JP2007129862A - Power supply unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power supply unit capable of facilitating adjustment of a driving voltage using voltage information applied to a current control portion and extremely reducing power consumption in the current control unit although the amount of the current to be supplied to the load is adjusted by PWM control. <P>SOLUTION: This power supply unit includes: a power supply portion provided on the upstream side of the load and for supplying the driving voltage to the load; the current control portion provided on the downstream side of the load and for introducing the current controlled to a predetermined amount from power supply portion through the load, in which the current control portion adjusts a duty ratio of the current by the PWM control, a sample hold portion for sampling and holding the voltage value on the downstream side of the load and the upstream side of the current control portion during on-duty in the PWM control, and a voltage adjusting portion for adjusting the value of the driving voltage corresponding to the hold value of the sample hold portion. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a power supply device for supplying power to an electrical load such as an LED.

  Conventionally, for example, a device as shown in FIG. 6 is used as a power supply device capable of adjusting the amount of current flowing through an electric load such as an LED (Light Emitting Diode) while supplying power to the electric load. It was. In this apparatus, the luminance is adjusted by controlling the duty ratio of the current supplied to the LED by PWM [Pulse Width Modulation] control.

  The configuration of this apparatus will be briefly described. As shown in FIG. 6, this apparatus includes a power supply unit 101, a current control unit 102, and the like, and supplies power to the LED 109 that is a load.

  The power supply unit 101 adjusts the voltage value of the drive voltage generated by the power supply 111 such as a battery by using, for example, a charge pump, and supplies it to the downstream side. The current control unit 102 generates a PWM signal, and draws a current corresponding to the duty ratio from the power supply unit 101 via the LED 109.

  With this configuration, the apparatus applies an appropriate voltage to the downstream side of the power supply unit 101 (the anode side of the LED) and draws the current from the cathode side of the LED 109, thereby causing the LED 109 to emit light. In addition, as a conventional technique for adjusting the luminance of an LED by PWM control, there is a device described in Patent Document 1.

In the power supply apparatus described above, the voltage on the downstream side of the power supply unit 101 (the anode side of the LED 109) is V _UP , the voltage drop in the LED 109 is Vf, and the voltage on the upstream side of the current control unit 102 (the cathode side of the LED 109) is V We define each as _DOWN and pay attention to the adjustment processing of the voltage adjustment unit.

In order to drive the current control unit 102, in other words, in order to draw a predetermined amount of current from the LED 109 side, V _DOWN needs to be set to at least a certain value. Therefore, the power supply unit 101 satisfies this condition. Therefore, it is necessary to supply a driving voltage. That is, if this constant value (minimum value) in V _DOWN is Vc, in order to operate the current control unit 102, it is necessary to supply a drive voltage so as to satisfy the condition of V _UP ≧ Vf + Vc.

On the other hand, Vf may vary in value depending on individual differences of LEDs 109, deterioration with time, environmental conditions, and the like. Therefore, in the prior art, V _UP is set to a slightly higher value so that the driving of the current control unit 102 is not hindered even if there is such a variation.
JP 2002-111786 A

Here, if the value of the current drawn by the current control unit 102 is Ic, the power consumed by the current control unit 102 is V _DOWN × Ic. Therefore, when the current value is fixed, V _DOWN is as small as possible, in other words, the one closer to Vc which is the minimum value in the range where there is no problem in driving the current control unit 102 is consumed in the current control unit 102. The power is reduced and the power loss is suppressed. However, in the above-described prior art, the drive voltage is set higher than necessary in consideration of the variation in the LEDs, so that V _DOWN is inevitably high, and the power loss in the current control unit 102 is relatively large. It has become.

To solve this problem, by feeding back the information of the V _DOWN, it is conceivable to adjust the drive voltage to V _DOWN equals always Vc. However, since the current control unit 102 adjusts the amount of current by PWM control, V _DOWN always fluctuates greatly accordingly. For this reason, the current control unit 102 consumes power only when the PWM control is on duty, but when the V _DOWN information at the time of off duty is fed back to adjust the drive voltage, The voltage value becomes very unstable. Therefore, it is difficult to adjust the drive voltage by feeding back the information of V _DOWN as it is.

In particular, when this device is applied as a backlight of a field sequential type liquid crystal display device, each color (for example, red, green, and blue) LED is repeatedly turned on and off at a frequency of 60 to 100 Hz or more. In order to adjust the brightness, the PWM period becomes very short. For this reason, it is very difficult to adjust the drive voltage by directly feeding back the information of V _DOWN .

  Therefore, in view of the above problems, the present invention adjusts the amount of current supplied to the load by PWM control, but easily adjusts the drive voltage using voltage information applied to the current control unit. An object of the present invention is to provide a power supply device that can reduce the power consumption of the power as much as possible.

  In order to achieve the above object, a power supply device according to the present invention is provided on the upstream side of an electrical load and supplies a drive voltage to the load side, and is provided on the downstream side of the load. And a current control unit that draws a current controlled to a predetermined amount from the power supply unit via the load. In the power supply apparatus that supplies the predetermined amount of current to the load, the current control unit is configured to A sample that adjusts the duty ratio of the current and samples and holds the voltage value on the downstream side of the load and on the upstream side of the current control unit when the PWM control is on-duty. A configuration (first configuration) is provided that includes a hold unit and a voltage adjustment unit that adjusts the value of the drive voltage in accordance with the hold value of the sample hold unit.

According to this configuration, the voltage on the downstream side of the load and the upstream side of the current control unit when the PWM control is always on-duty (when the power is consumed by the current control unit). The value of the drive voltage is adjusted according to the (V _DOWN ) value. Therefore, it can be avoided that the information of V _DOWN at the time of off-duty in the PWM control is used for adjustment of the drive voltage even though V _DOWN constantly varies by the PWM control of the current. As a result, while adjusting the amount of current supplied to the load by PWM control, the drive voltage is easily adjusted using voltage information applied to the current control unit, and the power consumption in the current control unit is minimized. Is possible.

  In the first configuration, the PWM control and the sampling by the sample hold unit may be performed according to a common PWM signal (second configuration).

  According to this configuration, the PWM control and the sampling process are performed according to a common PWM signal, so that the timings of both can be closely related. Therefore, it becomes easy to perform the sampling process at the time when it is on-duty in the PWM control, and as a result, the first configuration content can be easily realized.

  In the first or second configuration, the reference voltage generator for generating a predetermined reference voltage is compared with the sampled and held value and the value of the reference voltage, and a signal corresponding to the comparison result is obtained. The voltage adjustment unit may be configured to adjust the value of the drive voltage according to the output signal of the comparison unit (third configuration).

According to this configuration, the value of the drive voltage is adjusted according to the comparison result between the sampled and held value (V _DOWN value at the on-duty time) and the reference voltage value. Therefore, for example, an ideal voltage value at V _DOWN is set as the reference voltage value, and if the sampled and held value is lower than the reference voltage value, the drive voltage is increased, and if it is higher, the drive voltage is increased. If the voltage is lowered, V _DOWN can be maintained at a value close to the ideal voltage value.

  In any of the first to third configurations, a configuration (fourth configuration) may be provided in which boosting means for boosting the drive voltage is provided. If a booster (such as a charge pump or a switching regulator) is provided in this way, the drive voltage can be adjusted to be higher than the output level of the power supply.

  In any one of the first to third configurations, the boosting unit includes a switching element that switches according to a comparison result between a value of a predetermined periodic voltage and a hold value of the sample hold unit, and the switching element. A configuration (fifth configuration) that is a switching regulator including an inductor that stores energy at turn-on and releases energy at turn-off may be used.

According to this configuration, energy is stored / released according to the comparison result between the voltage value of the predetermined periodic signal and the hold value of the sample hold unit. Therefore, by comparing the voltage value of the predetermined periodic signal with the value of V _DOWN , it is possible to easily realize adjustment of the drive voltage including boosting according to the predetermined periodic signal state.

  In any one of the first to fifth configurations, the current control unit may include a current mirror circuit, and the current drawing may be performed by the current mirror circuit (sixth configuration). In this way, if the current is drawn by the current mirror circuit, it is possible to stably and easily realize a current having a predetermined magnitude.

  Further, if the power supply device according to any one of the first to sixth configurations and the LED lighting device (seventh configuration) including the LED as the load, the brightness of the LED can be adjusted by PWM control. The drive voltage can be easily adjusted using the voltage information applied to the current control unit, and the power consumption in the current control unit can be minimized.

  In addition, in the case of an image display device using a field sequential method using the LED lighting device described above as a backlight, it is easy to drive voltage using voltage information applied to the current control unit even though the PWM cycle is very short. Thus, it is possible to reduce power consumption in the current control unit as much as possible.

As described above, in the power supply device according to the present invention, at the time when the duty is always on-duty in the PWM control (when power is consumed by the current control unit), The value of the drive voltage is adjusted according to the voltage (V _DOWN ) value on the upstream side of the current control unit. Therefore, it can be avoided that the information of V _DOWN at the time of off-duty in PWM control is used for adjustment of the drive voltage even though V _DOWN is constantly fluctuating due to current PWM control.

  As a result, while adjusting the amount of current supplied to the load by PWM control, the drive voltage is easily adjusted using voltage information applied to the current control unit, and the power consumption in the current control unit is minimized. Is possible. In addition, when a battery is used as the power source, an effect of improving the life of the battery can be obtained.

As an embodiment of the present invention, a power supply device that supplies power to an LED as a load will be described as an example. As shown in FIG. 1, the power supply apparatus includes a power supply unit 1, a current control unit 2, a sample and hold circuit 3, an error amplifier 4, a reference voltage generating means 5, and the like. As shown in FIG. 1, the voltage on the downstream side of the power supply unit 1 (the anode side of the LED 9) is V _UP , the voltage drop in the LED 9 is Vf, and the voltage on the upstream side of the current control unit 2 (the cathode side of the LED 9) is V _DOWN .

  The power supply unit 1 includes a power supply 11, a voltage adjustment unit 12, a charge pump circuit 13, and the like. The power source 11 is a battery or the like and plays a role of supplying a driving voltage (electric power) to the downstream side. The voltage adjustment unit 12 is composed of an FET [Field Effect Transistor] or the like, and plays a role of adjusting the magnitude of the drive voltage according to the output signal of the error amplifier 4. The details of adjusting the drive voltage will be described later. The charge pump circuit 13 is provided downstream of the power supply 11 as boosting means. As a result, the adjustment of the drive voltage is wider and easier. A capacitor 6 for avoiding a sudden change in voltage may be provided downstream of the power supply unit 1.

  Further, instead of applying the charge pump circuit 13 described above, a switching regulator circuit may be used. FIG. 2 shows the configuration of the power supply unit 1 when a switching regulator circuit is used. As shown in the figure, the output side of the error amplifier 4 is connected to the non-inverting input terminal of the comparator 14. Further, the output side of the triangular wave generating means 15 and the feedback wiring from the switching element 18 merge and are connected to the inverting input terminal of the comparator 14. The output terminal of the comparator 14 is connected to the R input terminal of the RS flip-flop circuit 16, and the output side of the clock generator 17 is also connected to the S input terminal.

  The output side of the RS flip-flop circuit 16 is connected to the gate of a switching element 18 made of FET or the like. The switching element 18 is connected to the power source 11 via the inductor 19. Further, the wiring branches from between the switching element 18 and the inductor 19 and is connected to the downstream LED 9.

  With the above configuration, the comparator 14 outputs a high level signal when the output signal (error voltage) of the error amplifier 4 is larger than the sum of the triangular waveform voltage (periodic voltage) generated by the triangular wave generating means 15 and the feedback voltage. Output. The RS flip-flop circuit 16 outputs the output of the comparator 14 and a signal corresponding to the contents of the clock signal from the clock generator 17 to switch the switching element 18. Since the operation content of the RS flip-flop circuit is well known, description thereof is omitted.

When the switching element 18 is turned on, the energy from the power source 11 is accumulated in the inductor 19, and conversely, when the switching element 18 is turned off, the energy is released. The electric power generated by the released energy is rectified by the capacitor 20 and supplied downstream. By adopting such a switching regulator, energy is stored / released according to the comparison result between the value of the periodic voltage and the hold value of the sample hold unit. Therefore, adjustment of drive voltage including boosting can be easily realized according to the state of V _DOWN . Depending on the output level of the power source 11, the content of the load, etc., a charge pump, a switching regulator, or the like as a boosting unit may be omitted.

  The current control unit 2 is configured by a current mirror circuit using a reference current from the constant current source 21. The current mirror circuit is connected to an input side transistor 23 that receives the constant current source 21 as input, an output side transistor 24 that draws current corresponding to the input from the LED 9 side, and the bases of these two transistors. It has a ground switching transistor 25 that is switched by a PWM signal described later.

  The current mirror circuit draws a current of a predetermined value from the power supply unit 1 through the LED 9 as a load. By using the current mirror circuit in this way, it becomes possible to draw a predetermined amount of current stably and easily, and consequently, an appropriate amount of current can be supplied to the LED 9. It should be noted that another circuit may be used as the current drawing means, and for example, as shown in FIG.

  The current control unit 2 is provided with a PWM control unit 22 that generates a PWM signal. The PWM signal is input to the base of the ground switching transistor of the current mirror circuit described above. As a result, the current draw is turned on when the PWM signal is at a high level and is turned off when the PWM signal is at a low level. Therefore, the apparent magnitude (average value) of the current can be adjusted by the PWM control unit 22 through the duty ratio of the current.

The sample hold circuit 3 receives the PWM signal from the PWM control unit 22 and samples the value of V _DOWN from the rising edge to the falling edge of the signal. Then, during the arrival period of the low level pulse in the signal (that is, at the time of off-duty), the sample value at the time of the previous fall is held (stored) as it is. As described above, the current PWM control and the sampling are performed in accordance with the common PWM signal, so that the timings of both can be closely related. As a result, the sampling process is performed when the PWM control is on-duty. It becomes easy to make.

The error amplifier 4 has a voltage proportional to the difference (error) between the hold value in the sample hold circuit 3 and the reference voltage value generated by the reference voltage generating means 5 (hereinafter referred to as “error voltage: V _ERR ” as appropriate). ) Is output.

The reference voltage generating means 5 is an ideal value as a value of V _DOWN , that is, a constant voltage having the same level as the minimum voltage value necessary for driving the current control unit 2 (hereinafter referred to as “reference voltage: V _REF "
Is called). Therefore, if the sample value in the sample and hold circuit 3 exceeds the reference voltage, it is recognized that an excessive voltage is applied to the current control unit 2 and that excess power is consumed.

  The power supply device according to the present embodiment has the above-described configuration, and supplies a current subjected to PWM control to the LED 9 to be provided between the power supply unit 1 and the current control unit 2 to light it. In addition, the drive voltage supplied by the power supply unit 1 is controlled so that the power consumed by the current control unit 2 does not increase more than necessary.

Next, the control flow of the drive voltage will be described below with reference to FIG. First, the sample hold process will be described. The sample hold circuit 3 starts the V _DOWN sample hold process (step S2) due to the arrival of the rising edge of the PWM signal (Y in step S1). Thereafter, this process is repeated until the falling edge arrives. When the falling edge of the PWM signal comes (Y in step S3), the hold value at the falling edge (at the end of the on-duty period) is continuously held until the next rising edge comes (step S4).

As for the voltage adjustment process, the error amplifier 4 calculates an error voltage V _ERR corresponding to the difference between the value currently held by the sample hold circuit 3 and the reference voltage value (step S5), and the voltage adjustment unit 12 Output to. Then, the voltage adjustment unit 12 adjusts the drive voltage in an analog manner so that the value of V _ERR approaches 0 (step S6). That is, when the value of V _ERR is greater than 0, the drive voltage is lowered, and when it is smaller, the drive voltage is raised. The series of processes described above are continuously repeated during the operation of the power supply apparatus.

As a result, during the period in which the PWM signal is at a high level (period in which the current is on-duty), the value of V _DOWN is continuously sampled and held, and the drive voltage is adjusted in real time so that this value approaches the reference voltage value Is made. On the other hand, the period PWM signal is at low level (period current is off duty), since the value at the time of the fall just before is subsequently held, the sample hold circuit 3 is of V _DOWN due to the current is turned off It is not affected by large fluctuations.

  Next, the above-described control content will be specifically described by taking as an example a case where the voltage drop (Vf) at the LED starts to gradually decrease due to some factor. FIG. 5 shows a timing chart regarding the PWM signal and the voltage / current in this case. In the figure, (A) shows the state of the PWM signal, (B) shows the voltage / current state when voltage adjustment is performed (this embodiment), and (C) shows the case when voltage adjustment is not performed (prior art). Each voltage state is shown.

As shown in (B) and (C) in the figure, the value of Vf gradually decreases, and Vf ₁ > Vf ₂ > Vf ₃ . However, according to (B), since the drive voltage is adjusted so that the value of V _DOWN is equal to the reference voltage value, V _DOWN is maintained at a substantially constant value (reference voltage value). That effects of changes in Vf is absorbed by the drive voltage is adjusted, it has little effect on the value of V _DOWN. In this regard, if voltage adjustment is not performed, the value of V _DOWN increases as Vf decreases, as shown in (C).

  If sampling is also performed during the off-duty period, the sample value greatly increases during the off-duty period. Then, since the drive voltage is adjusted so that the sample hold value becomes equal to the reference voltage value, the drive voltage is greatly reduced. As a result, when the on-duty period comes next, it is necessary to rapidly increase the drive voltage, and the drive voltage becomes very unstable. Therefore, in this embodiment, the sample hold value is stabilized by continuously holding the sample value at the on-duty during the off-duty period, and this problem is solved.

As explained above, if the power supply device according to the present embodiment, despite the V _DOWN is fluctuating constantly by PWM control of the current, information V _DOWN during off-duty in the PWM control, the driving voltage It is possible to avoid being used for the adjustment of. In other words, during the off-duty period, the drive voltage is adjusted by feeding back V _DOWN during on-duty by the sample and hold circuit.

  As a result, while adjusting the amount of current supplied to the load by PWM control, the drive voltage is easily adjusted using voltage information applied to the current control unit, and the power consumption in the current control unit is minimized. Is possible. Therefore, even when the voltage drop in the load varies, it is possible to prevent a situation where power is consumed more than necessary in the current control unit.

  Also, if the power supply device is provided with an LED as an electrical load and used as an LED lighting device, the LED brightness can be adjusted by PWM control, but it can be easily driven using voltage information applied to the current control unit. It is possible to adjust the voltage and reduce the power consumption in the current control unit as much as possible.

  In addition, if it is an image display device based on a field sequential method using this LED lighting device as a backlight, the drive voltage can be easily adjusted using voltage information applied to the current control unit even though the PWM cycle is very short. In addition, the power consumption in the current control unit can be minimized.

  In the above embodiment, the description has been given by taking one LED as an example of an electrical load to which power is to be supplied, but the present invention is not limited to this, and a plurality of LEDs may be used as a load, It is also possible to target various electrical loads.

  The configuration of the present invention can be variously modified within the scope of the present invention in addition to the above embodiment.

  The present invention is a technique useful for a power supply device that supplies electric power to an electrical load such as an LED.

It is a block diagram of the power supply device which concerns on the Example of this invention. It is a block diagram of the switching regulator which concerns on the Example of this invention. It is explanatory drawing regarding an example of the current control part based on the Example of this invention. 4 is a flowchart of voltage control in an embodiment of the present invention. It is an example of timing charts, such as voltage adjustment, in the Example of this invention. It is a block diagram of the power supply device which concerns on a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,101 Power supply part 2,102 Current control part 3,103 Sample hold circuit (sample hold part)
4, 104 Error amplifier (comparator)
5 Reference voltage generating means 6 Capacitor 9, 109 LED (electric load)
DESCRIPTION OF SYMBOLS 11, 111 Power supply 12 Voltage adjustment part 13 Charge pump circuit 14 Comparator 15 Triangular wave generation means 16 RS flip-flop circuit 17 Clock generator 18 Switching element 19 Inductor 20 Capacitor 21 Constant current source 22 PWM control part 23 Input side transistor 24 Output side transistor 25 Ground switching transistor

Claims (8)

A power supply that is provided upstream of the electrical load and supplies a drive voltage to the load;
A power supply device provided on a downstream side of the load and including a current control unit that draws a current controlled to a predetermined amount from the power source via the load, and supplies the predetermined amount of current to the load;
The current control unit adjusts the duty ratio of the current by PWM control,
A sample-and-hold unit that samples and holds a voltage value on the downstream side of the load and on the upstream side of the current control unit at the time when the PWM control is on-duty;
A power supply apparatus comprising: a voltage adjustment unit that adjusts a value of the drive voltage in accordance with a hold value of the sample hold unit.   The power supply apparatus according to claim 1, wherein the PWM control and the sampling by the sample and hold unit are performed according to a common PWM signal. A reference voltage generator for generating a predetermined reference voltage;
A comparison unit that compares the sampled and held value with the reference voltage value and outputs a signal according to the comparison result,
The power supply apparatus according to claim 1, wherein the voltage adjustment unit adjusts the value of the drive voltage in accordance with an output signal of the comparison unit.   4. The power supply device according to claim 1, further comprising boosting means for boosting the drive voltage. The boosting means includes
A switching element that switches according to a comparison result between a value of a predetermined periodic voltage and a hold value of the sample hold unit;
5. The power supply device according to claim 4, wherein the switching device includes an inductor that stores energy when the switching element is turned on and discharges energy when the switching element is turned off. The current control unit includes a current mirror circuit,
6. The power supply device according to claim 1, wherein the current is drawn by an output side transistor of the current mirror circuit.   An LED lighting device comprising: the power supply device according to claim 1; and the LED as the load.   An image display device using a field sequential method, wherein the LED lighting device according to claim 7 is used as a backlight.

Images