JPH02199797A - Discharge lamp lighting device - Google Patents

Abstract

PURPOSE:To enable the precise control of oscillation of an inverter by detecting a waveform change from the current waveform in normal state and judging whether the state of a discharge lamp is normal or not when the state of the discharge lamp is changed from the normal state. CONSTITUTION:A first main transistor Q1 and a second transistor Q2 are connected in series to a DC power source E, a detection resistance R1 is connected on the emitter side of the main transistor Q1, a diode D1 is connected in reverse parallel to a series circuit of the main transistor Z1 and the detection resistance R1, and a diode D2 is connected in reverse parallel to the main transistor Q2. These two main transistors Q1, Q2 are alternately turned on and off by drive circuits 10, 20, respectively. In this case, when the state of discharge lamps DL1, DL2 is changed from normal state, the waveform change from a current waveform in the normal state is detected, and whether it is normal or not is judged. Hence, according to this result, the oscillation of an inverter can be precisely controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a discharge lamp lighting device for lighting a discharge lamp such as a fluorescent lamp at high frequency.

[Prior Art] FIG. 6 is a circuit diagram showing the main structure of a conventional discharge lamp lighting device (see Japanese Patent Application No. 626,484). In this conventional example, a switching transistor Q is used in an inverter-type discharge lamp.

A current detection resistor RI that converts the current flowing into a voltage into a voltage, and a detected voltage generated by the current detection resistor R1 are compared with a first reference voltage Vr, and if the detected voltage is equal to or higher than the first reference voltage Vr, A first detection circuit 1 that generates a detection signal I and a first detection voltage generated by the current detection resistor R1.
a second reference voltage Vr2 higher than the reference voltage Vr+ of In this case, the detection voltage generated by the current detection resistor R1 is higher than the first reference voltage Vr1 and the second reference voltage Vr1 is higher than the second reference voltage Vr1.
the first and second reference voltages Vr so as to be less than rz;
, Vr2 are set. In this way, at the end of the life of the discharge lamp, the detection voltage generated in the current detection resistor R1 according to the current flowing through the switching transistor Q is
The first reference voltage V r is the second reference voltage Vr2.
The first and second reference voltages Vr, , V
By setting r2, at the end of the life of the discharge lamp, the detection voltage generated by the current detection resistor R+ exceeds the first reference voltage Vr+, so the first detection circuit 1 generates the detection signal I, and the circuit When an overcurrent occurs due to an abnormality, the detection voltage generated in the current detection resistor R7 exceeds the second reference voltage Vr2, and the second detection circuit 2 generates the detection signal ■. According to the detection signals I and (2) of the circuit 1.2, it is possible to perform an appropriate protection operation according to each case.

The circuit configuration shown in FIG. 6 will be specifically explained below. A resistor R3 for current detection is connected in series to the emitter side of the transistor Q, which is the main switching element of the inverter circuit. The voltage drop occurring across this resistor R+ is detected by detection circuit 1 and detection circuit 2, and detection signal 1. I [obtained. Detection circuit 1 includes a comparator CPI and a reference voltage Vr.
+, AND gate G1, switch S field, etc. The detection circuit 2 also includes a comparator CP2, a reference voltage Vr2
Consists of. These detection circuits 1.2 connect comparators CP + and CP when the detection voltage vR1 by the detection resistor R1 becomes equal to or higher than the reference voltage Vr, Vr2, respectively.
The output of t becomes "High" level, and a detection signal is obtained.

However, in the detection circuit 1, the output of the comparator CP1 is input to the AND gate G1 together with the voltage signal at the connection point of the resistor R0 and the switch SW;
The output of 1 is used as a detection signal. The switch SW is turned on until the discharge lamp is completely lit. The voltage signal at the connection point between the resistor R0 and the switch SW is at a "Low" level when the switch SW is on, and is at a "High" level when the switch SW is off. Therefore, at the time of starting the discharge lamp, the detection voltage V Rl by the detection resistor R temporarily exceeds the reference voltage Vr, and the comparator CP
Even if the output of switch 1 becomes “High” level, the switch S
While W is on, the detection signal I can be kept at the "Lou+ level", and it is possible to prevent the inverter circuit from stopping due to overcurrent during startup.

FIG. 7 is an explanatory diagram of the operation of this embodiment, and shows the relative relationship between the levels of the reference voltages Vr, Vr2 in the circuit of FIG. The vertical axis is the detection voltage VR1 by the detection resistor R1, and the horizontal axis is the time t. As shown in the figure, the relationship between the reference voltages Vr, , Vr2 is such that the reference voltage Vr2 is set high and the reference voltage Vr1 is set low.

The peak value of the detection voltage VR1 by the detection resistor R5 during the discharge lamp starting process is set to be between the reference voltages Vr+ and Vrz, and the detection voltage VR1 during normal operation (normal lighting) is set to the reference voltage V r lJ: Make it smaller. Furthermore, the detection voltage VRI by the detection resistor R1 at the end of its life (when the emitter is exhausted) is the reference voltage Vr, , Vr! so that it is between. Thus the reference voltage V r 1 .

By setting Vr2, the end of the discharge lamp's life can be detected using the reference voltage Vr, and the detection signal can be used to display that the discharge lamp is at the end of its life, or to change the oscillation mode and change the inverter output. By reducing the stress on the switching element, the stress on the switching element is reduced.

In addition, overcurrent due to circuit abnormality etc. is detected using the reference voltage Vrt, and when this detection signal is obtained, the oscillation of the inverter circuit is immediately stopped or the oscillation mode is changed to reduce the inverter output. This prevents smoke, fire, explosion, etc., and ensures the safety of the lighting device.

FIG. 8 is a circuit diagram of another conventional example. This circuit is L
The detection circuits 1 and 2 described above are added to a discharge lamp lighting device using an inverter circuit having a C series resonant circuit. The circuit configuration will be explained below. A first main transistor Q and a second main transistor Q2 are connected in series to a DC power source E, and the main transistors Q, , Q.

Detection resistors R, , R2 are connected to the emitter sides of , and diodes D, , D are connected in antiparallel to each of them.

is connected. These two main transistors Q,
Q2 is turned on and off alternately. A discharge lamp DL having a capacitor C2 connected in parallel is connected to both ends of the series circuit of the main transistor Q and the resistor R1 via a choke coil L1 and a capacitor CI. In an inverter circuit having such a configuration, since there are two main transistors, two sets of detection circuits are also required. In the circuit shown in FIG. 8, the detection circuit 1 at the end of the discharge lamp life is the transistor Q.
.

A detection circuit 2 for ensuring safety in the event of a circuit abnormality is connected to each detection resistor R, , R2.

In an inverter circuit having an LC series resonant circuit as shown in FIG. 8, there is a large difference in the peak value of the current flowing through the switching element when the discharge lamp is normal and at the end of its life, and Since the difference in peak voltage values also increases, level detection is very effective.

[Problem to be solved by the invention] However, at the end of the life of the discharge lamp and during normal operation,
If the peak value of the current flowing through the switching element does not change much, it becomes very difficult to distinguish using the level detection method described above.For example, in a resonant circuit with two lamps in parallel as shown in Fig. , even if one lamp reaches the end of its life and its condition changes significantly, the lamp remains normal, so the resonance system will not change significantly, and the current flowing through the switching element will be as shown in Figures 10 (a) and (b). As shown in FIG. 2, the waveform has a peak value that is almost the same between the normal state and the end of its life, making it difficult to determine the state of the discharge lamp based on the peak value as in the past. At this time, although the stress on the switching element itself does not become so large, a larger current flows through the choke coil L1 and the balancer than in normal times, so there is a problem that heat generation increases.

The present invention has been made in view of these points, and its purpose is to provide an inverter-type discharge lamp lighting device that can be used even though the state of the discharge lamp changes significantly at the end of its life. An object of the present invention is to reliably determine the state of a discharge lamp and perform appropriate control even when the peak current of a switching element does not increase much.

[Means for Solving the Problems] In order to solve the above problems, the present invention provides a lighting device that lights a discharge lamp at high frequency using an oscillation output of an inverter circuit, in which the current waveform flowing through the switching element of the inverter circuit is a current waveform detection means for detecting a current waveform, a waveform change detection means for detecting a change from the normal current waveform when the state of the discharge lamp changes from a normal state, and an inverter detecting means according to the detection output of the waveform change detection means. The present invention is characterized by comprising a control means for controlling oscillation of the circuit.

[Function] According to the present invention, when the state of the discharge lamp changes from the normal state, the waveform change from the normal current waveform is detected. Even when the peak value of the current flowing through the switching elements hardly changes, it is possible to reliably determine whether the current is normal or not, and the inverter's oscillation can be controlled appropriately according to the result. It is something that can be done.

[Example 1] FIG. 1 is a circuit diagram of a first embodiment of the present invention.

The circuit configuration will be explained below. A first main transistor Q1 and a second main transistor Q2 are connected in series to a DC power source E, and a detection resistor R1 is connected in series to the emitter side of the main transistor Q1.

A diode D1 is connected in antiparallel to the series circuit of the main transistor Q1 and the detection resistor R1, and a diode D2 is connected in antiparallel to the main transistor Q2. These 2
The two main transistors Q, , Q2 are alternately turned on and off by drive circuits 10 and 20, respectively. Discharge lamp DL
DL2 is connected in parallel via a balancer L2, and capacitors C3 and C4 are connected in parallel to each non-power supply side. A capacitor C2 is connected in parallel to the parallel circuit of the discharge lamps DL, DL2, and is connected to both ends of a diode D via a choke coil L1 and a capacitor CI.

The detection voltage of the detection resistor R1 is applied to the positive input terminal of the comparator CP, and the negative input terminal of the comparator CP is held at the ground level. Comparator CP
The output of is connected to the trigger force of the monostable multivibrator MV and to one input of the AND circuit AN. The output of the monostable multivibrator MV is connected to the other input of the AND circuit AN.

The output of the AND circuit AN is connected to the input of the latch circuit LT, and the output of the latch circuit LT is connected to the base of the transistor Q via a resistor R3. Drive circuit 1 is connected between the collector and emitter of transistor Q.
0 input terminal 11 and is connected to the ground level. A rectangular wave signal is applied to the input terminal 11 of the drive circuit 10, and a rectangular wave signal whose logic is inverted from that of the input terminal 11 is applied to the input terminal 21 of the drive circuit 20. On the other hand, the transistor Q4 is connected between the trigger force of the monostable multi-by-break MV and the ground level, and the base of the transistor Q4 is connected to the resistor R.
The output of the timer circuit TM is connected via 1.

The operation of this embodiment will be explained below. The current waveform flowing through the transistor Q1, ie, the voltage across the detection resistor R, becomes the waveform A shown in FIG. 2(a).

By shaping this waveform by the comparator CP, a rectangular wave in which the period when the waveform A is above the ground level is at the 'High' level is obtained, as shown in FIG. 2(b). By triggering the monostable multivibrator MV at the falling edge, an output waveform as shown in No. 25(d) can be obtained.The measured time T of the monostable multivibrator MV is
, , is set to be a little shorter than the time from the fall to the rise of the output waveform of the comparator CP (see FIG. 2(b)) when DL2 is normal.

When the output waveform of the comparator CP shown in FIG. 2(b) and the output waveform of the monostable multivibrator MV shown in FIG. 2(d) are processed by an AND circuit AN, the output waveform shown in FIG. A zero level output waveform as shown in e) is obtained. Therefore, transistor Q is turned off,
The oscillation of the inverter is not controlled in any way.

Now, when the discharge lamps DL + and DL 2 reach the end of their lifespan, the voltage across the detection resistor R1 becomes a waveform B shown in FIG. 2(a). When this waveform is shaped by a comparator CP, an output waveform as shown in FIG. 2(c) is obtained. This output waveform is a waveform whose rising phase is more advanced than that of the normal waveform shown in FIG. 2(b). The output waveform of the comparator CP shown in FIG. 2(c) and the second
When the output waveform of the monostable multivibrator MV shown in FIG. 2(d) is processed by the AND circuit AN, a pulse-like output waveform as shown in FIG. 2 <r> is obtained as an AND output. As a result, the output of the latch circuit LT becomes “High”.
h'' level, the transistor Q is turned on, the input terminal 11 of the drive circuit 10 is shorted to the ground level, the drive signal is no longer supplied to the base of the transistor Q, and the oscillation of the inverter is stopped.

As described above, if the phase shift of the current waveform flowing through the switching elements in the inverter circuit is detected by pulse width discrimination, the end of the life of the discharge lamp can be reliably detected even if the peak current does not change, and the inverter Oscillation can be controlled. Furthermore, since the state of the discharge lamp is not directly detected, it is less susceptible to the effects of ambient temperature.

Note that the timer circuit TM, resistor R1, and transistor Q
4 is provided to prevent malfunction by forcibly shorting the output of the comparator CP to the ground level after the power is turned on until the discharge lamps DL, DL2 are started. That is, since the load impedance of the discharge lamp changes significantly until it is started, the detection operation is stopped during this period.

[Embodiment 2] FIG. 3 is a circuit diagram of a main part of a second embodiment of the present invention. Since the configuration of the main circuit is the same as that in FIG. 1, only the configuration of the control circuit will be described.

A differentiating circuit including a capacitor C6 and a resistor R6 is connected to both ends of the detection resistor R1. The output of the differentiator circuit is
The voltage is applied to the primary winding of the pulse transformer PT, and the secondary winding output of the pulse transformer PT is applied to the negative input terminal of the comparator CP.

A reference voltage Vr is applied to the positive input terminal of the comparator CP. A diode D is connected in parallel to the secondary winding of the pulse transformer PT with the polarity shown.

The output of the comparator CP is used as a trigger force for a retriggerable monostable multivibrator MV, and the output of this monostable multivibrator MV is used as an oscillation control signal.

FIG. 4 is an operational waveform diagram of this embodiment. The operation of this embodiment will be explained with reference to the same figure.

Detection resistor R1 connected to the emitter of transistor Q1
When the discharge lamp is operating normally, the voltage across the terminal becomes waveform A shown in FIG. 4 (&). By differentiating this waveform with a differentiator circuit consisting of a capacitor C6 and a resistor R6, a differentiated waveform as shown in FIG. 4(b) is obtained at both ends of the resistor R1. By reversing the negative voltage shown in FIG. 4(b) to a positive voltage using the pulse transformer PT, a waveform as shown in FIG. 4(d) is obtained.

On the other hand, at the end of the discharge lamp's life, the transistor Q,
The voltage across the detection resistor R1 connected to the emitter of is waveform B in FIG. 4(a). This waveform is converted to capacitor C1
By performing differentiation using a differentiating circuit consisting of a resistor R6 and a resistor R6, a differentiated waveform as shown in FIG. 4(c) is obtained at both ends of the resistor R6. Figure 4 (
By reversing the negative voltage shown in c) to a positive voltage, a waveform as shown in FIG. 4(e) is obtained. Figure 4(a)
Comparing waveform A and waveform B, waveform A has a higher peak value at the moment of falling when the discharge lamp is in normal operation, so
The output waveforms of the pulse transformer PT shown in FIGS. 4(d) and 4(e) are at a higher level when the discharge lamp is normal.

Therefore, the reference voltage Vr of the comparator CP is set to the fourth
If the level is set between the peak value of the waveform shown in Figure (d) and the peak value of the waveform shown in Figure 4(e), the output will be output from the comparator CP according to the switching cycle when the discharge lamp is normal. Pulses can be obtained, but at the end of the discharge lamp's life, no output pulses can be obtained. The output pulse of comparator CP is generated by retriggerable monostable multivibrator M
It is said to be V's trigger force. The clock time of this monostable multivibrator MV is set to be slightly longer than the switching period of the inverter. Therefore, during normal operation of the discharge lamp, the monostable multivibrator MV is triggered again by the output pulse of the comparator CP before the clocking time of the monostable multivibrator MV elapses, so the output of the monostable multivibrator MV is "Hi".
On the other hand, at the end of the life of the discharge lamp, the monostable multivibrator MV is no longer triggered, so its output becomes the "Low" level.The output of this monostable multivibrator MV is controlled to oscillate. By generating a signal, the oscillation of the inverter can be controlled.

As described above, if the phase shift of the current waveform flowing through the switching element in the inverter circuit is detected by the current value when the switching element is turned off, it is possible to ensure that the discharge lamp is at the end of its life even if the peak current hardly changes. can be detected and control the oscillation of the inverter.

[Embodiment 3] FIG. 5 is a circuit diagram of a main part of a third embodiment of the present invention. In this embodiment, in the circuit of FIG. 1, the transistor Q1, which is the main switching element, is replaced with a power MO8FET. Then, the current of the switching element is detected by reversing the polarity of the current by a pulse transformer PT. Since the power MO3FET has a built-in parasitic diode that conducts in the opposite direction, the antiparallel diode D is omitted. A diode D is connected in parallel to the secondary winding of the pulse transformer PT with the polarity shown. As a result, the secondary winding of the pulse transformer PT has
Only the reverse current of the main switching element flowing through the primary winding of the pulse transformer PT appears as a positive voltage. The cathode and anode of diode D are connected to the positive input terminal and negative input terminal of comparator CP, respectively.

The output of the comparator CP is connected to the trigger force of the monostable multivibrator MV, and the AND circuit A
Connected to one input of N. The output of the monostable multivibrator MV is connected to the other input of the AND circuit AN. The output of the AND circuit AN is applied via a diode D to a smoothing circuit made up of a parallel circuit of a capacitor Cs and a resistor Rs.

In the following, the operation of this embodiment will be explained. In this embodiment, the negative current shown by the dotted line in FIG. The comparator CP and the monostable multivibrator MV
By making a distinction using the AND circuit AN, it is possible to determine whether the discharge lamp is in a normal state or at the end of its life. The configuration and operation of the pulse width discrimination circuit including the comparator CP, the monostable multivibrator MV, and the AND circuit AN are the same as in the first embodiment. However, in this embodiment, since the time width in which the negative current flows in waveforms A and B in FIG. will not occur and will be at zero level. Therefore, instead of latching the output of the AND circuit AN by the latch circuit LT, it is connected to the capacitor C via the diode D for backflow prevention.
By integrating with a smoothing circuit consisting of S and resistor R5,
“High” level during normal operation, “Low” at the end of life.
The oscillation control signal that becomes the level is obtained.

Although Embodiment 1 exemplifies a two-lamp parallel lighting circuit, any circuit in which the current peak value of the switching element hardly changes between the normal state of the discharge lamp and the end of its life, and the phase of the current changes, may be used. , any lighting circuit may be used,
Furthermore, the present invention can be applied to half-bridge type, full-bridge type, and other arbitrary inverter circuits. Furthermore, the phase shift of the current waveform may be shifted in the opposite direction to that in the embodiment, and the current waveform itself does not have to be a waveform with a delayed phase with respect to the voltage of the switching element.

Furthermore, as means for detecting the current flowing through the switching element, in addition to the detection method using the detection resistor and pulse transformer exemplified in the embodiment, a detection method using other impedance elements such as a capacitor or an inductor may be used. Also, the reason why the condition of the discharge lamp changes significantly is
It does not matter if the discharge lamp is not at the end of its life, for example, if one of the multiple lamps is disconnected.In short,
The present invention can be applied as long as the peak value of the current waveform of the switching element does not change significantly and only the phase shifts.

[Effects of the Invention] As described above, in the present invention, in an inverter type discharge lamp lighting device, when the state of the discharge lamp changes from the normal state, a waveform change from the normal current waveform is detected. By doing this, it is determined whether the discharge lamp is in a normal state or not, so even if the peak value of the current flowing through the switching element hardly changes between normal and non-normal conditions, This has the advantage that the state of the discharge lamp can be reliably determined, and the oscillation of the inverter can be appropriately controlled according to the determination result.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of the first embodiment of the present invention, Fig. 2 is an operating waveform diagram of the same as above, Fig. 3 is a main circuit diagram of the second embodiment of the present invention, and Fig. 4 is an operating waveform of the same as above. 5 is a circuit diagram of the main part of the third embodiment of the present invention, FIG. 6 is a circuit diagram of the main part of the conventional example, and FIG.
The figure is the same operating waveform diagram as above, and Figure 8 is a circuit diagram of another conventional example.
FIG. 9 is a circuit diagram of still another conventional example, and FIG. 10 is an operation waveform diagram of the same. Q, , Q2 are transistors, DL, DL2 is a discharge lamp,
R, is a detection resistor, and CP is a comparator.

Claims (1)

[Claims] (1) In a lighting device that lights a discharge lamp at high frequency using the oscillation output of an inverter circuit, a current waveform detection means detects a current waveform flowing through a switching element of the inverter circuit, and when the state of the discharge lamp changes from a normal state, Waveform change detection means for detecting a change from a normal current waveform;
1. A discharge lamp lighting device comprising: control means for controlling oscillation of an inverter circuit in accordance with the detection output of the waveform change detection means.