JP3048620B2 - Discharge lamp lighting device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a discharge lamp lighting apparatus for lighting a discharge lamp at a high frequency using a so-called self-excited self-excited inverter circuit.

[Prior Art] FIG. 3 shows a conventional discharge lamp lighting device (Japanese Patent Application No. 02-34234).
FIG. Hereinafter, the circuit configuration will be described. A first switching element is provided at both ends of the DC power supply E.
Q ₁ and is connected to a second series circuit of the switching element Q _2. Between both ends of the switching element Q _1, the discharge lamp la, a capacitor C _1, to connect the series circuit of the primary winding n ₁ of the inductor L _1, the resistance induced output of the secondary winding n ₂ of the inductor L ₁ through R ₀ is input to the control terminal of the switching element Q ₁ (base-emitter). The non-power side of the filament of the discharge lamp la resonance and capacitor C ₂ for preheating current supply are connected in parallel. The switching element Q _1, a bipolar transistor is used, the diode D ₁ of the wheeling is connected in reverse parallel between the collector and the emitter.
Second as the switching element Q _2, the power MOSFET is used, anti-parallel diodes are built. A series circuit of a pair of resistors R ₁ and R ₂ is connected in parallel between both ends of the switching element Q ₂ . The series circuit of the resistors R ₁ and R ₂ divides the voltage V ₂ across the switching element Q ₂ to form an on-period detection section A that detects the on state of the switching element Q ₁ . When the switching element Q ₁ is on, the signal Sb voltage across V ₂ by dividing the switching element Q ₂ are "High" level, the switching element Q ₁ is turned off, the signal Sb becomes "Low" level. After the signal Sb detected by the resistors R ₁ and R ₂ is inverted by the inverting circuit 1,
Control signal Sa output from monostable multivibrator 4
Together, it is input to the AND circuit 2 sets the ON period of the switching element Q ₂ by the logical product output Sc, constitute another励信No. generator B. The monostable multivibrator 4 is a general-purpose integrated circuit for a timer (for example, μPD1555).
More it will have been set by the time constant circuit of the output pulse width resistor R ₃ and capacitor C _3. The output pulse width of the separate excitation signal generation section B is controlled by the ON period control section C, and can be made shorter by a preheating timer section 5 than the time of normal operation by a fixed time from the time of power-on.

4 and 5 are operation waveform diagrams of the above circuit. Hereinafter, the operation of the above circuit will be described. When the separately-excited signal Sc becomes “High” level, the switching element Q ₂ is turned on, and the current I flows through the path of the DC power supply E, the discharge lamp la, the capacitor C ₁ , the inductor L ₁ , the switching element Q ₂ , and the DC power supply E. ₂ flows. In this case, the primary winding n ₁ of the inductor L _1, it flows the same oscillating current I ₃ and the current I _2. On the other hand,
When Sc is "Low" level, the switching element Q ₂ is but turned off, the energy stored in the capacitor C ₂ and the inductor L ₁ for resonance, the oscillating current I ₃ is tries to continue to flow. At this time, the induced voltage V ₃ of the secondary winding n ₂ of the inductor L _1, the polarity is reversed. Here, the other励信No. Sc generated from other励信No. generator B, is set shorter period than the vibration current I _3. Immediately after the switching element Q ₂ is turned off, the inductor L _1, diode D _1, the discharge lamp la,
Capacitor C _1, the current I ₁ flows through a path of the inductor L _1. Further, the current flowing through the secondary winding n ₂ of the inductor L _1, since the switching element Q ₁ is turned on biased, if the direction of the resonant current reverses, the inductor L _1, a capacitor C _1, the discharge lamp la, the switching element Q _1, the current I ₁ flows through a path of the inductor L _1. Then the inductor
By a change in the oscillating current I ₃ flowing through the primary winding n ₁ of L _1, bias current flowing through the secondary winding n ₂ of the inductor L ₁ is decreased, the switching element Q ₁ is turned off. The period switching device Q ₁ is turned on, the voltage across V ₂ of the switching element Q ₂ is approximately equal to the output voltage of the DC power source E, the switching element Q ₁ is turned off, the voltage across the switching element Q ₂ is almost It becomes 0. Therefore, the switching element Q ₂
Signal Sb at the connection point of resistors R ₁ and R ₂ connected between both ends of
Accordingly, it detects the on or off switching elements Q _1. By the detection signal Sb, the switching elements Q ₁ and Q ₂
Simultaneously turned on to prevent, it controls the ON period of the switching element Q _2.

As described above, by turning on and off the switching elements Q _1, Q ₂ alternately, the inductor L ₁ oscillating current I ₃
Flows, and the discharge lamp la is lit at a high frequency. The preheating timer unit 5 is configured to shorten the on-period of the external excitation signal output from the external excitation signal generation unit B for a fixed time set by the preheating timer unit 5 from the time of turning on the power, and to supply energy to the discharge lamp la. Is reduced to preheat the filament without turning on the discharge lamp la. When the time set by the preheating timer unit 5 has elapsed, the on-period of the separate excitation signal gradually increases, and the discharge lamp la is turned on.

Simultaneous ON prevention of switching elements Q _1, Q _2, as described above, the resistor R ₁ connected in parallel with the switching element Q _2, R ₂
After the output signal Sb from the connection point is inverted by the inverting circuit 1, the output signal Sb is input to the AND circuit 2 together with the control signal Sa output from the monostable multivibrator 4, and the logical product signal Sc
It is accomplished by setting the ON period of the switching element Q ₂ by. That is, in this configuration, regardless of the control signal Sa outputted from the monostable multivibrator 4, until the switching element Q ₁ is turned off, since the output signal Sc from the AND circuit 2 does not become "High" level, both The switching elements Q ₁ and Q ₂ are prevented from being simultaneously turned on.

Monostable multivibrator 4, resistor R ₃ and a capacitor
It is set the pulse width of the output signal Sa by a time constant of C _3. The charging rate of the capacitor C _3, i.e. the charging current i ₂ to the capacitor C _3, the pulse width changes. When the switching transistor Q ₃ in the on-period control unit C is on, the charging current i ₂ to the capacitor C ₃ is equal to the constant current i ₁ from the current mirror CM _1, the i ₂ = i _1. When the switching transistor Q ₃ is turned off, the charging current i ₂ to the capacitor C ₃ is a current mirror CM
From the constant current i ₁ from ₁ subtracts the constant current i ₃ to the current mirror CM _2, a i ₂ = i ₁ -i _3. Therefore, when the switching transistor Q ₃ is turned off, the pulse width of the output signal Sa of the monostable multivibrator 4 is long. The on-off switching transistor Q ₃ are the output signal S of the parallel-connected resistors R _1, R ₂ at the connection point to the switching element Q ₂
b and the output signal Sa of the monostable multivibrator 4 are controlled by an output signal Sb of the NAND circuit 3 which inputs the output signal Sb.
As described above, the output signal Sb is output from the connection point of the resistors R ₁ and R _2.
The switching element Q ₁ is in the on becomes "High" level, when off the "Low" level. The switching element Q ₁ is in the on, when the control signal Sa outputted from the monostable multivibrator 4 rises, the output of the NAND circuit 3 is the switching element Q ₁ is becomes "Low" level to turn off. When the output of the NAND circuit 3 is in the "Low" level, the switching transistor Q ₃ are from turned off, so that the ON period of the control signal Sa is stretched. That is, when the on period of the switching element Q ₁ is longer, it becomes longer on-period of the other励信No. Sc output from the other励信No. generator B.

Thus, it is possible by changing the ON period of the switching element Q ₂ based on the ON period of the switching element Q _1, to suppress a change in the lamp current due to variation or temperature change of the switching element. In particular, as the ON period of the switching element Q ₁ is long, the switching element Q ₂
While decreasing the on-period, is controlled to increase the total time of the ON period switching element Q _1, a switching element Q _2, the effect of suppressing the change of the lamp current increases.

[Problem to be Solved by the Invention] In the above-described conventional example, although there is an effect of suppressing a change in lamp current with respect to variation in switching elements, there is no effect of suppressing a change in lamp current with respect to power supply fluctuation. For example, when the power supply voltage rises, increasing the bias current to the switching element Q _1, the switching element Q ₁
Becomes longer. As a result, the switching frequency decreases and the lamp current increases. In the above control,
When the on period of the switching element Q ₁ is increased, the switching element Q _1, a switching element total time Q ₂ 'of the on-period is increased, thereby switching frequency is further lowered, the lamp current increases. When the power supply voltage drops, the bias current decreases the switching element Q _1, the ON period of the switching element Q ₁ is shortened, the higher the switching frequency, the lamp current decreases. In the above control, when the on period of the switching element Q ₁ is shortened, the total time of the ON period of the switching element Q _1, a switching element Q ₂ is so reduced, the switching frequency is even higher, the lamp current decreases. That is, when the control in the above-described conventional example is performed, the fluctuation of the switching frequency with respect to the power supply fluctuation is large, and the fluctuation of the lamp current is also large.

The present invention has been made in view of such a point,
The purpose is to excite one of the pair of switching elements separately, control the other self-excitation to light the discharge lamp at a high frequency, and with the change of the ON period of the self-excited switching element, In a discharge lamp lighting device that controls the ON period of a switching element that is separately excited,
An object of the present invention is to make it possible to suppress a change in lamp current due to a power supply change.

[Means for Solving the Problems] In the discharge lamp lighting device of the present invention, in order to solve the above-described problems, as shown in FIG. By connecting a series circuit of Q ₁ and a second switching element Q ₂ , the first switching element Q ₁
The discharge lamp la a series circuit of a capacitor C ₁ and the inductor L ₁ connected in parallel, the on-off control by the second switching element Q ₂ other励信No., secondary winding provided on the inductor L ₁ The first switching element by the induced output of n ₂
By turning on and off the Q _1, in the discharge lamp lighting apparatus first switching element Q ₁ a discharge lamp la and alternately turns on and off the second and switching element Q ₂ so as to light up at a high frequency , the on period detection unit a which detects the first on period of the switching element Q _1, the other for generating the other励信No. turning on the second switching element Q ₂ in the first off-period of the switching element Q ₁ The excitation signal generator B and the first
Variation of the on period control unit C for changing the second on period of the switching element Q ₂ based on the ON period of the switching element Q _1, the power supply voltage variation rate of the second on-time switching element Q ₂ And a power supply fluctuation compensating unit D that changes in accordance with the power supply fluctuation.

In the [Operation] The present invention, thus, other switching elements due to the change of one of the on-period switching element Q ₁
Is provided with the power supply variation compensation section D varied according to the variation in power supply voltage change rate of the on period Q _2, in which the variation of the lamp current on the power supply variation can be suppressed.

Embodiment 1 FIG. 1 is a circuit diagram of a first embodiment of the present invention. In the present embodiment, the conventional example shown in FIG. 3, the emitter of the first one of the transistors of the current mirror CM ₁ is connected to the power source E, the second current determination of the current mirror CM ₂ the resistor R ₆ in parallel with the resistor R ₇ which are connected via a switching element Q _4. Current i ₁ from the first current mirror CM ₁ varies with the voltage level of the DC power source E.
If the voltage level of the DC power supply E increases, the current i ₁ increases. Conversely, if the voltage level of the DC power supply E decreases, the current i ₁
To reduce can control the charging current i ₂ of the capacitor C ₃ has set ON period of the switching element Q _2.

Further, in this embodiment, the current i ₃ of the _second current mirror CM ₂ is determined by the resistor R ₆ when the switching element Q ₄ is off, and the resistances R ₆ and R ₇ when the switching element Q ₄ is on.
Is determined by the combined resistance of With this configuration, when the switching element Q ₄ is on, the correction effect of the ON period shown in the conventional example becomes conspicuous, on period switching element Q ₄ is shown in the conventional example when being off The correction effect of is weakened. Therefore, it is possible to suppress the variation with respect to power supply variation by the current i ₁ from the first current mirror CM _1, by switching the current i ₃ of the current mirror CM _2, controls the correct working of the on period shown in the conventional example It becomes possible. In the present embodiment, it is made larger than the on-off switching element Q ₄ are has switching control by detecting the lighting of the discharge lamp la, corrective action at the time of lighting the correction effect at the time of starting.

In the preheating timer section 5, the capacitor C ₅ is charged via the resistor R ₁₀ at power-on, to over resistor R _11, a reference voltage obtained by dividing by R ₁₂ minute supply voltage for control thereof charge voltage, the comparator When the output terminal of CP goes to “High” level and a certain time has elapsed since the power was turned on, the capacitor C ₅
When the charging voltage exceeds the reference voltage, the comparator CP
Output terminal goes to “Low” level. When the output terminal of the comparator CP is "High" level, a bias current flows to the base of the transistor Q ₅ through a resistor R _8, transistor Q ₅ is turned on. Therefore, the current mirror
Current flowing through the CM ₁ is determined by the parallel resistance of the resistor R ₄ resistors R _5, increasing the current i ₁ of the current mirror CM ₁ is, the charging current i ₂ of the capacitor C ₃ is increased. Therefore, the capacitor
Charging rate of C ₃ is faster, monostable multi-vibrator 4
Output pulse width becomes short. Thus, the resonance voltage flowing through the inverter device is limited, and the discharge lamp la is preheated without being turned on. Thereafter, when the output terminal of the comparator CP becomes "Low" level, the transistor Q ₅ is turned off, the capacitor C ₅ is charged via the resistor R _5, in the end, the current flowing through the current mirror CM ₁ has resistance only it becomes current flowing through R _4. Thus, a current i ₁ of the current mirror CM ₁ is decreased, the charging current i ₂ of the capacitor C ₃ is reduced. Therefore, the charging rate of capacitor C ₃ is slower,
The output pulse width of the monostable multivibrator 4 becomes longer. As a result, the resonance current flowing through the inverter increases, and the discharge lamp la is turned on.

Embodiment 2 FIG. 2 is a circuit diagram of a second embodiment of the present invention. In the present embodiment, by connecting the other end of the resistor R ₆ that determines the current i ₃ flowing through the current mirror CM ₂ to the DC power source E,
It is possible to change the magnitude of the current i ₃ in accordance with the fluctuation of the DC power source E. If the voltage level of the DC power supply E increases,
Current i ₃ increases, with decreasing voltage level opposite to the DC power source E, since the current i ₃ decreases, controls the charging current i ₂ of the capacitor C ₃ has set ON period of the switching element Q ₂ it can.

Note that, in order to control the rate of change of the on-period according to the voltage fluctuation of the DC power supply E, the absolute value of the fluctuation of the power supply voltage may be detected, and the on-period may be set accordingly.

[Effects of the Invention] In the present invention, as described above, a series circuit of a first switching element and a second switching element is connected between both ends of a DC power supply, and a discharge lamp is connected to the first switching element. The series circuit of the capacitor and the inductor is connected in parallel,
The first switching element and the second switching element are controlled by turning on / off the switching element by a separate excitation signal and turning on / off the first switching element by an induced output of a secondary winding provided in the inductor. An on-period detection unit that detects an on-period of the first switching element, in a discharge lamp lighting device that turns on and off the elements alternately to light the discharge lamp at a high frequency;
A separate excitation signal generating unit for generating a separate excitation signal for turning on the second switching element during an off period of the first switching element, and an on period of the second switching element based on the on period of the first switching element And a power fluctuation compensator for controlling the rate of change of the ON period of the second switching element so that the fluctuation of the lamp current of the discharge lamp becomes smaller with respect to the power fluctuation. Therefore, there is an effect that, in addition to the variation in the characteristics of the switching elements and the change in the temperature characteristics, the change in the lamp current due to the power supply voltage change can be suppressed.

In particular, if the rate of change in the on-period is controlled in a direction in which the rate of change in the on-period is reduced in accordance with the fluctuation width of the power supply voltage, the effect of suppressing the change in the lamp current is enhanced.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a first embodiment of the present invention, FIG. 2 is a circuit diagram of a second embodiment of the present invention, FIG.
FIG. 5 and FIG. 5 are operation waveform diagrams of the above. E is a DC power supply, Q ₁ and Q ₂ are switching elements, la is a discharge lamp, C ₁ is a capacitor, L ₁ is an inductor, n ₁ is a primary winding,
n ₂ is 2 windings, A is the on-period detecting unit, B is other励信No. generator, C is on-period control unit, D is a power supply variation compensation section.

Claims (1)

(57) [Claims] 1. A series circuit of a first switching element and a second switching element is connected between both ends of a DC power supply, and a series circuit of a discharge lamp, a capacitor and an inductor is connected in parallel to the first switching element. , The second switching element is controlled to be turned on and off by a separate excitation signal, and the first switching element is turned on and off by an induced output of a secondary winding provided in the inductor. 2 switching elements alternately on
In a discharge lamp lighting device that is turned off to light a discharge lamp at a high frequency, an on-period detection unit that detects an on-period of a first switching element, and a second switching element during an off-period of the first switching element A separate excitation signal generating section for generating a separate excitation signal for turning on the second switching element, an on-period control section for changing the on-period of the second switching element based on the on-period of the first switching element, and the second switching section A discharge lamp lighting device, comprising: a power supply fluctuation compensating unit that changes a change rate of an on period of an element according to a power supply voltage fluctuation.