JP4467395B2 - Power supply - Google Patents

Description

  The present invention relates to a power supply device, and more particularly to a power supply device that drives a load circuit at a constant current.

  Small information terminals such as mobile phones and PDAs (Personal Digital Assistance) in recent years require a voltage higher than the output voltage of a battery, such as an LED (Light Emitting Diode) used for a liquid crystal backlight. Device exists. In these small information terminals, Li-ion batteries are often used, and the output voltage is usually about 3.5 V, and is about 4.2 V even when fully charged, but the LED has a drive voltage higher than the battery voltage. Requires high voltage. Thus, when a voltage higher than the battery voltage is required, it is necessary to boost the battery voltage using a power supply device such as a switching regulator or a switched capacitor system and drive a load circuit such as an LED. Getting a good voltage.

  In order to drive the LED as a load circuit with such a power supply device, a detection resistor is connected to the cathode terminal of the LED, feedback is performed so as to keep the voltage drop across the detection resistor constant, and the LED is driven. There is a method (see Patent Document 1). For example, when driving an LED with a threshold voltage of Vf connected in series in n stages, assuming that the resistance value of the detection resistor is R and the current flowing through the LED is Ic, the output voltage of the power supply device is Vout = Vf × n + R × Ic may be set. According to this technique, the power consumption of the detection resistor can be reduced by reducing the resistance value R of the detection resistor, and the efficiency of the entire circuit can be increased.

In addition, there is a method in which instead of the detection resistor R, a constant current source for supplying a current Ic to the LED is connected to perform constant current driving (see Patent Document 2). If the potential at the connection point between the constant current source and the LED is Vx, the output voltage of the power supply device is Vout = Vf × n + Vx. Since the constant current source can flow a constant current regardless of the value of Vx, the output voltage Vout is set to a desired value in a range in which the constant current source operates normally while flowing the constant current Ic to the LED. can do.
JP 2003-152224 A JP 2004-22929 A

  Under such circumstances, the present inventor has come to recognize the following problems. Now, consider a case where the load circuit is driven by switching between an LED and a second device that requires a higher drive voltage than the LED. When the output voltage necessary for driving the second device is Vout2, according to the technique described in Patent Document 1, the resistance value of the detection resistor is set as R2 = (Vout2−Vf × n) / Ic do it. However, according to this technique, Vout2 is applied to the load circuit even when only the LED is driven, so that the power loss at the detection resistor is Ic × compared to when the output voltage is Vout. It becomes larger by (Vout′−Vout), and the efficiency of the entire circuit at the time of LED driving is lowered. Furthermore, since the boosting factor of the booster circuit is increased, the input current to the booster circuit is increased, and the efficiency of the booster circuit is also deteriorated.

  In the technique described in Patent Document 2, the potential Vx of the connection point between the constant current source and the LED is set higher than a predetermined threshold voltage Vth so that transistors used in the constant current circuit are not saturated. There is a need. Therefore, even when only the LED is driven, the value of Vx cannot be lowered to Vth or less, and the power consumption of the constant current circuit cannot be reduced to Ic × Vth or less. End up.

  The present invention has been made in view of these problems, and an object thereof is to provide a power supply apparatus capable of generating a drive voltage by a feedback method suitable for the state of a load circuit.

  One embodiment of the present invention relates to a power supply device. This power supply apparatus includes a drive voltage generation unit that generates a drive voltage for driving a load circuit to be driven with a predetermined constant current, and a detection resistor connected in series with the load circuit, and a voltage drop across the detection resistor A first feedback circuit that feeds back a voltage at a connection point with the load circuit corresponding to the drive voltage generation unit, and a constant current circuit that generates a predetermined constant current connected in series with the load circuit and in parallel with the detection resistor And a second feedback circuit that feeds back a voltage at a connection point between the constant current circuit and the load circuit to the drive voltage generation unit. The drive voltage generator generates a drive voltage based on a voltage fed back from one selected from the first or second feedback circuit.

The first feedback circuit performs constant current driving by converting the current flowing through the load circuit into a voltage by a detection resistor and performing feedback control. The second feedback circuit performs constant current driving by connecting a constant current circuit to the load circuit.
According to this aspect, for the load circuit in which only the drive current is a problem, the first feedback circuit generates a drive voltage, and the load circuit in which the drive voltage is also a problem in addition to the drive current or the drive voltage is changed. For a load circuit that is desired, a drive voltage suitable for various load circuits can be generated by using the second feedback circuit.

When the first feedback circuit is selected, the drive voltage generator generates the drive voltage so that the voltage fed back from the first feedback circuit approaches a target value given by a product of a predetermined constant current and a detection resistor. When the second feedback circuit is selected, the drive voltage may be generated so that the voltage fed back from the second feedback circuit approaches a target value determined so that the constant current circuit operates normally.
The first feedback circuit can stabilize the current flowing through the load circuit at a predetermined constant current by keeping the voltage drop across the detection resistor constant. On the other hand, the second feedback circuit sets the control target value of the voltage at the connection point between the constant current circuit and the load circuit to be higher than a predetermined threshold voltage necessary for the constant current circuit to operate normally, The current flowing through the load circuit can be stabilized to a predetermined constant current.

The power supply apparatus may further include a variable gain amplifier provided on a voltage feedback path from the first and second feedback circuits to the drive voltage generation unit. The variable gain amplifier includes either the first feedback circuit or the second feedback circuit so that the signal level of the voltage fed back to the drive voltage generator is substantially the same when either the first feedback circuit or the second feedback circuit is selected. The gain may be switched depending on whether or not is selected.
The voltage fed back by the first feedback circuit and the second feedback circuit may have different signal levels. In such a case, the configuration of the drive voltage generator can be simplified by aligning the voltage levels fed back to the drive voltage generator by the variable gain amplifier.

  The load circuit may include a light emitting diode, and the detection resistor and the constant current circuit may be connected in parallel between the cathode terminal and the ground terminal of the light emitting diode.

The power supply device may further include a selection terminal for inputting a selection signal for selecting the first feedback circuit or the second feedback circuit.
In an electronic device equipped with a power supply device, an appropriate drive voltage is generated according to the load circuit by switching the feedback circuit of the power supply device according to a selection signal output from a circuit that comprehensively controls the state of the load circuit. It can be carried out.

  The resistance value of the detection resistor may be determined such that the first feedback voltage is lower than the second feedback voltage. By reducing the first feedback voltage, power consumption in the detection resistor can be reduced, and high efficiency can be achieved when the first feedback circuit is selected.

  Another embodiment of the present invention also relates to a power supply apparatus. This power supply apparatus includes a first load circuit and a drive voltage generation unit that generates a drive voltage for driving a second load circuit to be driven with a voltage higher than that of the first load circuit, and the first load circuit. And a first feedback circuit that feeds back a voltage at a connection point with the load circuit corresponding to a voltage drop across the detection resistor to the drive voltage generation unit, and a first load circuit in series And a constant current circuit that generates a predetermined constant current connected in parallel with the detection resistor, and a second feedback circuit that feeds back a voltage at a connection point between the constant current circuit and the load circuit to the drive voltage generation unit, Is provided. In the first mode in which the first load circuit is driven alone, the drive voltage generation unit generates a drive voltage based on the voltage fed back from the first feedback circuit, and the drive voltage generation unit In the second mode in which both are driven simultaneously, the drive voltage is generated based on the voltage fed back from the second feedback circuit.

  According to this aspect, when only the first load circuit is driven, only the drive current is monitored, and when the second load circuit is driven simultaneously with the first load circuit, the first load circuit is monitored. By monitoring both the driving current and the driving voltage of the second load circuit, it is possible to generate an appropriate driving voltage according to each load circuit.

  Another embodiment of the present invention also relates to a power supply apparatus. This power supply apparatus generates a drive voltage for driving a first load circuit to be driven with a predetermined constant current and a second load circuit to be driven with a voltage higher than that of the first load circuit. And a first feedback circuit that includes a detection resistor connected in series with the first load circuit and that feeds back a voltage at a connection point between the load circuit corresponding to the voltage drop across the detection resistor to the drive voltage generation unit, A constant current circuit that generates a predetermined constant current connected in series with the first load circuit and in parallel with the detection resistor is fed back to the drive voltage generation unit with the voltage at the connection point between the constant current circuit and the load circuit And a third feedback circuit that feeds back the drive voltage generated by the drive voltage generator to the drive voltage generator. In the first mode in which the first load circuit is driven alone, the drive voltage generation unit generates a drive voltage based on the voltage fed back from the first feedback circuit, and the drive voltage generation unit In the second mode in which both are driven simultaneously, the drive voltage is generated based on the voltage fed back from the second feedback circuit or the third feedback circuit.

  According to this aspect, when only the first load circuit to be driven with constant current is driven, only the drive current is monitored, and the second load circuit to be driven with constant voltage is driven simultaneously with the first load circuit. In this case, by monitoring both the drive current of the first load circuit and the drive voltage of the second load circuit, it is possible to generate an appropriate drive voltage according to each load circuit.

The power supply device is provided on a voltage feedback path from the first and second feedback circuits to the drive voltage generator, and a voltage fed back from the first or second feedback circuit to the drive voltage generator is supplied to the first or second feedback circuit. By switching and amplifying the gain in the second mode, the first amplifier that outputs the first feedback voltage having the same signal level in any mode, the third feedback circuit, and the drive voltage generator The voltage fed back from the third feedback circuit to the drive voltage generator is amplified so as to be substantially the same as the signal level of the first feedback voltage output from the first amplifier, and output as the second feedback voltage. And a minimum value circuit that selects and outputs the lower one of the first feedback voltage and the second feedback voltage. The drive voltage generation unit may generate a drive voltage based on the output of the minimum value circuit.

  By using the first amplifier and the second amplifier to make the first and second feedback voltages signals of substantially the same level and generating a drive voltage based on the lower one, one of the lower ones of the first and second feedback voltages is Since it is controlled to approach the target value and the other is stabilized to a voltage higher than the target value, none of the feedback voltages will be lower than the respective target value, so that the load circuit operates stably. Can do.

  The first load circuit may be a light emitting diode, and the detection resistor and the constant current circuit may be connected in parallel between the cathode terminal and the ground terminal of the light emitting diode.

  Another embodiment of the present invention also relates to a power supply apparatus. This power supply device includes a drive voltage generator that outputs a predetermined drive voltage to one end of a load circuit, a feedback circuit connected between the other end of the load circuit and a reference voltage, and a connection between the load circuit and the feedback circuit An output control circuit for controlling the value of the output voltage by feeding back the point voltage to the power supply voltage generation circuit. The feedback circuit is formed so that either a constant current circuit or a resistance circuit can be selected.

  According to this aspect, in the feedback circuit, the resistance circuit is selected for the load circuit in which only the drive current is a problem, and the load circuit in which the drive voltage is also a problem in addition to the drive current or the drive voltage is to be changed. For the load circuit, driving voltages suitable for various load circuits can be generated by selecting a constant current circuit.

  Note that any combination of the above-described constituent elements and the constituent elements and expressions of the present invention replaced with each other among methods, apparatuses, systems, etc. are also effective as an aspect of the present invention.

  With the power supply device according to the present invention, it is possible to generate a drive voltage according to the state of the load circuit.

(First embodiment)
FIG. 1 is a circuit diagram showing a power supply device 100 according to the first embodiment of the present invention. The power supply device 100 is a boost converter that boosts and outputs an input voltage.
The power supply device 100 is connected to an LED 80, which is a first load circuit, and a second load circuit 82, and two operation modes are switched and used according to the state of the load circuit. Hereinafter, a state in which only the LED 80 is driven is referred to as a first mode, and a state in which the LED 80 and the second load circuit 82 are driven is referred to as a second mode.

  The power supply apparatus 100 includes an input terminal 102, an output terminal 104, an LED terminal 106, and a selection terminal 108 as terminals. The voltages applied to or appearing at the respective terminals are referred to as an input voltage Vin, an output voltage Vout, a cathode voltage Vled, and a selection signal Vsel.

The LED 80, which is the first load circuit, is composed of four stages of LEDs having a forward voltage Vf connected in series. That is, the relationship of Vout = Vf × 4 + Vled is established between the voltages at the terminals. If Vf = 3.2V, the power supply apparatus 100 outputs Vout1 = 12.8 + Vled. However, in the state where only the LED 80 is driven, it is sufficient that the constant current Iref flows through the LED 80, and the output voltage Vout1 is not particularly problematic.
The second load circuit is a device that requires a drive voltage higher than that of the LED 80, and Vout2 = 15V or more is required as the drive voltage.
The power supply device 100 according to the present embodiment generates drive voltages suitable for these two load circuits.

  The power supply device 100 includes a booster circuit 10, a PWM control circuit 20, a current control circuit 16, and a gain control circuit 50.

  The booster circuit 10 is a general switching regulator and boosts the input voltage Vin input to the input terminal 102 and outputs the boosted voltage to the output terminal 104. The input / output terminal of the booster circuit 10 corresponds to the input / output terminal of the power supply apparatus 100 as it is. The booster circuit 10 includes a switching transistor SW1, a rectifying diode 12, an inductor L1, and an output capacitor Co, and boosts the input voltage Vin by performing energy conversion by the inductor L1 and the output capacitor Co by turning on and off the switching transistor SW1. Output.

An LED 80 is connected to the power supply apparatus 100 as a first load circuit. The anode terminal of the LED 80 is connected to the output terminal 104, and the cathode terminal is connected to the LED terminal 106.
The current control circuit 16 is a circuit for controlling the current flowing through the LED 80 and is connected to the cathode terminal of the LED 80 and has a function of adjusting the luminance of the LED 80. The current control circuit 16 includes a first feedback circuit 30, a second feedback circuit 40, and an inverter 18. A selection signal Vsel is input from the selection terminal 108 to the current control circuit 16. An inverter 18 is provided between the second feedback circuit 40 and the selection terminal 108, and inverts the high level and the low level of the selection signal Vsel. When the selection signal Vsel is at a high level, the first feedback circuit 30 operates, and when the selection signal Vsel is at a low level, the second feedback circuit 40 operates.

The first feedback circuit 30 includes a detection resistor R1 and a switch SW2. When the selection signal Vsel is at a high level, the switch SW2 is turned on, and the detection resistor R1 is connected to the LED terminal 106. If the current flowing through the LED 80, which is the first load circuit, is Ic, the voltage drop at the detection resistor R1 is given by R1 × Ic. If the voltage drop at the switch SW2 is ignored, the voltage Vled at the cathode terminal of the LED 80 is Vled = R1 × Ic. Since the power consumed by the detection resistor R1 is a loss, the resistance value is set as small as possible.
In the first feedback circuit 30, assuming that the constant current to be passed through the LED 80 is Iref, feedback is applied so that Ic = Iref when the cathode terminal voltage Vled is controlled to approach the target value Vref1 = Iref × R1. The desired constant current Iref flows through the LED 80. The resistance value of the detection resistor R1 is determined by the relational expression R1 = Vref1 / Iref1. For example, the target value Vref1 is set to 0.1V.

  The second feedback circuit 40 is provided in parallel with the first feedback circuit 30 and includes a constant current circuit 42 that generates a constant current Iref. The constant current circuit 42 is connected to the cathode terminal of the LED 80 via the LED terminal 106, and a predetermined constant current Iref flows through the LED 80 during a period in which the second feedback circuit 40 operates.

2A to 2B show circuit configuration examples of the constant current circuit 42. FIG.
The constant current circuit 42 in FIG. 2A includes an error amplifier 202, a transistor M2, and a resistor R10. The transistor M2 is a P-type MOSFET having a source terminal connected to the LED terminal 106 and a drain terminal connected to the resistor R10. A connection point between the resistor R10 and the transistor M2 is connected to a non-inverting input terminal of the error amplifier 202. The reference voltage Vref4 is input to the inverting input terminal of the error amplifier 202. Since the error amplifier 202 controls the gate voltage of the transistor M2 that is the output so that the potential difference between the inverting input terminal and the non-inverting input terminal approaches 0, the voltage at the connection point between the resistor R10 and the transistor M2 is the reference voltage Vref4. Will approach. As a result, a current of Iref = Vref4 / R10 flows through the resistor R10, and this constant current Iref flows through the LED 80.

  The constant current circuit 42 in FIG. 2B includes a constant current source 204, a transistor M4, and a transistor M6. The transistors M4 and M6 form a current mirror circuit, and the constant current Iref flowing through the constant current source 204 flows to the LED 80 via the LED terminal 106.

2A and 2B, the transistor M2 or M6 is provided between the LED terminal 106 and the ground potential. These constant current circuits 42 can cause the constant current Iref to flow through the LED 80 when the transistors M2 and M6 operate in the saturation region, that is, when the drain-source voltage Vds of the transistor operates at a certain voltage or higher. Conversely, when the transistors M2 and M6 operate in the non-saturated region (triode region), the constant current circuit 42 does not operate normally. Therefore, although the cathode voltage Vled of the LED terminal 106 depends on the semiconductor manufacturing process or the like, the threshold voltage Vth is set to about 0.7 V, and the threshold voltage Vth is controlled so as not to fall below this threshold voltage Vth. The constant current Iref can be passed through the LED 80.
When the transistors M2 and M6 are bipolar transistors, the threshold voltage Vth may be determined so that the transistors M2 and M6 always operate in the active region.

  The cathode voltage Vled when driving the second load circuit 82 can be obtained by substituting Vf = 3.2V and Vout2 = 15V into the relational expression Vout2 = Vf × n + Vled, and Vref2 = 15−3.2 × 4. The feedback may be performed with = 2.2V as a target value. This target value Vref2 = 2.2V is higher than the threshold voltage Vth = 0.7V at which the constant current circuit 42 operates normally, and the constant current circuit 42 operates normally. When considering the variation in the forward voltage Vf of the LED, the drive voltage is generated as a target value by using a value obtained by adding a margin to the target value 2.2V of the above-mentioned Vled, so that Vout2 = 15V can be surely set as the drive voltage. The above can be obtained.

  Returning to FIG. As described above, during the operation of the first feedback circuit 30, the current control circuit 16 performs feedback using the cathode voltage Vled of the LED terminal 106 as a target value Vref1 = Iref × R1. Further, during the operation of the second feedback circuit 40, feedback is performed with Vref2 = Vout2−Vf × n as a target value. In this embodiment, Vref1 = 0.1V and Vref2 = 2.2V.

  The gain control circuit 50 amplifies the fed back cathode voltage Vled. The gain control circuit 50 includes a first amplifier 52, and the gain is switched by the selection signal Vsel input to the gain control circuit 50. If the gain in the first mode is g1, and the gain in the second mode is g2, the respective gains are set so that g1 × Vref1 = g2 × Vref2. The gains g1 and g2 may be 1 or less to attenuate the signal. When Vref1 = 0.1 V and Vref2 = 2.2 V, the gain ratio between the first mode and the second mode is set to g1: g2 = 2.2: 0.1. The feedback voltage Vfb fed back to the PWM control circuit 20 by the gain control circuit 50 becomes substantially the same when either the first or second feedback circuit is selected.

  The PWM control circuit 20 controls on / off of the switching transistor SW1 by a PWM signal Vpwm (Pulse Width Modulation) to adjust the output voltage Vout. The PWM control circuit 20 includes a voltage comparator 22, an error amplifier 24, a sawtooth wave oscillator 26, and a reference voltage source 28.

The reference voltage source 28 generates a reference voltage Vref. The reference voltage Vref is set to satisfy Vref = g1 × Vref1 = g2 × Vref2.
The error amplifier 24 receives the reference voltage Vref and the feedback voltage Vfb, and outputs an error signal Verr so that the two voltages are equal. The error signal Verr is input to the voltage comparator 22 and compared with the sawtooth voltage Vsaw. When Verr> Vsaw, a high level is output, and when Verr <Vsaw, a low level is output. The PWM signal Vpwm controls the on / off period of the switching transistor SW1 of the booster circuit 10 to generate an output voltage Vout that satisfies Vfb = Vref.

In the first mode, Vfb = g1 × Vled, and the reference voltage Vref in the PWM control circuit 20 is set so that Vref = g1 × Vref1. Therefore, when Vref approaches Vfb, Vled = Vref1. The return will take place so that Similarly, in the second mode, since Vfb = g2 × Vled and Vref = g2 × Vref2 hold, feedback is applied so that Vled = Vref2.
Since the output voltage Vout of the power supply device 100 is Vout = 3.2 × 4 + Vled, it is stabilized so that Vout1 = 12.9V in the first mode and Vout2 = 15V in the second mode. .

The operation of the power supply apparatus 100 configured as described above will be described.
FIG. 3 shows each voltage waveform of the power supply device 100 according to the present embodiment. Both the horizontal axis and the vertical axis are shown differently from the actual scale for easy viewing. Times T0 to T1 indicate the first mode in which only the LED 80 is driven, and times T1 to T2 indicate the operation state in the second mode in which the LED 80 and the second load circuit are simultaneously driven.

At times T0 to T1, the first feedback circuit 30 is selected by the selection signal Vsel, and the gain of the gain control circuit 50 is set to g1.
In the first mode, Vfb = Vled × g1, and the output voltage Vout is generated so that Vfb approaches Vref. As a result, Vled = Vref1 = 0.1V as described above. The output voltage Vout1 at this time is Vout1 = Vf × n + Vled = 12.8 + 0.1 = 1.29 V by adding a voltage drop at the LED 80 to the cathode voltage Vled.

  In the second mode, the second feedback circuit 40 is selected by the selection signal Vsel, and the gain of the gain control circuit 50 is set to g2. In the second mode, the feedback voltage Vfb = Vled × g2, and this Vfb approaches Vref, so that it is stabilized at Vled = Vref2 = 2.2V. The output voltage Vout2 at this time is Vout2 = 12.8 + 2.2 = 15V.

As described above, the power supply device 100 according to the present embodiment operates the first feedback circuit 30 including the detection resistor R1 in the first mode, thereby reducing the control target value of the cathode voltage Vled of the LED 80 to a small value. In the second mode, the output voltage Vout2 required to drive the second load circuit 82 is obtained by switching to the second feedback circuit 40 including the constant current circuit 42 in the second mode. Thus, the cathode voltage Vled is adjusted.
If the power supply device does not include the first feedback circuit 30, the LED 80 is driven by the constant current circuit 42 even in the first mode. In this case, since the cathode voltage Vled cannot be lowered below the threshold voltage Vth, the output voltage is Vout ′ = 12.8 + 0.7 = 13.5V. In order to increase the output voltage Vout, it is necessary to increase the boosting factor of the booster circuit 10, so that the input current Iout increases and the efficiency of the booster circuit 10 is deteriorated.

  In the power supply device 100 according to the present embodiment, by switching the two feedback circuits, the efficiency of the entire circuit when only the LED 80 is driven can be improved as compared with the case where only the constant current circuit is driven.

In power supply device 100 according to the present embodiment, in the first mode, by changing gain g1 of gain control circuit 50, it is also possible to change the current flowing through LED 80, that is, the luminance of LED 80.
In the second mode, the cathode voltage Vled can be adjusted by changing the gain g2 of the gain control circuit 50, so that the output voltage Vout can be changed. This is because, for example, as the second load circuit, when a device having a different power supply voltage depending on the state of the mounted electronic device is connected, or a plurality of load circuits having different power supply voltages are connected. In such a case, various load circuits can be driven by changing the gain g2.

(Second Embodiment)
In the first embodiment, in the second mode, the output voltage Vout2 necessary for the second load circuit is generated by feeding back only the cathode voltage Vled without feeding back the output voltage. The power supply apparatus 200 according to the second embodiment provides means for driving the second load circuit more stably by feeding back the output voltage Vout in addition to the cathode voltage Vled.

FIG. 4 shows a configuration of a power supply apparatus 200 according to the second embodiment of the present invention. In FIG. 4, the same components as those in FIG.
The power supply device 200 includes a third feedback path 90 and a minimum value circuit 60 in addition to the booster circuit 10, the PWM control circuit 20, the current control circuit 16, and the gain control circuit 50. The power supply apparatus 200 operates in the first mode in the same manner as the power supply apparatus 100 according to the first embodiment, and the feedback method in the second mode is different from that in the first embodiment. The power supply apparatus 200 has a third feedback path 90 for returning the output voltage Vout.

In addition to the cathode voltage Vled, the output voltage Vout is input to the gain control circuit 50. The output voltage Vout is multiplied by a gain g3 by the second amplifier 54 and output as the second feedback voltage Vfb2. That is, Vfb2 = g3 × Vout.
Since the target value of the output voltage in the second mode is Vout2, the gain g3 of the second amplifier 54 is between Vref = g1 × Vref1 = g2 × Vref2 = g3 and the reference voltage Vref in the PWM control circuit 20. What is necessary is just to determine so that xVout2 may be formed.

  In the first embodiment, the target value Vref2 of the cathode voltage Vled fed back by the second feedback circuit 40 is determined so that the output voltage Vout2 is obtained. In the power supply device 200 according to the present embodiment, the output voltage Vout is directly fed back from the third feedback path 90 in order to generate the output voltage Vout2 for driving the second load circuit 82 in the second mode. Therefore, the target value Vref2 of the cathode voltage Vled fed back by the second feedback circuit 40 is set to the threshold voltage Vth for operating the constant current circuit 42 normally.

  That is, in the power supply device 200 according to the present embodiment, in the first mode, the cathode voltage Vled fed back by the first feedback circuit is controlled so as to approach the target value Vref1 = 0.1V. In the second mode, the output voltage Vout fed back by the third feedback path 90 is controlled so as to approach the target value Vout2 = 15 V, and the cathode voltage Vled fed back by the second feedback circuit 40 is controlled by the constant current circuit 42. Control is performed so as to approach the threshold voltage Vth for normal operation.

  The minimum value circuit 60 receives the first feedback voltage Vfb1 and the second feedback voltage Vfb2. The minimum value circuit 60 constitutes a so-called minimum value circuit that selects and outputs the lower one of the first feedback voltage Vfb1 and the second feedback voltage Vfb2.

  FIG. 5 shows a configuration example of the minimum value circuit 60. The minimum value circuit 60 includes a constant current source 68, a first transistor M60, a second transistor M62, a first error amplifier 64, and a second error amplifier 66. The gate terminal of the first transistor M60 is connected to the output of the first error amplifier 64, and the drain terminal is connected to the inverting input terminal of the first error amplifier 64. The feedback voltage Vfb is input to the non-inverting input terminal of the first error amplifier 64. Accordingly, the first feedback voltage Vfb1 appears at the drain terminal of the first transistor M60. The second transistor M62 and the second error amplifier 66 are similarly connected, and the second feedback voltage Vfb2 appears at the drain terminal of the second transistor M62. Now, the sum of the currents flowing through the first transistor M60 and the second transistor M62 is controlled to be equal to the current value determined by the constant current source 68. As a result, the minimum value circuit 60 has the first feedback voltage Vfb1 and the second feedback. The voltage Vfb2 functions as a minimum value circuit that selects the lower voltage and outputs it to the PWM control circuit 20 as the voltage Vfb ′.

  A lower one of the first feedback voltage Vfb1 and the second feedback voltage Vfb2 is fed back to the PWM control circuit 20 as a feedback voltage Vfb ′, and a PWM signal is generated so that this Vfb ′ approaches the reference voltage Vref, The switching of the booster circuit 10 is controlled to generate the output voltage Vout.

The operation of the power supply apparatus 200 configured as described above will be described.
In the first mode, the first feedback circuit 30 is selected by the selection signal Vsel, and the gain of the first amplifier 52 in the gain control circuit 50 is set to g1. In the first mode, since the output voltage Vout is not feedback-controlled, the gain of the second amplifier 54 is increased, the second error amplifier 66 of the minimum value circuit 60 is turned off, and the output Vfb ′ of the minimum value circuit 60 is always set. Is a feedback voltage from the first feedback circuit 30. As a result, in the first mode, feedback control is performed so that the cathode voltage Vled approaches Vref1 = 0.1 V, so that highly efficient operation can be performed.

  In the second mode, the second feedback circuit 40 is selected by the selection signal Vsel, and the gain of the first amplifier 52 in the gain control circuit 50 is set to g2. In the gain control circuit 50, the cathode voltage Vled is multiplied by g2 by the first amplifier 52, and the first feedback voltage is output as Vfb1 = Vled × g2. On the other hand, the output voltage Vout is multiplied by g3 by the second amplifier 54, and the second feedback voltage is output as Vfb2 = Vout × g3.

  In the minimum value circuit 60, when the first feedback voltage Vfb1 based on the cathode voltage Vled is low, the PWM control circuit 20 performs control so that the first feedback voltage Vfb1 = Vled × g2 approaches Vref = Vref2 × g2. Therefore, the cathode voltage Vled approaches the target value Vref2 = Vth, and the current control circuit 16 operates normally. At this time, since the second feedback voltage always satisfies Vfb2 = Vout × g3> Vfb1 = Vref, it is guaranteed that the output voltage Vout is higher than the desired value Vout2.

  Conversely, when the second feedback voltage Vfb2 based on the output voltage Vout is lower, Vfb ′ = Vfb2 is output by the minimum value circuit 60 so that Vfb2 = Vout × g3 approaches Vref in the PWM control circuit 20. Since it is controlled, the output voltage Vout = Vout2. Since the cathode voltage Vled at this time is guaranteed to be higher than the target value Vref2 = Vth, the current control circuit 16 operates normally.

  As described above, according to the power supply apparatus 200 according to the present embodiment, even when a plurality of load circuits are connected and the loads are switched and used, each load circuit can be operated stably. Can do. In particular, in the power supply device 200 according to the present embodiment, even when the forward voltage Vf of the LED 80 varies, the output voltage Vout in the second mode does not become lower than a predetermined value, so that the load circuit can be more stable. Can be driven. This means that it is not necessary to consider the margin voltage when the output voltage Vout is generated based on the cathode voltage Vled as in the first embodiment, and an unnecessary high voltage is not output. This also increases the efficiency of the entire circuit.

  Also in the present embodiment, as in the first embodiment, in the first mode, by changing the gain g1 of the first amplifier 52, the current flowing to the LED 80, that is, the luminance of the LED 80 can be changed. It becomes. In the second mode, it is also possible to change the output voltage Vout by changing the gain g3 of the second amplifier 54. This is because, for example, as the second load circuit, when a device having a different power supply voltage depending on the state of the mounted electronic device is connected, or a plurality of load circuits having different power supply voltages are connected. In such a case, it is possible to drive various load circuits by changing the gain g3.

  Those skilled in the art will understand that the above-described embodiment is an exemplification, and that various modifications can be made to combinations of the respective constituent elements and processing processes, and such modifications are also within the scope of the present invention. is there.

  In this embodiment, a switching regulator is used as the booster circuit 10, but the present invention is not limited to this, and the present invention can also be applied to a booster circuit using another method such as a switched capacitor method.

  In the present embodiment, the LED is described as an example of the first load circuit. However, other devices may be used as long as the circuit is driven by a boosted voltage. Further, although an example in which the cathode voltage is controlled as a voltage to be fed back has been described, this can be changed as appropriate according to the device to be driven.

  In the embodiment, feedback control is performed so as to approach the same target value Vref by level-shifting the cathode voltage Vled and the output voltage Vout fed back by the gain control circuit 50 and setting the voltage levels substantially the same. However, it is not limited to this. For example, feedback control may be performed by switching the value of the reference voltage Vref according to each mode.

  In the embodiment, the case where only the LED is driven as the first mode and both the LED and the second load are driven as the second mode is described. However, the present invention is not limited to this, and only the second load circuit is driven. A plurality of load circuits may be driven. By selecting the feedback circuit and controlling the feedback gain in accordance with the state of each load circuit, each load circuit can be suitably driven.

  In the present embodiment, the transistor to be used is an FET, but another type of transistor such as a bipolar transistor may be used. Selection of these transistors includes design specifications required for the power supply device, semiconductor manufacturing process to be used, and the like. You can decide by.

  In the present embodiment, all the elements constituting power supply devices 100 and 200 may be integrated, or a part thereof may be constituted by discrete components. Which part is integrated may be determined by cost, occupied area, or the like.

It is a circuit diagram which shows the structure of the power supply device which concerns on the 1st Embodiment of this invention. 2A to 2B are circuit diagrams showing the configuration of the constant current circuit. It is a figure which shows each voltage waveform of the power supply device of FIG. It is a circuit diagram which shows the structure of the power supply device which concerns on the 2nd Embodiment of this invention. FIG. 5 is a diagram illustrating a configuration of a minimum value circuit in FIG. 4.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Booster circuit, 16 Current control circuit, 18 Inverter, 20 PWM control circuit, 30 1st feedback circuit, 40 2nd feedback circuit, 42 Constant current circuit, 50 Gain control circuit, 52 1st amplifier, 54 2nd amplifier, 60 Minimum value circuit, 80 LED, 82 second load circuit, 90 third feedback path, 100 power supply, 102 input terminal, 104 output terminal, 106 LED terminal, 108 selection terminal, 200 power supply, Vin input voltage, Vout output voltage Vsel selection signal, Vled cathode voltage.

Claims (8)

A drive voltage generator for generating a drive voltage for driving a load circuit to be driven with a predetermined constant current;
A first feedback circuit that includes a detection resistor connected in series with the load circuit, and that feeds back a voltage at a connection point with the load circuit corresponding to a voltage drop across the detection resistor to the drive voltage generation unit;
Including a constant current circuit that generates the predetermined constant current connected in series with the load circuit and in parallel with the detection resistor, and a voltage at a connection point between the constant current circuit and the load circuit is the drive voltage generator. A second feedback circuit that returns to
And the drive voltage generator generates the drive voltage based on a voltage fed back from a selected one of the first and second feedback circuits. The drive voltage generator is
When the first feedback circuit is selected, a drive voltage is generated so that a voltage fed back from the first feedback circuit approaches a target value given by a product of the predetermined constant current and the detection resistor,
When the second feedback circuit is selected, a driving voltage is generated so that a voltage fed back from the second feedback circuit approaches a target value determined so that the constant current circuit operates normally. The power supply device according to claim 1.   A variable gain amplifier provided on a voltage feedback path from the first and second feedback circuits to the drive voltage generation unit, the variable gain amplifier having a signal level of a voltage fed back to the drive voltage generation unit; However, the gain is switched depending on which of the first or second feedback circuit is selected so that it is substantially the same when either of the first or second feedback circuit is selected. The power supply device according to claim 1 or 2.   The power supply apparatus according to claim 1, wherein the load circuit includes a light emitting diode, and the detection resistor and the constant current circuit are connected in parallel between a cathode terminal and a ground terminal of the light emitting diode. A drive voltage generator for generating a drive voltage for driving the first load circuit and a second load circuit to be driven at a higher voltage than the first load circuit;
A first feedback circuit that includes a detection resistor connected in series with the first load circuit, and that feeds back a voltage at a connection point with the load circuit corresponding to a voltage drop across the detection resistor to the drive voltage generator; ,
A constant current circuit for generating the predetermined constant current connected in series with the first load circuit and in parallel with the detection resistor; and driving the voltage at a connection point between the constant current circuit and the load circuit A second feedback circuit that feeds back to the voltage generator;
The drive voltage generator generates the drive voltage based on the voltage fed back from the first feedback circuit in the first mode in which the first load circuit is driven alone, and In the second mode in which both the first and second load circuits are driven simultaneously, the drive voltage is generated based on the voltage fed back from the second feedback circuit. A drive voltage generator for generating a drive voltage for driving a first load circuit to be driven with a predetermined constant current and a second load circuit to be driven with a voltage higher than the first load circuit;
A first feedback circuit that includes a detection resistor connected in series with the first load circuit, and that feeds back a voltage at a connection point with the load circuit corresponding to a voltage drop across the detection resistor to the drive voltage generator; ,
A constant current circuit for generating the predetermined constant current connected in series with the first load circuit and in parallel with the detection resistor; and driving the voltage at a connection point between the constant current circuit and the load circuit A second feedback circuit that feeds back to the voltage generator;
A third feedback circuit that feeds back the drive voltage generated by the drive voltage generator to the drive voltage generator;
The drive voltage generator generates the drive voltage based on the voltage fed back from the first feedback circuit in the first mode in which the first load circuit is driven alone, and In the second mode in which both the first and second load circuits are simultaneously driven, the drive voltage is generated based on the voltage fed back from the second feedback circuit or the third feedback circuit. apparatus. The voltage provided on the voltage feedback path from the first and second feedback circuits to the drive voltage generator, and the voltage fed back from the first or second feedback circuit to the drive voltage generator is the first or second A first amplifier that outputs as a first feedback voltage whose signal level is substantially the same in any mode by switching and amplifying the gain in the two modes;
A voltage of a first feedback voltage output from the first amplifier is provided between the third feedback circuit and the drive voltage generator, and a voltage fed back from the third feedback circuit to the drive voltage generator. A second amplifier that amplifies the signal so as to be substantially equal to the level and outputs the second feedback voltage;
A minimum value circuit for selecting and outputting the lower one of the first feedback voltage and the second feedback voltage;
The power supply apparatus according to claim 6, further comprising: the drive voltage generation unit that generates the drive voltage based on an output of the minimum value circuit. A drive voltage generator for outputting a predetermined drive voltage to one end of the load circuit;
A feedback circuit connected between the other end of the load circuit and a reference voltage;
An output control circuit for controlling a value of the output voltage by feeding back a voltage at a connection point between the load circuit and the feedback circuit to the power supply voltage generation circuit;
The feedback circuit is formed so that one of a constant current circuit and a resistance circuit can be selected.

Images