JP7201900B2 - Power supply device, semiconductor integrated circuit and ripple suppression method - Google Patents

Description

The present invention relates to a power supply device, a semiconductor integrated circuit, and a ripple suppression method.

In recent years, there has been an increasing demand for harmonic suppression in power-saving lighting equipment using light-emitting diodes. If the harmonic suppression function is strengthened in a power supply that generates a DC voltage from an AC power supply, ripples that depend on the frequency of the AC power supply are likely to occur in the output stage.

Patent Literature 1 discloses a constant-current power supply that generates a DC voltage from an AC power supply to light a light-emitting diode. In this constant-current power supply, a current detection resistor and a transistor that is turned on/off to switch between lighting and extinguishing of the light-emitting diode are connected in series to the current path of the output current that is output to the light-emitting diode.

Japanese Unexamined Patent Application Publication No. 2012-200118

Even if a ripple occurs in the voltage output to the load, the ripple can be removed from the current output to the load by performing constant current control. The present inventors have investigated a constant current circuit in which a current control transistor is provided in the current path of the output current, and the on-resistance of this transistor is controlled to limit the current flowing through the load to a predetermined current. According to this configuration, as shown in FIG. 1A, even if a ripple occurs in the output voltage VLED+ on the high potential side, the ripple component is removed from the output current by changing the ON resistance of the current control transistor. be able to. That is, by adding an in-phase ripple component to the output voltage VLED− on the low potential side, the voltage between the pair of output terminals becomes a predetermined voltage, and the ripple-free output current can be supplied to the load.

However, in such a configuration, there is a problem that the loss caused by the current control transistor increases, as shown in FIG. 1B, depending on the setting of the current value limited by the constant current circuit. Compared to the setting of the current value in FIG. 1A, the setting of the current value in FIG. On the other hand, as shown in FIG. 1(C), if the current value that the constant current circuit limits is set too low, for example, when the power supplied from the input stage fluctuates, the current control transistor will generate ripple voltage. could not be absorbed, resulting in insufficient suppression of output current ripple.

The constant current power supply device of Patent Document 1 realizes constant current control by feeding back a signal detected by using a current detection resistor provided in the current path of the output current to the control circuit of the DC/DC converter. . However, with such control, there is a problem that it is difficult to sufficiently suppress ripples from the output current when the harmonic suppression function is enhanced.

The present invention provides a power supply device that converts AC power into DC voltage and supplies it to a load, and is capable of suppressing ripples in output current with low loss even if ripples are added to the DC voltage, a semiconductor integrated circuit, and ripples. It is an object to provide a suppression method.

According to one aspect of the present invention, there is provided a power supply device comprising:
a voltage conversion circuit that generates a DC voltage from an AC power supply and outputs the DC voltage between a pair of output terminals;
a current control unit provided on a first current path through which an output current flows and controlling the current in the first current path;
a voltage at a first potential point set on a path from a high-potential-side output section of the voltage conversion circuit to the current control section in the first current path; and a current detection voltage indicating magnitude of the output current. a current control circuit that drives the current control unit so as to suppress ripples occurring in the output current based on;
characterized by comprising

According to this configuration, by outputting the DC voltage generated from the AC power supply by the voltage conversion circuit between the pair of output terminals, the DC voltage including the ripple voltage is output. However, ripples occurring in the output current can be suppressed by the current control section that controls the current in the first current path through which the output current flows, and the current control circuit that drives the current control section. Further, the current control circuit is based on the current detection voltage indicating the magnitude of the output current and the voltage at the first potential point set on the path from the high potential side output section of the voltage conversion circuit to the current control section. Therefore, the current control section can be driven such that the loss generated in the current control section does not increase while suppressing the ripple generated in the output current. Therefore, an output current with suppressed ripple can be supplied to the load with low loss.

here,
The current control circuit may be configured to drive the current control section so that the bottom voltage of the ripple voltage at the first potential point converges to a minimum voltage, ie, a balanced voltage.

According to this configuration, by controlling the bottom voltage of the ripple voltage at the first potential point to a balanced voltage, it is possible to output an output current with a low loss and suppressed ripple.

Further, the current control circuit is
a voltage holding unit that holds a reference voltage;
a differential circuit that outputs a drive signal to the current controller so that the difference between the reference voltage and the current detection voltage is reduced;
a pull-down circuit capable of pulling down the reference voltage;
a first voltage dividing circuit that divides the reference voltage to generate a first divided voltage;
a first comparator that compares the first divided voltage and the current detection voltage and causes the reduction circuit to reduce the reference voltage when the current detection voltage is lower than the first divided voltage;
may have

According to this configuration, the ripple of the output current is suppressed to a small ripple determined by the voltage dividing ratio of the first voltage dividing circuit. Furthermore, the output current is controlled such that a small ripple occurs in the output current, so the loss of the current control section is low. As a result, it is possible to output an output current with low loss and suppressed ripple.

Furthermore, the current control circuit
a first pull-up circuit capable of pulling up the reference voltage;
A second comparison for comparing a predetermined reference voltage with the voltage at the first potential point, and causing the first pull-up circuit to pull up the reference voltage when the voltage at the first potential point is higher than the reference voltage. vessel and
may have

According to this configuration, when the voltage at the first potential point increases and the loss in the current control section increases, the reference voltage can be increased to reduce the loss in the current control section. By combining this control with the control for suppressing the ripple, it is possible to stably output the output current with the ripple suppressed at a low loss.

moreover,
the reference voltage is higher than the voltage at the first potential point at which the ripple of the output current is zero;
A voltage dividing ratio of the first voltage dividing circuit may be set to 1-(ratio of magnitude of allowable ripple current to the upper end value of the output current). With such a setting, the ripple of the output current can be suppressed below the allowable value.

moreover,
A voltage pull-down capability of the pull-down circuit may be lower than a voltage pull-up capability of the first pull-up circuit. As the reference voltage is higher than the appropriate value, the current that the current control section can flow increases. Therefore, when the current supply capability of the voltage conversion circuit cannot catch up with the amount of current that the current control unit can flow, the ripple generated in the output current increases. On the other hand, the smaller the reference voltage is than the proper value, the smaller the current that the current control section can flow. Therefore, if the output power of the voltage conversion circuit is large, the loss of the current control section increases. Therefore, the relationship between the voltage raising capability of the first raising circuit and the voltage lowering capability of the voltage-lowering circuit allows the reference voltage to be quickly increased when the reference voltage is smaller than the proper value. Then, it can be gradually converged to an appropriate value. As a result, it is possible to avoid a state in which the loss of the current control unit is high for a long period of time at the time of transition of the circuit state, such as when the output power of the voltage conversion circuit is switched between high and low levels.

Furthermore, the current control circuit
a second pull-up circuit capable of pulling up the reference voltage with a capability lower than the voltage pull-down capability of the pull-down circuit;
a second voltage dividing circuit that divides the reference voltage and generates a second divided voltage that is higher than the first divided voltage;
a logic unit that causes the second pull-up circuit to pull up the reference voltage when the period during which the current detection voltage does not fall below the first divided voltage exceeds a predetermined period;
may further have

According to such a configuration, the suppressed magnitude of ripple generated in the output current can be converged to a ratio determined by the voltage dividing ratio of the first voltage dividing circuit. As a result, it is possible to avoid the situation where the ripple becomes zero and the loss of the current control unit fluctuates to a higher level due to the influence of some fluctuating factors.

Furthermore, the current control circuit
a second pull-up circuit capable of pulling up the reference voltage with a capability lower than the voltage pull-down capability of the pull-down circuit;
a logic unit that causes the second pull-up circuit to pull up the reference voltage when the period during which the current detection voltage does not fall below the first divided voltage exceeds a predetermined period;
a second voltage dividing circuit that divides the reference voltage and generates a second divided voltage that is higher than the first divided voltage;
a third comparator that compares the second divided voltage and the current detection voltage;
further comprising
The logic unit
Based on the comparison result of the second comparator and the comparison result of the third comparator, it is determined whether the current detection voltage falls below the first divided voltage after the current detection voltage falls below the second divided voltage. The second pull-up circuit may be caused to pull up the reference voltage when the non-current period exceeds a predetermined period.

According to such a configuration, it is possible to stably detect that the suppressed ripple generated in the output current continues to be smaller than the ratio determined by the voltage dividing ratio of the first voltage dividing circuit. Then, based on this detection, the reference voltage can be raised to converge the ripple of the output voltage to the above ratio. Therefore, it is possible to stably avoid that the loss of the current control unit fluctuates to a higher level due to the influence of some fluctuating factor.

On the other hand, the current control circuit
a voltage holding unit that holds a reference voltage;
a differential circuit that outputs a drive signal to the current controller so that the difference between the reference voltage and the current detection voltage is reduced;
a bottom voltage control unit that inputs the voltage at the first potential point as a detection voltage and controls the reference voltage based on comparison of the detection voltages at different timings;
It is good also as a structure which has.

According to this configuration, the bottom voltage control section can detect when the loss of the current control section increases due to the detected voltage. Therefore, based on this detection, the current control circuit can implement control to converge the bottom voltage of the ripple voltage appearing at the first potential point to a balanced voltage that reduces loss occurring in the current control section.

Here, the current control circuit may further include a variation adding section that adds variation to the reference voltage held by the voltage holding section. If the detection voltage becomes stable, there is a possibility that the increase or decrease in the loss of the current circuit or the ripple of the output current cannot be detected. Therefore, according to this configuration, it is possible to prevent the detection voltage from being stabilized due to the fluctuation applied by the fluctuation adding section, and to suppress the state where the loss increase or decrease of the current circuit or the ripple of the output current cannot be detected. . Therefore, based on the detected voltage, it is possible to control the bottom voltage of the ripple voltage appearing at the output terminal on the cathode side to quickly converge to the balanced voltage within the range in which the ripple of the output current is suppressed.

Furthermore, the power supply device according to the present invention may have a configuration in which a lighting device is connected between the pair of output terminals. According to this configuration, it is possible to provide a power supply device capable of suppressing flicker of a lighting device (for example, a light emitting diode, an organic EL element, etc.) with low loss while suppressing harmonics.

A semiconductor integrated circuit according to one aspect of the present invention includes:
It is installed in a power supply device having a voltage conversion circuit that generates a DC voltage from an AC power supply and outputs the DC voltage between a pair of output terminals, and drives a current control unit that can control the current of the current path through which the output current flows. A semiconductor integrated circuit,
a differential circuit that outputs a drive signal to the current controller so that the difference between the reference voltage and the current detection voltage indicating the magnitude of the output current is reduced;
a first comparator that compares a first divided voltage obtained by dividing the reference voltage with the current detection voltage and reduces the reference voltage when the current detection voltage is lower than the first divided voltage;
comparing a voltage at a first potential point set on a current path through which the output current flows from the high-potential-side output section of the voltage conversion circuit to the current control section with a predetermined reference voltage; a second comparator for increasing the reference voltage when the voltage at the first potential point is higher than the reference voltage;
characterized by comprising

Another aspect of the present invention provides a semiconductor integrated circuit comprising:
It is installed in a power supply device having a voltage conversion circuit that generates a DC voltage from an AC power supply and outputs the DC voltage between a pair of output terminals, and drives a current control unit that can control the current of the current path through which the output current flows. A semiconductor integrated circuit,
a differential circuit that outputs a drive signal to the current controller so that a difference between a current detection voltage indicating the magnitude of the output current and a reference voltage is reduced;
A balance in which the bottom voltage of the ripple voltage at the first potential point set on the path from the high potential side output section of the voltage conversion circuit to the current control section in the current path through which the output current flows is the minimum voltage. a bottom voltage controller that changes the reference voltage so as to converge to a voltage;
characterized by comprising

These semiconductor integrated circuits can be incorporated in a power supply device in which a DC voltage including a ripple voltage is output between a pair of output terminals from a voltage conversion circuit. As a result, it is possible to reduce the loss in the current control section while suppressing the ripple of the output current of the power supply device by driving the current control section.

A ripple suppression method according to one aspect of the present invention includes:
In a power supply device having a voltage conversion circuit that generates a DC voltage from an AC power supply and outputs the DC voltage between a pair of output terminals, driving a current control unit capable of controlling a current in a current path through which the output current flows, A ripple suppression method for suppressing ripple generated in an output current,
while outputting a drive signal to the current control unit so that the difference between the current detection voltage indicating the magnitude of the output current and the reference voltage becomes small;
comparing a first divided voltage obtained by dividing the reference voltage with the current detection voltage, and decreasing the reference voltage when the current detection voltage is lower than the first divided voltage;
comparing a voltage at a first potential point set on a current path through which the output current flows from the high-potential-side output section of the voltage conversion circuit to the current control section with a predetermined reference voltage; and increasing the reference voltage when the voltage at the first potential point is higher than the reference voltage.

A ripple suppression method according to another aspect of the present invention includes:
In a power supply device having a voltage conversion circuit that generates a DC voltage from an AC power supply and outputs the DC voltage between a pair of output terminals, driving a current control unit capable of controlling a current in a current path through which the output current flows, A ripple suppression method for suppressing ripple generated in an output current,
while outputting a drive signal to the current control unit so that the difference between the current detection voltage indicating the magnitude of the output current and the reference voltage becomes small;
A balance in which the bottom voltage of the ripple voltage at the first potential point set on the path from the high potential side output section of the voltage conversion circuit to the current control section in the current path through which the output current flows is the minimum voltage. A method is adopted in which the reference voltage is changed so as to converge on the voltage.

According to these methods, even if a DC voltage including a ripple voltage is output from the voltage conversion circuit between the pair of output terminals, the ripple of the output current can be suppressed by the current control unit, and the current control unit can Losses that occur can be reduced.

INDUSTRIAL APPLICABILITY According to the present invention, in a power supply apparatus that converts AC power into DC voltage and supplies it to a load, even if ripple is added to the DC voltage, the power supply apparatus and the semiconductor integrated circuit can suppress the ripple generated in the output current with low loss. and the effect that a ripple suppression method can be provided.

FIG. 4 is a diagram showing the output characteristics of a power supply device in which a constant current circuit is provided in the current path of the output current, (A) is a waveform diagram at the time of ideal current setting, and (B) is a power supply device with respect to (A). is a waveform diagram when the power controlled by is increased and the output current is increased, and (C) is a waveform diagram when the power controlled by the power supply device is decreased with respect to (A) and the output current is decreased. 1 is a circuit diagram showing a power supply device according to Embodiment 1 of the present invention; FIG. FIG. 4 is a signal waveform diagram for explaining the operation of the power supply when changing the current value of the constant current circuit; It is a circuit diagram which shows the power supply device of Embodiment 2 which concerns on this invention. It is a circuit diagram which shows the power supply device of Embodiment 3 which concerns on this invention. It is a circuit diagram which shows the power supply device of Embodiment 4 which concerns on this invention. FIG. 10 is a diagram illustrating the action of bottom voltage control in Embodiment 4, where (A) shows changes in power supplied from the primary side, (B) shows changes in voltage on the secondary side, and (C) shows changes in output voltage on the cathode side. (D) shows the change in the bottom voltage and the change in the output current, respectively. It is a circuit diagram which shows the power supply device of Embodiment 5 which concerns on this invention. It is a circuit diagram which shows the power supply device of Embodiment 6 which concerns on this invention. FIG. 11 is a waveform diagram for explaining the control operation of the power supply device of Embodiment 6; FIG. 4 is a signal waveform diagram for explaining the control operation of the first comparator; FIG. 10 is a signal waveform diagram for explaining the control operation of the second comparator; It is a circuit diagram which shows the power supply device of Embodiment 7 which concerns on this invention. FIG. 14 is a circuit diagram showing an example of a configuration of a logic unit in FIG. 13; 15 is a time chart for explaining the operation of the logic part of FIG. 14; FIG. 10 is a circuit diagram showing a modification of the logic section; 17 is a time chart for explaining the operation of the logic part of FIG. 16;

Hereinafter, each embodiment of the present invention will be described in detail with reference to the drawings.

(Embodiment 1)
FIG. 2 is a circuit diagram showing a power supply device according to Embodiment 1 of the present invention. A power supply device 1 according to the first embodiment includes a rectifier circuit 2 that rectifies the voltage of an alternating current power supply AC, a DC/DC converter 11 that receives the output voltage of the rectifier circuit 2 and converts it into a DC voltage, and a current path of an output current Iout. and a bottom voltage control section 31 for controlling the current limited by the constant current circuit 21 . A light-emitting diode 61 for lighting is connected to the power supply device 1 as a load between the output terminals ta and tb.

Among the above configurations, the rectifier circuit 2 and the DC/DC converter 11 correspond to an example of the voltage conversion circuit according to the present invention. The transistor M1 of the constant current circuit 21 corresponds to an example of the current controller according to the invention. A configuration in which the bottom voltage control section 31, the error amplifier 22 of the constant current circuit 21, and the capacitor Cr are combined corresponds to an example of the current control circuit according to the present invention. The capacitor Cr corresponds to an example of the voltage holding section according to the invention. The error amplifier 22 corresponds to an example of a differential circuit according to the invention. Also, the drain terminal (output terminal tb on the low potential side) of the transistor M1 corresponds to an example of the first potential point according to the present invention. The source voltage V_MOS_S corresponds to an example of the current detection voltage according to the invention.

The DC/DC converter 11 is, for example, a flyback converter, and converts the output voltage of the rectifier circuit 2 into a DC voltage. The DC/DC converter 11 includes a flyback type transformer T0, a switching element M0 such as a field effect transistor, a control circuit 14 for driving the switching element M0, and a rectifier diode D1 connected to the secondary side of the transformer T0. , and an output capacitor Cout. The control circuit 14 receives feedback of a voltage value, a current value, or both from a detection element (not shown) connected to the secondary side of the transformer T0, and controls the switching element M0 so as to keep them at predetermined values. By controlling the switching element M0 by the control circuit 14, the DC/DC converter 11 operates to exert a harmonic suppression effect.

A constant current circuit 21 is provided in the current path of the output current Iout and limits the output current Iout to a target current. The constant current circuit 21 controls the transistor M1 based on the detection voltage detected by the current control transistor M1 and the current detection resistor R1, which are connected in series in order from the output terminal tb on the low potential side, and the current detection resistor R1. It has an error amplifier 22 that controls a terminal (gate terminal) and a capacitor Cr that generates a reference voltage.

The transistor M1 is, for example, a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) transistor, and is provided on the current path of the output current Iout so that the output current Iout flows between the source and the drain. The transistor M1 is a current control element capable of controlling the drain current by changing the ON resistance between the source and the drain by controlling the gate voltage.

The current detection resistor R1 is connected between the reference potential on the secondary side (potential on the low potential side of the output capacitor Cout) and the transistor M1. The current detection resistor R1 outputs a detection voltage corresponding to the output current Iout to a connection point with the transistor M1. In other words, a detection voltage proportional to the output current Iout is output between both terminals of the current detection resistor R1.

Capacitor Cr generates a reference voltage Vref and supplies it to the non-inverting input terminal of error amplifier 22 .

The error amplifier 22 inputs the voltage detected by the current detection resistor R1 to its inverting input terminal, and outputs a voltage corresponding to the difference between the detected voltage and the reference voltage Vref to the control terminal of the transistor M1. If the reference voltage Vref is the target current Ia×(resistance value of the resistor R1), the control terminal of the transistor M1 is adjusted so that the on-resistance of the transistor M1 increases when the current flowing through the resistor R1 becomes larger than the target current Ia. The output voltage of the error amplifier 22 input to is controlled. This reduces the output current Iout. On the other hand, when the current flowing through the resistor R1 becomes smaller than the target current Ia, the output voltage of the error amplifier 22 input to the control terminal of the transistor M1 is controlled so that the ON resistance of the transistor M1 becomes smaller. This increases the output current Iout. Such an operation controls the output current Iout to converge to the target current Ia.

The bottom voltage control unit 31 controls the constant current circuit 21 so that the bottom voltage of the ripple voltage output to the output terminal tb on the low potential side becomes the balanced voltage VD (see FIG. 3). The balanced voltage VD means the minimum voltage among the above bottom voltages within the range in which the ripple of the output current Iout is suppressed. The range in which the ripple of the output current Iout is suppressed is not limited to the range in which no ripple occurs completely, and includes, for example, a range that includes a small amount of ripple current at a level at which flicker cannot be captured even when photographed with a digital camera or the like. It may be If a current containing ripples of a size that cannot be ignored flows through a light-emitting diode, a phenomenon in which a striped pattern appears in an image taken with a digital camera, that is, flicker occurs. The bottom voltage control unit 31 inputs the output voltage VLED− on the low potential side as a detection voltage, and controls the value of the reference voltage Vref of the constant current circuit 21 to increase or decrease, thereby changing the current value controlled by the constant current circuit 21. Let

The bottom voltage controller 31 includes a loss detection circuit 32, a comparator 37, two current sources I1 and I2, and a switch SW1. The loss detection circuit 32 includes a bottom detection unit 33 that detects the bottom voltage of the ripple voltage, voltage holding units 34 and 35 that hold the bottom voltages detected at different timings, and the voltages held in the voltage holding units 34 and 35. and a subtractor 36 for obtaining the difference between . Among the above configurations, the current source I2 corresponds to an example of the variation adding section according to the present invention.

The bottom detection unit 33 removes the noise component to detect the minimum voltage of the ripple voltage, and causes one voltage holding unit 34 to hold it. The voltage holding unit 34 shifts the previously held voltage to the other voltage holding unit 35 each time the bottom detection unit 33 detects a new bottom voltage. The two voltage holding units 34 output the held voltages to the subtractor 36 . The subtractor 36 calculates the voltage difference between the voltage holding units 34 and 35 and outputs the result to the comparator 37 . For example, the subtractor 36 outputs a positive voltage if the detected bottom voltage is rising in chronological order, and outputs a negative voltage if it is falling. The bottom detection unit 33, the voltage holding units 34 and 35, and the subtractor 36 may be a digital circuit that performs the above-described processing on the output voltage VLED- on the low potential side that has been converted to a digital value, or may be an analog circuit. It may be an analog circuit that performs the above processing at the same time.

A comparator 37 compares the reference potential with the output of the subtractor 36, turns on the switch SW1 if a positive voltage is input from the subtractor 36, and turns off the switch SW1 otherwise. One current source I2 always draws a minute current from the capacitor Cr of the constant current circuit 21, and exerts a varying action to gradually lower the reference voltage Vref of the constant current circuit 21. FIG. The other current source I1, when the switch SW1 is on, causes a minute current to flow into the capacitor Cr of the constant current circuit 21 to raise the reference voltage Vref of the constant current circuit 21. FIG. The current amount of the current source I1 is set larger than the current amount of the current source I2.

In the power supply device 1 of FIG. 2, the bottom voltage controller 31, the error amplifier 22 of the constant current circuit 21, and the current control transistor M1 are provided in a one-chip semiconductor integrated circuit. Note that the current control transistor M1 may not be included in the semiconductor integrated circuit, but may be externally attached to the semiconductor integrated circuit.

<Description of operation>
In the power supply device 1 of FIG. 2, harmonics are suppressed in the DC/DC converter 11, so that a ripple voltage dependent on the frequency of the AC power supply AC is added to the output voltage VLED+ converted by the DC/DC converter 11. be done. On the other hand, the output current Iout of the power supply device 1 is controlled to a target current by the constant current circuit 21 . Therefore, normally, a ripple voltage of the same phase and magnitude also occurs in the output voltage VLED- on the low potential side, and the ripple is removed from the output current Iout flowing to the load.

FIG. 3 is a signal waveform diagram for explaining the operation of the power supply when the bottom voltage control section is stopped and the current value controlled by the constant current circuit is changed. In FIG. 3, "VLED-" is the output voltage of the output terminal tb on the low potential side, "Vref" is the reference voltage Vref of the error amplifier 22, "V_MOS_S" is the source voltage of the transistor M1, and "Iout" is the output current. . In FIG. 3, the horizontal axis represents time, and FIG. 3 shows waveforms when the current of the constant current circuit 21 decreases at a predetermined speed.

First, the voltage and current at each connection point of the power supply device 1 when the control of the bottom voltage control unit 31 is omitted and the reference voltage Vref of the constant current circuit 21 is decreased at a predetermined speed will be described.

In this case, as shown in the range H1 in FIG. 3, in the range where the reference voltage Vref is higher than the voltage VR, the ripple generated in the output voltage VLED− on the low potential side is small, and the output voltage VLED− The rate of change of the bottom voltage of the ripple voltage of is small. Also, in the range H1, there is a period Tb in which the operating region of the transistor M1 for current control reaches the saturation region. Ripple occurs in the output current Iout.

On the other hand, as shown in the range H2 in FIG. 3, in the range where the reference voltage Vref is lower than the voltage VR, the ripple bottom voltage generated in the output voltage VLED− on the low potential side according to the change in the reference voltage Vref is relatively large. increase in proportion. This increase in bottom voltage corresponds to the loss caused by the transistor M1. In the range H2, the current control transistor M1 operates in the non-saturation region for the entire period, so that the current can be controlled to the target current. Therefore, no ripple occurs in the output current Iout.

From the characteristics shown in FIG. 3, the most suitable setting for the target current of the constant current circuit 21 is the range H2 in which no ripple is generated in the output current Iout, and the bottom voltage of the ripple generated in the output voltage VLED− on the low potential side is the most suitable. This setting results in a low equilibrium voltage VD. A setting in which the bottom voltage is equal to the balanced voltage VD results in the least loss in the transistor M1 as long as the ripple is removed from the output current Iout. Equilibrium voltage VD is at the boundary where the slope, which indicates the rate of change in bottom voltage with respect to change in target current, changes from a relatively large slope to a small slope close to zero.

The bottom voltage control unit 31 uses the characteristics of FIG. 3 to control the target current of the constant current circuit 21 so that the ripple bottom voltage of the output voltage VLED− on the low potential side converges to the balanced voltage VD. Specifically, first, the bottom voltage control unit 31 applies a variation such that the voltage gradually decreases to the reference voltage Vref of the constant current circuit 21 by the current source I2. As a result, if the value of the reference voltage Vref is in the range H2 in FIG. As a result, the switch SW1 is turned on, the reference voltage Vref increases, and the bottom voltage changes toward the equilibrium voltage VD.

On the other hand, if the value of the reference voltage Vref is in the range H1 in FIG. 3, the bottom voltage does not change over time or changes only slightly even if there is a change due to the current source I2. Then, no positive output is produced from the subtractor 36 . Therefore, the switch SW1 is not turned on, the reference voltage Vref drops due to the fluctuation of the current source I2, and the bottom voltage changes in the direction approaching the equilibrium voltage VD. By such action, the ripple bottom voltage of the output voltage VLED− converges to the balanced voltage VD.

As described above, according to the power supply device 1 of Embodiment 1 and its ripple suppression method, by generating a DC voltage from the AC power supply AC while suppressing harmonics, even if ripples occur in the converted DC voltage, , the control of the constant current circuit 21 can sufficiently suppress the ripple of the output current Iout output to the load. As a result, it is possible to suppress the occurrence of flicker in the illumination light of the light emitting diode 61, for example.

Further, according to the power supply device 1 and its ripple suppressing method of Embodiment 1, the bottom voltage control section 31 controls the bottom voltage of the output voltage VLED− on the low potential side to converge to the balanced voltage VD. As a result, the loss generated in the transistor M1 of the constant current circuit 21 can be reduced while suppressing the ripple of the output current Iout.

For example, as a comparative example, in a configuration in which the target current of the constant current circuit 21 is set to a predetermined current, it is assumed that the DC/DC converter 11 has an error that increases the output power. In this case, as shown in FIG. 1B, the transistor M1 of the constant current circuit 21 is controlled to increase the amount of voltage drop, and the target current of the constant current circuit 21 is maintained. In this case, the loss corresponding to the voltage drop Vb occurs in the transistor M1. However, even if such an error occurs, according to the power supply device 1 of the first embodiment, the bottom voltage control unit 31 increases the target current of the constant current circuit 21 to increase the bottom voltage of the output voltage VLED− to Converge to the equilibrium voltage VD. As a result, in the constant current circuit 21, the ON resistance of the transistor M1 is controlled to be low so that the output current Iout increases, and the loss generated in the constant current circuit 21 is reduced. Since the forward voltage Vf of the light emitting diode 61 slightly changes according to the current value, the voltage dropped across the light emitting diode 61 increases as the output current Iout increases. As a result, the on-resistance of the transistor M1 is reduced, thereby realizing an operation with less loss in the constant current circuit 21 as shown in FIG. 1(A).

Also, as a comparative example, it is assumed that in a configuration in which the target current of the constant current circuit 21 is constant, an error occurs in the DC/DC converter 11 in the direction of decreasing the output power. In this case, as shown in FIG. 1C, when control is performed in accordance with a constant target current, a period Tb occurs during which the transistor M1 of the constant current circuit 21 operates in the saturation region, causing a ripple in the output current Iout. occurs. However, even in such a case, according to the power supply device 1 of the first embodiment, the bottom voltage control unit 31 reduces the target current of the constant current circuit 21 to reduce the ripple of the voltage "VLED-" of the output terminal tb. The bottom voltage converges to the equilibrium voltage VD. As a result, the ON resistance of the transistor M1 of the constant current circuit 21 is controlled to be high so that the output current Iout becomes small, and the period Tb during which the transistor M1 operates in the saturation region is reduced. As a result, ripples in the output current Iout are completely removed, or suppressed to a level at which flicker cannot be captured even when photographed with a digital camera or the like. Even in this case, if the output power of the DC/DC converter 11 does not drop to a level at which the load cannot be driven, the light emitting diode 61 can be normally driven with the ripple of the output current Iout suppressed.

(Embodiment 2)
FIG. 4 is a circuit diagram showing a power supply device according to Embodiment 2 of the present invention.

A power supply device 1A of the second embodiment mainly differs in the configuration of a bottom voltage control section 131, and the other components are the same as those of the first embodiment. Only different components are described in detail below.

The bottom voltage control unit 131 of the second embodiment receives the voltage at the connection point between the transistor M1 of the constant current circuit 21 and the current detection resistor R1, that is, the source voltage V_MOS_S of the transistor M1 as the detection voltage. Based on the detected voltage, the bottom voltage control unit 131 raises or lowers the value of the reference voltage Vref of the constant current circuit 21, changes the value of the current flowing through the constant current circuit 21, and changes the output voltage VLED- on the low potential side. is controlled so that the bottom voltage of is equal to the equilibrium voltage VD.

The bottom voltage control section 131 includes a ripple detection circuit 132, a comparator 137, two current sources I3 and I4, and a switch SW2. Among the above configurations, the current source I3 corresponds to an example of the variation adding section according to the present invention.

The ripple detection circuit 132 receives the source voltage V_MOS_S obtained by voltage-converting the output current Iout, and detects the presence or absence of ripples in the output current Iout. Specifically, ripple detection circuit 132 includes peak detection section 133 that detects the peak voltage of source voltage V_MOS_S, bottom detection section 134 that detects the bottom voltage of source voltage V_MOS_S, peak detection section 133 and bottom detection section 134 . and a subtractor 135 for subtracting the detected value of . The peak detection unit 133 and the bottom detection unit 134 detect the peak voltage and the bottom voltage of the source voltage V_MOS_S for each period corresponding to the frequency of the AC power supply AC. A peak detection unit 133 and a bottom detection unit 134 detect the peak voltage and the bottom voltage of the source voltage V_MOS_S with noise components removed. The subtractor 135 subtracts the detection value of the bottom detection section 134 from the detection value of the peak detection section 133 and outputs the result to the comparator 137 . That is, when the output current Iout includes a ripple of a predetermined magnitude or more, the subtractor 135 calculates the difference between the peak voltage and the bottom voltage as a positive value and outputs a positive voltage. On the other hand, when the output current Iout does not contain a ripple of a predetermined magnitude or more, the difference between the peak voltage and the bottom voltage becomes zero, so that the subtractor 135 does not output a positive voltage. Note that the peak detector 133, the bottom detector 134, and the subtractor 135 may be digital circuits that perform the above processing on the source voltage V_MOS_S converted into a digital value.

A comparator 137 compares the reference potential with the output of the subtractor 135, turns on the switch SW2 if a positive voltage is input from the subtractor 135, and turns off the switch SW2 otherwise. On the other hand, the current source I3 constantly feeds a minute current into the capacitor Cr of the constant current circuit 21 and exerts a fluctuation action to gradually increase the reference voltage Vref of the constant current circuit 21 . The other current source I4 draws a very small current from the capacitor Cr of the constant current circuit 21 when the switch SW2 is on, and acts to decrease the reference voltage Vref of the constant current circuit 21. FIG. The current value of the current source I4 is set larger than the current value of the current source I3.

In the power supply device 1A of FIG. 4, the bottom voltage controller 131, the error amplifier 22 of the constant current circuit 21, and the current control transistor M1 are provided in a one-chip semiconductor integrated circuit. Note that the current control transistor M1 may not be included in the semiconductor integrated circuit, but may be externally attached to the semiconductor integrated circuit.

<Description of operation>
In the power supply device 1A of the second embodiment, as in the first embodiment, a ripple voltage is added to the DC voltage converted by the DC/DC converter 11, and the output is controlled to the target current value by the constant current circuit 21. A current Iout is output to the light emitting diode 61 .

Furthermore, in the power supply device 1A of the second embodiment as well, if the operation of the bottom voltage control section 131 is stopped and the reference voltage Vref of the constant current circuit 21 is uniformly varied, the voltage and current of each section as shown in FIG. changes. That is, in the range H1 where the reference voltage Vref is higher than the value corresponding to the balanced voltage VD, a ripple occurs in the output current Iout, and in the range H2 where the reference voltage Vref is lower than the value corresponding to the balanced voltage VD, the constant current circuit 21 The loss caused by the transistor M1 of is increased. The bottom voltage control unit 131 according to the second embodiment uses the characteristics shown in FIG. 3 to control the reference voltage Vref of the constant current circuit 21 so that the bottom voltage of the output voltage VLED- change.

First, the bottom voltage control unit 131 applies a variation such that the voltage gradually increases to the reference voltage Vref of the constant current circuit 21 using one of the current sources I3. If the reference voltage Vref is in the range H2 in FIG. 3, no ripple occurs in the output current Iout. Therefore, the subtractor 135 does not produce a positive output. In this case, the signal for closing the switch SW2 is not output from the comparator 137, and the switch SW2 remains open. Therefore, the reference voltage Vref increases due to the action of the current source I3, and the bottom voltage acts so as to approach the equilibrium voltage VD.

On the other hand, if the reference voltage Vref is in the range H1 in FIG. 3, a ripple occurs in the output current Iout, and the detection value of the peak detection section 133 of the ripple detection circuit 132 becomes larger than the detection value of the bottom detection section 134. , a positive output is produced from the subtractor 135 . In this case, a signal for closing the switch SW2 is output from the comparator 137, and the switch SW2 is closed. Therefore, the current source I4 draws current from the capacitor Cr, the reference voltage Vref decreases, and the bottom voltage approaches the balanced voltage VD. By such action, the ripple bottom voltage of the output voltage VLED− on the low potential side converges to the balanced voltage VD.

As described above, according to the power supply device 1A of the second embodiment, by generating a DC voltage from the AC power supply AC while suppressing harmonics, even if ripples occur in the converted DC voltage, the constant current circuit 21 can sufficiently suppress the ripple of the output current Iout output to the load. As a result, it is possible to suppress the occurrence of flicker in the illumination light of the light emitting diode 61, for example.

Furthermore, according to the power supply device 1A of the second embodiment, the bottom voltage control section 131 controls the bottom voltage of the output voltage VLED− on the low potential side to converge to the balanced voltage VD. As a result, the loss caused by the transistor M1 of the constant current circuit 21 can be reduced while suppressing the ripple of the output current Iout by the same action as described in the first embodiment.

(Embodiment 3)
FIG. 5 is a circuit diagram showing a power supply device according to Embodiment 3 of the present invention.

The power supply device 1B of the third embodiment differs from the first or second embodiment in the configuration of the bottom voltage control section 231, and the other components are the same as those of the first or second embodiment. Only different components are described in detail below.

The constant current circuit 21 of the third embodiment includes a capacitor Crb having one end connected to a reference potential as an element that supplies the reference voltage Vref.

The bottom voltage controller 231 of the third embodiment includes a loss detection circuit 232, a ripple detection circuit 233, an error calculator 234, a current amplifier 235 and a voltage source 236.

The loss detection circuit 232 is the same as the loss detection circuit 32 of the first embodiment, and outputs a voltage corresponding to the amount of change in the bottom voltage of the output voltage VLED-.

The ripple detection circuit 233 is similar to the ripple detection circuit 132 of the second embodiment, and outputs a voltage corresponding to the magnitude of the ripple of the output current Iout.

The error calculator 234 subtracts the output value of the ripple detection circuit 233 from the output value of the loss detection circuit 32 and outputs a voltage according to the result to the non-inverting input terminal of the current amplifier 235 .

The current amplifier 235 has an inverting input terminal to which a predetermined positive voltage is input from the voltage source 236, and a non-inverting input terminal to which a voltage corresponding to the calculation result is input from the error calculator 234. Output to Crb. The positive voltage input to the inverting input terminal is set to a low voltage, and when the output of the error calculator 234 is zero, a minute negative current is output from the current amplifier 235, and the minute current from the capacitor Crb is converted into the current amplifier 235. drawn into. Then, the reference voltage Vref of the constant current circuit 21 is given a downward fluctuation.

In the power supply device 1B of FIG. 5, the bottom voltage controller 231, the error amplifier 22 of the constant current circuit 21, and the current control transistor M1 are provided in a one-chip semiconductor integrated circuit. Note that the current control transistor M1 may not be included in the semiconductor integrated circuit, but may be externally attached to the semiconductor integrated circuit.

<Description of operation>
In the power supply device 1B of the third embodiment, as in the second embodiment, a ripple is added to the DC voltage converted by the DC/DC converter 11, while the current value of the target current is controlled by the constant current circuit 21. An output current Iout is output to the light emitting diode 61 .

Furthermore, in the power supply device 1B of Embodiment 3 as well, if the operation of the bottom voltage control section 131 is stopped and the reference voltage Vref of the constant current circuit 21 is uniformly varied, the voltage and current of each section as shown in FIG. changes. That is, in the range H1 where the reference voltage Vref is higher than the voltage VR, ripples occur in the output current Iout, and in the range H2 where the reference voltage Vref is lower than the voltage VR, the loss caused by the transistor M1 of the constant current circuit 21 increases. The bottom voltage control unit 231 according to the third embodiment uses the characteristics shown in FIG. 3 to adjust the reference voltage Vref of the constant current circuit 21 so that the bottom voltage of the output voltage VLED- change.

First, when the reference voltage Vref is in the range H1 in FIG. 234 provides a negative output. As a result, a negative current is output from the current amplifier 235, current is drawn from the capacitor Crb, and the reference voltage Vref decreases. Therefore, the bottom voltage of the output voltage VLED− on the low potential side approaches the balanced voltage VD.

On the other hand, when the reference voltage Vref shifts from range H1 to range H2 in FIG. Output is done. As a result, a positive current is output from the current amplifier 235, the current flows into the capacitor Crb, and the reference voltage Vref increases. Therefore, the bottom voltage of the output voltage VLED− on the low potential side approaches the balanced voltage VD. Due to this action, the bottom voltage of the output voltage VLED- converges to the balanced voltage VD.

Also, even when the reference voltage Vref is about to stabilize at an arbitrary value within the range H2 in FIG. variation is given. As a result, the reference voltage Vref is not stabilized at an arbitrary value within the range H2 for a long time, and the bottom voltage of the output voltage VLED− on the low potential side converges to the balanced voltage VD as described above.

As described above, according to the power supply device 1B of Embodiment 3, by generating a DC voltage from the AC power supply AC while suppressing harmonics, even if a ripple occurs in the converted DC voltage, the constant current circuit 21 can sufficiently suppress the ripple of the output current Iout output to the load. As a result, it is possible to suppress the occurrence of flicker in the illumination light of the light emitting diode 61, for example.

Furthermore, according to the power supply device 1B of the third embodiment, the bottom voltage control section 231 controls the bottom voltage of the output voltage VLED− on the low potential side so as to converge to the balanced voltage VD. As a result, the loss caused by the transistor M1 of the constant current circuit 21 can be reduced while suppressing the ripple of the output current Iout by the same action as described in the first embodiment.

(Embodiment 4)
FIG. 6 is a circuit diagram showing a power supply device according to Embodiment 4 of the present invention.

A power supply device 1C of the fourth embodiment differs from that of the third embodiment in the configuration of a bottom voltage control section 331, and the other components are the same as those of the third embodiment. Only different components are described in detail below.

The bottom voltage control section 331 of the fourth embodiment is configured to control the bottom voltage of the output voltage VLED− on the low potential side so as to converge to the balanced voltage VD set as a fixed value in advance. The balanced voltage VD is calculated in advance in consideration of the size of the load connected to the power supply device 1</b>C, the operating environment, etc., and set in the bottom voltage control section 331 . The bottom voltage control unit 331 includes a bottom voltage detection unit 332 that detects and holds the bottom voltage of the output voltage VLED− on the low potential side, a reference circuit 333 that generates a reference voltage VDref, and a current to the capacitor Crb of the constant current circuit 21. and a current amplifier 334 for inserting and removing the . The reference voltage VDref is set equal to the balanced voltage VD calculated above.

In the power supply device 1C of FIG. 6, the bottom voltage controller 331, the error amplifier 22 of the constant current circuit 21, and the current control transistor M1 are provided in a one-chip semiconductor integrated circuit. Note that the current control transistor M1 may not be included in the semiconductor integrated circuit, but may be externally attached to the semiconductor integrated circuit.

<Description of operation>
In the bottom voltage control section 331, the bottom voltage detection section 332 detects and holds the bottom voltage of the output voltage VLED- for each ripple waveform of one cycle. The period of the ripple waveform depends on, for example, the frequency of the alternating current power supply AC. The current amplifier 334 outputs a current corresponding to the voltage difference between the held bottom voltage and the reference voltage VDref to the capacitor Crb. As a result, the reference voltage Vref of the constant current circuit 21 rises and falls as a result of the current being inserted/extracted from the capacitor Crb, and the output current Iout fluctuates, so that the bottom voltage of the output voltage VLED− converges to the balanced voltage VD.

7A and 7B are diagrams for explaining the action of the bottom voltage control in the fourth embodiment, where (A) is the change in power supplied from the primary side, (B) is the voltage change on the secondary side, and (C) is the low potential. (D) shows the change in the bottom voltage of the side output voltage, and the change in the output current, respectively.

According to the power supply device 1C of the fourth embodiment, the variation error of the circuit is, for example, as shown in FIG. Suppose an error occurs in In this case, as shown in FIG. 7B, the voltage value of the DC voltage sent to the secondary side of the transformer T0 similarly increases or decreases.

Here, if there is no control by the bottom voltage control unit 331, the output voltage VLED− on the low potential side changes in accordance with the change in the output voltage VLED+ on the high potential side, as indicated by the characteristic line A in FIG. 7(C). The bottom voltage also increases or decreases. In this case, since the output current Iout is set to a predetermined current by constant current control, the output voltage VLED− on the low potential side increases or decreases, as shown in FIGS. 1(B) and 1(C). , the loss generated in the transistor M1 increases (when the power increases), or ripples occur in the output current Iout (when the power decreases) because the ripple cannot be absorbed by the transistor M1.

However, according to the power supply device 1C of Embodiment 4, the bottom voltage of the output voltage VLED− on the low potential side is reduced to the equilibrium voltage by the control of the bottom voltage control section 331, as indicated by the characteristic line B in FIG. maintained at VD. As a result, as shown in FIG. 7(D), the current controlled by the constant current circuit 21 is increased or decreased, and the output current Iout increases or decreases according to the change in the supplied power. As a result, the current flowing through the light-emitting diode 61, which is the load, increases or decreases in accordance with changes in the power supply. Furthermore, when the current controlled by the constant current circuit 21 is optimized and the supplied power increases, the on-resistance of the transistor M1 is reduced to reduce the loss caused by the transistor M1. can obtain the effect of increasing the on-resistance of the transistor M1 and suppressing the ripple of the output current Iout.

Similarly, it is assumed that the capacitance value of the output capacitor Cout of the DC/DC converter 11 has decreased due to deterioration over time, etc., and a fluctuation such that the ripple of the converted DC voltage has increased has occurred. In such a case, if the bottom voltage control unit 331 does not control and the output current Iout is controlled to a predetermined current, ripples may occur in the output current Iout. However, since the bottom voltage control unit 331 performs control to maintain the bottom voltage, the ON resistance of the transistor M1 is increased and the output current Iout is reduced, thereby suppressing the ripple generated in the output current Iout. .

As described above, according to the power supply device 1C of Embodiment 4, by generating a DC voltage from the AC power supply AC while suppressing harmonics, even if ripples occur in the converted DC voltage, the constant current circuit 21 can sufficiently suppress the ripple of the output current Iout output to the load. Furthermore, the bottom voltage control unit 331 maintains the bottom voltage of the output voltage VLED− on the low potential side at the balanced voltage VD, so that the ripple generated in the transistor M1 of the constant current circuit 21 is suppressed while suppressing the ripple of the output current Iout. Loss can be reduced.

(Embodiment 5)
FIG. 8 is a circuit diagram showing a power supply device according to Embodiment 5 of the present invention.

A power supply device 1D according to the fifth embodiment mainly has a configuration in which a lowest potential clamp circuit 25 is added to the power supply device 1A according to the second embodiment.

The power supply device 1A of the second embodiment described above is configured to change the reference voltage Vref by inserting and extracting the current of the capacitor Cr using the two current sources I3 and I4 and the switch SW2. On the other hand, the power supply device 1D of FIG. 8 is configured to change the reference voltage Vref by inserting and extracting current from the capacitor Crb by the positive current or negative current output from the current amplifier 137D. Although these configurations are different, the action on the reference voltage Vref based on the detection result of the ripple detection circuit 132 is the same.

The lowest potential clamp circuit 25 is a circuit that clamps the reference voltage Vref so that it does not fall below a predetermined lowest value even when the reference voltage Vref of the constant current circuit 21 is controlled to drop by the bottom voltage controller 131. . The lowest potential clamp circuit 25 may be provided in one semiconductor integrated circuit together with the bottom voltage control section 131 .

For example, when the capacitance value of the output capacitor Cout of the DC/DC converter 11 is reduced due to aged deterioration or the like, the ripple of the converted DC voltage becomes large. In the power supply devices 1 to 1B of the first to third embodiments, the reference voltage Vref of the constant current circuit 21 is infinitely decreased by the bottom voltage control units 31, 131, and 231 in order to remove the ripple of the output current Iout. It changes the value. As a result, the power consumed by the transistor M1 increases and the amount of heat generated increases.

In the power supply device 1D of the fifth embodiment, even if the bottom voltage control unit 131 controls to lower the reference voltage Vref, the lowest potential clamp circuit 25 clamps it so that it does not drop below a predetermined potential. As a result, for example, even if the heat resistance temperature of the transistor M1 or its surroundings is low, the amount of heat generated by the transistor M1 can be suppressed within a predetermined range so as not to exceed the heat resistance temperature. Note that the lowest potential clamp circuit 25 can be added to the power supply devices 1 to 1B of the first to third embodiments to achieve the same effect.

(Embodiment 6)
FIG. 9 is a circuit diagram showing a power supply device according to Embodiment 6 of the present invention. A power supply device 1</b>E according to the sixth embodiment includes a rectifier circuit 2 , a DC/DC converter 11 , a transistor M<b>1 as a current control section, a current detection resistor R<b>1 , and a current control circuit 50 . A light-emitting diode 61 for lighting is connected as a load between the output terminals ta and tb of the power supply device 1E. Components that are the same as those of the first embodiment are denoted by the same reference numerals as those of the first embodiment, and detailed descriptions thereof are omitted.

The current control circuit 50 controls the output current Iout by driving the transistor M1 so that the difference between the reference voltage Vref and the source voltage V_MOS_S (current detection voltage) becomes small. Further, the current control circuit 50 detects the ripple voltage of the output current Iout based on the output voltage VLED- including the ripple voltage of the DC/DC converter 11 and the source voltage (current detection voltage) V_MOS_S indicating the magnitude of the output current. The reference voltage Vref is controlled such that the loss in the transistor M1 is reduced while the is suppressed.

Specifically, the current control circuit 50 outputs a drive signal to the capacitor Cr that holds the reference voltage Vref and a drive signal to the transistor M1 so that the difference between the reference voltage Vref and the source voltage V_MOS_S (current detection voltage) becomes small. and an amplifier 22 . Further, the current control circuit 50 includes a first current source I11 and a switch SW1 (corresponding to a first pull-up circuit) capable of pulling up the reference voltage Vref held in the capacitor Cr, and the reference voltage Vref held in the capacitor Cr. It comprises a pull-down second current source I12 and a switch SW2E (corresponding to pull-down circuit). Further, the current control circuit 50 has a reference voltage V0 generation circuit E51, a voltage dividing circuit 53 having a buffer 54 and voltage dividing resistors R51 and R52, a first comparator 51, and a second comparator 52.

The first comparator 51 compares the divided voltage V53 generated by the voltage dividing circuit 53 with the source voltage V_MOS_S, and turns on the switch SW2 when the source voltage V_MOS_S is lower than the divided voltage V53 to generate the reference voltage Vref. pull down. The second comparator 52 compares the reference voltage V0 and the output voltage VLED-, and turns on the switch SW1 to pull up the reference voltage Vref when the output voltage VLED- is higher than the reference voltage V0.

The voltage dividing circuit 53 generates a divided voltage V53 by dividing the reference voltage Vref by a predetermined voltage dividing ratio. The voltage division ratio is set to 1-(ratio of allowable ripple current to upper limit value of output current Iout). For example, if the load is lighting and the specifications of the lighting device allow a ripple of 10%, the voltage division ratio is 90%. Therefore, when the ripple current contained in the output current Iout exceeds the permissible ratio, the first comparator 51 operates to turn on the switch SW2E.

The reference voltage V0 is set in advance to a voltage value higher than the output voltage VLED- when the ripple of the output current Iout becomes zero. On the other hand, the reference voltage V0 is set to a value smaller than a certain voltage value. For example, when the output power of the DC/DC converter 11 is configured to be switchable by the dimming function, the output voltage VLED− increases immediately after the output power is largely switched. In this case, the reference voltage V0 is set to a value smaller than this increased voltage value. With this setting, the second comparator 52 operates to turn on the switch SW1 when the output power is switched by the dimming function, for example.

The voltage pull-up capability of current source I11 is higher than the voltage pull-down capability of current source I12 (for example, two times or more). That is, the amount of current flowing into the current source I11 and the amount of current drawn out from the current source I12 per unit time are larger in the former. As a result, the amount of increase in the reference voltage Vref when the switch SW1 is turned on is large, and the amount of decrease in the reference voltage Vref when the switch SW2 is turned on is reduced.

In the power supply device 1E of FIG. 9, the current control circuit 50, the transistor M1 and the current detection resistor R1 are provided in a one-chip semiconductor integrated circuit. Any or all of the current control transistor M1, the current detection resistor R1, and the voltage dividing resistors R51 and R52 may be externally attached to the semiconductor integrated circuit without being included in the semiconductor integrated circuit.

<Description of operation>
FIG. 10 is a waveform diagram for explaining the control operation of the power supply device of the sixth embodiment. FIG. 11 is a signal waveform diagram for explaining the control operation of the first comparator. FIG. 12 is a signal waveform diagram for explaining the control operation of the second comparator.

In the power supply apparatuses 1 to 1C of the first to fourth embodiments, the states of the power supply apparatuses 1 to 1D converge on the boundary between the range H1 and the range H2 in FIG. 3, depending on the change in the bottom voltage of the output voltage VLED−. Transistor M1 was being controlled. On the other hand, in the power supply device 1E of the sixth embodiment, when the source voltage V_MOS_S indicating the magnitude of the output current Iout has a slight ripple remaining in the suppressed range (for example, when a 10% ripple remains), , to fix the control of transistor M1. As a result, the state of the power supply device 1E is controlled to converge around the boundary between the range H1 and the range H2 in FIG. That is, the bottom voltage of the output voltage VLED− converges to the minimum balanced voltage VD within the range where the ripple of the output current Iout is suppressed to, for example, 10%.

Assume that the output power of the DC/DC converter 11 is switched to a large value by starting the power supply device 1E or by the dimming function. Then, the output capability of the DC/DC converter 11 increases with respect to the amount of current (reference voltage Vref) that can flow through the transistor M1, thereby increasing the output voltage VLED− (period T51, FIGS. 10 and 12). The second comparator 52 compares the output voltage VLED- and the reference voltage V0. As shown in FIG. 12, the output voltage VLED- exceeds the reference voltage V0 in the period T51. Output becomes high level. This causes the first current source I11 to pull up the reference voltage Vref. As a result of this pull-up, the state of the power supply device 1E transitions from the state of the range H2 in FIG. 3 to the state of the range H1 (the state in which ripples occur in the output current Iout). Since the capability of the first current source I11 is high, the reference voltage Vref is quickly raised.

When the reference voltage Vref increases according to the output of the DC/DC converter 11 and the amount of current that the transistor M1 can flow increases relative to the output capability of the DC/DC converter 11, ripples occur in the output current Iout and the source voltage V_MOS_S. (Period T52). As shown in FIG. 11, the first comparator 51 compares the source voltage V_MOS_S with the divided voltage V53. The divided voltage V53 is set to, for example, 90% of the reference voltage Vref. When the ripple becomes, for example, 10% or more of the upper end voltage of the source voltage V_MOS_S, the output of the first comparator 51 becomes high level. . That is, the first comparator 51 detects that there is a ripple of 10% or more. This detection causes the second current source I12 to gradually lower the reference voltage Vref.

When the reference voltage Vref drops, the amount of current that can flow through the transistor M1 becomes balanced with the output capability of the DC/DC converter 11, and the ripple of the source voltage V_MOS_S becomes smaller. That is, the state of the power supply device 1E approaches the boundary with the range H2 from the left side of the range H1 in FIG. When the magnitude of the ripple falls below 10%, the source voltage V_MOS_S does not fall below the divided voltage V53, so the output of the first comparator 51 remains low (period T53, FIG. 11). At this time, the state of the power supply device 1E is a state in which the output current Iout includes a ripple (slight ripple) in a suppressed range around the boundary between the range H1 and the range H2 in FIG.

In this state, both the output of the first comparator 51 and the output of the second comparator 52 become low level, the reference voltage Vref is fixed, and the state of the power supply device 1E is maintained. That is, the ripple of the output current Iout is suppressed and the loss of the transistor M1 is kept at a minimum.

As described above, according to the power supply device 1E of the sixth embodiment, the second comparator 52, the first current source I11 for raising the reference voltage Vref according to the comparison result of the second comparator 52, and the switch SW1 are provided. . As a result, when the power supply device 1E is started or when the output capability is increased by the dimming function, the reference voltage Vref is increased, and the state of the power supply device 1E is changed to the range H1 (see FIG. 3) where ripples occur in the output current Iout. ) can be transitioned to the state of Furthermore, according to the power supply device 1E of the sixth embodiment, the first comparator 51 that compares the divided voltage V53 of the reference voltage Vref and the source voltage V_MOS_S, and the reference voltage Vref according to the comparison result of the first comparator 51 has a second current source I12 and a switch SW2E that pulls down . As a result, when the ripple of the output current Iout becomes large, the ripple can be converged to a suppressed range. In addition, since the first comparator 51 ends the reduction of the reference voltage Vref when a small amount of ripple remains, the power supply device 1E does not operate until the range H2 (FIG. 3) where the ripple becomes zero and the loss of the transistor M1 increases. do not transition the state of Such a control operation suppresses the ripple of the output current Iout and minimizes the loss of the transistor M1.

Furthermore, according to the power supply device 1E of Embodiment 6, the capability of the first current source I11 is set higher than the capability of the second current source I12. As a result, the reference voltage Vref can be quickly raised when the power supply device 1E is activated or when the output capability is increased by the dimming function. Further, when converging the ripple of the output current Iout to the suppressed range, the reference voltage Vref can be gradually lowered, and the reference voltage Vref can be adjusted to an appropriate value.

(Embodiment 7)
FIG. 13 is a circuit diagram showing a power supply device according to Embodiment 7 of the present invention. In addition to the components of the sixth embodiment, the power supply device 1F of the seventh embodiment includes elements (dividing resistors R51a and R51b) that generate the second divided voltage V59, a third comparator 57, and a logic unit 58. , and a third current source I13 and a switch SW3 (corresponding to a second pull-up circuit) are added. Components similar to those of the sixth embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

A third current source I13 and a switch SW3 can supply current to the capacitor Cr to pull up the reference voltage Vref held in the capacitor Cr. The voltage pull-up capability of the third current source I13 is lower than the voltage pull-down capability of the current source I12 (for example, two times or more lower). That is, the amount of current drawn by the current source I12 and the amount of current injected by the current source I13 per unit time are larger in the former. As a result, the amount of increase in the reference voltage Vref when the switch SW3 is turned on can be made smaller than the amount of decrease in the reference voltage Vref when the switch SW2E is turned on.

The second voltage dividing circuit 59 generates a divided voltage V59 by dividing the reference voltage Vref with a predetermined voltage dividing ratio. The voltage division ratio of the second voltage division voltage V59 is set to be greater than the voltage division ratio of the first voltage division voltage V53. For example, the voltage division ratio of the first divided voltage V53 is set to 90%, and the voltage division ratio of the second divided voltage V59 is set to 95%.

The third comparator 57 compares the divided voltage V59 and the source voltage V_MOS_S, and outputs a high level signal when the source voltage V_MOS_S is lower than the divided voltage V59.

FIG. 14 is a circuit diagram showing an example of a configuration of a logic section; FIG. 15 is a time chart for explaining the operation of the logic section.

Based on the output of the first comparator 51 and the output of the third comparator 57, the logic unit 58 detects over-throttling when a predetermined time longer than the ripple period has passed without the output of the first comparator 51. A signal is output to turn on the switch SW3 for a predetermined time. Specifically, as shown in FIG. 15, the logic unit 58 starts counting by the timer 587 when the third comparator 57 rises, and starts counting by the timer 587 when the first comparator 51 falls. Reset. Alternatively, when the timer 587 counts the predetermined time T60, the count of the timer 587 is reset. Then, when the count value of the timer 587 exceeds a predetermined time T60 which is longer than the ripple period, an over-diaphragm detection signal is output to turn on the switch SW3 for a predetermined pulse period. The predetermined time T60 may be set to a value of about 12 ms if the ripple period is 100 Hz or 120 Hz, for example. Excessive throttling means a state in which the proportion (magnitude) of the ripple in the output current Iout is smaller than the target convergence value (for example, 10%).

For example, as shown in FIG. 14, the logic unit 58 includes a rising edge detector 581 that detects the rising edge of the output of the third comparator 57, an inverter 582 that detects the falling edge of the output of the first comparator 51, and a and a rising edge detector 583 . Further, the logic section 58 includes a flip-flop 586 that inputs the output of the rising edge detector 581 to the set terminal via an OR circuit 584, and performs a counting operation while the output of the flip-flop 586 is at a high level to count a predetermined time T60. It has a timer 587 that Further, the logic section 58 has a one-shot circuit 588 and a delay device 589 for outputting a pulse of a predetermined width when the timer 587 counts the predetermined time T60. The delay device 589 outputs a reset signal to the flip-flop 586 when the over-restriction detection signal is output, and delays the flip-flop 586 so that the set signal is output again after the reset. The output of rising edge detector 583 is input to the reset terminal of flip-flop 586 via OR circuit 585 , and the output of delay 589 is sent to two OR circuits 584 and 585 . The delay device 589 should provide a delay (for example, 100 ns) that does not make the operation of the timer 587 unstable. With such a circuit example, the operation of the logic section 58 described above can be realized.

As described above, according to the power supply device 1F of the seventh embodiment, by the same operation as in the first embodiment, the output current Iout is brought into a balanced state in which ripples (slight ripples) within a suppressed range are generated. Furthermore, according to the power supply device 1F of the seventh embodiment, after the balanced state is reached, the logic unit 58 controls the suppression of narrowing down of the reference voltage Vref. After reaching a balanced state in which the output current Iout includes a small amount of ripple, if there is some variable factor, the ripple in the output current Iout becomes smaller, which may cause a transition to a state in which the loss in the transistor M1 increases. However, if the time during which the bottom voltage of the source voltage V_MOS_S is between the second divided voltage V59 and the first divided voltage V53 becomes longer under the control of the logic unit 58, the reference voltage Vref is increased to increase the output current Iout. slightly increase the ripple of . This suppresses the magnitude of the ripple of the output current Iout from deviating from the ratio (eg, 10%) set by the first divided voltage V53. Such control makes it possible to more stably maintain the state in which the ripple of the output current Iout is suppressed and the loss of the transistor M1 is minimized.

In the power supply device 1F of the seventh embodiment, the second divided voltage V59 is generated, and the comparison result between this and the source voltage V_MOS_S is used to count the period during which there is no output from the first comparator 51. rice field. However, without providing the second divided voltage V59 and the third comparator 57, the period in which there is no high level output from the first comparator 51 is counted from the previous high level output of the first comparator 51. , based on this period, the detection of over-stopping may be similarly performed. In addition, although the logic unit 58 of the seventh embodiment employs a configuration that counts the period using the timer 587, the period can be determined using the cycle of the ripple included in the output voltage VLED− without using the timer 587. You can do it. A specific example employing these configurations is the modified example of FIG. The logic part 58 of Embodiment 7 may be changed to the logic part 58G of FIG. 16, the configuration for generating the second divided voltage V59 and the third comparator 57 are not required.

(Modification)
FIG. 16 is a circuit diagram showing a modification of the logic section. FIG. 17 is a time chart explaining the operation of the logic part of FIG.

The modified logic section 58G has two comparators 591, 592 and two one-shot circuits 593, 594 that compare the output voltage VLED− with two reference voltages V1, V2 to provide a period criterion. . The reference voltages V1 and V2 are generated by the generation circuits E61 and E62 so as to be between the bottom voltage and the top voltage of the ripple voltage generated in the output voltage VLED-. With these, two trigger signals Trg1 and Trg2 having substantially ripple cycles can be generated.

Further, the logic unit 58G has a one-shot circuit 595 that detects the rise of the output of the first comparator 51 and outputs a trigger signal Trg3, and inputs the trigger signal Trg3 to the set terminal and inputs the trigger signal Trg1 to the reset terminal. and a flip-flop 596 that As a result, when there is a high level output from the first comparator 51, the flip-flop 596 can output the ripple detection signal DR' overlapping with the trigger signal Trg2.

Further, the logic section 58G has a D flip-flop 597 that receives the ripple detection signal DR' at its D terminal and the trigger signal Trg2 at its clock terminal. As a result, the D flip-flop 597 can maintain the detection result as to whether or not there is a high level output from the first comparator 51 during one ripple period using the trigger signal Trg2 as a clock signal. As a result, the D flip-flop 597 outputs the ripple detection hold signal DR'_H in which the above detection result is maintained (maintained for the period of the ripple period) and the ripple detection hold signal DR'_HB which is the inversion thereof. .

Further, the logic section 58G has an AND circuit 598 that receives the trigger signal Trg1 and the ripple detection hold signal DR'_HB at its two input terminals, and outputs an over-diaphragm detection signal from the AND circuit 598.

According to the logic section 58G configured as described above, the operation of each section described above generates a signal as shown in FIG. If not, an over-aperture signal is output. Then, the over-throttling signal causes the reference voltage Vref to rise slightly and the ripple of the output current Iout to slightly increase. This suppresses the amount of ripple in the output current Iout from deviating from the ratio (for example, 10%) set by the first divided voltage V53. Such control makes it possible to more stably maintain the state in which the ripple of the output current Iout is suppressed and the loss of the transistor M1 is minimized.

Each embodiment of the present invention has been described above. However, the invention is not limited to the above embodiments. For example, in the above embodiment, an example is shown in which the output terminal tb on the low potential side (drain voltage of the transistor M1) is applied as the first potential point at which the DC voltage including ripple is output from the voltage conversion circuit. However, the first potential point according to the present invention may be set anywhere on the current path of the output current from the high potential side output section of the voltage conversion circuit to the current control section. Further, in the above embodiment, an example is shown in which the source voltage V_MOS_S is applied as the current detection voltage indicating the magnitude of the output current. However, the current detection voltage is not limited to this, and if a current detection element (such as a current detection resistor) is provided at another location on the output current path, the current detection voltage may be input from there. good. For example, in the above embodiments, the constant current circuit has the current detection resistor R1. However, the constant current circuit may be configured to omit the current detection resistor R1 and use loads connected to the output terminals ta and tb instead of the current detection resistor R1 to generate the current detection voltage. Further, in the above embodiment, the first to third comparators are explained as comparators, but the configuration may be such that differential circuits or logic circuits are combined for comparison.

Further, in the above-described embodiment, an example in which the present invention is applied to a power supply device that drives a light-emitting diode is shown, but the power supply device according to the present invention is also applicable to a power supply device that drives an organic EL (Electro Luminescence) element for lighting. In addition, it may be applied to a power supply device that drives any load that consumes a constant current. Also, as the DC/DC converter, various modifications such as a forward converter or a non-isolated buck-boost converter can be applied. In addition, the configurations specifically shown in the embodiments, such as the type of current control transistor and the configuration of the variation addition unit that adds variation to the current value controlled by the current circuit, can be changed as appropriate without departing from the spirit of the invention. is.

1, 1A, 1B, 1C, 1D, 1E, 1F power supply device 2 rectifier circuit 11 DC/DC converter 14 control circuit 21 constant current circuit 22... error amplifier, 25... lowest potential clamp circuit, 31, 131, 231, 331... bottom voltage control section, 32, 232... loss detection circuit, 33, 134... bottom detection section , 34, 35... Voltage holding unit 36, 135... Subtractor 37, 137... Comparator 61... Light emitting diode 132, 233... Ripple detection circuit 133... Peak Detector 137D, 235, 334 Current amplifier 234 Error calculator 236 Voltage source 332 Bottom voltage detector 333 Reference circuit AC Alternating current Power supply, Cout... output capacitor, Cr, Crb... capacitor, T0... transformer, M0... switching element, M1... transistor (current control unit), R1... current detection resistor, SW1 , SW2... switch, ta, tb... output terminal, I1 to I4, I11 to I13... current source, Iout... output current, Vref... reference voltage, VD... balance voltage, VDref...reference voltage, VLED+, VLED-...output voltage, V_MOS_S...source voltage, 50...current control circuit, SW1, SW2E, SW3...switches, 51...first comparator , 52... second comparator, 57... third comparator, 53, 59... voltage dividing circuit, 58, 58G... logic section, 587... timer

Claims (12)

a voltage conversion circuit that generates a DC voltage from an AC power supply and outputs the DC voltage between a pair of output terminals;
a current control unit provided on a first current path through which an output current flows and controlling the current in the first current path;
a voltage at a first potential point set on a path from a high-potential-side output section of the voltage conversion circuit to the current control section in the first current path; and a current detection voltage indicating magnitude of the output current. a current control circuit that drives the current control unit so as to suppress ripples occurring in the output current based on;
with
The current control circuit is
a voltage holding unit that holds a reference voltage;
a differential circuit that outputs a drive signal to the current controller so that the difference between the reference voltage and the current detection voltage is reduced;
a pull-down circuit capable of pulling down the reference voltage;
a first voltage dividing circuit that divides the reference voltage to generate a first divided voltage;
a first comparator that compares the first divided voltage and the current detection voltage and causes the reduction circuit to reduce the reference voltage when the current detection voltage is lower than the first divided voltage;
A power supply device comprising: 2. The power supply device according to claim 1, wherein the current control circuit drives the current control unit so that the bottom voltage of the ripple voltage at the first potential point converges to a minimum equilibrium voltage. . The current control circuit is
a first pull-up circuit capable of pulling up the reference voltage;
A second comparison for comparing a predetermined reference voltage with the voltage at the first potential point, and causing the first pull-up circuit to pull up the reference voltage when the voltage at the first potential point is higher than the reference voltage. vessel and
3. The power supply device according to claim 1 or 2 , characterized by comprising: the reference voltage is higher than the voltage at the first potential point at which the ripple of the output current is zero;
4. The power supply device according to claim 3 , wherein the voltage dividing ratio of said first voltage dividing circuit is set to 1-(ratio of magnitude of allowable ripple current to upper limit value of said output current). 5. The power supply device according to claim 3 , wherein the voltage pull - down capability of the pull-down circuit is lower than the voltage pull-up capability of the first pull-up circuit. The current control circuit is
a second pull-up circuit capable of pulling up the reference voltage with a capability lower than the voltage pull-down capability of the pull-down circuit;
a logic unit that causes the second pull-up circuit to pull up the reference voltage when the period during which the current detection voltage does not fall below the first divided voltage exceeds a predetermined period;
6. The power supply device according to any one of claims 1 to 5 , further comprising: The current control circuit is
a second pull-up circuit capable of pulling up the reference voltage with a capability lower than the voltage pull-down capability of the pull-down circuit;
a logic unit that causes the second pull-up circuit to pull up the reference voltage when a period during which the current detection voltage does not fall below the first divided voltage exceeds a predetermined period;
a second voltage dividing circuit that divides the reference voltage and generates a second divided voltage that is higher than the first divided voltage;
a third comparator that compares the second divided voltage and the current detection voltage;
further comprising
The logic unit
Based on the comparison result of the second comparator and the comparison result of the third comparator, it is determined whether the current detection voltage falls below the first divided voltage after the current detection voltage falls below the second divided voltage. 4. The power supply device according to claim 3 , wherein said second pull-up circuit pulls up said reference voltage when said non-current period exceeds a predetermined period. a voltage conversion circuit that generates a DC voltage from an AC power supply and outputs the DC voltage between a pair of output terminals;
a current control unit provided on a first current path through which an output current flows and controlling the current in the first current path;
a voltage at a first potential point set on a path from a high-potential-side output section of the voltage conversion circuit to the current control section in the first current path; and a current detection voltage indicating magnitude of the output current. a current control circuit that drives the current control unit so as to suppress ripples occurring in the output current based on;
with
The current control circuit is
a voltage holding unit that holds a reference voltage;
a differential circuit that outputs a drive signal to the current controller so that the difference between the reference voltage and the current detection voltage is reduced;
a bottom voltage control unit that inputs the voltage at the first potential point as a detection voltage and controls the reference voltage based on comparison of the detection voltages at different timings;
has
A power supply device , wherein the current control unit is driven such that the bottom voltage of the ripple voltage at the first potential point converges to a minimum voltage, ie, an equilibrium voltage . The current control circuit is
9. The power supply device according to claim 8 , further comprising a variation adding section that adds variation to the reference voltage held by said voltage holding section. The power supply device according to any one of claims 1 to 9 , wherein a lighting device is connected between the pair of output terminals. It is installed in a power supply device having a voltage conversion circuit that generates a DC voltage from an AC power supply and outputs the DC voltage between a pair of output terminals, and drives a current control unit that can control the current of the current path through which the output current flows. A semiconductor integrated circuit,
a differential circuit that outputs a drive signal to the current controller so that the difference between the reference voltage and the current detection voltage indicating the magnitude of the output current is reduced;
a first comparator that compares a first divided voltage obtained by dividing the reference voltage with the current detection voltage and reduces the reference voltage when the current detection voltage is lower than the first divided voltage;
comparing a voltage at a first potential point set on a current path through which the output current flows from the high-potential-side output section of the voltage conversion circuit to the current control section with a predetermined reference voltage; a second comparator for increasing the reference voltage when the voltage at the first potential point is higher than the reference voltage;
A semiconductor integrated circuit comprising: In a power supply device having a voltage conversion circuit that generates a DC voltage from an AC power supply and outputs the DC voltage between a pair of output terminals, driving a current control unit capable of controlling a current in a current path through which the output current flows, A ripple suppression method for suppressing ripple generated in an output current,
while outputting a drive signal to the current control unit so that the difference between the current detection voltage indicating the magnitude of the output current and the reference voltage becomes small;
comparing a first divided voltage obtained by dividing the reference voltage with the current detection voltage, and decreasing the reference voltage when the current detection voltage is lower than the first divided voltage;
comparing a voltage at a first potential point set on a current path through which the output current flows from the high-potential-side output section of the voltage conversion circuit to the current control section with a predetermined reference voltage; and increasing the reference voltage when the voltage at the first potential point is higher than the reference voltage.

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