JP2004328950A - Switching constant current power supply device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a switching constant current power supply device in which load current can be stabilized even under the condition that the current flowing to a load (e.g., a display unit, etc. including an LED) repeats an intermittence. <P>SOLUTION: A voltage detector circuit 7 for generating a voltage signal in response to the output voltage of a power converter circuit 3 is provided at the output side of the power converter circuit 3. Further, a feedback circuit 8 is provided between a current detector circuit 5 for generating a first feedback signal in response to the load current and a control circuit 4 for driving the power converter circuit 3. Here, the feedback circuit 8 has a signal holding means 9 for outputting a second feedback signal generated by referring to the voltage signal at a certain time point. The feedback circuit 8 supplies a first feedback signal output from the current detector circuit 5 to the control circuit 4 when the load current flows, and supplies a second feedback signal output from a signal holding means 9 to the control circuit when the load current does not flow. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a switching type constant current power supply device for supplying a stable current to a load that is repeatedly turned on and off.
[0002]
[Prior art]
Generally, a switching type power supply device is often used as a constant voltage source for supplying a stable voltage to a load. However, the switching type power supply can be used as a constant current source that supplies a substantially constant current to the load by connecting and configuring as shown in FIG. 4 and making the feedback signal correspond to the output current. It is.
In FIG. 4, 1 is an input terminal for receiving power supply from an external battery or the like, and 2a and 2b are output terminals for stably supplying a predetermined current to a load 6 connected therebetween. A power conversion circuit 3 is connected between the input terminal 1 and one output terminal 2a. The power conversion circuit 3 is configured such that the choke coil L1, the switching transistor Q1, the rectifier diode D1, and the smoothing capacitor C1 are connected to form a boost chopper converter. I have.
[0003]
A current for detecting a current flowing through the load 6 (hereinafter, referred to as a load current) between the other output terminal 2b and the ground as a reference potential point of the circuit and generating a feedback signal corresponding to the load current. The detection circuit 5 is connected. A control circuit 4 for receiving a feedback signal from the current detection circuit 5 and driving the power conversion circuit 3 according to the level of the feedback signal is connected between the power conversion circuit 3 and the current detection circuit 5. ing. (Here, it is assumed that the control circuit 4 is a control IC of a general common PWM control system.)
The power conversion circuit 3, the control circuit 4, and the detection circuit 5 form a switching constant current power supply. The element C0 connected between the input terminal 1 and the ground is an input filter capacitor.
[0004]
The operation of the switching constant current power supply device of FIG. 4 will be briefly described. The switching transistor Q1 in the power conversion circuit 3 turns on and off according to a signal supplied from the control circuit 4. (The frequency of the ON / OFF operation is about several hundred kHz.) With the ON / OFF operation of the switching transistor Q1, a current flows from the choke coil L1 to the smoothing capacitor C1 via the rectifier diode D1. As a result, the smoothing capacitor C1 is charged to a voltage higher than the input voltage supplied to the input terminal 1, and a current corresponding to the voltage between the terminals of the capacitor C1 flows through the load 6 and the current detection circuit 5. Then, a feedback signal corresponding to the load current is generated in the current detection circuit 5, and the signal is fed back to the control circuit 4.
[0005]
The feedback signal provided from the current detection circuit 5 to the control circuit 4 is not at a level according to the output voltage as in a normal switching power supply, but at a level according to the output current (= load current). Therefore, the control circuit 4 generates an on-duty pulse-like signal according to the feedback signal (= load current) according to the internal control logic, and supplies it to the switching transistor Q1. Then, the switching transistor Q1 turns on and off with an on-duty corresponding to the magnitude of the load current. For example, when the load current is lower than the stabilization target value, the voltage across the terminals of the smoothing capacitor C1 is increased. Induce the load current to increase. As a result of such an operation, the load current is stabilized in the device of FIG.
[0006]
By the way, display devices and lighting devices of various sizes are mounted on electronic devices in recent years, and light-emitting diodes (hereinafter, referred to as LEDs) are increasingly used as light sources of the display devices and lighting devices. When an LED is used as a light source, it is required to stabilize the current supplied to the LED in order to make the amount of light emitted, the luminance, and the like constant. Therefore, in recent electronic devices, a switching constant-current power supply device as shown in FIG. 4 is provided in association with a display device or a lighting device, and a stable current is supplied from the power supply device to the LED. There were things. (See Patent Documents 1 to 3)
[0007]
[Patent Document 1]
JP-A-11-068161 [Patent Document 2]
JP 2001-215913 A [Patent Document 3]
JP-A-2002-203988
[Problems to be solved by the invention]
Some display devices and lighting devices that use LEDs as light sources in recent years repeatedly turn on and off LEDs at a speed (specifically, several hundred Hz) that cannot be recognized by the human eye to reduce power consumption and dimming. There is something we do. In such a display device or a lighting device, a period during which a current flows through the LED (hereinafter, referred to as a current flowing period) and a period during which no current flows (hereinafter, referred to as a current blocking period) naturally occur. Then, when a power supply for supplying a current to the LED is a switching constant current power supply device as shown in FIG. 4, the current is supplied from the current detection circuit 5 to the control circuit 4 during a current cutoff period caused by a load interruption. The feedback signal becomes almost zero level.
[0009]
The control circuit 4 supplied with such a feedback signal tries to set the on-duty of the on / off operation of the switching transistor Q1 to the maximum during the current cutoff period, and turns on the on / off operation according to the feedback signal during the next current flowing period. Try to set duty. Here, when the on-duty becomes maximum during the current cutoff period, the voltage between the terminals of the smoothing capacitor C1 increases rapidly and more than necessary, and during the next load current flow period, the voltage exceeds the stabilization target value for a relatively long time. , A load current flows.
[0010]
As one of measures against such load current instability, for example, it is conceivable that the feedback signal is smoothed by a capacitor having a relatively large capacity and then supplied to the control circuit 4. However, if a large-capacity capacitor capable of maintaining the feedback signal at a significant level during the current interruption period is provided, the feedback signal processed by the control circuit 4 has an average value over a relatively long period. For this reason, when the load current fluctuates due to aperiodic load interruption or a cause other than the interruption, the load current that deviates from the stabilization target value cannot be quickly returned to the target value. As a result, the load current becomes unstable due to a cause different from the current interruption period.
[0011]
As described above, when the power supply device having the configuration shown in FIG. 4 is used, under the condition that the load is interrupted, the control circuit 4 passes through the switching transistor Q1, the smoothing capacitor C1, the load 6, and the current detection circuit 5 again to control the control circuit 4. There is a possibility that the response speed of the feedback loop control operation cannot follow the change in load, and the load current cannot be stabilized.
Therefore, an object of the present invention is to provide a switching constant current power supply device capable of stabilizing a load current even under a condition where a load repeats intermittently.
[0012]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a switching type power conversion circuit for supplying a predetermined current to a load, a current / current detection circuit for generating a first feedback signal corresponding to a load current, and a first feedback In a switching constant current power supply device including a control circuit that drives a power conversion circuit so as to stabilize a load current according to a signal, a voltage detection circuit that generates a voltage signal according to an output voltage of the power conversion circuit; A signal holding unit provided between the detection circuit and the control circuit for outputting a second feedback signal generated with reference to the voltage signal, and the first feedback signal according to the load state; And a feedback circuit for supplying one of the second feedback signal to the control circuit.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
In a switching constant current power supply device including a power conversion circuit that supplies a stable current to a load, a control circuit that drives the power conversion circuit, and a current detection circuit that generates a first feedback signal according to the load current, A feedback circuit is provided between the current detection circuit and the control circuit, and a voltage detection circuit that generates a voltage signal corresponding to the output voltage is provided on the output side of the power conversion circuit. Here, the feedback circuit includes a signal holding unit that outputs a second feedback signal. When a load current is flowing, the feedback circuit supplies a first feedback signal output by the current detection unit to the control circuit, and the load current is When the signal does not flow, the second feedback signal output from the signal holding means is supplied to the control circuit. The second feedback signal is generated with reference to the voltage signal of the voltage detection circuit, and the signal level in the maintained state is the first feedback signal when the specified load current flows through the load. It is set to be a value larger than the signal.
[0014]
In a switching constant current power supply device incorporating such a feedback circuit, when a load current is flowing, the feedback circuit supplies the first feedback signal to the control circuit, thereby stabilizing the load current as in the conventional circuit. To work.
On the other hand, when a load current is not flowing, the switching constant current power supply device incorporating such a feedback circuit provides an operation (= switching) of the power conversion circuit by supplying the second feedback signal to the control circuit. (On / off operation of the transistor). This prevents the voltage between terminals of the smoothing capacitor from unnecessarily increasing during the current interruption period under the condition that the load is interrupted.
[0015]
【Example】
FIG. 1 shows the basic configuration of a switching constant current power supply according to the present invention.
The switching constant current power supply device shown in the block diagram of FIG. 1 includes a voltage detection circuit 7 formed by a series circuit of resistors R1 and R2 between one output terminal 2a and ground, and further includes a control circuit 4 and a current detection circuit. 5 is substantially the same as the conventional circuit shown in FIG. The feedback circuit 8 shown in FIG. 1 is roughly divided into a signal holding means 9 for outputting a second feedback signal, and one of the first feedback signal output from the current detection circuit 5 and the second feedback signal. To the control circuit 4. Here, the selection means 10 is switched in accordance with the state of the load 6 (in other words, the operation of turning on and off the LED).
[0016]
In the switching constant current power supply device having such a feedback circuit 8, when a load current is flowing, the first feedback signal output from the current detection circuit 5 is supplied to the control circuit by the selecting means 10 in the feedback circuit 8. 4 selectively. In this state, the power supply device of FIG. 1 operates exactly the same as the conventional circuit of FIG. 4 to stabilize the load current.
Here, the signal holding means 9 in the feedback circuit 8 refers to the voltage signal output from the voltage detection circuit 7 while the load current is flowing, and generates a predetermined signal for generating the second feedback signal. The operation of is performed.
[0017]
On the other hand, when the load current is not flowing, the second feedback signal output from the signal holding means 9 is selectively supplied to the control circuit 4 by the selection means 10.
Here, the second feedback signal has a signal level higher than that of the first feedback signal, and the control circuit 4 which has received the supply of the second feedback signal turns on / off the switching transistor Q1 (= power conversion circuit). 3) is stopped.
When the operation of the switching transistor Q1 is stopped in this way, the voltage between the terminals of the smoothing capacitor C1 does not increase during the current cutoff period, and an inconvenient phenomenon that a load current equal to or more than the stabilization target value flows during the next current circulation period. No longer occurs. As a result, the load current can be stabilized even when the load repeats intermittently.
[0018]
FIG. 2 shows a first embodiment of a switching constant current power supply according to the present invention.
The circuit of FIG. 2 has basically the same configuration as that of the circuit of FIG. 1, but a feedback circuit 8 which is a main part of the present invention is configured as follows.
A sample-and-hold circuit 11 and a sampling signal generation circuit 12 are provided, and are connected so that a sampling signal is supplied from the sampling signal generation circuit 12 to the sample-and-hold circuit 11. The connection is made so that a voltage signal is supplied from the voltage detection circuit 7 to the sample hold circuit 11, and the sampling signal generation circuit 12 is connected so that a signal corresponding to the state of the load 6 is supplied. The output terminal of the sample and hold circuit 11 is connected to one connection terminal a of a changeover switch SW that is switched in synchronization with the state of the load 6.
[0019]
The common terminal c of the changeover switch SW is connected to the control circuit 4, and the other connection terminal b is connected to the output terminal of the error amplifier EA. One input terminal of the error amplifier EA is connected to the current detection circuit 5, and the other input terminal is connected to a common connection point of the resistors R3 and R4 connected in series between the output terminal of the error amplifier EA and the ground.
Here, the sample and hold circuit 11 and the sampling signal generation circuit 12 correspond to the signal holding circuit 9 in FIG. 1, and the changeover switch SW corresponds to the selection means 10 in FIG. Note that the circuit portion of the error amplifier EA and the resistors R3 and R4 is merely an amplifier circuit for setting the signal level of the first feedback signal to a level that can be processed by the control circuit 4.
[0020]
In the feedback circuit 8 shown in FIG. 2, when a load current is flowing, the changeover switch SW linked to the state of the load 6 is switched to the connection terminal b side. Therefore, the feedback circuit 8 selectively supplies the first feedback signal amplified by the error amplifier EA to the control circuit 4 after being output from the current detection circuit 5.
Here, upon detecting a state in which the load current is flowing from the input signal, the sampling signal generation circuit 12 outputs a pulse-like sampling signal to the sample and hold circuit 11 at a predetermined timing. Upon receiving this sampling signal, the sample hold circuit 11 resets the signal output up to that point, refers to the voltage signal output from the voltage detection circuit 7 at this time, and determines the signal level corresponding to the voltage signal. A second feedback signal is newly generated. Note that the signal level of the second feedback signal is maintained until the next sampling signal is supplied.
[0021]
When the state of the load 6 is switched to a state where no load current flows, the changeover switch SW is switched to the connection terminal a side. Therefore, the feedback circuit 8 selectively supplies the second feedback signal output from the sample and hold circuit 11 to the control circuit 4. Here, since the second feedback signal is set to have a signal level higher than that of the first feedback signal, the control circuit 4 having received the supply of the second feedback signal controls the on / off operation of the switching transistor Q1. Will be stopped.
By the operation of the feedback circuit 8, the power supply device of FIG. 2 can stabilize the load current even when the load repeats, like the power supply device of FIG.
[0022]
FIG. 3 shows a second embodiment of the switching constant current power supply device according to the present invention.
In the circuit of FIG. 3, the feedback circuit 8 has a configuration in which a peak hold circuit 13 is provided in place of the sample and hold circuit 11 in FIG. 2, and a reset signal generation circuit 14 is provided in place of the sampling signal generation circuit 12. Therefore, the operation of the feedback circuit 8 shown in FIG. 3 is slightly different from that of the feedback circuit 8 shown in FIG.
[0023]
That is, the reset signal generation circuit 14 outputs a pulse-like reset signal to the peak hold circuit 13 at a predetermined timing when detecting a state in which the load current is flowing from the input signal. When receiving the reset signal, the peak hold circuit 13 resets the signal output up to that time. However, as soon as the reset signal pulse disappears, the second feedback signal having a signal level corresponding to the voltage signal is generated by referring to the voltage signal output from the voltage detection circuit 7. Then, the signal level of the second feedback signal is updated to a value corresponding to the maximum value of the voltage signal newly generated after the reset, and is maintained until the next reset signal is supplied.
[0024]
When the state of the load 6 is switched to a state where no load current flows, the changeover switch SW is switched to the connection terminal a side. Therefore, the feedback circuit 8 selectively supplies the second feedback signal output from the peak hold circuit 13 to the control circuit 4. Here, if the second feedback signal is set to have a higher signal level than the first feedback signal, the control circuit 4 receiving the supply of the second feedback signal stops the on / off operation of the switching transistor Q1. become. Therefore, finally, the power supply device of FIG. 3 performs the same operation as that of the power supply device of FIG. 2, and can stabilize the load current even when the load repeats intermittently.
[0025]
In the circuit of FIG. 3, the second feedback signal may be set to have a signal level substantially equal to that of the first feedback signal. The control circuit 4 receiving the supply of the second feedback signal having the same signal level as the first feedback signal continues the on / off operation of the switching transistor Q1 immediately after the current cutoff period. However, the second feedback signal output from the peak hold circuit 13 increases as the voltage between the terminals of the smoothing capacitor C1 increases. Therefore, when the second feedback signal exceeds a predetermined level, the control circuit 4 stops the on / off operation of the switching transistor Q1, and prevents the voltage across the smoothing capacitor C1 from further increasing.
Thus, in the circuit of FIG. 3, it is not always necessary to set the signal level of the second feedback signal to be higher than the signal level of the first feedback signal.
[0026]
In the above description of each embodiment of the switching constant current power supply device according to the present invention, the power conversion circuit 3 is assumed to be a boost chopper type circuit, and the control circuit 4 is assumed to be a separately excited PWM type control IC. The switching constant current power supply to which the invention is applied is not limited to this. The current detection circuit 5 and the voltage detection circuit 7 may also use a detection method other than the resistance detection, and it goes without saying that a specific circuit configuration can be modified as long as the gist of the present invention is not changed. There is no.
[0027]
【The invention's effect】
As described above, the switching constant current power supply according to the present invention includes the voltage detection circuit that generates the voltage signal according to the output voltage of the power conversion circuit, and generates the first feedback signal according to the load current. And a feedback circuit for selectively supplying one of the first feedback signal and the second feedback signal to the control circuit according to the load state between the current detection circuit and the control circuit for driving the power conversion circuit. Provide a circuit. Here, the second feedback signal is generated in the signal holding means inside the feedback circuit with reference to the voltage signal of the voltage detection circuit, and has a higher signal level than the first feedback signal. The control circuit that receives the supply of the second feedback signal during a period in which no current flows through the load stops the operation of the power return circuit.
[0028]
According to the present invention, the voltage between the terminals of the smoothing capacitor does not increase during the current interruption period, and the situation where the response speed of the current control operation of the feedback loop cannot follow the load fluctuation is prevented. As a result, it is possible to provide a switching constant current power supply that can stabilize the load current even when the load is interrupted.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a basic configuration of a switching constant current power supply device according to the present invention.
FIG. 2 is a block diagram showing a first embodiment of a switching constant current power supply device according to the present invention.
FIG. 3 is a block diagram showing a second embodiment of the switching constant current power supply according to the present invention.
FIG. 4 is a circuit diagram of an example of a conventional switching constant current power supply device.
[Explanation of symbols]
1: input terminal 2a, 2b: output terminal 3: power conversion circuit 4: control circuit 5: current detection circuit 6: load (load that repeats intermittent) 7: voltage detection circuit 8: feedback circuit 9: signal holding means 10: selection Circuit 11: Sample hold circuit 12: Sampling signal generation circuit 13: Peak hold circuit 14: Reset signal generation circuit

Claims (6)

A switching type power conversion circuit for supplying a predetermined current to a load, a current detection circuit for generating a first feedback signal according to the load current, and stabilizing the load current according to the first feedback signal. A switching constant current power supply device having a control circuit for driving the power conversion circuit,
A voltage detection circuit that generates a voltage signal according to the output voltage of the power conversion circuit;
A signal holding means is provided between the current detection circuit and the control circuit and outputs a second feedback signal generated with reference to the voltage signal, and the signal holding means is provided in accordance with a load state. A feedback circuit that supplies one of the first feedback signal and the second feedback signal to the control circuit;
A switching constant current power supply device comprising: The signal holding unit generates the second feedback signal larger than the first feedback signal generated when a prescribed load current flows through the load with reference to the voltage signal at a certain time, and During the period, when the load current is flowing, the feedback circuit supplies the first feedback signal to the control circuit, and when the load current is not flowing, the feedback circuit supplies the second feedback signal to the control circuit. The switching constant-current power supply according to claim 1, wherein the switching constant-current power supply is supplied to a control circuit. The switching circuit according to claim 2, wherein the control circuit substantially stops the operation of the power conversion circuit while the second feedback signal in a state where the signal level is maintained is supplied. Constant current power supply. 4. The switching constant current power supply device according to claim 1, wherein said signal holding means includes a sample hold circuit and a sampling signal generation circuit. 4. The switching constant current power supply according to claim 1, wherein the signal holding means includes a peak hold circuit and a reset signal generation circuit. The switching constant current power supply device according to any one of claims 1 to 5, wherein the load includes a light emitting diode element that repeats blinking at a high speed.

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