JP6988515B2 - Light source device, projection type display device, and semiconductor device - Google Patents

Description

The present invention relates to a light source device using a semiconductor light source such as a laser diode (LD) or a light emitting diode (LED), and a projection type display device using such a light source device. Furthermore, the present invention relates to semiconductor devices and the like suitable for use in such light source devices.

Digital dimming and analog dimming are known as methods for adjusting the brightness in a light source device using a semiconductor light source such as a laser diode or a light emitting diode. For example, digital dimming is realized by controlling the switching element connected in series with the semiconductor light source by PWM (pulse width modulation) to adjust the length of the period during which the current flows through the semiconductor light source. On the other hand, analog dimming is realized by controlling a switching power supply circuit that supplies a current or a voltage to the semiconductor light source to adjust the magnitude of the current flowing through the semiconductor light source.

However, when a current is passed through the semiconductor light source, the temperature of the junction of the semiconductor light source rises and the forward voltage drops. Since the light output (light beam) of a semiconductor light source is determined by the supplied current and the forward voltage, when the temperature of the junction of the semiconductor light source rises, the forward voltage drops and a constant current is supplied to the semiconductor light source. Even so, the phenomenon that the light output decreases occurs.

As a related technique, Patent Document 1 describes that the temperature of the junction portion of the semiconductor laser diode changes depending on the on-time ratio of PWM control, and the forward voltage of the semiconductor laser diode changes. As a result, in digital dimming, there arises a problem that the on-time ratio of PWM control is not proportional to the optical output of the actual semiconductor light source.

JP-A-2016-225285 (paragraphs 0029-0032, FIGS. 1, 3)

In Patent Document 1, the target value setting unit 108 (FIG. 1) sets the target average current value using the characteristic curve when the semiconductor light source is actually driven, which is shown by the solid line in FIG. 3, the target value table 108a. Is set. If this target average current value is compared with the average current value of the semiconductor laser diode 102 and the switching power supply 101 is feedback-controlled using the comparison output, the average current value of the semiconductor laser diode 102 becomes the on-time ratio of the PWM control. Correspondingly, it becomes equal to the target average current value set by the target value setting unit 108.

However, since the characteristics of the semiconductor laser diode 102 vary, it is necessary to adjust the current value one by one for each product before shipping. Further, if the target value table 108a is written to the ROM, the target value table 108a cannot be rewritten when the semiconductor laser diode 102 is changed. In order to change the target value table 108a, it is necessary to replace the IC with a built-in ROM. On the other hand, even when the target value table 108a is written to the flash memory or the like, a large number of man-hours are required to rewrite the target value table 108a.

Therefore, in view of the above points, the first object of the present invention is a PWM signal with a relatively simple circuit configuration without using a target value table set by using a characteristic curve at the time of driving an actual semiconductor light source. It is to improve the linearity of the optical output of the semiconductor light source with respect to the on-duty ratio of. A second object of the present invention is to provide a projection type display device using such a light source device. Furthermore, a third object of the present invention is to provide a semiconductor device or the like suitable for use in such a light source device.

In order to solve at least a part of the above problems, in the light source device according to the first aspect of the present invention, a semiconductor light source, a first switching element connected in series to the semiconductor light source, and a PWM signal are activated. A first switching element including a drive circuit that activates the first control signal to turn on the first switching element and a second switching element that performs a switching operation according to the second control signal. The switching power supply circuit that supplies current to the semiconductor light source when is on, the first current detector that detects the current flowing through the semiconductor light source and outputs the first current detection signal, and the on-duty of the PWM signal. The difference between the compensation circuit that generates a compensation signal having a voltage that changes according to the ratio, the addition circuit that adds the current control signal and the compensation signal at a predetermined ratio, and the output signal of the addition circuit and the first current detection signal. An error amplifier that amplifies and generates an error signal, a second current detector that detects the current flowing through the second switching element and outputs a second current detection signal, and a second current detection signal and error signal. A switching power supply control circuit that generates a second control signal based on the above is provided.

According to the first aspect of the present invention, the compensation circuit generates a compensation signal according to the on-duty ratio of the PWM signal, and the adder circuit adds the current control signal and the compensation signal at a predetermined ratio, so that the output of the adder circuit By controlling the switching power supply circuit based on the signal, the on-duty ratio of the PWM signal can be achieved with a relatively simple circuit configuration without using the target value table set using the characteristic curve when driving the actual semiconductor light source. It is possible to improve the linearity of the optical output of the semiconductor light source.

Here, the compensation circuit may include an integrating circuit that generates a compensation signal having a voltage proportional to the on-duty ratio of the PWM signal. In that case, the compensation circuit is configured using an integrator circuit, which is a relatively simple analog circuit. Therefore, by using the resistor or capacitor included in the integrator circuit as an external component, the light source device can be used before shipment. The compensation characteristics can be adjusted according to the variation in the characteristics of the semiconductor light source.

Further, the light source device may further include a voltage limiting circuit that limits the voltage of the output signal of the adder circuit so as not to exceed a predetermined voltage. As a result, even if the voltage of the current control signal or the compensation signal becomes high, it is prevented that an overcurrent flows through the semiconductor light source, and the current flowing through the semiconductor light source exceeds the rated current, or the light source device or its light source device is mounted. It is possible to prevent the power consumption of the projection type display device and the like from exceeding the rated power.

In the above, the switching power supply circuit is connected to the inductor connected between the semiconductor light source and the second switching element, the capacitor connected between one end of the inductor and the power supply node, and the other end of the inductor. It further includes a diode with a cathode connected to the anode and power supply node, and when the first and second switching elements are in the ON state, current flows through the semiconductor light source and the inductor to store energy in the inductor. When the switching element 1 is on and the second switching element is off, the energy stored in the inductor may cause a current to flow through the semiconductor light source and the diode.

In such a switching power supply circuit, by increasing the on-duty ratio of the second control signal according to the on-duty ratio of the PWM signal, the period in which the second switching element is in the on state becomes longer, so that the semiconductor light source The current flowing through increases. As a result, when the on-duty ratio of the PWM signal is large, even if the temperature of the junction of the semiconductor light source rises and the forward voltage drops, the power supplied to the semiconductor light source can be brought close to constant.

The projection type display device according to the second aspect of the present invention includes any of the above light source devices. According to the second aspect of the present invention, the semiconductor with respect to the on-duty ratio of the PWM signal has a relatively simple circuit configuration without using the target value table set by using the characteristic curve at the time of driving the actual semiconductor light source. The brightness of the projected image can be accurately controlled by using a light source device having improved linearity of the light output of the light source.

The semiconductor device according to the third aspect of the present invention activates the first control signal when the PWM signal is activated, and turns on the first switching element connected in series with the semiconductor light source. Switching power supply control that generates a second control signal that controls the second switching element that performs switching operation in the drive circuit and the switching power supply circuit that supplies current to the semiconductor light source when the first switching element is in the ON state. The circuit, the first current detection circuit that detects the current flowing through the first current detection element connected in series to the semiconductor light source and outputs the first current detection signal, and the voltage that changes according to the on-duty ratio of the PWM signal. An error signal that amplifies the difference between the output signal of the adder circuit and the first current detection signal, the compensator circuit that generates the compensator signal having A second current detection circuit that detects the current flowing through the second current detection element connected in series to the second switching element and outputs a second current detection signal is provided for switching. The power supply control circuit generates a second control signal based on the second current detection signal and the error signal.

Also according to the third aspect of the present invention, the switching power supply circuit is actually controlled based on the output signal of the adder circuit that adds the current control signal and the compensation signal according to the on-duty ratio of the PWM signal at a predetermined ratio. It is possible to improve the linearity of the optical output of the semiconductor light source with respect to the on-duty ratio of the PWM signal with a relatively simple circuit configuration without using the target value table set by using the characteristic curve at the time of driving the semiconductor light source.

The circuit diagram which shows the structural example of the light source apparatus which concerns on one Embodiment of this invention. The circuit diagram which shows the structural example of the compensation circuit shown in FIG. The figure which shows the relationship between the on-duty ratio of a PWM signal and the temperature of a semiconductor light source. The figure which shows the relationship between the temperature of the junction of a semiconductor light source, and the forward voltage. The figure which shows the relationship between the forward voltage of a semiconductor light source, and the current supplied to a semiconductor light source. The block diagram which shows the structural example of the projection type display device which concerns on one Embodiment of this invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The same reference number is assigned to the same component, and duplicate description will be omitted.
<Light source device>
FIG. 1 is a circuit diagram showing a configuration example of a light source device according to an embodiment of the present invention. As shown in FIG. 1, the light source device includes a semiconductor device (IC) 100, a semiconductor light source 110, N-channel MOS transistors QN1 and QN2, diodes D1 to D3, a Zener diode D4, an inductor L1, and a capacitor. It contains C1 to C6 and resistors R1 to R4.

The high potential side power supply potential VDD (for example, 50V) is supplied to the node N1 of the light source device, and the low potential side power supply potential VSS is supplied to the node N2. FIG. 1 shows a case where the power supply potential VSS is the ground potential (0V). A resistor R1, a semiconductor light source 110, a transistor QN1, an inductor L1, a transistor QN2, and a resistor R2 are connected in series between the node N1 and the node N2.

The resistor R1 is connected between the node N1 and one end of the semiconductor light source 110 and is a first current detection element for detecting the current flowing through the semiconductor light source 110. For example, a resistance value as small as about 50 mΩ to 100 mΩ can be obtained. Have. The semiconductor light source 110 includes, for example, at least one laser diode or a light emitting diode, and emits light with a brightness corresponding to the magnitude of the supplied current. The light output (luminous flux) of the semiconductor light source 110 is determined by the supplied current and the forward voltage.

The transistor QN1 is a first switching element connected in series to the semiconductor light source 110 for digital dimming by PWM control, and is connected to a drain connected to the other end of the semiconductor light source 110 and one end of the inductor L1. It has a source and a gate to which the first control signal DDRV is applied via the capacitor C5. The transistor QN1 is turned on when the first control signal DDRV is activated to a high level, and is turned off when the first control signal DDRV is deactivated to a low level.

When the first control signal DDRV is alternately activated and deactivated, the transistor QN1 performs a switching operation. Therefore, by changing the duty ratio of the first control signal DDRV, it is possible to perform digital dimming by changing the period during which the current flows through the semiconductor light source 110. A P-channel MOS transistor may be used instead of the N-channel MOS transistor QN1, but in that case, a part of the circuit shown in FIG. 1 is modified.

The transistor QN2 is a second switching element that constitutes a switching power supply circuit together with a diode D1, an inductor L1, a capacitor C4, and the like, and is connected to a node N2 via a drain connected to the other end of the inductor L1 and a resistor R2. It has a connected source and a gate to which a second control signal GATE is applied. The transistor QN2 is turned on when the second control signal GATE is activated to a high level and turned off when the second control signal GATE is deactivated to a low level.

When the second control signal GATE is alternately activated and deactivated, the transistor QN2 performs a switching operation. When the transistor QN2 performs the switching operation according to the second control signal GATE, the switching power supply circuit supplies a current to the semiconductor light source 110 when the transistor QN1 is in the ON state.

Therefore, by changing the duty ratio of the second control signal GATE, the magnitude of the current flowing through the semiconductor light source 110 can be changed to perform analog dimming. As the switching element, a bipolar transistor, an IGBT (insulated gate bipolar transistor), a cylister, or the like can be used in addition to the MOS transistor.

The diode D1 has an anode connected to the other end of the inductor L1 and a cathode connected to the node N1. As the diode D1, for example, a Schottky barrier diode having a lower forward voltage and a faster switching speed than a PN junction diode is used.

The resistor R2 is a second current detection element connected between the source of the transistor QN2 and the node N2 and for detecting the current flowing through the transistor QN2, and has a small resistance value of, for example, about 50 mΩ to 100 mΩ. ing. The capacitor C1 is connected between the node N1 and the node N2 to smooth the power supply voltage (VDD-VSS). The capacitor C4 is connected between one end of the inductor L1 and the node N1 to smooth the step-down voltage obtained by stepping down the power supply voltage (VDD-VSS).

<Semiconductor device>
The semiconductor device 100 is supplied with a PWM signal (digital dimming signal) PWM and a current control signal (analog dimming signal) IADJ from an external microcomputer or the like to control the transistors QN1 and QN2 of the light source device. At least a part of the components of the semiconductor device 100 shown in FIG. 1 may be a discrete component or an external IC, and the diode D1, the resistor R1, the resistor R2, or the like may be built in the semiconductor device 100. You may.

As shown in FIG. 1, the semiconductor device 100 includes internal regulators 10a and 10b, level shifters (L / S) 11 and 12, a drive circuit 20, a compensation circuit 30, an addition circuit 31, and a current detection circuit 40. The error amplifier 50, the switch circuit (SW) 51, the comparator 52, the slope compensation circuit 60, the clock signal generation circuit 70, the switching control circuit 80, and the drive circuit 90 are included, and further, voltage limitation is provided. The circuit 32 may be included.

The internal regulators 10a and 10b include, for example, a reference voltage generation circuit composed of a bandgap reference circuit or the like, and have internal power supply potentials VDA and VDC supplied to the internal circuit of the semiconductor device 100 based on the power supply potential VDD, respectively. Generate. The capacitor C2a is connected between the output terminal of the internal regulator 10a and the node N2 to smooth the internal power supply voltage (VDA-VSS). The capacitor C2b is connected between the output terminal of the internal regulator 10b and the node N2 to smooth the internal power supply voltage (VDR-VSS).

The level shifters 11 and 12 shift the high-level potential of the PWM signal supplied from the outside of the semiconductor device 100 to a potential suitable for the internal circuit of the semiconductor device 100. The drive circuit 20 includes, for example, a driver amplifier and the like, and generates a first control signal DDRV based on a PWM signal supplied from the level shifter 11.

For example, the drive circuit 20 activates the first control signal DDRV to a high level when the PWM signal is activated to turn on the transistor QN1, and the first is when the PWM signal is deactivated. The control signal DDRV of is deactivated to a low level to turn off the transistor QN1.

The first control signal DDRV transitions between a low level (eg, 0V) and a high level (eg, 7.5V). When the first control signal DDRV is activated to a high level, a current flows from the drive circuit 20 to the gate of the transistor QN1 via the capacitor C5, the gate-source voltage of the transistor QN1 rises, and the transistor QN1 becomes Turns on. The Zener diode D4 is clamped so that the gate-source voltage of the transistor QN1 does not exceed a predetermined voltage (for example, 7.5V).

During the period in which the first control signal DDRV is maintained in the activated state, the third control signal GATE'transitions between the low level and the high level. As a result, the capacitor C6 and the diodes D2 and D3 perform a rectifying operation, so that the gate-source voltage of the transistor QN1 is maintained above the threshold voltage.

If the second control signal GATE is maintained in the deactivated state during the deactivation period of the first control signal DDRV, the second control signal GATE should also be used as the third control signal GATE'. Can be done. On the other hand, when the second control signal GATE is activated and deactivated during the deactivation period of the first control signal DDRV, the PWM signal or the first control signal DDRV and the second control signal GATE The third control signal GATE'may be generated by providing the switching control circuit 80 with an AND circuit for obtaining the logical product of the above.

When the first control signal DDRV is deactivated to a low level, the gate-source voltage of the transistor QN1 drops, and the transistor QN1 is turned off. The resistor R4 lowers the gate-source voltage of the transistor QN1 to keep the transistor QN1 in the off state when the light emitting device stops the light emission for a long time in the standby mode or the like.

When the on-duty ratio of the PWM signal becomes large, the ratio of the period during which the current flows through the semiconductor light source 110 in digital dimming increases, so that the temperature of the junction of the semiconductor light source 110 rises and the forward voltage drops. Therefore, the compensation circuit 30 generates a compensation signal VPWM having a voltage that changes according to the on-duty ratio of the PWM signal supplied from the level shifter 12 in order to compensate for the decrease in the optical output of the semiconductor light source 110. It is desirable that the compensation signal VPWM has a voltage that monotonically increases as the on-duty ratio of the PWM signal increases.

For example, the compensation circuit 30 is composed of an integrating circuit (low-pass filter) that generates a compensation signal VPWM having a voltage proportional to the on-duty ratio of the PWM signal. In that case, since the compensation circuit 30 is configured by using an integrator circuit which is a relatively simple analog circuit, the light source device is shipped by using the resistor or capacitor included in the integrator circuit as an external component. Previously, the compensation characteristics can be adjusted according to the variation in the characteristics of the semiconductor light source 110. Since the resistance value of the resistor used in the integrator circuit is temperature-dependent, the voltage of the compensation signal VPWM does not have to be completely proportional to the on-duty ratio of the PWM signal, and it depends on the heat generation of the resistor. The error is acceptable.

FIG. 2 is a circuit diagram showing a configuration example of the compensation circuit shown in FIG. In the example shown in FIG. 2, the compensation circuit 30 is connected between the resistor R5 to which the PWM signal supplied from the level shifter 12 is supplied to one end, the other end of the resistor R5, and the wiring of the power supply potential VSS. It includes a capacitor C7 and is composed of an integrating circuit that generates a compensation signal VPWM at a connection point between the resistor R5 and the capacitor C7.

Referring to FIG. 1 again, the addition circuit 31 adds the current control signal IADJ and the compensation signal VPWM at a predetermined ratio. The addition ratio in the addition circuit 31 may also be adjustable by an external component. Assuming that the voltage during the activation period of the PWM signal is Von and the on-duty ratio is Duty, the voltage of the compensation signal VPWM added to the current control signal IADJ by the addition circuit 31 is expressed by the following equation.
VPWM = Von x Duty x K
Here, K is a conversion coefficient. For example, when Von is 5V and Duty is 50%, Von × Duty is 2.5V, which is too large. Therefore, for example, by setting K to 0.1, the voltage of the compensation signal VPWM can be set to 0.25V.

The voltage limiting circuit 32 is composed of, for example, a clamp element such as a Zener diode connected between the output terminal of the adder circuit 31 and the wiring of the power supply potential VSS, and the voltage of the output signal of the adder circuit 31 is a predetermined voltage. Limit so that it does not exceed. As a result, even if the voltage of the current control signal IADJ or the compensation signal VPWM becomes high, it is prevented that an overcurrent flows through the semiconductor light source 110, and the current flowing through the semiconductor light source 110 exceeds the rated current, or the light source device or its light source. It is possible to prevent the power consumption of the projection type display device or the like on which the device is mounted from exceeding the rated power.

The current detection circuit 40 includes, for example, a current sense amplifier that amplifies the voltage between both ends of the current detection resistor R1 connected in series with the semiconductor light source 110, and detects the current flowing through the current detection resistor R1. It corresponds to the first current detection circuit that outputs the current detection signal of 1. Here, the current detection circuit 40, together with the current detection resistor R1, constitutes a first current detection unit that detects the current flowing through the semiconductor light source 110 and outputs a first current detection signal. The output signal of the current detection circuit 40 is supplied to the inverting input terminal of the error amplifier 50.

The error amplifier 50 amplifies the difference between the output signal of the adder circuit 31 and the first current detection signal to generate an error signal ERR, and supplies the error signal ERR to the switch circuit 51. The switch circuit 51, the comparator 52, the slope compensation circuit 60, the clock signal generation circuit 70, the switching control circuit 80, and the drive circuit 90 have a second current detection signal DET obtained by detecting the current flowing through the transistor QN2. A switching power supply control circuit that generates a second control signal GATE based on the error signal ERR is configured.

The switch circuit 51 is composed of, for example, an analog switch or the like, and is turned on when the PWM signal supplied from the level shifter 12 is activated, and turned off when the PWM signal is deactivated. .. As a result, the voltage of the error signal ERR generated when the transistor QN1 is in the ON state is held in the capacitor C3 and supplied to the inverting input terminal of the comparator 52.

The slope compensation circuit 60 includes, for example, a current sense amplifier that amplifies the voltage between both ends of the current detection resistor R2 connected in series with the transistor QN2, and detects the current flowing through the current detection resistor R2 to provide a second. Corresponds to the second current detection circuit that outputs the current detection signal DET of. Here, the slope compensation circuit 60, together with the resistor R2 for current detection, constitutes a second current detection unit that detects the current flowing through the transistor QN2 and outputs a second current detection signal DET.

For example, the slope compensation circuit 60 generates a second current detection signal DET by amplifying the voltage between both ends of the current detection resistor R2 and adding a bias voltage, and the second current detection signal DET is used as a comparator. It is supplied to the non-inverting input terminal of 52. The comparator 52 compares the voltage of the second current detection signal DET with the voltage of the error signal ERR, and when the voltage of the second current detection signal DET is higher than the voltage of the error signal ERR, the reset signal RST To activate.

The clock signal generation circuit 70 includes, for example, a CR oscillation circuit and the like, and generates a clock signal CLK having a predetermined frequency by performing an oscillation operation. The oscillation frequency of the CR oscillation circuit is determined by the time constant, which is the product of the capacitance value of the capacitor and the resistance value of the resistor. The resistor R3 is externally attached to the semiconductor device 100 in order to adjust the oscillation frequency of the CR oscillation circuit.

The switching control circuit 80 includes, for example, an RS flip-flop and the like, and generates a second control signal GATE for controlling the transistor QN2 based on the clock signal CLK and the reset signal RST. The second control signal GATE is applied to the gate of the transistor QN2 via a drive circuit 90 composed of a driver amplifier or the like. For example, the switching control circuit 80 activates the second control signal GATE to a high level in synchronization with the rising edge of the clock signal CLK. As a result, the transistor QN2 is turned on.

When the transistors QN1 and QN2 are in the ON state, a current flows from the node N1 to the node N2 via the semiconductor light source 110 and the inductor L1, and the electric energy is converted into magnetic energy and stored in the inductor L1. Further, when the transistor QN1 is in the off state and the transistor QN2 is in the on state, a current flows from the capacitor C4 to the node N2 via the inductor L1 and the like, and energy is stored in the inductor L1.

The current flowing through the inductor L1 gradually increases with time. As the current flowing through the current detection resistor R2 via the inductor L1 and the like increases, the voltage of the second current detection signal DET also rises. When the voltage of the second current detection signal DET exceeds the voltage of the error signal ERR, the reset signal RST is activated to a high level. The switching control circuit 80 deactivates the second control signal GATE to a low level in synchronization with the rising edge of the reset signal RST. As a result, the transistor QN2 is turned off.

When the transistor QN1 is on and the transistor QN2 is off, the magnetic energy stored in the inductor L1 is released as electrical energy, and a current flows through the semiconductor light source 110, the diode D1 and the like. Further, when the transistors QN1 and QN2 are in the off state, the magnetic energy stored in the inductor L1 is released as electric energy, and a current flows through the capacitor C4, the diode D1 and the like.

In such a switching operation, when the voltage of the current control signal IADJ rises, the on-duty ratio of the second control signal GATE increases, the period during which the transistor QN2 is in the ON state becomes longer, and the semiconductor light source 110 becomes The flowing current increases. Therefore, by changing the current control signal IADJ, the current flowing through the semiconductor light source 110 can be changed to perform analog dimming.

Alternatively, the switching control circuit 80 generates a second control signal GATE based on the PWM signal supplied from the level shifter 11 in addition to the clock signal CLK and the reset signal RST, so that the first control signal DDRV The second control signal GATE may be maintained in the deactivated state during the deactivated period.

In that case, the analog dimming transistor QN2 is turned off during the period when the digital dimming transistor QN1 is turned off and no current flows through the semiconductor light source 110. As a result, it is possible to suppress the energy stored in the inductor L1 from being released without being used for light emission, and to reduce the power loss.

<Operation example>
FIG. 3 is a diagram showing the relationship between the on-duty ratio of the PWM signal and the temperature of the junction of the semiconductor light source. In FIG. 3, the horizontal axis represents the on-duty ratio of the PWM signal, and the vertical axis represents the temperature T of the junction of the semiconductor light source 110. As shown in FIG. 3, when the on-duty ratio of the PWM signal becomes large, the temperature T of the junction portion of the semiconductor light source 110 rises.

FIG. 4 is a diagram showing the relationship between the temperature of the junction of the semiconductor light source and the forward voltage. 4, the horizontal axis represents the temperature T of the junction of the semiconductor light source 110, the vertical axis represents the forward voltage V _F of the semiconductor light source 110. As shown in FIG. 4, when the temperature T of the junction of the semiconductor light source 110 is increased, the forward voltage V _F of the semiconductor light source 110 is lowered.

Therefore, when the on-duty ratio of the PWM signal is a second value larger than the first value as compared with the case where the on-duty ratio of the PWM signal is the first value, the junction of the semiconductor light source 110 When the temperature T of the increases by [Delta] T, the forward voltage V _F is decreased by [Delta] V _F. Since the light output of the semiconductor light source 110 is determined by the current supplied and the forward voltage V _F, when the forward voltage V _F is decreased, even by supplying a constant current to the semiconductor light source 110 light output decreases The phenomenon of closing occurs.

Therefore, in the present embodiment, the compensation circuit 30 generates the compensation signal VPWM according to the on-duty ratio of the PWM signal, and the addition circuit 31 adds the current control signal IADJ and the compensation signal VPWM at a predetermined ratio. When the on-duty ratio of the PWM signal is small, the voltage of the compensation signal VPWM becomes low, and the voltage of the output signal of the adder circuit 31 is mainly determined by the current control signal IADJ. Therefore, the current ILD supplied to the semiconductor light source 110 is mainly controlled by the current control signal IADJ.

On the other hand, when the on-duty ratio of the PWM signal is large, the voltage of the compensation signal VPWM becomes high and the voltage of the output signal of the adder circuit 31 increases. In the switching power supply circuit, by increasing the on-duty ratio of the second control signal GATE according to the on-duty ratio of the PWM signal, the period in which the transistor QN2 is in the ON state becomes longer, so that the current flowing through the semiconductor light source 110 is increased. To increase. Thereby, when the on-duty ratio of the PWM signal is large, even if the reduced forward voltage V _F temperature T of the junction of the semiconductor light source 110 is increased, close the power supplied to the semiconductor light source 110 at a constant be able to.

FIG. 5 is a diagram showing the relationship between the forward voltage of the semiconductor light source and the current supplied to the semiconductor light source. 5, the horizontal axis represents the forward voltage V _F of the semiconductor light source 110, the vertical axis represents the current ILD to the current control signal IADJ is supplied to the semiconductor light source 110 when the constant. FIG. 5 shows, as an example, operating points at 0 ° C, 25 ° C, and 50 ° C.

When the on-duty ratio of the PWM signal is large, the forward voltage V _F is decreased higher junction temperature of the semiconductor light source 110, but by controlling the switching power supply circuit based on an output signal of the adder 31, The current ILD supplied to the semiconductor light source 110 can be increased to bring the power supplied to the semiconductor light source 110 close to a constant value. As a result, the linearity of the optical output of the semiconductor light source with respect to the on-duty ratio of the PWM signal is improved with a relatively simple circuit configuration without using the target value table set by using the characteristic curve when driving the actual semiconductor light source. can do.

<Projection type display device>
Next, a projection type display device (video projector) according to an embodiment of the present invention will be described.
FIG. 6 is a block diagram showing a configuration example of a projection type display device according to an embodiment of the present invention. The projection type display device 200 is supplied with a power supply voltage from the outside, and image data is supplied from an image data supply device such as a personal computer or a video player, and an image is displayed on a screen (projection surface) 300 based on the image data. Project.

As shown in FIG. 6, the projection type display device 200 includes a power supply circuit 210, an image data processing unit 220, a control unit 230, a light source device 240, a panel 250, and a projection optical system 260. Here, the light source device 240 is a light source device according to an embodiment of the present invention, and includes a semiconductor device 100 and a semiconductor light source 110.

For example, the power supply circuit 210 generates a DC logic power supply voltage based on the AC100V power supply voltage supplied from the outside and supplies it to the image data processing unit 220, the control unit 230, and the like, and is higher than the logic power supply voltage. A DC power supply voltage is generated and supplied to the semiconductor device 100 or the like of the light source device 240.

The image data processing unit 220 and the control unit 230 are composed of, for example, at least one microcomputer or the like. The image data processing unit 220 drives the panel 250 by processing the image data supplied from the outside to generate an image signal and a synchronization signal for display, and supplying the image signal and the synchronization signal to the panel 250. Draw.

The control unit 230 controls each unit of the projection type display device 200 according to an operation performed by the operator using a remote controller or an operation panel (not shown). When the operator instructs dimming, the control unit 230 generates a PWM signal and a current control signal IADJ for realizing dimming instructed by the operator, and supplies the PWM signal and the current control signal IADJ to the semiconductor device 100 of the light source device 240. do. As a result, the semiconductor device 100 controls the light emitting operation of the semiconductor light source 110.

The light source device 240 emits light with a brightness according to the PWM signal and the current control signal IADJ supplied from the control unit 230, and irradiates the panel 250 with light. For example, when the semiconductor light source 110 includes a plurality of laser diodes that generate blue light, the light source device 240 includes a phosphor that receives the blue light generated by some of the laser diodes and generates yellow light, and yellow according to the wavelength. It may further include a spectroscopic unit that separates red light and green light from the light. In that case, the light source device 240 can generate light of three colors of R (red), G (green), and B (blue).

The panel 250 modulates the light emitted from the light source device 240 according to the image signal and the synchronization signal supplied from the image data processing unit 220. For example, the panel 250 may include three liquid crystal panels corresponding to three colors of RGB. Each liquid crystal panel forms an image by changing the transmittance of light in a plurality of pixels arranged in a matrix. The modulated light modulated by the panel 250 is guided to the projection optical system 260.

The projection optical system 260 includes at least one lens. For example, the projection lens, which is a lens group for projecting the modulated light modulated by the panel 250 onto the screen 300 to form an image, and the aperture state, zoom state, shift position, etc. of the projection lens are adjusted. Various adjustment mechanisms are provided in the projection optical system 260. These adjustment mechanisms are controlled by the control unit 230. The projection optical system 260 projects the modulated light onto the screen 300, so that the image is displayed on the screen 300.

According to the present embodiment, the light of the semiconductor light source 110 with respect to the on-duty ratio of the PWM signal is used with a relatively simple circuit configuration without using the target value table set by using the characteristic curve at the time of driving the actual semiconductor light source. The brightness of the projected image can be accurately controlled by using the light source device 240 with improved output linearity.

When setting the target value table for each product or model, a lot of man-hours are required and the cost increases, but according to this embodiment, the compensation characteristics can be adjusted only by a relatively simple analog circuit. Therefore, the light source device 240 or the projection type display device 200 can be manufactured at low cost.

The present invention is not limited to the embodiments described above, and many modifications can be made within the technical idea of the present invention by a person having ordinary knowledge in the art.

10a, 10b ... Internal regulator, 11, 12 ... Level shifter, 20 ... Drive circuit, 30 ... Compensation circuit, 31 ... Addition circuit, 32 ... Voltage limiting circuit, 40 ... Current detection circuit, 50 ... Error amplifier, 51 ... Switch circuit , 52 ... Comparator, 60 ... Slope compensation circuit, 70 ... Clock signal generation circuit, 80 ... Switching control circuit, 90 ... Drive circuit, 100 ... Semiconductor device, 110 ... Semiconductor light source, 200 ... Projection type display device, 210 ... Power supply Circuit, 220 ... Image data processing unit, 230 ... Control unit, 240 ... Light source device, 250 ... Panel, 260 ... Projection optical system, 300 ... Screen, QN1, QN2 ... N channel MOS transistor, D1 to D3 ... Diode, D4 ... Zener diode, L1 ... inductor, C1 to C7 ... capacitor, R1 to R5 ... resistor

Claims (6)

With a semiconductor light source
The first switching element connected in series to the semiconductor light source and
A drive circuit that activates the first control signal when the PWM signal is activated to turn on the first switching element, and
A switching power supply circuit that includes a second switching element that performs a switching operation according to a second control signal and supplies a current to the semiconductor light source when the first switching element is in the ON state.
A first current detection unit that detects the current flowing through the semiconductor light source and outputs a first current detection signal.
A compensation circuit that generates a compensation signal having a voltage that changes according to the on-duty ratio of the PWM signal, and a compensation circuit.
An adder circuit that adds the current control signal and the compensation signal at a predetermined ratio,
An error amplifier that amplifies the difference between the output signal of the adder circuit and the first current detection signal to generate an error signal, and
A second current detection unit that detects the current flowing through the second switching element and outputs a second current detection signal, and a second current detection unit.
A switching power supply control circuit that generates the second control signal based on the second current detection signal and the error signal.
A light source device equipped with. The light source device according to claim 1, wherein the compensation circuit includes an integration circuit that generates a compensation signal having a voltage proportional to the on-duty ratio of the PWM signal. The light source device according to claim 1 or 2, further comprising a voltage limiting circuit that limits the voltage of the output signal of the adder circuit so as not to exceed a predetermined voltage. The switching power supply circuit
An inductor connected between the semiconductor light source and the second switching element,
A capacitor connected between one end of the inductor and the power supply node,
A diode having an anode connected to the other end of the inductor and a cathode connected to the power supply node,
When the first and second switching elements are in the ON state, a current flows through the semiconductor light source and the inductor to store energy in the inductor, and the first switching element is in the ON state. The light source device according to any one of claims 1 to 3, wherein when the second switching element is in the off state, a current flows through the semiconductor light source and the diode by the energy stored in the inductor. A projection type display device including the light source device according to any one of claims 1 to 4. A drive circuit that activates the first control signal when the PWM signal is activated and turns on the first switching element connected in series with the semiconductor light source.
A switching power supply control circuit that generates a second control signal for controlling a second switching element that performs a switching operation in a switching power supply circuit that supplies a current to the semiconductor light source when the first switching element is in the ON state. ,
A first current detection circuit that detects the current flowing through the first current detection element connected in series to the semiconductor light source and outputs a first current detection signal.
A compensation circuit that generates a compensation signal having a voltage that changes according to the on-duty ratio of the PWM signal, and a compensation circuit.
An adder circuit that adds the current control signal and the compensation signal at a predetermined ratio,
An error amplifier that amplifies the difference between the output signal of the adder circuit and the first current detection signal to generate an error signal, and
A second current detection circuit that detects the current flowing through the second current detection element connected in series to the second switching element and outputs a second current detection signal.
The semiconductor device, wherein the switching power supply control circuit generates the second control signal based on the second current detection signal and the error signal.

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