JP4710591B2 - Discharge lamp lighting device and image display device - Google Patents

Description

  The present invention relates to a discharge lamp lighting device for lighting a discharge lamp by an output of a switching circuit, and an image display device using the same.

  In general, the tube voltage of a high-pressure discharge lamp, particularly a mercury lamp or a metal halide lamp is low immediately after start-up, and thereafter has an inherent time change characteristic that the tube voltage increases and stabilizes as the lamp internal temperature increases. In addition, the ultra-high pressure short arc discharge lamp used for projectors, rear projection televisions, and the like has a feature that the tube voltage after being further stabilized greatly fluctuates due to electrode wear during use.

  As an example of this type of discharge lamp lighting device, there is a configuration shown in FIG. The DC power source 1 is a stabilized DC voltage source made up of, for example, a boost chopper circuit. The electric power supplied to the discharge lamp 3 as a load is controlled by turning on / off the switching element Q1. The detection circuit 4 in the control circuit 6 monitors the voltage of the switching element Q1 indirectly by monitoring the voltage Vr of the regenerative diode D1.

  The circuit operation of FIG. 5 will be described. When the switching element Q1 is turned on by the drive circuit 5 in the control circuit 6 and the current flowing through the path of the switching element Q1 → the inductor L1 → the capacitor C1 (and the discharge lamp 3) → the resistor R1 increases, the comparator in the control circuit 6 52, the output is turned off when the detected voltage at the + input terminal reaches the reference voltage at the −input terminal, and a High signal is given to the reset terminal Rst of the D flip-flop 53. Therefore, the output Q of the D flip-flop 53 is Low. The switching element Q1 is turned off.

  When the switching element Q1 is turned off, the current flowing in the route from the switching element Q1 to the inductor L1 is commutated to the route from the diode D1 to the inductor L1, and the energy stored in the inductor L1 while the switching element Q1 is turned on. When the discharge is completed, the diode D1 is turned off. When the diode D1 is turned off, the junction capacitance of the diode D1 is charged from the capacitor C1 through the inductor L1, so that the reverse voltage Vr of the diode D1 rises, and the voltage at the −input terminal of the comparator 42 of the detection circuit 4 becomes + input. When it becomes equal to the comparison reference value of the terminal, the output of the detection circuit 4 is turned on, a down edge signal is given to the clock input terminal CLK of the D flip-flop 53, and the D flip-flop 53 outputs High of the data input terminal D to the output Q. Then, the switching element Q1 is turned on. Thereafter, by repeating this cycle, the switching element Q1 is turned on / off, and the load power is stably controlled.

Note that, in a switching circuit used for an electronic ballast of a discharge lamp lighting device, a technique for detecting the fact that the switching element's off-time voltage has become a substantially minimum voltage and turning on the switching element is disclosed in Patent Document 1.
Japanese Patent No. 3430629

FIG. 6 shows the reverse voltage Vr (= Vin−V _Q1 ) of the diode D1 when the control circuit 6 does not instruct the next ON of the switching element Q1 in the conventional example of FIG. During the ton period, a current flows through the inductor L1 via the switching element Q1. During the toff period, the energy of the inductor L1 is released through the diode D1. When the current flowing through the diode D1 disappears and both the switching element Q1 and the diode D1 are turned off, the reverse voltage Vr of the diode D1 converges to the load voltage Vla while oscillating due to the capacitance components of the switching element Q1 and the diode D1.

Vr = Vla · [1-exp (−αt) · {cosβt + (α / β) · sinβt}] (1) where
α = R / 2L
β = √ (4L / C−R ² ) / 2L
R ² ≪4L / C

  In the above equation, R is the internal resistance of the inductor L1, the capacitor C1, the switching element Q1, the internal resistance of the diode D1, other internal resistances, and the copper foil resistance. L is an inductive component of the inductor L1 and an inductive component such as the capacitor C1, the switching element Q1, the diode D1, and the copper foil. C is a capacitance component of the switching element Q1 and the diode D1, and a capacitance component of a snubber circuit that is arranged in parallel to the switching element Q1 or the diode D1 (not shown) to prevent noise. It is assumed that the load voltage Vla can be regarded as constant in the time order of the period of continuous switching.

Since the attenuation factor at the time of convergence varies depending on the resistance component, it varies depending on the current and frequency flowing in the vibration loop, and particularly depends on the design of the inductor L1. The center of vibration Vrc is as follows.
Vrc≈Vla {1-exp (−t · R / 2L)}

  The peak of the oscillating voltage Vr increases or decreases according to the load voltage Vla. For example, as shown in FIG. 6, when the load voltage Vla is VlaA (large), the peak of the oscillating voltage Vr is high (the voltage of the switching element Q1 is low). Conversely, when the load voltage Vla is VlaB (small), the peak of the oscillating voltage Vr is low (the voltage of the switching element Q1 is high).

The damped oscillation period T is T = 2π · 2L / √ (4L / C−R ² ) ≈2π√ (L · C). Therefore, when the damped oscillation period T is small and R / L is small, the peak of Vr is large and the peak voltage of the switching element Q1 is low.

  The switching loss varies depending on the turn-on timing of the switching element Q1, and if the voltage of the switching element Q1 immediately before the turn-on is small, the switching loss when the switching element Q1 is turned on is small.

  Conventionally, since the absolute value of the switching loss is small when the output is small, the comparison reference value of the comparator 42 in the detection circuit 4 of FIG. 5 is often set to approximately 0V. However, if the output is increased and the switching loss of the switching element Q1 is large, it is necessary to reduce it. In such a case, conventionally, the comparison reference value of the detection circuit 4 shown in the example of FIG. 5 is set to a fixed value larger than 0 V, and the turn-on is delayed to reduce the switching loss of the switching element Q1.

  However, as shown in FIG. 6, if the comparison reference value of the detection circuit 4 is increased, there is a possibility that the next switching element Q1 cannot be turned on. Therefore, the comparison reference value is the value at the time of VlaB where the load voltage is minimum. It is necessary to set the threshold value Vb or less.

  When the threshold value Vb of FIG. 6 is set as the comparison reference value, the turn-on timing is b when the load voltage is low VlaB, the switching loss is small, but the turn-on timing when the load voltage is high VlaA is a. Therefore, it deviates from the timing c originally desired to be set, and as a result, the switching loss of the switching element Q1 increases.

  The present invention is intended to solve such a problem, and in a discharge lamp lighting device for lighting a discharge lamp whose tube voltage fluctuates due to a rise in tube temperature or electrode wear by the output of a switching circuit, the load voltage is high. It is an object to make it possible to reduce the switching loss of the switching element even when the case is low.

  According to the present invention, in order to solve the above-described problem, as shown in FIG. 1, the power supplied to the discharge lamp 3 is adjusted by being connected between the DC power supply 1 and the discharge lamp 3 as a load. A switching circuit 2; a detection circuit 4 for monitoring the off-time voltage of the switching element Q1 constituting the switching circuit 2 and detecting that the off-time voltage has become a substantially minimum voltage; and receiving a detection signal of the detection circuit 4 And a driving circuit 5 for turning on the switching element Q1, wherein the detection circuit 4 detects when the voltage Vr at the detection point provided in the switching circuit 2 is equal to or higher than a comparison reference value. Comparison means for outputting a detection signal (comparator 42) and comparison reference value setting means for detecting the load voltage Vla supplied to the discharge lamp 3 and setting the comparison reference value higher as the load voltage Vla increases ( It is characterized in that it has a calculation circuit 41) and.

  According to the present invention, even when the load voltage is high or low, the switching element can be turned on at the timing when the switching-off voltage of the switching element becomes substantially the minimum voltage. A discharge lamp whose tube voltage varies depending on the factor can always be lit efficiently.

(Embodiment 1)
FIG. 1 is a circuit diagram of Embodiment 1 of the present invention. Hereinafter, the circuit configuration will be described. The DC power supply 1 is a DC stabilized power supply circuit made up of, for example, a step-up chopper circuit, which converts a commercial AC voltage into a stable DC voltage Vin and outputs it. The negative output terminal of the DC power supply 1 is grounded, and the positive output terminal is connected to one end of the switching element Q1. The switching element Q1 is made of a power MOSFET, for example, and is turned on / off at a high frequency by the output of the control circuit 6. One end of a chopper inductor L1 and the cathode of a diode D1 are connected to the other end of the switching element Q1. The other end of the inductor L1 is connected to the positive electrode of the smoothing capacitor C1. The negative electrode of the smoothing capacitor C1 is connected to the anode of the diode D1. The anode of the diode D1 is connected to the negative output terminal of the DC power supply 1 through the low resistance R1 for detecting the chopper current. A discharge lamp 3 as a load is connected to both ends of the smoothing capacitor C1. The discharge lamp 3 is a high-intensity high-pressure discharge lamp (HID lamp) such as a mercury lamp or a metal halide lamp. The switching circuit 2 including the switching element Q1, the diode D1, and the inductor L1 constitutes a step-down chopper circuit that steps down the input DC voltage Vin to an arbitrary load voltage Vla and outputs it. The load voltage Vla is detected by the control circuit 6, and the ON period of the switching element Q1 is controlled so that optimum power is supplied to the discharge lamp 3 according to the detected voltage.

  Next, the configuration of the control circuit 6 will be described. The control circuit 6 has a detection circuit 4 and a drive circuit 5. A low DC voltage is supplied from the control power source E to the detection circuit 4 and the drive circuit 5. This DC low voltage is applied to a series circuit of bipolar transistors Q2 and Q3 connected in a totem pole connection. The primary winding of the driving transformer T1 is connected to both ends of the transistor Q3 via a coupling capacitor C2. The secondary winding of the drive transformer T1 is connected to the control terminal of the switching element Q1 via the resistor R2. The control terminals of the transistors Q2 and Q3 are connected to the Q output terminal of the D flip-flop 53 via the resistor R3. When the Q output terminal of the D flip-flop 53 becomes high level, the transistor Q2 is turned on, the transistor Q3 is turned off, and the switching element Q1 of the switching circuit 2 is turned on. Further, when the Q output terminal of the D flip-flop 53 becomes low level, the transistor Q2 is turned off, the transistor Q3 is turned on using the coupling capacitor C2 as a power source, and the switching element Q1 of the switching circuit 2 is turned off.

  The power supply terminal Vdd and the ground terminal Vss of the D flip-flop 53 are connected to the positive electrode and the negative electrode of the control power supply E, respectively. The data input terminal D of the D flip-flop 53 is connected to the level of the control power supply E, and when a falling trigger (down edge signal) is input to the clock input terminal CLK, the Q output terminal becomes High level. . Further, when the reset input terminal Rst becomes High level, the Q output terminal becomes Low level. The reset input terminal Rst is connected to the output terminal of the comparator 52 for determining the ON time, and this output terminal is pulled up to the level of the control power supply E by the resistor R4. The detection voltage of the resistor R1 for detecting the chopper current is input to the + input terminal of the comparator 52, and the target voltage output from the arithmetic circuit 51 is input to the − input terminal. The arithmetic circuit 51 detects the load voltage Vla supplied to the discharge lamp 3, and compares the voltage according to the target peak current value of the chopper current so that the optimum lamp power is supplied according to the load voltage Vla. 52 to the negative input terminal. When the chopper switching element Q1 is turned on, a gradually increasing current flows through a path of the DC power source 1 → the switching element Q1 → the inductor L1 → the smoothing capacitor C1 (and the discharge lamp 3) → the current detection resistor R1. As a result, the detection voltage of the resistor R1 increases, and when the detection voltage at the + input terminal of the comparator 52 reaches the target voltage at the −input terminal, the output of the comparator 52 is turned off (high impedance state), and the resistance R4 Therefore, the reset input terminal Rst of the D flip-flop 53 becomes high level, and the Q output terminal becomes low level. As a result, the switching element Q1 is turned off.

Next, monitoring of the off-time voltage of the switching element Q1 will be described. The detection circuit 4 monitors the off-time voltage of the switching element Q1 constituting the switching circuit 2. When the detection circuit 4 detects that the off-time voltage has become a substantially minimum voltage, the detection circuit 4 causes the drive circuit 5 to turn on the switching element Q1 again. The detection signal for output is output. In the circuit of FIG. 1, the voltage V _Q1 (= Vin−Vr) across the switching element Q1 is substantially monitored by detecting the potential Vr of the cathode of the diode D1 for energizing the regenerative current of the chopper. The detection circuit 4 is a comparator that outputs a falling trigger (down edge signal) when the voltage at the detection point (the potential Vr of the cathode of the diode D1) provided in the switching circuit 2 is equal to or higher than a comparison reference value. 42. The comparator 42 comprises an open collector or open drain output comparator, and its output terminal is pulled up to the level of the control power supply E (High level) by a resistor R5. A voltage according to the potential Vr of the cathode of the diode D1 is applied to the negative input terminal of the comparator 42 via the resistor Rx, and the output voltage of the arithmetic circuit 41 is applied as a reference voltage to the positive input terminal. Yes. The arithmetic circuit 41 is a circuit that detects the load voltage Vla supplied to the discharge lamp 3 and sets the reference voltage of the + input terminal of the comparator 42 higher as the load voltage Vla increases. As the simplest circuit example of the arithmetic circuit 41, a voltage obtained by dividing the load voltage Vla by a resistance voltage dividing circuit may be supplied to the + input terminal of the comparator 42 as a reference voltage. When the detection voltage of the negative input terminal of the comparator 42 exceeds the reference voltage of the positive input voltage, the output of the comparator 42 is turned on (short-circuited with the ground), and a falling trigger (down edge signal) is given to the drive circuit 5.

  In the D flip-flop 53 of the drive circuit 5, since the data input terminal D is connected to the level (High level) of the control power supply E, when a falling trigger (down edge signal) is input to the clock input terminal CLK. , Q output terminal becomes High level. As a result, the switching element Q1 is turned on again. (Note that a high-level signal is applied to the set input terminal Set of the D flip-flop 53 from the arithmetic circuit 51 or the like when a down edge signal cannot be obtained from the detection circuit 4 even after waiting for a certain period of time or when oscillation starts immediately after power-on. The switching element Q1 may be forcibly turned on.)

  FIG. 2 is an operation waveform diagram of the first embodiment. According to the first embodiment, the determination reference value of the detection circuit 4 is changed to threshold values 1, 2, 3,..., X as the load voltage Vla increases, and the arithmetic circuit 41 As shown in FIG. 2, Vla is measured, and an appropriate threshold voltage according to the load voltage Vla is output, which is used as a turn-on timing determination reference value for the switching element Q1 of the detection circuit 4. Since this threshold voltage is approximately proportional to the load voltage Vla, it may be simply a divided voltage (proportional value) of the load voltage, but more accurately, it is preferable to take into account the attenuation due to the above-described resistance component. In projectors, rear projection televisions, and the like, in order to obtain a stable light output, control is performed so that constant power is supplied to the load. Therefore, if the load voltage Vla is small (large current), it is lower than the proportional value. If the load voltage Vla is large (small current), it is preferable to make it higher than the proportional value. It is difficult to grasp the heat generation due to current conduction and the change of the resistance component due to the frequency change. In practice, it is optimal to set the threshold value from the operation waveform after designing the inductor L1.

  As described above, according to the first embodiment, an appropriate turn-on timing is not lost even when the load voltage fluctuates, and the off-time voltage of the switching element is substantially the same regardless of whether the load voltage is high or low. Since the switching element can be turned on at the timing when the minimum voltage is reached, switching loss can be reliably reduced, and a discharge lamp whose tube voltage fluctuates due to a rise in tube temperature or electrode wear can always be lit efficiently. .

  Since the arithmetic circuit 51 that performs power control is often configured by a microcomputer, it is preferable that a part of the arithmetic circuit 41 is used without increasing the number of parts. Furthermore, as described above, since the resistance component involved in the attenuation characteristic varies depending on the temperature and frequency of the component (particularly the inductor L1) during operation, the relationship between the optimum comparison reference value of the detection circuit 4 and the load voltage Vla is not necessarily limited. If it is configured not to be linear but to be set by a high-order function arithmetic expression or table data on a memory using a microcomputer, the circuit is not complicated and the switching loss can be minimized at a low cost.

(Embodiment 2)
FIG. 3 is a circuit diagram of the second embodiment of the present invention. In the second embodiment, a comparison reference value for determining the turn-on timing of the switching element Q1 of the detection circuit 4 is set including the amount that the peak value of the oscillating voltage Vr varies with the input DC voltage Vin. With this configuration, the switching loss can be reduced even when the input DC voltage Vin varies. For example, the frequency is f = (Vin−Vla) · Vla ² / (2 × L1 × P × Vin), and the attenuation rate when the input DC voltage Vin changes is uniquely increased according to the input DC voltage Vin. The same applies to the resistance value that determines the attenuation. Therefore, when setting the comparison reference value to be changed according to the input DC voltage Vin, it is optimal to set it from the operation waveform after actually designing the inductor L1 as in the first embodiment. Specifically, the optimum comparison reference value according to the input DC voltage Vin and the load voltage Vla is obtained from the operation waveform, set as table data on the microcomputer memory, and optimum by referring to the table. A simple comparison reference value may be output. Alternatively, an arithmetic expression corresponding to the table data is created in advance, and a comparison reference value calculated by the microcomputer according to the input DC voltage Vin and the load voltage Vla may be output.

  In the above description, the switching circuit 2 is configured as a step-down chopper circuit. However, depending on design conditions such as the input voltage fluctuation range, a step-up chopper circuit or a step-up / step-down chopper circuit may be used instead of the step-down chopper circuit. is there. Needless to say, the present invention can be applied to such a case.

(Embodiment 3)
The discharge lamp lighting device of each of the above-described embodiments is used for lighting a discharge lamp serving as a light source of an image display device such as a projector or a rear projection television. Here, the case where it mounts in a projector is illustrated. FIG. 4 is a schematic configuration diagram showing the internal configuration of the image display device 30. In the figure, 31 is a projection window, 32 is a power supply unit, 33a, 33b and 33c are cooling fans, 34 is an external signal input unit, 35 is an optical system, 36 is a main control board, 40 is a discharge lamp lighting device, 3 Is a discharge lamp. A main control board 36 is mounted in a frame indicated by a broken line. In the middle of the optical system 35, image display means (a transmissive liquid crystal display panel or a reflective image display element) that transmits or reflects light from the discharge lamp 3 is provided. The optical system 35 is designed to project the reflected light onto the screen. As described above, the discharge lamp lighting device 40 is mounted inside the image display device 30 together with the discharge lamp 3. However, by adopting the discharge lamp lighting device 40 of the present invention, the switching loss can be reduced as compared with the conventional case. Therefore, it is not necessary to obtain a large heat dissipation (cooling) effect, and the cooling fan can be made quieter, the device can be made smaller, and the price can be reduced.

It is a circuit diagram of the discharge lamp lighting device of Embodiment 1 of the present invention. It is an operation | movement waveform diagram of Embodiment 1 of this invention. It is a circuit diagram of the discharge lamp lighting device of Embodiment 2 of the present invention. It is a schematic block diagram which shows the internal structure of the image display apparatus which concerns on Embodiment 3 of this invention. It is a circuit diagram of the conventional discharge lamp lighting device. It is an operation | movement waveform diagram of the conventional discharge lamp lighting device.

Explanation of symbols

1 DC power supply 2 Switching circuit 3 Discharge lamp 4 Detection circuit 41 Arithmetic circuit (comparison reference value setting means)
42 Comparator 5 Drive circuit Q1 Switching element

Claims (3)

A switching circuit connected between a DC power source and a discharge lamp as a load for adjusting power supplied to the discharge lamp;
A detection circuit that monitors the off-time voltage of the switching elements constituting the switching circuit and detects that the off-time voltage has become a substantially minimum voltage;
A discharge lamp lighting device comprising a drive circuit that receives the detection signal of the detection circuit and turns on the switching element,
The detection circuit includes:
Comparison means for outputting a detection signal when the voltage at the detection point provided in the switching circuit is equal to or higher than a comparison reference value;
A discharge lamp lighting device comprising: a comparison reference value setting means for detecting a load voltage supplied to the discharge lamp and setting the comparison reference value higher as the load voltage increases. 2. The discharge lamp lighting device according to claim 1, wherein the comparison reference value setting means adjusts an increase / decrease amount of the comparison reference value according to an input DC voltage from a DC power source. 3. A discharge lamp lighting device according to claim 1; a discharge lamp that is lit by the discharge lamp lighting device; an image display means that transmits or reflects light from the discharge lamp; and transmitted light or reflection that passes through the image display means. An image display device comprising an optical system for projecting light onto a screen.

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