JP2010141067A - Drive device of semiconductor light source - Google Patents

Abstract

Power consumption of a semiconductor switch in a drive circuit of a semiconductor light source is suppressed.
A switch driving circuit controls a semiconductor switch to an OFF state when a control signal Vc is at an L level, and controls the semiconductor switch to an ON state when the control signal Vc is at an H level. The current control circuit 9 controls the constant current power supply 100 so that when the control signal Vc is at the L level by the level setting of the current setting voltage Vref, the constant current power supply 100 causes the driving current of 30 A to flow to the LED 3. When the current is at the H level, the constant current power supply 100 is controlled so that the constant current power supply 100 outputs a driving current of 10A.
[Selection] Figure 1

Description

  The present invention relates to a driving device used for a semiconductor light source such as a light emitting diode (hereinafter referred to as “LED”) or a semiconductor laser.

  The conventional semiconductor light source driving device is configured as a constant current power source, detects the current flowing through the semiconductor light source, feeds back this, and adjusts the output voltage by changing the duty ratio of the PWM signal. The duty ratio is controlled so that the current flowing through the semiconductor light source becomes a constant value. And when interrupting | blocking a semiconductor light source, the electric current which flows into a semiconductor light source is interrupted by opening the switch connected in series with the semiconductor light source.

  However, when the current is cut off by the switch, almost no current flows. Therefore, when the switch is closed again, a pulsed current flows immediately after that, or it takes time to settle to the desired current. The problem that occurred.

  As an improvement measure, a switch by a PNP transistor is arranged in parallel with the LED, and the current to the LED is cut off by turning on the PNP transistor (see, for example, Patent Document 1). In addition, there is an example in which a MOSFET is used as the switch instead of a switch using a PNP transistor (see Non-Patent Document 1, for example).

Japanese Patent Laid-Open No. 5-129665 (FIG. 1) MAX16818 data sheet from MAXIM, P1 and P19

  However, in the OFF state in which the LED is shut off, most of the current output from the constant current power source flows to the semiconductor switch side such as a MOSFET. For this reason, in the case where a large current exceeding 30 A is required, such as a high-intensity LED, the power consumption in the semiconductor switch (flows through the semiconductor switch output from the constant current power source). (Constant current value) x (Drain-source voltage of the semiconductor switch) The power consumption of the semiconductor switch is remarkably increased, and the power efficiency of the entire device is reduced and the heat generation of the switch is a problem. Emerge as.

  The present invention has been made to eliminate such technical concerns, and its main purpose is to improve the power use efficiency in the driving device of the semiconductor light source and to reduce the cost through the downsizing of the driving device. The goal is to realize down.

  The subject of the present invention is a semiconductor light source driving device for controlling the light emission of a semiconductor light source to an ON state or an OFF state, the constant current power source driving the semiconductor light source being connected in parallel with the semiconductor light source When a semiconductor switch and a semiconductor light source ON / OFF control signal are received and the semiconductor light source ON / OFF control signal is at the first level, the semiconductor switch is controlled to be in an OFF state, while the semiconductor light source ON / OFF control signal is Is a second level different from the first level, a switch drive circuit for controlling the semiconductor switch to an ON state, the semiconductor light source ON / OFF control signal, and a first drive when the semiconductor light source is in the ON state Receiving first information indicating current and second information indicating second driving current when the semiconductor light source is in the OFF state; When the semiconductor light source ON / OFF control signal is at the first level, the constant current power source controls the constant current power source so as to output the first drive current, while the semiconductor light source ON / OFF control signal is And a current control circuit for controlling the constant current power supply so that the constant current power supply outputs the second drive current having a value smaller than the first drive current when in the second level. To do.

  According to the subject matter of the present invention, a constant current power source during a period when the semiconductor light source is in an OFF state, that is, a value of a current output from the constant current power source when the semiconductor switch is in an ON state. Since the current control circuit controls the constant current power supply so that the output current becomes smaller than the output current, the power consumption that can occur in the semiconductor switch can be reduced, and a cooling device such as a radiator is required. Therefore, the drive device can be reduced in size and weight. Therefore, it is possible to improve the power use efficiency in the driving device and reduce the cost of the driving device.

  Hereinafter, various embodiments of the subject of the present invention will be described in detail along with the effects and advantages thereof with reference to the accompanying drawings.

(Embodiment 1)
FIG. 1 is a block diagram illustrating a configuration of a semiconductor light source driving device according to the present embodiment. In the present embodiment, an example in which an LED is used as a semiconductor light source is illustrated. FIG. 2 is a timing chart showing the operation of the semiconductor light source driving device of FIG.

  In FIG. 1, the DC / DC step-down power supply 2, the current detection resistor 5, and the differential amplifier 6 constitute a constant current power supply 100. An input voltage 12V serving as a source of the constant current power supply 100 is supplied from the power supply input terminal 1, and as a result, the input voltage 12V is supplied to the DC / DC step-down power supply 2. The DC / DC step-down power supply 2 drives the LED 3 by converting the input voltage 12V into the forward voltage (forward voltage) of the LED 3 and applying the forward voltage to the LED 3. Here, the forward voltage of the LED 3 varies depending on the process of the LED itself. For example, in the case of a red LED, the forward voltage is about 2.5V, about 5V for green, and about 4.5V for blue. Further, the current Iled generated by the DC / DC step-down power supply 2 and flowing through the LED 3 is a large value of about 30 A in the case of a high-intensity LED used for a projector or the like.

  As shown in FIG. 1, a current detection resistor 5 is connected between the LED 3 and the power supply ground. In the current detection resistor 5, a voltage Vsense indicated by the product of the value of the drive current Iled flowing through the LED 3 and the value of the current detection resistor 5 is generated. This voltage Vsense and an output voltage value Vref of a current setting circuit 9 to be described later are compared by the differential amplifier 6, and the PWM (Pulse Width) of the DC / DC step-down power supply 2 is selected according to the comparison result output by the differential amplifier 6. Modulation) duty ratio is controlled. If Vref> Vsense, the DC / DC step-down power supply 2 receives the comparison result of the differential amplifier 6, determines that the current value of the LED 3 is relatively small, and increases the PWM duty ratio. On the other hand, when Vref <Vsense, the DC / DC step-down power supply 2 receives the comparison result of the differential amplifier 6 and determines that the current value of the LED 3 is relatively large, and lowers the PWM duty ratio. By the feedback operation as described above, the DC / DC step-down power supply 2 controls the duty ratio of PWM so that Vref = Vsense.

Next, from the semiconductor light source ON / OFF control signal input terminal 7, the semiconductor light source ON / OFF control signal Vc for controlling the ON state or OFF state of the LED 3 whose waveform of the pulse signal is shown in FIG. Is input to the switch drive circuit 8. In FIG. 2A, when the semiconductor light source ON / OFF control signal is at the “L” level (corresponding to the first level), the LED 3 is in the ON state, for example, a large drive current (first 1A) of 30 A. (This corresponds to the drive current.) Iled is flowing in the LED 3. On the other hand, when the semiconductor light source ON / OFF control signal Vc is at the “H” level (corresponding to the second level), the LED 3 is in the OFF state. That is, the switch drive circuit 8 outputs a pulse signal Vs having a waveform as shown in FIG. 2B to the gate electrode of the semiconductor switch (here, n-type MOSFET) 4 connected in parallel to the LED 3. The OFF / ON state of the semiconductor switch 4 is controlled. When the voltage between the gate electrode and the source electrode changes from the “L” level to the “H” level at time t1, the semiconductor switch 4 is in a conductive state because the resistance value between the drain region and the source region decreases. (ON state). As a result, most of the drive current Iled output from the DC / DC step-down power supply 2 (corresponding to the second drive current) flows into the semiconductor switch 4 that is in a lower resistance state than the LED 3, and the LED 3 is in the ON state. It changes to the cut-off state or OFF state. Even in this case, the constant current power supply 100 is controlled so as to always flow a constant current. Therefore, when the power consumption in the semiconductor switch 4 is displayed as Pswitch and the ON resistance of the semiconductor switch 4 is displayed as Ron, if Iled = 30 A and Ron = 5 mΩ,
Pswitch = (Iled) ² × Ron = 4.5W.

Further, depending on the configuration of the constant current power supply 100, the minimum output voltage of the constant current power supply 100 may be limited. In this case, the power consumption Pswitch of the semiconductor switch 4 is the drain-source voltage Vds of the semiconductor switch 4. If 0.6V,
Pswitch = Iled × Vds = 30 A × 0.6 V = 18 W.

  Therefore, in the present embodiment, the drive current (current output from the constant current power supply 100) is set by setting the level of the output signal (current setting voltage) Vref of the current setting circuit 9 having a waveform as shown in FIG. The setting current is changed from the first driving current (for example, 30 A) to the second driving current having a value (for example, 10 A) smaller than the first driving current. That is, the current setting circuit 9 is (1) the semiconductor light source ON / OFF control signal Vc input from the semiconductor light source ON / OFF control signal input terminal 7 and the drive current information input terminal 10 together. LED drive current information (corresponding to the first information) and (3), which are preset information, (2) a value of a first drive current (for example, 30 A) flowing through the LED 3 when the LED 3 is in the ON state. The current information (corresponding to the second information) indicating the value (for example, 10 A) of the second driving current output from the DC / DC step-down power supply 2 when the LED 3 is in the OFF state is received, and the difference between the constant current power supplies 100 is received. A current setting voltage Vref for controlling the constant current power supply 100 by applying to the negative terminal of the dynamic amplifier 6 is created.

If the value of the second drive current flowing to the semiconductor switch 4 side is set to, for example, 10 A during the OFF period of the LED 3 (time t1 to time t2 shown in FIG. 2C) (second information), the current setting voltage Vref Is applied to the negative terminal of the differential amplifier 6, the power consumption Pswitch of the semiconductor switch 4 becomes Pswitch = (Iled) ² × Ron = 0.5 W. With such low power consumption, it is possible to sufficiently cool the semiconductor switch 4 with a printed circuit board or the like without using a radiator or the like. Therefore, it is possible to reduce the power consumption of the semiconductor switch 4 during the OFF period of the LED 3 (that is, to achieve improvement in power utilization efficiency) and to reduce the cost of the driving device through the realization of the downsizing and weight reduction of the driving device. I can plan.

  Moreover, as shown in FIG. 2C, the set current (drive current) is sloped from 10 A to 30 A within the rising period Δt from the “L” level to the “H” level within the OFF period of the LED 3. Thus, even when the LED 3 is controlled to be in the ON state, the LED 3 can be driven at a high speed with the first drive current Iled having a large value of, for example, 30 A. The control of the slope SL is similarly performed in the transition period (time t1 to time (t1 + period Δt)) of the LED 3 from the ON state to the OFF state.

  Control of the set current value of the second drive current Iled and the slope SL of the current setting voltage Vref in the OFF period (time t1 to time t2) of the LED 3 depends on the response characteristics of the constant current power supply 100. . That is, if the response characteristic of the constant current power supply 100 is relatively good, the set current value of the second drive current Iled can be set to be lower than 10 A, and is matched to the response characteristic of the constant current power supply 100 to be used. The second information may be set.

(Appendix)
While the embodiments of the present invention have been disclosed and described in detail above, the above description exemplifies aspects to which the present invention can be applied, and the present invention is not limited thereto. In other words, various modifications and variations to the described aspects can be considered without departing from the scope of the present invention.

  The present invention is suitable, for example, for driving a light source for a projector. In particular, in an image display system that uses a single-chip Digital Mirror Device as a light valve, it is necessary to switch the light emission timing of each of the R, G, and B color semiconductor light sources in a time-sharing manner. In contrast, the present invention can be effectively used. Also, in the general lighting field, brightness control by PWM drive is common, but when a PWM signal is supplied as a control signal for a semiconductor switch, the same effect can be obtained by applying the present invention.

It is a block diagram which shows the structure of the drive device of the semiconductor light source which concerns on Embodiment 1 of this invention. 2 is a timing chart showing the operation of the semiconductor light source driving device of FIG. 1.

Explanation of symbols

  1 power input terminal, 2 DC / DC step-down power supply, 3 LED, 4 semiconductor switch, 5 current detection resistor, 6 differential amplifier, 7 semiconductor light source ON / OFF control signal input terminal, 8 switch drive circuit, 9 current setting circuit 10 Driving current information input terminal, 100 constant current power supply.

Claims (2)

A semiconductor light source driving device for controlling light emission of a semiconductor light source to an ON state or an OFF state,
A constant current power source for driving the semiconductor light source;
A semiconductor switch connected in parallel with the semiconductor light source;
When the semiconductor light source ON / OFF control signal is received and the semiconductor light source ON / OFF control signal is at the first level, the semiconductor switch is controlled to be in the OFF state, while the semiconductor light source ON / OFF control signal is the first light source. A switch driving circuit for controlling the semiconductor switch to an ON state when the second level is different from the level;
The semiconductor light source ON / OFF control signal, the first information indicating the first driving current when the semiconductor light source is in the ON state, and the second information indicating the second driving current when the semiconductor light source is in the OFF state When the information is received and the semiconductor light source ON / OFF control signal is at the first level, the constant current power supply is controlled so that the constant current power supply outputs the first drive current, while the semiconductor light source ON A current control circuit for controlling the constant current power supply so that the constant current power supply outputs the second drive current having a value smaller than the first drive current when the / OFF control signal is at the second level; It is characterized by having,
Drive device for semiconductor light source. A driving device for a semiconductor light source according to claim 1,
When the semiconductor light source ON / OFF control signal is at the second level, the current control circuit has the constant current power supply so that the value of the second drive current has a slope corresponding to the response characteristic of the constant current power supply. Characterized by controlling
Drive device for semiconductor light source.

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