light load mode. Since the threshold voltage is reached, the discharge lamp can be stably operated in both the light load mode and the constant power heavy load mode.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing one embodiment of the present invention.

FIG. 2 is a waveform chart for explaining the operation of FIG.

FIG. 3 is a block diagram illustrating an overall configuration of a lamp power supply circuit.

FIG. 4 is a circuit diagram of a conventional example.

FIG. 5 is a waveform chart for explaining the operation of FIG. 4;

FIG. 6 is a waveform chart for explaining the operation of FIG. 4;

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 AC power supply 11, 12 control circuit 13 lamp current detection circuit 20 rectifying / smoothing circuit 30 converter circuit 40 boost output circuit 50 high-voltage pulse generation circuit 60 discharge lamp 70 trigger pulse generation circuit 121 oscillator 122 comparator 123 RS flip-flop 124 OR circuit C1, C3 Smoothing capacitor D0 Bridge diode (rectifier circuit) D1, D2 Rectifier diode D3 Flywheel diode L1, L2 Choke coil RS1, RS2, RS3 Detection resistor S1, S2, S3 Switch element T1 Transformer

Claims (2)

[Claims] 1. A rectifying and smoothing circuit for rectifying and smoothing an AC voltage from an AC power supply to generate a DC output voltage, a converter circuit for controlling the DC output voltage to control the power of a discharge lamp, and starting the discharge lamp. A power supply circuit for a lamp, comprising: a high-voltage pulse generating circuit for generating a high-voltage pulse for causing the power supply to generate a high-voltage pulse; wherein the converter circuit includes a primary winding and a secondary winding, and the primary winding is rectified. A transformer connected to a smoothing circuit; a switch element connected to the primary winding; a rectifier diode and a smoothing capacitor connected to the secondary winding; and a power supplied to the discharge lamp being constant. A control circuit that controls on / off of the switch element, wherein the control circuit uses a charge / discharge circuit including a resistor and a capacitor; An oscillator that generates a wave pulse, a reference voltage is input to its inverting input terminal, and a voltage obtained by detecting a current flowing through the primary winding and a mixed voltage of a trigger pulse are input to its non-inverting input terminal, and reset. A comparator that outputs a pulse; an RS flip-flop to which the square-wave pulse output from the oscillator and the reset pulse are input; and a square-wave pulse output from the oscillator and the output of the RS flip-flop. An OR circuit that amplifies the output of the OR circuit to drive the switch element; and generates the trigger pulse by using a charge / discharge waveform by the charge / discharge circuit and reliably generates the reset pulse. And a trigger pulse generation circuit for supplying the pulse signal to the comparator. 2. A lamp current detection circuit for detecting an amount of current flowing to the discharge lamp, and the trigger from the lamp current detection circuit is provided only in a light load mode such as a start of lighting of the discharge lamp. The lamp power supply circuit according to claim 1, further comprising a trigger pulse generation circuit that generates a pulse.