Patent Application
20100213856
1. Technical Field
The present invention relates to a power supply apparatus, a method for driving the power supply apparatus, a light source apparatus that is equipped with the power supply apparatus, and an electronic apparatus.
2. Related Art
A switching-type power supply apparatus that includes analog elements and performs pulse width modulation is disclosed in JP-A-7-15952. The power supply apparatus disclosed in the above patent document is provided with a feedback (FB) circuit that is an analog circuit. The analog FB circuit detects a change in an output voltage and performs feedback control. The feedback control is performed in such a way as to ensure that the output voltage is kept substantially constant at a target voltage value on the basis of the result of detection. In addition, it is described in the above patent document that the power supply apparatus is used as a power source for a discharge lamp. Generally, in the field of a power supply apparatus that is used as a power source for a load device whose power consumption at the time of the initiation of lighting-up operation is different from power consumption during lighting operation, that is, a load device whose load changes or fluctuates, there is a demand for good tracking ability for responding to a load change. An example of a load device having such power consumption characteristics (i.e., load variation characteristics) is a discharge lamp. Good tracking ability for raising an output voltage to a target voltage value speedily is demanded not only for a discharge lamp but also for various kinds of solid-state light sources that are required to be capable of lighting up quickly, for example, a laser light source.
However, circuit efficiency decreases as a drive frequency increases. The horizontal axis of
The power supply apparatus of related art that is provided with the analog FB circuit as disclosed in JP-A-7-15952 has a problem of circuit oscillation, which occurs when a drive frequency is changed. That is, there is a problem in that it is practically impossible or difficult to change a drive frequency.
The detection voltage Vo is inputted from the detection circuit 2 to a negative input terminal (i.e., minus terminal) of the operational amplifier 13. A reference voltage Vref is inputted from the reference voltage generation circuit 14 to a positive input terminal (i.e., plus terminal) of the operational amplifier 13. The phase compensation circuit 11 is connected between the negative input terminal of the operational amplifier 13 and an output terminal of the operational amplifier 13. With these circuits, an output voltage Vf that reflects a deviation obtained as a result of comparison of the detection voltage Vo that is proportional to the output voltage of the DC/DC converter 1 with the reference voltage Vref is outputted from the operational amplifier 13. The output voltage Vf is inputted to a negative input terminal of the operational amplifier 12. A triangular wave Vt is inputted from the triangular wave generation circuit 15 to a positive input terminal of the operational amplifier 12. A pulse wave is outputted from an output terminal of the operational amplifier 12. The pulse wave outputted from the operational amplifier 12 is inputted to a gate terminal of the FET 6 and an input terminal of the inverter 4. An output terminal of the inverter 4 is connected to a gate terminal of the FET 7. Accordingly, the FET 7 is set in an OFF state when the FET 6 is set in an ON state. The FET 6 is set OFF when the FET 7 is set ON. As explained above, the output voltage of the DC/DC converter 1 is compared with the reference voltage Vref. Pulse width modulation (PWM) control is performed with reflection of a deviation obtained as a result of comparison.
The phase compensation circuit 11 is made up of a resistor 11a and a capacitor 11b. The circuit constant of these circuit components is set at a constant for negative-feedback control in accordance with the transfer function of the circuit. That is, a specific drive frequency is taken as a precondition when the resistor 11a and the capacitor 11b are selected. For this reason, circuit stability decreases when the drive frequency is changed, resulting in the oscillation of the circuit, which is a problem that remains to be solved. In other words, since the phase compensation circuit 11 is a dedicated circuit whose multiplier factor has been set for driving the power supply apparatus 140 at a specific drive frequency, operation is not stable when it is off the specific drive frequency, that is, when driven at any frequency other than the specific drive frequency. Thus, it is practically impossible or difficult to change the drive frequency. In addition, even assuming that it were possible to change the driving frequency in the configuration of a power supply apparatus of related art, as explained earlier, circuit efficiency would decrease as tracking ability improves. To put it the other way around, tracking ability must be compromised for greater circuit efficiency, which is another problem that remains to be solved. In other words, in related art, it is difficult to achieve excellent tracking ability and great circuit efficiency, which have a trade-off relationship therebetween, in a compatible manner, thereby having it both ways.
In order to address the above-identified problems without any limitation thereto, the invention provides, as various aspects thereof, a power supply apparatus, a method for driving the power supply apparatus, a light source apparatus that is equipped with the power supply apparatus, and an electronic apparatus having the following novel and inventive features.
A power supply apparatus includes a direct current power source; a chopper circuit into which a voltage outputted from the direct current power source is inputted; a detection circuit that detects a value of a voltage corresponds to an output voltage value of the chopper circuit, which is hereinafter referred to as output voltage value; and a digital signal processor that generates a driving signal that is used for driving the chopper circuit, the digital signal processor including a storing section that stores a target voltage value, a control formula that is used for generating the driving signal, and a plurality of sets of coefficients, and an arithmetic operating section that calculates a deviation of the output voltage value from the target voltage value, wherein each of the plurality of sets of coefficients corresponds to one of a plurality of frequencies that are different from each other or one another, the digital signal processor determines a drive frequency of the driving signal on the basis of the deviation, and the digital signal processor inputs a set of coefficients that corresponds to the drive frequency selectively among the plurality of sets of coefficients to generate the driving signal.
In the operation of the above power supply apparatus, the digital signal processor generates a plurality of driving signals whose drive frequencies are different from each other or one another. Driving operation is performed by means of the plurality of driving signals. The coefficients of a control formula used for generating a driving signal vary depending on a deviation. The deviation is an index value that indicates a load change state. Therefore, it is possible to achieve both excellent tracking ability and great circuit efficiency in a compatible manner by adjusting the coefficients of the control formula in accordance with the variation of the deviation. That is, the power supply apparatus changes the coefficients of the control formula to use a relatively high drive frequency when the deviation is large where the load change is large. The power supply apparatus changes the coefficients of the control formula to use a relatively low drive frequency when the deviation is small where the load change is small. In other words, it is possible to enhance tracking ability when the load change is large. In addition, it is possible to increase circuit efficiency when the load change is small. Therefore, the power supply apparatus makes it possible to achieve both excellent tracking ability and great circuit efficiency in a compatible manner. Moreover, since the power supply apparatus performs digital processing, a drive-frequency changeover can be achieved without causing circuit oscillation.
In the configuration of the above power supply apparatus, it is preferable that the chopper circuit should be driven by means of the driving signal that has a first drive frequency when the deviation is larger than a predetermined value; and the chopper circuit should be driven by means of the driving signal that has a second drive frequency, which is lower than the first drive frequency, when the deviation has become equal to or smaller than the predetermined value. It is preferable that the above power supply apparatus should further include a drive time cumulative counting section that counts elapsed time that is measured from a point in time at which operation of the direct current power source is started, wherein the chopper circuit is driven by means of the driving signal that has a first drive frequency upon the start of the operation of the direct current power source, and the chopper circuit is driven by means of the driving signal that has a second drive frequency, which is lower than the first drive frequency, after the elapsed time has reached a predetermined point in time.
A light source apparatus includes the above power supply apparatus and a solid-state light source that emits light, wherein the power supply apparatus controls a light ON/OFF state of the solid-state light source. It is preferable that the above light source apparatus should further include a light amount detecting section that detects the amount of light emitted by the solid-state light source as a current value; and a converting section that converts the current value, which indicates the amount of light, into a voltage value that corresponds to an output voltage value, wherein the arithmetic operating section calculates the deviation with the use of the converted voltage value.
An electronic apparatus includes the light source apparatus according to Claim 4; and a light modulating section that modulates light emitted by the light source apparatus into modulated light in accordance with an image signal.
In addition, a method for driving a power supply apparatus is provided. The power supply apparatus is provided with a chopper circuit into which a voltage outputted from a direct current power source is inputted, a detection circuit that detects a value of a voltage corresponds to an output voltage value of the chopper circuit (output voltage value), and a digital signal processor that generates a driving signal that is used for driving the chopper circuit, the digital signal processor including a storing section that stores a target voltage value, a control formula that is used for generating the driving signal, and a plurality of sets of coefficients, each set of which corresponds to one of a plurality of drive frequencies that are different from each other or one another. The driving method includes (a) detecting the output voltage value and calculating a deviation of the output voltage value from the target voltage value; (b) comparing the calculated deviation with a predetermined deviation; and (c) switching the driving signal from a current driving signal to another driving signal whose drive frequency is lower than that of the current driving signal when the calculated deviation is not larger than the predetermined deviation.
The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements.
The power supply apparatus 100 includes an AC/DC circuit 5, a DC/DC converter 1, a detection circuit 2, a digital IC 101, and a gate driver 106 as main components. The AC/DC circuit 5 is an example of a direct current power source according to an aspect of the invention. In this embodiment, the AC/DC circuit 5, an example of the direct current power source, is a rectification circuit such as a bridge circuit or the like. The AC/DC circuit 5 converts an alternating voltage (i.e., AC voltage) into a direct voltage (i.e., DC voltage) and outputs the converted voltage to the DC/DC converter 1. The direct current power source is not limited to a rectification circuit. Any power source that can output a DC voltage can be adopted as the direct current power source. For example, it may be a battery. The DC/DC converter 1 is a chopper circuit. The DC/DC converter 1 drives its field effect transistors (FETs) 6 and 7 in a PWM driving scheme to convert an input voltage supplied from the AC/DC circuit 5 into a target voltage. The DC/DC converter 1 supplies a DC voltage after conversion to a load 10. The DC/DC converter 1 includes the FETs 6 and 7, an inductor 8, a capacitor 9, and the like. Each of the FETs 6 and 7 is an N-channel type metal oxide semiconductor (MOS) functioning as a switching element. A drain terminal of the FET 6 is connected to a positive terminal of the AC/DC circuit 5. A source terminal of the FET 6 is connected to one terminal of the inductor 8. The other terminal (output terminal) of the inductor 8 is connected to one terminal of the capacitor 9, one terminal of the load 10, and one terminal of the detection circuit 2. The other terminal of the capacitor 9 is connected to a negative terminal of the AC/DC circuit 5, the other terminal of the load 10, and a source terminal of the FET 7. A drain terminal of the FET 7 is connected to the source terminal of the FET 6 and the one terminal of the inductor 8.
The detection circuit 2 is made up of two resistors 21 and 22 that are connected in series. Accordingly, the serial pair of resistors 21 and 22 is connected to the one terminal of the capacitor 9. An output line for a detection voltage Vo that is tapped from a connection point of the two resistors 21 and 22 for division of a load voltage is connected to an A/D converter 102 of the digital IC 101. A terminal of the resistor 22 that is opposite a connection-point-side terminal is grounded. The voltage division ratio of the resistors 21 and 22 is predetermined according to the rating of the next processing block, that is, the rating of the A/D converter 102. Specifically, the voltage division ratio of the resistors 21 and 22 is set in such a way as to ensure that the level of the detection voltage Vo falls within the rated input range of the A/D converter 102.
The digital IC 101, which functions as a digital FB circuit, includes the A/D converter 102, a CPU 103, a memory 104, a PWM 105, and the like. The digital IC 101 is a digital signal processor. The CPU 103 is a central processing unit that controls each block in accordance with control program stored in the memory 104. Though not illustrated in the drawing, an oscillation circuit that includes an oscillation element such as a crystal oscillator is attached thereto. The CPU 103 including the oscillation circuit, the memory 104, and the like constitute a drive time cumulative count unit and an arithmetic operation unit, which will be explained later. The memory 104 is a nonvolatile memory such as a flash memory. Besides a target voltage value, a drive program that will be explained later, a control formula, a data table that contains parameters including constants of the control formula and sets of coefficients, and the like, are stored in the memory 140. The A/D converter 102 converts the analog detection voltage Vo that is proportional to the output voltage of the DC/DC converter 1 into digital data and then outputs the digital data to the CPU 103. The PWM 105 outputs a drive pulse for PWM control in accordance with the result of computation performed by the CPU 103 on the basis of a drive program and a control formula. For example, the PWM 105 outputs a drive pulse that switches over between a 3.3V voltage output state and a 0V state at predetermined time intervals in a variable repetition frequency. The digital IC 101 that includes the above components operates as follows. The A/D converter (ADC) 102 detects a voltage value. The CPU 103 reads the control formula out of the memory 104. The CPU 103 performs arithmetic operation with the use of the read control formula. Then, the PWM 105 outputs a pulse signal having a PWM waveform.
The gate driver 106 is provided with one input terminal and two output terminals. The PWM waveform pulse outputted from the digital IC 101 is inputted to the input terminal of the gate driver 106. One of the two output terminals of the gate driver 106 is connected to a gate terminal of the FET 6. The other output terminal is connected to a gate terminal of the FET 7. The gate driver 106 inverts the received PWM waveform and outputs the inverted waveform to the FET 7. On the other hand, the gate driver 106 outputs the received PWM waveform to the FET 6 without waveform inversion. By this means, the gate driver 106 drives the two FETs 6 and 7 alternately. That is, these FETs are put in an energized state in alternate shifts. If its driving capability is high enough, the inverter 4 (refer to
In contrast, a digital power source (power supply apparatus 100) according to the present embodiment of the invention determines a duty value on the basis of a digital control formula. Therefore, it is possible to change the drive frequency without causing circuit oscillation. Specifically, phase delay and phase advance are controlled with the use of a control formula (formula (3)) in which integration elements and differentiation elements are considered. A more detailed explanation of the control formula will be given later.
The formula (1) shown below is a fundamental formula used for obtaining phase compensation illustrated in
The control formula (1) used for obtaining phase compensation illustrated in
In the above formula (2), A0 and A1 denote constants that are obtained as a result of Z-transformation of the denominator of the formula (1), whereas B0, B1, and B2 denote constants that are obtained as a result of Z-transformation of the numerator of the formula (1). The following control formula (3) can be derived from the formula (2).
duty[0]=A0·duty[1]+A1·duty[2]+B0·e[0]+B1·e[1]+B2·e[2] (3)
In the above formula (3), duty [0] denotes a current duty value, which is applied currently. Duty [1] denotes the last duty value. Duty [2] denotes the duty value immediately before the last. In the formula (3), e[0], e[1], and e[2] denote a current deviation between an output voltage value and a target voltage value, the last deviation, and the deviation immediately before the last, respectively. That is, it is possible to calculate the current duty value on the basis of the multiplication of each value of duty and deviation by the corresponding value of a set of coefficients (A0, A1, B0, B1, B2). It is especially important that discretization should be performed relative to the drive frequency of the DC/DC converter 1 when the set of coefficients (A0, A1, B0, B1, B2) is calculated through discretization processing. For example, it is calculated with 4 μs when discretized at a drive frequency of 250 KHz. It is calculated with 1 μs when discretized at a drive frequency of 1 MHz. Therefore, it is necessary to set a set of coefficients (A0, A1, B0, B1, B2) for each frequency.
In a step S1, upon receiving an instruction for activating the power supply apparatus 100, the power supply apparatus 100 starts driving operation at a drive frequency f2 in order to output a target voltage value αV. In this activation operation, a set of coefficients that corresponds to the drive frequency f2 is selected among the sets of coefficients that are stored in the data table of the memory 104. The selected set of coefficients is substituted into the formula (3) to obtain a control formula (i.e., controlling expression) C2. The control formula C2 is used for phase compensation. A drive pulse of the drive frequency f2 that has been subjected to phase compensation by means of the control formula C2 corresponds to a second driving signal according to an aspect of the invention. In a step S2, an output voltage value is measured on the basis of the detection voltage Vo of the detection circuit 2. Specifically, the value is found with reference to the data table of the memory 104 in which a relationship between digital data of the detection voltage Vo and output voltage values is stored. In a step S3, an error (%) is calculated on the basis of the target voltage value αV and the output voltage value measured in the step S2. Then, it is judged whether or not the error is not greater than 10%. The error (%) is a value expressed in percentage; the output voltage value is subtracted from the target voltage value αV as a deviation; the target voltage value αV is taken as 100 to express the deviation, that is, the remaining value after subtraction, as the percentage value. The digital IC 101 functions as an arithmetic operation unit to calculate the error. If the error is not greater than 10% (S3: YES), the process proceeds to a step S4. If the error is greater than 10% (S3: NO), the process returns to the step S1. In the step S4, the drive frequency is switched over from the drive frequency f2 to a drive frequency f1, which is lower than the drive frequency f2. A set of coefficients that corresponds to the drive frequency f1 is selected among the sets of coefficients that are stored in the data table of the memory 104. The selected set of coefficients is substituted into the formula (3) to obtain a control formula C1. The control formula C1 is used for phase compensation. A drive pulse of the drive frequency f1 that has been subjected to phase compensation by means of the control formula C1 corresponds to a first driving signal according to an aspect of the invention.
For example, when the power supply apparatus 100 is used as a power source for a solid-state light source such as a laser, a light-emitting diode (LED), or the like, the input voltage supplied from the AC/DC converter (i.e., AC/DC circuit) 5 (refer to
As explained in detail above, the power supply apparatus 100 according to the present embodiment of the invention and a method for driving the power supply apparatus 100 produce the following advantageous effects. A control formula is stored in the memory 104. A dedicated control formula that is to be used for phase compensation can be individually set for each of a plurality of drive frequencies. Unlike a power supply apparatus of related art, which is provided with an analog phase compensation circuit that is dedicated for a single drive frequency, the power supply apparatus 100 according to the present embodiment of the invention makes it possible to switch over from one drive frequency to the other or another. In other words, since the digital IC 101 digitizes phase compensation, circuit oscillation does not occur even when the drive frequency is changed. Therefore, a driving method according to the present embodiment of the invention makes it possible to perform a drive-frequency changeover without causing any circuit oscillation. In addition, the power supply apparatus 100 with the adoption of such a driving method is provided.
As illustrated in
First of all, in the present embodiment of the invention, a third driving signal is used in addition to the aforementioned first driving signal and second driving signal. The drive frequency of the third driving signal, which is denoted as f3, is higher than the drive frequency f2. That is, the third driving signal has the highest drive frequency f3 whereas the first driving signal has the lowest drive frequency f1 (the drive frequency f3>the drive frequency f2>the drive frequency f1). In a step S11, upon receiving an instruction for activating the power supply apparatus 100, the power supply apparatus 100 starts driving operation at a drive frequency f3 in order to output a target voltage value αV. In addition, the CPU 103, which behaves as a drive time cumulative count unit, starts the counting (i.e., measurement) of elapsed time when triggered by the instruction for activation (i.e., command). A set of coefficients that corresponds to the drive frequency f3 is selected among the sets of coefficients that are stored in the data table of the memory 104. The selected set of coefficients is substituted into the formula (3) to obtain a control formula C3. The control formula C3 is used for phase compensation. A drive pulse of the drive frequency f3 that has been subjected to phase compensation by means of the control formula C3 corresponds to a third driving signal according to an aspect of the invention. In a step S12, it is judged whether time t21 has elapsed or not. In other words, it is judged whether elapsed time has reached the point in time t21 or not. If it is judged that elapsed time has reached the point in time t21 (S12: YES), the process proceeds to a step S13. If it is judged that elapsed time has not reached the point in time t21 yet (S12: NO), the process returns to the step S11. In the step S13, the driving signal is switched over from the third driving signal to the second driving signal. In the step S14, it is judged whether elapsed time has reached a point in time t22 or not. If it is judged that elapsed time has reached the point in time t22 (S14: YES), the process proceeds to a step S15. If it is judged that elapsed time has not reached the point in time t22 yet (S14: NO), the process returns to the step S13. In the step S15, the driving signal is switched over from the second driving signal to the first driving signal.
The point in time t21 (time t21) and the point in time t22 are pre-stored in the memory 104 as constants for the drive program. These points in time t21 and t22 are experimentally found values that can optimize tracking ability and circuit efficiency. For example, when the power supply apparatus 100 is used as a power source for a solid-state light source such as a laser, an LED, or the like, the output voltage of the DC/DC converter 1 is set at approximately 4V when the input voltage supplied from the AC/DC converter 5 (refer to
As explained in detail above, in addition to the advantageous effects of the first embodiment of the invention, a power supply apparatus according to the present embodiment of the invention and a method for driving the power supply apparatus produce the following advantageous effects. In a driving method according to the present embodiment of the invention, drive-frequency switchover control is performed in three steps according to accumulated drive time. As shown by the curve 71 in the graph, the drive frequency f3 is used for driving till the point in time t21. As a result, load-tracking ability improves. Thereafter, the drive frequencies f2 and f1 are selected sequentially depending on the magnitude of load variation, in other words, depending on the level of a deviation. Therefore, it is possible to achieve the greatest circuit efficiency with the use of the lowest drive frequency after the point in time t22. Thus, it is possible to provide a driving method that offers both excellent load-tracking ability and great circuit efficiency in a compatible manner. In addition, a power supply apparatus with the adoption of such a driving method is provided.
The light source apparatus 1000 explained here as the first light source apparatus includes a power supply apparatus 110, a solid-state light source 1001, and the like. The configuration of the power supply apparatus 110 is modified from that of the power supply apparatus 100 according to the first embodiment of the invention. The power supply apparatus 110 includes one AC/DC circuit 5, one digital IC 101, three DC/DC converters 1R, 1G, and 1B, three detection circuits 2R, 2G, and 2B, and three gate drivers 106R, 106G, and 106B as main components. That is, the single digital IC 101 controls the driving operation of the three DC/DC converters 1R, 1G, and 1B. The solid-state light source 1001 is made up of a red light source 1001R, which emits a beam of red light Lr, a green light source 1001G, which emits a beam of green light Lg, and a blue light source 1001B, which emits a beam of blue light Lb. The solid-state light source 1001 is not limited to a laser-type light source. For example, the solid-state light source 1001 may be an LED-type light source.
As connection between the power supply apparatus 110 and the solid-state light source 1001, each of the three DC/DC converters 1R, 1G, and 1B is connected to the corresponding one of the three light sources 1001R, 1001G, and 1001B. That is, the red light source 1001R is connected as a load of the DC/DC converter 1R. The green light source 1001G is connected as a load of the DC/DC converter 1G. The blue light source 1001B is connected as a load of the DC/DC converter 1B. In order to supply a voltage that is required for operating each of the three light sources 1001R, 1001G, and 1001B, the digital IC 101 generates a driving signal that reflects a detection voltage from the corresponding one of the three detection circuits 2R, 2G, and 2B. Then, the digital IC 101 performs PWM-driving control on each of the three DC/DC converters 1R, 1G, and 1B.
As explained above, the light source apparatus 1000 according to the present embodiment of the invention produces the following advantageous effects. The light source apparatus 1000 is equipped with the power supply apparatus 110 that is capable of achieving both excellent tracking ability and great circuit efficiency. Therefore, it is possible to light each of the three primary-color light sources 1001R, 1001G, and 1001B up to a predetermined illumination level quickly. In addition, it is possible to ensure great circuit efficiency after the lighting-up thereof. The excellent tracking ability of the power supply apparatus 110 enables each of the light sources 1001R, 1001G, and 1001B to light up at a high speed at the time of activation. In addition, it can be driven for continued illumination with great circuit efficiency during stable driving operation. Thus, the light source apparatus 1000 makes it possible to achieve both excellent tracking ability at the time of lighting-up operation upon activation and great circuit efficiency after lighting-up in a compatible manner.
The light source apparatus 1100 includes a power supply apparatus 111, the solid-state light source 1001, a light amount detection unit 1200, and the like. The configuration of the power supply apparatus 111 is different from that of the power supply apparatus 110 (refer to
The APC control is performed for the green light source 1001G and the blue light source 1001B in the same way as above. As a result, it is possible to provide an image with constant amount of light to a viewer. Specifically, the half mirrors 1201G and 1201B reflect a part of green light Lg emitted from the green light source 1001G and a part of blue light Lb emitted from the blue light source 1001B, respectively. The reflected light enters the photodiodes PD of the detection circuits 1202G and 1202B as incident light, respectively. The incident light is converted into voltage values that indicate the amount of the green light and the amount of the blue light, respectively. The voltage values are inputted into the A/D converter 102 of the digital IC 101, respectively. It is explained above that the power supply apparatus 111 is not provided with the detection circuit 2. However, the configuration of the light source apparatus 1100 is not limited to such an example. For example, the light source apparatus 1100 may be provided with the detection circuit 2 in addition to the light amount detection unit 1200. In such a modified configuration, feedback control may be performed on the basis of averaged detection data, which is obtained by averaging detection signals outputted from both of them. Or, feedback control may be performed on the basis of weighted average detection data, which is obtained by weighting and averaging detection signals outputted from both of them. With such a modified configuration, it is possible to increase feedback control reliability on the basis of two detection data.
As explained above, in addition to the advantageous effects produced by the first light source apparatus 1000, the light source apparatus 1100 according to the present embodiment of the invention produces the following advantageous effects. The light source apparatus 1100 is capable of detecting the amount of light emitted by each of its light sources and then performing APC control on the basis of the detected amount of light. In addition, the light source apparatus 1100 makes it possible to achieve both excellent tracking ability at the time of lighting-up operation upon activation and great circuit efficiency after lighting-up in a compatible manner.
A projector 500 is equipped with either the first light source apparatus 1000 or the second light source apparatus 1100, which functions as a light source unit of the projector 500. Though the light source apparatus 1000 appears in the following description, the light source apparatus 1000 may be replaced with the light source apparatus 1100. The projector 500 includes liquid crystal light valves 504R, 504G, and 504B, a cross-dichroic prism 506, and a projection lens 507. The light source apparatus 1000 emits red light Lr, green light Lg, and blue light Lb. A light valve (LV) driving circuit 200 sends an image signal to each of the liquid crystal light valves 504R, 504G, and 504B. The liquid crystal light valves 504R, 504G, and 504B, which constitute an example of a light modulating section according to an aspect of the invention, modulate the light Lr, Lg, and Lb in accordance with the image signals, respectively. The cross-dichroic prism 506 combines the modulated beams of light outputted respectively from the liquid crystal light valves 504R, 504G, and 504B and then directs the combined light to the projection lens 507. The projection lens 507 projects an image formed by the liquid crystal light valves 504R, 504G, and 504B with the enlargement of an image size onto a screen 510.
The projector 500 further includes equalizing optical systems 502R, 502G, and 502B. Each of the equalizing optical systems 502R, 502G, and 502B is provided at the downstream side of an optical path, which is downstream as viewed from the light source apparatus 1000. The equalizing optical systems 502R, 502G, and 502B equalize the illumination distribution of the light Lr, Lg, and Lb emitted from the light source apparatus 1000, respectively. Accordingly, the liquid crystal light valves 504R, 504G, and 504B are illuminated with light having the equalized illumination distribution. For example, a hologram, a field lens, or the like can be used for the equalizing optical systems 502R, 502G, and 502B.
The three beams of light that have been modulated by the liquid crystal light valves 504R, 504G, and 504B enter the cross-dichroic prism 506 as incident beams of light. The cross-dichroic prism 506 includes four right-angle prisms that are attached to one another. A dielectric multilayer film that reflects red light and a dielectric multilayer film that reflects blue light are provided in the shape of a cross inside the cross-dichroic prism 506. These dielectric multilayer films combine the three beams of light, thereby generating light that reproduces a color image. The projection lens 507, which is a projection optical system, projects the combined light onto the screen 510. As a result, an enlarged image is displayed on the screen 510.
As explained above, the projector 500 according to the present embodiment of the invention produces the following advantageous effects. The projector 500 is equipped with either the light source apparatus 1000 or the light source apparatus 1100, which functions as the light source unit of the projector 500. Therefore, it is possible to obtain each light Lr, Lg, and Lb that has a predetermined illumination level quickly. Thus, the projector 500 can project an image speedily after activation. In addition, it is possible to ensure great circuit efficiency after the lighting-up thereof. Therefore, power consumption can be reduced. Thus, the projector 500 can achieve both speedy projection of an image after activation and low power consumption in a compatible manner.
The scope of the invention is not limited to exemplary embodiments described above. The invention may be modified, adapted, changed, or improved in a variety of modes in its actual implementation. A variation example is explained below.
A variation example is explained with reference to
The entire disclosure of Japanese Patent Application No. 2009-040322, filed Feb. 24, 2009 is expressly incorporated by reference herein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-040322 | Feb 2009 | JP | national |
