JP2012253876A - Load driving device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a load driving device that supplies stable pulse current to a load even when the electrical characteristic of the load varies in a process of repeating supply and interception of current flowing through the load.SOLUTION: Under a main feedback control state, the output voltage of a load (first feedback voltage VFB1) is selected, the output of a reference voltage circuit 14 (first reference voltage VR) is selected, a power conversion circuit 3 is driven so as to reduce the difference between the first feedback voltage VFB1 and the first reference voltage VR, and a signal holding circuit 13 continues to sample the output of a voltage detection circuit 9 (second feedback voltage VFB2). Under an auxiliary feedback control state, the signal holding circuit 13 holds and outputs the second feedback voltage sampled under the main feedback control state (second reference voltage VFB2'), selects a second feedback voltage VFB2, selects the second reference voltage VFB2' and drives the power conversion circuit 3 so as to reduce the difference between the second feedback voltage VFB2 and the second reference voltage VFB2'.

Description

  The present invention relates to a load driving device.

2. Description of the Related Art In recent years, light emitting elements such as LEDs that are widely used as new light sources are required to maintain a stable luminance by flowing a stable current. Therefore, for example, there is a load driving device that realizes stable brightness of an LED by repeatedly energizing or interrupting the current flowing in the LED to control an average current flowing in the LED (generally called PWM control). Several proposals have been made.
[Conventional example 1]
FIG. 7 is a diagram showing the configuration of the load driving device of Conventional Example 1 disclosed in Patent Document 1. In FIG.

  First, the configuration of the load driving device shown in FIG. 7 will be described. The load driving device shown in FIG. 7 connects an input terminal 1 to which a DC voltage is applied from the outside and both ends of a load 6 (for example, a light emitting element such as an LED) to supply a predetermined current or voltage to the load 6. Output ends 2a and 2b. Furthermore, the load driving device shown in FIG. 7 includes a switch SW1, a power conversion circuit 3, a PWM control circuit 4, a feedback voltage generation circuit 5, and a feedback voltage switching circuit 7.

  The switch SW1 is provided for interrupting or conducting (PW) a current flowing through the load 6 (hereinafter referred to as a load current).

  The power conversion circuit 3 includes a coil L1 and a rectifier diode D1 connected in series between the input terminal 1 and the output terminal 2a, and a smoothing connected to the transistor Q1 and the cathode terminal connected to the anode terminal of the rectifier diode D1. And a booster type power conversion circuit including a capacitor C1.

  The PWM control circuit 4 includes an error amplifier EA1, a reference voltage source VR1, and a drive circuit DR. The voltage of the reference voltage source VR1 and the output of the feedback voltage switching circuit 7 (first feedback voltage VFB1 or second feedback voltage VR2). Is generated as an error signal VE (= α · (VFB1-VR1) or α · (VR2-VR1)), and a pulsed PWM signal for driving the transistor Q1 based on the error signal VE Create a VP.

  The feedback voltage generation circuit 5 detects a load current and generates a first feedback voltage VFB1 corresponding to the load current.

  The feedback voltage switching circuit 7 includes a fixed signal generation circuit 8 for generating a second feedback voltage VR2 fixed at a certain voltage level, and a first feedback voltage VFB1 or a fixed signal output from the feedback voltage generation circuit 5. A switch SW20 connected to one of the second feedback voltages VR2 output from the generation circuit 8 is provided. An input filter capacitor C0 is connected between the input terminal 1 and the coil L1.

  Next, the technical significance of the load driving device shown in FIG. 7 will be described. First, if the feedback voltage switching circuit 7 is not taken into consideration, a negative feedback control system is formed that makes the first feedback voltage VFB1 corresponding to the load current equal to the voltage of the reference voltage source VR1. A light emitting element such as an LED is used as the load 6. In order to adjust the luminance of the light emitting element, the switch SW1 performs duty control for adjusting a ratio (duty ratio) between an on period and an off period. When the switch SW1 is in the on state, the load driving device shown in FIG. 7 performs negative feedback control so that the reference voltage source VR1 and the first feedback voltage VFB1 are equal. On the other hand, when the switch SW1 is turned off, the load 6 connected between the output terminal 2a and the other output terminal 2b is released from the load driving device, and the negative feedback control system is in an open loop state. It becomes. In this case, the voltage of the first feedback voltage VFB1 is lowered and becomes smaller than the reference voltage source VR1. As a result, the on-duty of the transistor Q1 (the ratio of the on-period to the switching cycle) is increased, and control is performed to increase the voltage of the output terminal 2a. Therefore, if this state is left as it is, the transistors Q1, Defects such as the smoothing capacitor C1, the switch SW1, etc. exceeding the withstand voltage occur.

  Therefore, in the load driving device shown in FIG. 7, the feedback voltage switching circuit 7 is provided, and the connection of the switch SW20 of the feedback voltage switching circuit 7 is switched in conjunction with the on / off state of the switch SW1. . Specifically, when the switch SW1 is in the on state, the switch SW20 is connected to the first feedback voltage VFB1, so that the negative feedback control system is in a closed loop state. On the other hand, when the switch SW1 is in the OFF state, the switch SW20 is connected to the second feedback voltage VR2. The second feedback voltage VR2 is set as a fixed signal having a voltage level that is substantially the same as the reference voltage source VR1 or higher than the reference voltage source VR1. Therefore, when the switch SW1 is switched from the on state to the off state, the switch SW20 is connected to the second feedback voltage VR2 that is higher than the voltage of the reference voltage source VR1, and therefore the output of the PWM control circuit 4 gradually decreases. Eventually it becomes zero. As a result, the power conversion circuit 3 is stopped so that the transistor Q1 remains off, and the voltage increase at the output terminal 2a can be prevented.

[Conventional example 2]
FIG. 8 is a diagram showing a configuration of a load driving device of Conventional Example 2 disclosed in Patent Document 2. In FIG.

  First, the configuration of the load driving device shown in FIG. 8 will be described. The load driving device shown in FIG. 8 is different from the load driving device shown in FIG. 7 in that a voltage detection circuit 9 is newly provided and the configuration of the feedback voltage switching circuit 7 is different. The voltage detection circuit 9 is configured by connecting resistors R1 and R2 in series between the power conversion circuit 3 and the output terminal 2a, and generates a voltage detection signal corresponding to the output voltage of the power conversion circuit 3. The feedback voltage switching circuit 7 includes a differential amplifier EA2, a sample hold circuit 11, a sampling signal generation circuit 12, and a switch SW21. The first feedback voltage VFB1 corresponding to the load current is connected from the feedback voltage generation circuit 5 to the non-inverting input terminal of the differential amplifier EA2, and the output terminal of the differential amplifier EA2 is connected to the inverting input terminal of the differential amplifier EA2. A common connection point of resistors R3 and R4 connected in series is connected between the reference potential and the reference potential. A signal corresponding to the state of the load 6 (the presence or absence of load current) is supplied to the sampling signal generation circuit 12, a sampling signal is supplied from the sampling signal generation circuit 12 to the sample hold circuit 11, and sampling is performed from the feedback voltage switching circuit 7. A voltage detection signal is supplied to the hold circuit 11. The second feedback voltage VFB2 output from the sample hold circuit 11 is connected to one connection end a of the switch SW21, and the first connection amplified by the differential amplifier EA2 is connected to the other connection end b of the switch SW21. The feedback voltage VFB1 ′ is connected, and the output terminal c of the switch SW21 is connected to the PWM control circuit 4. The switch SW21 has an output terminal c connected to one connection terminal a (first feedback voltage VFB1 ′) when the switch SW1 is in an ON state, and the output terminal c connected to the other connection terminal when the switch SW1 is in an OFF state. It is configured to be connected to b (second feedback voltage VFB2).

  Next, the technical significance of the load driving device shown in FIG. 8 will be described. First, when the switch SW1 is in the ON state, the first feedback voltage VFB1 'is input to the PWM control circuit 4 from the differential amplifier EA2 via the switch SW21, and the negative feedback control system is in a closed loop state. Thus, control is performed so that the first feedback voltage VFB1 'becomes equal to the voltage of the reference voltage source VR1 of the PWM control circuit 4. In this case, the sample hold circuit 11 repeats sampling of the voltage detection signal detected by the voltage detection circuit 9. On the other hand, when the switch SW1 is switched to the OFF state, the sample hold circuit 11 holds the voltage detection signal detected by the feedback voltage switching circuit 7 and serves as the second feedback voltage VFB2 via the switch SW21 and the PWM control circuit 4. Output to. Here, the second feedback voltage VFB2 is set as having a voltage level higher than the first feedback voltage VFB1 when a predetermined current flows through the load 6 when the switch SW1 is in the ON state. Yes. Therefore, when the switch SW1 is switched from the on state to the off state, the power conversion circuit 3 is stopped by the second feedback voltage VFB2, and an increase in the voltage at the output terminal 2a can be prevented.

Japanese Patent No. 3747036 Japanese Patent No. 3747037

  The load driving circuit of Conventional Example 1 shown in FIG. 7 has the following problems.

  When the switch SW1 is switched from the off state (the negative feedback control system is in the open loop state) to the on state again (the negative feedback control system is in the closed loop state), the power conversion circuit 3 outputs the output terminal up to the voltage required for the load 6. It is necessary to increase the voltage of 2a. For this reason, it takes some time until a predetermined current flows through the load 6 by the switching operation of the power conversion circuit 3 after the switch SW1 is turned on again. Note that the period during which the power conversion circuit 3 performs the switching operation is limited to a state in which the switch SW1 is turned on and the first feedback voltage VFB1 is selected by the switch SW20. Here, when the on-duty (the ratio of the on-period) of the switch SW1 is very small, the power conversion circuit 3 cannot supply a sufficient voltage to the load 6, and a predetermined current cannot flow through the load 6. For example, when an LED is used as the backlight of the liquid crystal display device, the on-duty of the switch SW1 is on the order of several us.

  In addition to the method of setting the second feedback voltage VR2 of the fixed signal generation circuit 8 as a fixed signal having a voltage level larger than that of the reference voltage source VR1, the voltage of the output terminal 2a when the switch SW1 is in the OFF state However, even if the second feedback voltage VR2 of the fixed signal generation circuit 8 is set to a certain voltage so that the voltage of the output terminal 2a when the switch SW1 is in the ON state is maintained, the voltage rise of the output terminal 2a Can be prevented. Thereby, after the switch SW1 is switched to the ON state again, the necessary voltage is already supplied to the load 6, and a predetermined current can be quickly supplied to the load 6.

  However, when the electrical characteristics of the load 6 fluctuate due to external factors such as temperature, the voltage required to flow a predetermined current through the load 6 fluctuates. For example, it is assumed that the temperature generated by the LED rises and the forward voltage of the LED fluctuates as the switch SW1 is turned on and the current driving of the LED used as the backlight of the liquid crystal television advances. Here, for example, when the electrical characteristics of the load 6 fluctuate and the voltage necessary for flowing a predetermined current through the load 6 increases, the load 6 is switched to the load 6 when the switch SW1 is turned on again. Some time is required until a predetermined current flows. In particular, when the on-duty of the switch SW1 is very small, current may not flow through the load 6.

  On the other hand, when the electrical characteristics of the load 6 fluctuate and the voltage required to cause a predetermined current to flow through the load 6 is further reduced, when the switch SW1 is turned on again, the output terminal 2a Since this voltage becomes higher than necessary, an excessive current flows through the load 6.

  As described above, in the conventional example 1 shown in FIG. 7, the operation of the power conversion circuit 3 when the switch SW1 is in the OFF state varies depending on the setting of the second feedback voltage VR2. When the switch SW1 is switched from the OFF state to the ON state, the voltage at the output terminal 2a when the switch SW1 is OFF is the same as that when the switch SW1 is ON. The second feedback voltage VR2 must be set to a certain voltage so as to be maintained at the voltage of the output terminal 2a. However, in the conventional example 1 shown in FIG. 7, when the electrical characteristics of the load 6 fluctuate, the level of the second feedback voltage VR2 cannot follow the fluctuation, so the switch SW1 is turned off. When switching from ON to ON again, there is a problem that it is difficult to quickly supply a predetermined current to the load 6.

  The load driving circuit of the second conventional example shown in FIG. 8 has the following problems.

  When the switch SW1 is changed from the off state (the negative feedback control system is in the open loop state) to the on state again (the negative feedback control system is in the closed loop state), the power conversion circuit 3 reaches the voltage required by the load 6 by the switching operation. Since it is necessary to increase the voltage of the output terminal 2a, it takes some time until a predetermined current flows through the load 6. The period during which the power conversion circuit 3 performs the switching operation is only when the switch SW1 is turned on and the first feedback voltage VFB1 'is selected by the switch SW21. In particular, when the on-duty of the switch SW1 is very small, the power conversion circuit 3 cannot supply a sufficient voltage to the load 6 and cannot flow a predetermined current to the load 6.

  Further, the voltage detection circuit 9 is adjusted so that the voltage at the output terminal 2a when the switch SW1 is in the off state is maintained at the voltage at the output terminal 2a when the switch SW1 is in the on state, thereby adjusting the second feedback voltage VFB2. Even when the level is set, the voltage rise of the output terminal 2a can be prevented. In this case, when the switch SW1 is in the off state, the power conversion circuit 3 performs a switching operation, and the voltage at the output terminal 2a maintains the same voltage as when the switch SW1 is in the on state (the negative feedback control system is in the closed loop state). To do. Thereafter, when the switch SW1 is turned on again, a necessary voltage is supplied to the load 6 and a predetermined current can be supplied to the load 6 quickly.

  However, when the electrical characteristics of the load 6 vary due to external factors such as temperature, the voltage to be supplied to the load 6 varies. For example, when the electrical characteristics of the load 6 fluctuate and the voltage necessary for flowing a predetermined current through the load 6 increases, the power conversion circuit 3 is turned on when the switch SW1 is turned on again from the off state. The voltage of the output terminal 2a must be increased to a necessary voltage by the switching operation, and it takes some time until a predetermined current flows through the load 6 after the switch SW1 is turned on. In particular, when the switch SW1 has a small on-duty, no current flows through the load 6.

  On the other hand, when the electrical characteristics of the load 6 fluctuate and the voltage required to pass a predetermined current through the load 6 decreases, the output terminal 2a is switched when the switch SW1 is turned on again from the off state. Since the voltage becomes higher than necessary, an excessive current flows through the load 6.

  Therefore, the present invention was made to solve such a problem, and even when the electrical characteristics of the load fluctuate in the process of repeatedly energizing or interrupting the current flowing through the load, An object of the present invention is to provide a load driving device capable of supplying a stable pulse current to a load.

  In order to solve the above problems, a load driving apparatus according to an aspect of the present invention supplies power to a load channel in which a load and a current driving circuit element that supplies current to the load are connected in series. And a power conversion circuit configured to convert and output input power into a form according to the load, a reference voltage circuit configured to generate and output a predetermined reference voltage, and the power A voltage detection circuit configured to detect and output a voltage according to the output voltage of the conversion circuit; a signal holding circuit configured to hold and output the voltage detected by the voltage detection circuit; When the current is flowing through the load, the main feedback control state is established. When no current is flowing through the load, the auxiliary feedback control state is established, and the feedback voltage and the voltage corresponding to the main feedback control state or the auxiliary feedback control state are obtained. An error amplifier that amplifies a difference from a comparison voltage; and a negative feedback control circuit configured to drive the power conversion circuit so as to reduce the difference based on an error signal output from the error amplifier. In the main feedback control state, the negative feedback control circuit selects a voltage (hereinafter referred to as a first feedback voltage) applied to the current drive circuit element as the feedback voltage and outputs the reference voltage circuit as the comparison voltage ( Hereinafter, the first reference voltage) is selected, the power conversion circuit is driven so as to reduce the difference between the first feedback voltage and the first reference voltage, and the signal holding circuit is the voltage detection circuit. Output (hereinafter referred to as second feedback voltage) is continuously sampled, and the auxiliary feedback control state is the first sampled when the signal holding circuit is in the main feedback control state. 2, and the negative feedback control circuit selects the second feedback voltage as the feedback voltage and uses the second reference voltage as the comparison voltage. And the power conversion circuit is driven to reduce the difference between the second feedback voltage and the second reference voltage.

  In the load driving device, a first switching unit configured to energize or interrupt a current flowing through the load in the load channel, and one of the first feedback voltage and the second feedback voltage to be input. And a second switching unit configured to output to the one input terminal of the error amplifier, and whether to input the second feedback voltage from the voltage detection circuit to the signal holding circuit. A third switching unit configured to be switched, and one of the first reference voltage and the second reference voltage to be input is selected and output to the other input terminal of the error amplifier. A fourth switching unit, wherein the main feedback control state controls the first switching unit to energize the current flowing through the load, and the first feedback voltage The second switching unit is controlled to select and output to one input terminal of the error amplifier, and the second feedback voltage is input from the voltage detection circuit to the signal holding circuit. 3 and controlling the fourth switching unit to select and output the first reference voltage to the other input terminal of the error amplifier, and the auxiliary feedback control state is: The first switching unit is controlled so as to cut off a current flowing through the load, and the second switching unit is selected so as to select and output the second feedback voltage to one input terminal of the error amplifier. Controlling the third switching unit so that the second feedback voltage is not input from the voltage detection circuit to the signal holding circuit, and selecting the second reference voltage to select the error amplifier. The fourth switching unit may be controlled to output to the other input terminal.

  According to this configuration, when a current flows through the load, negative feedback control (main feedback control state) is performed such that the first feedback voltage is set to a voltage that is substantially equal to the first reference voltage. At this time, the first reference voltage of the reference voltage circuit is set so that the first feedback voltage becomes a voltage such that the load has an appropriate constant current characteristic. As a result, negative feedback control is performed so that the first feedback voltage, and thus the output voltage of the power conversion circuit, is an appropriate voltage, and stable current driving can be performed for the load 6. In the main feedback control state, the signal holding circuit continues to sample the second feedback voltage output from the voltage detection circuit.

  On the other hand, when no current flows through the load, negative feedback control (auxiliary feedback control state) is performed so that the second feedback voltage is substantially equal to the second reference voltage. Here, the second reference voltage is a voltage holding the output of the voltage detection circuit in a state before switching to a state in which no current flows to the load (main feedback control state). This voltage follows the fluctuation of electrical characteristics. By performing negative feedback control so that the second feedback voltage and the second reference voltage are substantially equal, the output voltage of the power conversion circuit in the main feedback control state is maintained even in the auxiliary feedback control state. ing. Therefore, when the current flows again through the load, the output voltage of the power conversion circuit is maintained at the voltage in the previous main feedback control state, so that the first feedback voltage is such that the load has an appropriate constant current characteristic. Immediate transition to voltage. As a result, a predetermined current can be quickly passed through the load.

  As described above, even when the electrical characteristics of the load fluctuate in the process of repeatedly energizing or interrupting the current flowing through the load, it is possible to flow a predetermined pulse current that is stable to the load.

  In the load driving device, the current driving circuit element may be a constant current source, and the load channel may be plural.

  In the load driving device, the negative feedback control circuit enters the main feedback control state when a current flows through at least one of the loads of the plurality of load channels, and The auxiliary feedback control state may be set when no current flows through all the loads.

  In the load driving device, the negative feedback control circuit selects a minimum voltage among the voltages applied to the constant current sources of the plurality of load channels as the first feedback voltage in the main feedback control state. It may be configured.

  In the load drive device, a load, a first switching unit configured to energize or cut off a current flowing through the load based on a current drive command, a detection terminal that detects an output voltage of the load, and A second switching circuit configured to switch whether or not to input the second feedback voltage from the voltage detection circuit to the signal holding circuit for a plurality of load channels including a constant current source in this order. And the first reference voltage and the second reference voltage are input, and one of the first reference voltage or the second reference voltage is selected and output to one input terminal of the error amplifier. The third switching unit configured as described above and the first feedback voltage or the second feedback voltage are input, and one of the first feedback voltage or the second feedback voltage is selected and the error is selected. amplifier A fourth switching unit configured to output to the other input terminal; the current drive command for each of the plurality of load channels; and the load detected at the detection terminal of each of the plurality of load channels. The output voltage is input, and the voltage when the current is flowing through the load among the output voltages of the plurality of loads based on the plurality of current drive commands is detected and the minimum voltage is detected. A minimum value detection circuit configured to output as a first feedback voltage, and the negative feedback control circuit selects the first reference voltage in the main feedback control state to select the error amplifier. The second switching unit is controlled to output to one input terminal of the first amplifier, and the third switching unit is selected to output the first feedback voltage to one input terminal of the error amplifier by selecting the first feedback voltage. System And the fourth switching unit is controlled such that the second feedback voltage is input from the voltage detection circuit to the signal holding circuit, and in the auxiliary feedback control state, the signal is output from the voltage detection circuit. The third switching unit is controlled so that the second feedback voltage is not input to the holding circuit, and the second reference voltage is selected and output to the other input terminal of the error amplifier. And the fourth switching unit may be controlled so that the second feedback voltage is selected and output to one input terminal of the error amplifier.

  According to this configuration, when current flows to any one of the loads of the plurality of load channels, the negative feedback control (main feedback control state) is performed so that the first feedback voltage is approximately equal to the first reference voltage. ) Is performed. The first reference voltage of the reference voltage circuit is set so that the minimum voltage among the detection end voltages of each of the plurality of load channels is an appropriate voltage that causes the constant current source to have an appropriate constant current characteristic. Thus, negative feedback control is performed so that the minimum voltage (and the output voltage of the power conversion circuit) among the voltages at the plurality of detection terminals becomes an appropriate voltage.

  If negative feedback control is performed so that the minimum voltage among the plurality of detection terminal voltages is an appropriate voltage, the voltages of the other load channels are necessarily larger than the appropriate voltages. Generally, a constant current source has stable constant current characteristics when a voltage higher than the minimum necessary bias voltage is applied. Therefore, if the minimum voltage detected by the minimum value detection circuit is an appropriate voltage, In other load channels, stable current driving is realized. At this time, the signal holding circuit repeats sampling of the second feedback voltage output from the voltage detection circuit.

  Next, when current does not flow through all of the loads of each of the plurality of load channels, negative feedback control is performed so that the second feedback voltage is approximately equal to the second reference voltage. Here, the second reference voltage holds a voltage corresponding to the output voltage of the power conversion circuit when a current flows through one of the loads of each of the plurality of load channels (main feedback control state). Therefore, the second feedback voltage and the second reference voltage are substantially equal to each other, so that the power conversion circuit in a state where the current flows to one of the loads of the plurality of load channels (main feedback control state). The output voltage is maintained. When the current flows again to one of the loads of each of the plurality of load channels (main feedback control state), the output voltage of the power conversion circuit is maintained at the voltage in the main feedback control state. The voltage at the end can quickly shift to a voltage at which the constant current source has an appropriate constant current characteristic, and as a result, a predetermined current can be quickly supplied to the load.

  As described above, in the case of a plurality of load channels, in the process of repeatedly energizing or interrupting the current flowing through the load of each of the plurality of load channels (including the case where all are interrupted), the electrical characteristics of the plurality of loads are Even when it fluctuates, a stable pulse current can flow through the load of each of the plurality of load channels.

  In the load driving device, a load, a detection terminal that detects an output voltage of the load, a first switching unit configured to energize or cut off a current flowing through the load based on a current driving command, A second switching circuit configured to switch whether or not to input the second feedback voltage from the voltage detection circuit to the signal holding circuit for a plurality of load channels including a constant current source in this order. A third switching unit configured to select one of the input first reference voltage or the second reference voltage and output the selected one to the one input terminal of the error amplifier; The load output voltage detected at the detection end of each load channel and the second feedback voltage output from the voltage detection circuit are input, and the plurality of load channels are input. When a current is flowing through any one of the loads, a minimum voltage that is a voltage when a current flows through the load is detected from a plurality of output voltages of the loads. A minimum value detection circuit configured to output as the first feedback voltage and to output the second feedback voltage when current does not flow through all the loads of each of the plurality of load channels. The negative feedback control circuit controls the second switching unit to select and output the first feedback voltage to one input terminal of the error amplifier in the main feedback control state; The third switching unit is controlled so that the second feedback voltage is input from the voltage detection circuit to the signal holding circuit, and in the auxiliary feedback control state, the second feedback voltage is selected and the second feedback voltage is selected. One input of the error amplifier The second switching unit may be controlled to output to the end, and the third switching unit may be controlled so that the second feedback voltage is not input from the voltage detection circuit to the signal holding circuit. .

  According to this configuration, when a current flows through one of the loads of each of the plurality of load channels, the minimum value detection circuit outputs the voltage at each of the plurality of detection terminals and the second feedback output from the voltage detection circuit. The minimum voltage is detected. Since the second feedback voltage output from the voltage detection circuit is set to have a value slightly larger than the voltages at the plurality of detection terminals, the minimum value detection circuit is eventually configured to have a plurality of detection voltages. The minimum voltage of the end voltages is detected.

  In addition, the voltage at the detection end corresponding to the load channel in which the first switching unit is off is raised to almost the same voltage as the output voltage of the power conversion circuit because no current flows through the corresponding load. The voltage is higher than the voltage at the detection end corresponding to the load channel in which the first switching unit is on. Therefore, the first feedback voltage output from the minimum value detection circuit is the minimum voltage among the voltages at the detection end corresponding to the load channel in which the first switching unit is turned on. For this reason, the minimum value detection circuit does not require a circuit configuration for identifying the voltage at the detection end corresponding to the load channel in which the first switching unit is on. There is no need to enter it.

  Note that negative feedback control (main feedback control state) is performed so that the first feedback voltage is approximately equal to the first reference voltage. By setting the first reference voltage of the reference voltage circuit so that the minimum voltage among the plurality of detection end voltages becomes a voltage at which the corresponding constant current source has an appropriate constant current characteristic, Negative feedback control is performed so that the minimum voltage of the detection end voltages is an appropriate voltage. In addition, when the minimum voltage among the voltages at the plurality of detection terminals is subjected to negative feedback control to an appropriate voltage, the voltages of the other load channels are necessarily larger than the appropriate voltages. In general, the constant current source has a stable constant current characteristic when a voltage higher than the minimum necessary bias voltage is applied, so that stable current driving is realized also for other load channels. Note that the signal holding circuit continues to sample the second feedback voltage output from the voltage detection circuit.

  Next, when the current does not flow to all of the loads of each of the plurality of load channels, the signal holding circuit performs the second operation when the current flows to any one of the loads of the plurality of load channels (main feedback control state). The feedback voltage is held and output. In this case, since no current flows in all the loads of the plurality of load channels, the voltages at the plurality of detection terminals are raised to almost the same voltage as the output voltage of the power conversion circuit. Therefore, since the second feedback voltage output from the voltage detection circuit is the minimum voltage, the signal output from the minimum value detection circuit is eventually the second feedback voltage VFB2 output from the voltage detection circuit. It becomes. As described above, when the current does not flow through all the loads of the plurality of load channels, the second feedback voltage is automatically output from the minimum value detection circuit, and thus the fourth switching unit may be omitted. It is possible.

  At this time, negative feedback control is performed so that the second feedback voltage is substantially equal to the second reference voltage. Here, the second reference voltage holds a voltage corresponding to the output voltage of the power conversion circuit in the main feedback control state. Therefore, in the auxiliary feedback control system, the output voltage of the power conversion circuit in the main feedback control state is maintained when the second feedback voltage and the second reference voltage are substantially equal.

  Further, when the main feedback control state is entered again, the output voltage of the power conversion circuit is maintained at the voltage in the previous main feedback control state, so that the constant current source has an appropriate constant current characteristic for the voltage at the detection end. Immediate transition to voltage. As a result, a predetermined current can be quickly passed through all the loads.

  As described above, even when the electrical characteristics of the load fluctuate in the process of repeatedly energizing or interrupting the current flowing through the load of each of the plurality of load channels (including the case where all of the currents are interrupted), a stable pulse current in the load Can flow. In addition, since the fourth switching unit and the like can be omitted, the circuit configuration can be simplified.

  In the load driving device, the load may be a light emitting element.

  According to this configuration, for example, a stable pulse current can be supplied to an LED channel used for a backlight of a liquid crystal television.

  According to the present invention, a stable pulse current can be supplied to a load even when the electrical characteristics of the load fluctuate in the process of repeatedly energizing or interrupting the current flowing through the load.

FIG. 1 is a circuit diagram showing a configuration example of a load driving device according to Embodiment 1 of the present invention. FIG. 2 is a diagram showing a logic example applied to each switch shown in FIG. FIG. 3 is a circuit diagram showing another configuration example of the load driving apparatus according to Embodiment 1 of the present invention. FIG. 4 is a circuit diagram showing a configuration example of the load driving device according to Embodiment 2 of the present invention. FIG. 5 is a diagram showing a logic example applied to each switch shown in FIG. FIG. 6 is a circuit diagram showing a configuration example of a load driving device according to Embodiment 3 of the present invention. FIG. 7 is a circuit diagram showing a configuration of the load driving device of the first conventional example. FIG. 8 is a circuit diagram showing a configuration of the load driving device of the second conventional example.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In the following description, the same or corresponding elements are denoted by the same reference symbols throughout the drawings, and redundant description thereof is omitted.
(Embodiment 1)
[Configuration example]
FIG. 1 is a circuit diagram showing a configuration example of a load driving device according to Embodiment 1 of the present invention.

  The load driving device shown in FIG. 1 has an input terminal 1 to which a DC power supply voltage is applied from the outside, one connection terminal 30 for connecting both ends of a load 6 (for example, a light emitting element such as an LED), and the other connection. An end 31, an output end 20 of the power conversion circuit 3 for supplying current to the load 6, and a detection end 21 for detecting a feedback voltage (first feedback voltage VFB 1) corresponding to the output of the load 6. I have. The output end 20 and one connection end 30 may be shared. In addition, a connection end for externally attaching the coil L1 and the smoothing capacitor C1 may be provided.

  1 is a negative feedback including a power conversion circuit 3, a voltage detection circuit 9, a signal holding circuit 13, a reference voltage circuit 14, an error amplifier 15, a PWM modulation circuit 16, and a control unit 19. A control circuit 160, a constant current source 40, a switch SW1, a switch SW11, a switch SW12, and a switch SW13 are provided. In the load driving device shown in FIG. 1, for example, the configuration excluding the coil L1, the smoothing capacitor C1, the load 6, and the constant current source 21 is integrated on one semiconductor chip, and the coil L1, the smoothing capacitor C1, and the load are integrated on the semiconductor chip. 6. The constant current source 21 is externally provided. Similar to the configuration of the load driving device shown in FIGS. 7 and 8, an input filter capacitor C0 may be connected between the input terminal 1 and the coil L1.

  The power conversion circuit 3 is a boost type power conversion circuit configured to output a voltage higher than the power supply voltage applied to the input terminal 1 to one connection terminal 20. For example, the power conversion circuit 3 includes a coil L1 and a rectifier diode D1 connected in series between the input end 1 and one connection end 30, and a transistor Q1 and a cathode end connected to the anode end of the rectifier diode D1. And a smoothing capacitor C1 connected, and is configured to change the voltage at one connection end 20 by changing the on-duty (the ratio of the on-period occupying the switching period) of the transistor Q1.

  The voltage detection circuit 9 is configured to output a voltage (second feedback voltage VFB2) corresponding to the voltage of the output terminal 20 (output voltage of the power conversion circuit 3). For example, the voltage detection circuit 9 connects two resistors in series between the output terminal 20 and the reference potential, and the voltage obtained by dividing the voltage appearing at the output terminal 20 by the two resistors is the second voltage. Is output as the feedback voltage VFB2.

  The signal holding circuit 13 is configured to continue sampling the voltage detected by the voltage detection circuit 9 and to hold (hold) the voltage when the switch SW12 is OFF.

  The reference voltage circuit 14 is configured to output a first reference voltage VR having a predetermined level.

  The error amplifier 15 is output from the first feedback voltage VFB1 or the second feedback voltage VFB2 input to the inverting input terminal and the output of the signal holding circuit 13 or the reference voltage circuit 14 input to the non-inverting input terminal. An error signal VE obtained by amplifying the difference from the first reference voltage VR is output.

  The negative feedback control circuit 160 controls the entire load driving device, and includes the PWM modulation circuit 16 and the control unit 19. The PWM modulation circuit 16 generates a pulse-shaped PWM signal VP having a constant cycle for driving the transistor Q1 based on the error signal VE output from the error amplifier 15. For example, the PWM modulation circuit 16 is realized by a triangular wave generation circuit that generates a triangular wave signal, and a comparator that generates a PWM signal VP by comparing the triangular wave signal and the error signal EA output from the error amplifier 15. . The control unit 19 controls switching of switches SW1, SW11, SW12, and SW13, which will be described later, and is realized by, for example, a logic circuit.

  The constant current source 40 is a current drive circuit element that supplies current to the load 6 and is configured to output a predetermined current.

  The switch SW1 switches between the other connection end 31 of the load 6 and the detection end 21 for detecting the first feedback voltage VFB1 in order to switch whether or not the current generated by the constant current source 40 is supplied to the load 6. It is provided in between. For example, the switch SW1 is constituted by a single pole single throw (1 circuit 1 contact) switch. A predetermined current can be supplied to the load 6 by turning on / off the switch SW1 at a certain period (for example, 120 Hz or 240 Hz), and an average current amount flowing through the load 6 can be changed by changing the on-duty of the switch SW1. Can be adjusted.

  The switch SW11 is configured to switch the first feedback voltage VFB1 of the detection terminal 21 or the second feedback voltage VFB2 of the voltage detection circuit 9 as a signal to be input to the inverting input terminal of the error amplifier 15. For example, the switch SW11 is composed of a single-pole double-throw (one circuit and two contacts) switch having a common contact and two contacts, and the common contact is connected to the inverting input terminal of the error amplifier 15, and two contacts are provided. Among them, one contact is connected to the detection end 1, and the other contact is connected to the voltage detection circuit 9.

  The switch SW12 is provided between the output terminal (second feedback voltage VFB2) of the voltage detection circuit 9 and the input terminal of the signal holding circuit 13, and the output terminal of the voltage detection circuit 9 is connected to the input terminal of the signal holding circuit 13. It is configured to switch whether or not to connect. For example, the switch SW12 is configured by a single pole single throw (one circuit, one contact) switch.

The switch SW13 switches the output of the signal holding circuit 13 (second feedback voltage VFB2) or the first reference voltage VR output from the reference voltage circuit 14 as a signal to be input to the non-inverting input terminal of the error amplifier 15. It is configured.
[Operation example]
The operation of the load driving device shown in FIG. 1 will be described based on the logic applied to each switch shown in FIG.

  First, when the switch SW1 is on, the switch SW11 is connected to the detection terminal 21 (first feedback voltage VFB1), the switch SW12 is turned on, and the switch SW13 is output from the reference voltage circuit 14 (first reference voltage VR). Connected with. At this time, the first feedback voltage VFB1 is input from the detection terminal 21 to the inverting input terminal of the error amplifier 15, and the first reference voltage output from the reference voltage circuit 14 is input to the non-inverting input terminal of the error amplifier 15. The voltage VR is input.

  At this time, the error amplifier 15 outputs an error signal EA obtained by amplifying the difference (= VR−VFB1) between the first reference voltage VR and the first feedback voltage VFB1. The PWM modulation circuit 16 PWM-modulates the error signal EA output from the error amplifier 7 and amplifies the current, and then outputs the current signal to the control electrode of the transistor Q1, and the difference between the first reference voltage VR and the first feedback voltage VFB1. The transistor Q1 is driven in accordance with the on-duty according to. The power conversion circuit 3 performs voltage control based on the on-duty of the transistor Q1. That is, when the first feedback voltage VFB1 is higher than the first reference voltage VR, the on-duty of the transistor Q1 is increased to raise the voltage at the output terminal 20. On the other hand, when the first feedback voltage VFB1 is smaller than the first reference voltage VR, the on-duty of the transistor Q1 is reduced to lower the voltage at the output terminal 20.

  Note that the voltage at the detection end 21 also changes in the same manner as the voltage change at the output end 20. As a result, negative feedback control is performed such that the voltage at the detection terminal 21 is made approximately equal to the first reference voltage VR. Here, the first reference voltage VR of the reference voltage circuit 14 is set so that the voltage of the detection terminal 21 becomes a voltage that allows the constant current source 40 to have an appropriate constant current characteristic. As a result, negative feedback control is performed so that the voltages at the detection end 21 and the output end 20 become appropriate voltages, and a stable current drive can be performed on the load 6. On the other hand, the voltage detection circuit 9 outputs a second feedback voltage VFB2 obtained by dividing the voltage of the output terminal 20 by a certain voltage division ratio. The signal holding circuit 13 continues to sample the second feedback voltage VFB2 output from the voltage detection circuit 9.

  The control state of the load driving device as described above is referred to as a “main feedback control state”.

  On the other hand, when the switch SW1 is turned off, the switch SW11 is connected to the second feedback voltage VFB2 output from the voltage detection circuit 9, the switch SW12 is turned off, and the switch SW13 is connected to the output of the signal holding circuit 13. The At this time, the signal holding circuit 13 has a second feedback voltage VFB2 (hereinafter referred to as a second reference voltage) output from the voltage detection circuit 9 in a state (main feedback control state) before the switch 12 is switched from on to off. (Referred to as VFB2 ′) and output toward the non-inverting input terminal of the error amplifier 15. The second feedback voltage VFB2 output from the voltage detection circuit 9 is input to the inverting input terminal of the error amplifier 15. The error amplifier 15 outputs an error signal EA obtained by amplifying the difference between the second reference voltage VFB2 'and the second feedback voltage VFB2.

  The PWM modulation circuit 16 performs PWM modulation on the error signal EA output from the error amplifier 15 and amplifies the current, and then outputs the amplified signal to the control electrode of the transistor Q1 to output the second reference voltage VFB2 ′ and the second feedback voltage VFB2. The transistor Q1 is driven according to the on-duty corresponding to the difference between the two. When the second feedback voltage VFB2 is larger than the second reference voltage VFB2 ', the on-duty of the transistor Q1 is increased to raise the voltage at the output terminal 20. On the other hand, when the second feedback voltage VFB2 is smaller than the second reference voltage VFB2 ', the on-duty of the transistor Q1 is reduced to lower the voltage at the output terminal 20. Similarly, the second feedback voltage VFB2 changes according to the voltage change of the output terminal 20. In this way, negative feedback control is performed so that the second feedback voltage VFB2 is substantially equal to the second reference voltage VFB2 '.

  Here, as described above, the second reference voltage VFB2 ′ is a voltage obtained by dividing the voltage of the output terminal 20 in the state before the switch SW1 is switched from the on state to the off state (main feedback control state). Is a voltage that holds Therefore, when the switch SW1 is switched from on to off, the second feedback voltage VFB2 and the second reference voltage VFB2 ′ are substantially equal to each other, so that the main feedback control state when the switch SW1 is in the on state The voltage at the output terminal 20 is maintained. Furthermore, when the switch SW1 is switched from the off state to the on state again, the voltage at the output terminal 20 is maintained at the voltage when the switch SW1 was previously in the on state (main feedback control state). The voltage immediately shifts to a voltage at which the constant current source 40 has an appropriate constant current characteristic. As a result, a predetermined current can be passed through the load 6 quickly.

  The control state of the load driving device as described above is referred to as “auxiliary feedback control state”.

  In this way, even when the electrical characteristics of the load 6 fluctuate in the process of repeatedly turning on and off the switch SW1, a stable predetermined pulse current can flow through the load 6.

[Modification]
FIG. 3 is a circuit diagram showing a modification of the load driving device according to Embodiment 1 of the present invention. The only difference is that the constant current source 40 is changed to a resistor 41 in the configuration of the load driving device shown in FIG. This configuration also has the same effect.

  Besides the configuration in which the switch SW1 is connected between the load 6 and the constant current source 40, the same effect can be obtained even if the position of the switch SW1 is changed as long as the load current can be energized or cut off.

  The same effect can be obtained by omitting the switch SW1 and driving the constant current source 40 so that the current value of the constant current source 40 becomes zero to cut off the load current.

  The switch SW1 and the other switches SW11, SW12, SW13 can be semiconductor switches such as MOS transistors.

  Alternatively, the switches SW11, SW12, and SW13 are not necessarily provided as long as the main feedback control state or the auxiliary feedback control state can be switched depending on the load current state.

The power conversion circuit 3 may be a step-down or step-up / step-down power conversion circuit in addition to the step-up power conversion circuit.
(Embodiment 2)
FIG. 4 is a circuit diagram showing a configuration example of the load driving device according to Embodiment 2 of the present invention.

  The load driving device shown in FIG. 4 includes constant current sources 40a, 40b, 40c, and 40d for four load channels as compared with the configuration of the load driving device shown in FIG. In addition to this, the load 6, the constant current source 40, the switch SW1, the connection terminals 30, 31 and the detection terminal 21 shown in FIG. 1 correspond to four load channels, respectively, and correspond to each of the four load channels. The difference is that a minimum value detection circuit 17 is newly provided for the purpose of stable driving of all the constant current sources 40a, 40b, 40c, and 40d.

  Loads 6a, 6b, 6c and 6d, constant current sources 40a, 40b, 40c and 40d, switches SW1a, SW1b, SW1c and SW1d, and detection terminals 21a, 21b, 21c and 21d are the load 6 and constant current shown in FIG. Since they have functions similar to those of the source 40, the switch SW1, and the detection end 21, detailed descriptions thereof are omitted. In addition, since the constituent elements denoted by the same reference numerals as those in FIG. 1 have the same functions as those shown in FIG. 1, their descriptions are omitted.

  The minimum value detection circuit 17 receives the voltages of the detection terminals 21a, 21b, 21c, and 21d and the current drive commands Pa, Pb, Pc, and Pd for the constant current sources 40a, 40b, 40c, and 40d, respectively. The current drive commands Pa, Pb, Pc, and Pd are commands that substantially turn on and off the switches SW1a, SW1b, SW1c, and SW1d. Based on the current drive commands Pa, Pb, Pc, and Pd, the minimum value detection circuit 17 has the switches SW1a, SW1b, SW1c, and SW1d turned on (main feedback) among the voltages at the detection terminals 21a, 21b, 21c, and 21d. The minimum voltage is detected from among the voltages in the control state), and is output to the switch SW11 as the first feedback voltage VFB1. When only one load channel is turned on, the minimum value detection circuit 17 outputs the voltage at the detection end corresponding to the turned-on load channel as the minimum voltage.

  The reason why the voltages at the detection terminals 21a, 21b, 21c, and 21d are different from each other is when the voltages required for the loads 6a, 6b, 6c, and 6d vary. For example, when LEDs are used as the loads 6a, 6b, 6c, and 6d, the voltages necessary for flowing a predetermined current through the loads 6a, 6b, 6c, and 6d differ from each other due to variations in forward voltage of the LEDs. Is the case.

The logic gate 18 is provided in the negative feedback control circuit 160 and receives current drive commands Pa, Pb, Pc, Pd, and performs a predetermined logic operation according to the logic applied to each switch shown in FIG. The predetermined logical operation is, for example, an active low 4-input AND gate or an active high 4-input OR gate. Note that the connections of the switches SW11 and SW13 are switched by the output of the logic gate 18. Specifically, the switch SW11 is connected to the first feedback voltage VFB1 output from the minimum value detection circuit 17 or the second feedback voltage VFB2 output from the voltage detection circuit 9 according to the output of the logic gate 18. It is configured to be. The switch SW13 is connected to the first reference voltage VR output from the reference voltage circuit 14 or the second reference voltage VFB2 ′ held in the signal holding circuit 13 according to the output of the logic gate 18. It is configured as follows.
[Operation example]
The operation of the load driving device shown in FIG. 4 will be described based on the logic applied to each switch shown in FIG.

  Connections of the switches SW1a, SW1b, SW1c, SW1d, SW11, SW12, and SW13 shown in FIG. 4 are set as shown in FIG. 5 according to the output of the logic gate 18.

  First, when any of the switches SW1a, SW1b, SW1c, and SW1d is on, the switch SW11 is connected to the output of the minimum value detection circuit 17 (first feedback voltage VFB1), the switch SW12 is turned on, and the switch SW13 is the reference The output of the voltage circuit 14 (first reference voltage VR) is connected. At this time, the first reference voltage VR output from the reference voltage circuit 14 is input to the non-inverting input terminal of the error amplifier 15, and the first value output from the minimum value detection circuit 17 is input to the inverting input terminal of the error amplifier 15. 1 feedback voltage VFB1 is connected. That is, the main feedback control state is set. Note that the first feedback voltage VFB1 output from the minimum value detection circuit 17 is the minimum of the voltages of the connection ends 21a, 21b, 21c, and 21d of the load channel in which the switches SW1a, SW1b, SW1c, and SW1d are on. Is the voltage.

  At this time, the error amplifier 15 outputs an error signal EA obtained by amplifying the difference between the first reference voltage VR and the first feedback voltage VFB1. The PWM modulation circuit 16 performs PWM modulation on the error signal EA output from the error amplifier 15 and amplifies the current, and then outputs the amplified signal to the control electrode of the transistor Q1 to obtain the difference between the first reference voltage VR and the first feedback voltage VFB1. The transistor Q1 is driven in accordance with the on-duty according to. When the first feedback voltage VFB1 is higher than the first reference voltage VR, the on-duty of the transistor Q1 is increased to raise the voltage at the output terminal 20. On the other hand, when the first feedback voltage VFB1 is smaller than the first reference voltage VR, the on-duty of the transistor Q1 is reduced to lower the voltage at the output terminal 20. The voltages at the detection terminals 21a, 21b, 21c, and 21d also change in the same manner as the voltage change at the output terminal 20. As a result, negative feedback control is performed so that the first feedback voltage VFB1 is substantially equal to the first reference voltage VR.

  It should be noted that the reference voltage circuit is such that the minimum voltage among the voltages at the detection terminals 21a, 21b, 21c, and 21d is an appropriate voltage that causes the constant current sources 40a, 40b, 40c, and 40d to have appropriate constant current characteristics. 14 first reference voltage VR is set. As a result, negative feedback control is performed so that the minimum voltage (and the voltage at the output terminal 20) of the detection terminals 21a, 21b, 21c, and 21d becomes an appropriate voltage, and the loads 6a, 6b, 6c, Stable current drive can be performed for 6d.

  Here, when the minimum voltage among the voltages of the detection terminals 21a, 21b, 21c, and 21d is negatively feedback-controlled to an appropriate voltage, the voltage of the other load channel becomes a voltage higher than the appropriate voltage. In general, the constant current source can obtain a constant current characteristic by applying a voltage higher than the necessary minimum bias voltage. Therefore, if the minimum voltage detected by the minimum value detection circuit 17 becomes an appropriate voltage, Stable current drive can be performed for the load channels. The voltage detection circuit 9 outputs a second feedback voltage VFB2 obtained by dividing the voltage of the output terminal 20 at a certain voltage division ratio. The signal holding circuit 13 repeats sampling of the second feedback voltage VFB2 output from the voltage detection circuit 9.

  Next, when all of the switches SW1a, SW1b, SW1c, and SW1d are turned off, the switch SW11 is connected to the output of the voltage detection circuit 9 (second feedback voltage VFB2), the switch SW12 is turned off, and the switch SW13 is turned on. It is connected to the output of the signal holding circuit 13 (second reference voltage VFB2 ′). At this time, the voltage detection circuit 9 and the signal holding circuit 13 are disconnected, and the second feedback voltage VFB2 (second reference voltage VFB2) output from the voltage detection circuit 9 before the signal holding circuit 13 is disconnected. ') Is held and output. The second reference voltage VFB2 ′ output from the signal holding circuit 13 is input to the non-inverting input terminal of the error amplifier 15, and the second feedback output from the voltage detection circuit 9 is input to the inverting input terminal of the error amplifier 15. The voltage VFB2 is input. That is, the auxiliary feedback control state is set.

  At this time, the error amplifier 15 outputs an error signal EA obtained by amplifying the difference between the second reference voltage VFB2 'and the second feedback voltage VFB2. The PWM modulation circuit 16 PWM-modulates the error signal EA output from the error amplifier 15 and amplifies the current, and then outputs the amplified signal to the control electrode of the transistor Q1 to obtain the second reference voltage VFB2 ′ and the second feedback voltage VFB2. The transistor Q1 is driven according to the on-duty according to the difference. When the second feedback voltage VFB2 is larger than the second reference voltage VFB2 ', the on-duty of the transistor Q1 is increased to raise the voltage at the output terminal 20. On the other hand, when the second feedback voltage VFB2 is smaller than the second reference voltage VFB2 ', the on-duty of the transistor Q1 is reduced to lower the voltage at the output terminal 20. The second feedback voltage VFB2 changes in the same manner as the voltage change at the output terminal 20. In this way, negative feedback control is performed so that the second feedback voltage VFB2 is substantially equal to the second reference voltage VFB2 '. Here, the second reference voltage VFB2 ′ holds a voltage obtained by dividing the voltage of the output terminal 20 in a state where any of the switches SW1a, SW1b, SW1c, and SW1d is turned on (main feedback control state). It is a thing.

  Therefore, in a state where all of the switches SW1a, SW1b, SW1c, and SW1d are turned off (auxiliary feedback control state), the second feedback voltage VFB2 and the second reference voltage VFB2 ′ become substantially equal voltages, so that the switch SW1a , SW1b, SW1c, and SW1d are held at the voltage at the output terminal 20 in a state where the switch is turned on (main feedback control state). When the switch SW1 is turned on again (main feedback control state), the voltage at the output terminal 20 is detected because the voltage at the previous switch SW1 is kept on (main feedback control state). The voltages at the ends 21a, 21b, 21c, and 21d can quickly shift to voltages that allow the constant current sources 40a, 40b, 40c, and 40d to have appropriate constant current characteristics, and consequently the loads 6a, 6b, 6c, A predetermined current can be quickly supplied to 6d.

  As described above, the electrical characteristics of the loads 6a, 6b, 6c, and 6d fluctuate in the process of repeatedly turning on and off the respective switches of the plurality of load channels (including the case where all the switches are turned off). However, a stable pulse current can flow through the loads 6a, 6b, 6c and 6d.

[Modification]
A modification similar to that of the first embodiment can be adopted. Moreover, although the case of four load channels was illustrated, it is not limited to this number of channels.
(Embodiment 3)
[Configuration example]
FIG. 6 is a circuit diagram showing a configuration example of the load driving device according to Embodiment 3 of the present invention.

  The load driving device shown in FIG. 6 includes constant current sources 6a, 6b, 6c, and 6d for four load channels, similarly to the load driving device shown in FIG. However, in the load driving device shown in FIG. 6, the positions of the detection ends 21a, 21b, 21c, and 21d are loads 6a, 6b, 6c, and 6d and switches SW1a, SW1b, as compared with the configuration of the load driving device shown in FIG. In addition to the voltages of the detection terminals 21a, 21b, 21c, and 21d, the second feedback voltage VFB2 output from the voltage detection circuit 9 is input to the minimum value detection circuit 15 and the point between the SW1c and SW1d. The difference is that the switch SW11 is omitted.

  The minimum value detection circuit 15 detects the minimum voltage from the voltages of the detection terminals 21a, 21b, 21c, and 21d and the second feedback voltage VFB2 output from the voltage detection circuit 9, and uses it to detect the first voltage. The feedback voltage VFB1 is output. The second feedback voltage VFB2 output from the voltage detection circuit 9 is set to be a value slightly larger than the maximum value among the voltages at the detection terminals 21a, 21b, 21c, and 21d.

  The other components having the same numbers as the components shown in FIG. 4 have the same functions as those shown in FIG.

[Operation example]
The operation of the load driving device shown in FIG. 6 will be described based on the logic applied to each switch shown in FIG.

  Connections of the switches SW1a, SW1b, SW1c, SW1d, SW11, SW12, and SW13 shown in FIG. 6 are set as shown in FIG. 5 according to the output of the logic gate 18.

  First, to simplify the description, only the voltages of the detection terminals 21a, 21b, 21c, and 21d are input to the minimum value detection circuit 17, and the switches SW1a, SW1b, SW1c, and SW1d are all turned on. Assume a case.

  In this case, the switch SW12 is turned on, and the switch SW13 is connected to the output of the reference voltage circuit 14 (first reference voltage VR). At this time, the first reference voltage VR output from the reference voltage circuit 14 is input to the non-inverting input terminal of the error amplifier 15, and the first value output from the minimum value detection circuit 17 is input to the inverting input terminal of the error amplifier 15. 1 feedback voltage VFB1 is connected. The minimum value detection circuit 17 outputs the minimum voltage among the voltages at the detection terminals 21a, 21b, 21c, and 21d.

  At this time, the error amplifier 15 outputs an error signal EA obtained by amplifying the difference between the first reference voltage VR and the first feedback voltage VFB1. The PWM modulation circuit 16 PWM-modulates the error signal EA output from the error amplifier 15 and outputs current to the control electrode of the transistor Q1, and then outputs a difference between the first reference voltage VR and the first feedback voltage VFB1. The transistor Q1 is driven in accordance with the on-duty according to. When the first feedback voltage VFB1 is higher than the first reference voltage VR, the on-duty of the transistor Q1 is increased to raise the voltage at the output terminal 20. On the other hand, when the first feedback voltage VFB1 is smaller than the first reference voltage VR, the on-duty of the transistor Q1 is reduced to lower the voltage at the output terminal 20. The voltages at the detection terminals 21a, 21b, 21c, and 21d also change in the same manner as the voltage change at the output terminal 20. As a result, negative feedback control is performed so that the first feedback voltage VFB1 is substantially equal to the first reference voltage VR.

  Here, the reference voltage is set so that the minimum voltage among the respective voltages of the detection terminals 21a, 21b, 21c, and 21d becomes an appropriate voltage at which the constant current sources 40a, 40b, 40c, and 40d have appropriate constant current characteristics. By setting the first reference voltage VR of the circuit 14, negative feedback control is performed so that the minimum voltage among the respective voltages of the detection terminals 21a, 21b, 21c, and 21d becomes an appropriate voltage, and consequently the load Stable current drive can be performed for 6a, 6b, 6c, and 6d. Note that negative feedback control is performed so that the minimum voltage of the detection terminals 21a, 21b, 21c, and 21d is an appropriate voltage, but the voltages of the other load channels are larger than the appropriate voltages. It is a voltage. In general, the constant current sources 40a, 40b, 40c, and 40d can obtain a stable constant current characteristic when a necessary bias voltage or more is applied, so that stable current driving can be performed for other load channels. It becomes like this.

  Next, when any of the switches SW1a, SW1b, SW1c, and SW1d is on, the switch SW12 is turned on, and the switch SW13 is connected to the output (first reference voltage VR) of the reference voltage circuit 14. At this time, the first reference voltage VR output from the reference voltage circuit 14 is input to the non-inverting input terminal of the error amplifier 15, and the first value output from the minimum value detection circuit 17 is input to the inverting input terminal of the error amplifier 15. 1 feedback voltage VFB1 is input. That is, the main feedback control state is set.

  The minimum value detection circuit 17 is configured to detect the minimum voltage among the voltages of the detection terminals 21a, 21b, 21c, and 21d and the second feedback voltage VFB2 output from the voltage detection circuit 9. The second feedback voltage VFB2 output from the voltage detection circuit 9 is set to have a value slightly larger than the voltages of the detection terminals 21a, 21b, 21c, and 21d. The value detection circuit 17 detects the minimum voltage among the voltages at the detection terminals 21a, 21b, 21c, and 21d.

  In addition, among the switches SW1a, SW1b, SW1c, and SW1d, the voltages of the detection terminals 21a, 21b, 21c, and 21d corresponding to the load channel that is turned off are the loads 6a and 6b that correspond to the load channel that is turned off. , 6c, 6d, the voltage is raised to almost the same voltage as the voltage at the output terminal 20, and is higher than the voltage at the detection terminals 21a, 21b, 21c, 21d corresponding to the load channel that is turned on. It becomes. Accordingly, the first feedback voltage VFB1 output from the minimum value detection circuit 17 is the voltage of each of the detection terminals 21a, 21b, 21c, and 21d corresponding to the load channel in which the switches SW1a, SW1b, SW1c, and SW1d are turned on. The lowest voltage among them. Therefore, the minimum value detection circuit 17 does not require a circuit configuration for identifying the voltages of the detection terminals 21a, 21b, 21c, and 21d corresponding to the load channel that is turned on. Thus, it is not necessary to input the current drive commands Pa, Pb, Pc, Pd to the minimum value detection circuit 17.

  At this time, the error amplifier 15 outputs an error signal EA obtained by amplifying the difference between the first reference voltage VR and the first feedback voltage VFB1. The PWM modulation circuit 16 PWM-modulates the error signal EA output from the error amplifier 15 and outputs current to the control electrode of the transistor Q1, and outputs the difference between the first reference voltage VR and the first feedback voltage VFB1. The transistor Q1 is driven according to the corresponding on-duty. For example, when the first feedback voltage is higher than the first reference voltage VR, the on-duty of the transistor Q1 is increased to raise the voltage at the output terminal 20. On the other hand, when the first feedback voltage is smaller than the first reference voltage VR, the on-duty of the transistor Q1 is reduced to lower the voltage at the output terminal 20. The voltages at the detection terminals 21a, 21b, 21c, and 21d also change in the same manner as the voltage change at the output terminal 20. As a result, negative feedback control is performed so that the first feedback voltage VFB1 is substantially equal to the first reference voltage VR.

  The reference voltage circuit 14 is configured such that the minimum voltage among the respective voltages at the detection terminals 21a, 21b, 21c, and 21d is a voltage at which the corresponding constant current sources 40a, 40b, 40c, and 40d have appropriate constant current characteristics. By setting the first reference voltage VR, negative feedback control is performed so that the minimum voltage among the voltages of the detection terminals 21a, 21b, 21c, and 21d becomes an appropriate voltage. Thereby, stable current driving can be performed for the loads 6a, 6b, 6c, and 6d. It should be noted that the voltage of the other load channels is always higher than the appropriate voltage by performing negative feedback control of the minimum voltage of the detection terminals 21a, 21b, 21c, and 21d to an appropriate voltage. . In general, the constant current source has a stable constant current characteristic when a voltage higher than the minimum necessary bias voltage is applied, so that stable current driving is realized also for other load channels. On the other hand, the voltage detection circuit 9 outputs a signal obtained by dividing the voltage at the output terminal 20 by a certain voltage division ratio, and the signal holding circuit 13 samples the second feedback voltage VFB2 output from the voltage detection circuit 9. I keep doing it.

  Next, when all of the switches SW1a, SW1b, SW1c, and SW1d are turned off, the signal holding circuit 13 starts from the voltage detection circuit 9 when any of the switches SW1a, SW1b, SW1c, and SW1d is turned on. The output second feedback voltage VFB2 is held and output. In this case, the switch SW12 is turned off, the voltage detection circuit 9 and the signal holding circuit 13 are disconnected, and the switch SW13 is connected to the output of the signal holding circuit 13 (second reference voltage VFB2 '). On the other hand, the voltages of the detection terminals 21a, 21b, 21c, and 21d are all raised to substantially the same voltage as that of the output terminal 20 because no current flows through all the loads 6a, 6b, 6c, and 6d. Therefore, since the second feedback voltage VFB2 output from the voltage detection circuit 9 is the minimum voltage, the signal output from the minimum value detection circuit 17 is eventually the second output from the voltage detection circuit 9. Feedback voltage VFB2. The second reference voltage VFB2 ′ output from the signal holding circuit 13 is input to the non-inverting input terminal of the error amplifier 15, and the second reference voltage VFB2 ′ output from the voltage detection circuit 9 is input to the inverting input terminal of the error amplifier 15. The feedback voltage VFB2 is input. That is, the auxiliary feedback control state described above. As described above, when all of the switches SW1a, SW1b, SW1c, and SW1d are turned off, the second feedback voltage VFB2 is automatically output from the minimum value detection circuit 17, so that the switch SW11 shown in FIG. It can be omitted.

  At this time, the error amplifier 15 amplifies the difference between the second reference voltage and the second feedback voltage and outputs an error signal. The PWM modulation circuit 16 PWM modulates the error signal output from the error amplifier 15 and amplifies the current, and then drives the transistor Q1. When the second feedback voltage is higher than the second reference voltage, the on-duty of the transistor Q1 is increased to raise the voltage at the output terminal 20. On the other hand, when the second feedback voltage is smaller than the second reference voltage, the on-duty of the transistor Q1 is reduced to lower the voltage at the output terminal 20. The second feedback voltage changes in the same manner as the voltage change at the output terminal 20.

  In this way, negative feedback control is performed so that the second feedback voltage is approximately equal to the second reference voltage. Here, the second reference voltage is a voltage obtained by dividing the voltage of the output terminal 20 in the main feedback control state in which the switch SW1 is turned on. Therefore, in the auxiliary feedback control system in which all of the switches SW1a, SW1b, SW1c, and SW1d are turned off, the second feedback voltage and the second reference voltage become substantially equal to each other, whereby the switches SW1a, SW1b, SW1c, and SW1d. Thus, the voltage of the output terminal 20 in the main feedback control state in which any of the above is turned on is held.

  After that, when the switch SW1 is turned on again (main feedback control state), the voltage at the output terminal 20 is maintained at the voltage when the previous switch SW1 is turned on, so that the detection terminals 21a, 21b, 21c, and 21d are constant. The current sources 40a, 40b, 40c, and 40d quickly shift to voltages that have appropriate constant current characteristics. As a result, a predetermined current can be quickly passed through the loads 6a, 6b, 6c, 6d.

In this manner, even when the electrical characteristics of the load fluctuate in the process of repeatedly turning on and off the switches SW1a, SW1b, SW1c, and SW1d of each of the four load channels (including when all of them are off). A stable pulse current can flow through the load. Further, the feedback voltage can be automatically selected according to the load state without using the switch SW11 or the minimum value detection circuit 17.
[Modification]
A modification similar to that of the first embodiment can be adopted. Moreover, although the case of four load channels was illustrated, it is not limited to this number of channels.

  From the foregoing description, many modifications and other embodiments of the present invention are obvious to one skilled in the art. Accordingly, the foregoing description should be construed as illustrative only and is provided for the purpose of teaching those skilled in the art the best mode of carrying out the invention. The details of the structure and / or function may be substantially changed without departing from the spirit of the invention.

  The load driving device of the present invention is useful for an LED channel used for a backlight of a liquid crystal television, for example.

DESCRIPTION OF SYMBOLS 1 ... Input end 20 ... Output end 30, 31, 30a-30d, 31a-31d ... Connection end 3 ... Power conversion circuit L1 ... Coil D1 ... Rectifier diode Q1 ... Transistor C1 ... smoothing capacitor
6, 6a to 6d ... load 21, 21a to 21d ... detection end 40, 40a to 40d ... constant current source (current drive circuit element)
DESCRIPTION OF SYMBOLS 9 ... Voltage detection circuit 13 ... Signal holding circuit 14 ... Reference voltage circuit 15 ... Error amplifier 16 ... PWM modulation circuit 17 ... Minimum value detection circuit 18 ... Logic gate 19 ..Control unit 160 ... negative feedback control circuit SW1 ... switch (first switching unit)
SW12 ... switch (second switching unit)
SW11 ... switch (fourth switching unit)
SW13... Switch (third switching unit)
VFB1 ... first feedback voltage VFB2 ... second feedback voltage VR ... first reference voltage VFB2 '... second reference voltage EA ... error signal

Claims (8)

Power configured to supply power to a load channel in which a load and a current drive circuit element that supplies current to the load are connected in series, and convert input power into a form corresponding to the load and output the power A conversion circuit;
A reference voltage circuit configured to generate and output a predetermined reference voltage;
A voltage detection circuit configured to detect and output a voltage according to the output voltage of the power conversion circuit;
A signal holding circuit configured to hold and output the voltage detected by the voltage detection circuit;
When the current is flowing through the load, the main feedback control state is entered, and when the current is not flowing through the load, the auxiliary feedback control state is entered, and the feedback voltage according to the main feedback control state or the auxiliary feedback control state and its An error amplifier for amplifying the difference from the comparison voltage;
A negative feedback control circuit configured to drive the power conversion circuit so as to reduce the difference based on an error signal output from the error amplifier, and
The main feedback control state is
The negative feedback control circuit selects a voltage (hereinafter referred to as a first feedback voltage) applied to the current drive circuit element as the feedback voltage, and outputs the reference voltage circuit (hereinafter referred to as a first reference voltage) as the comparison voltage. And the power conversion circuit is driven so as to reduce the difference between the first feedback voltage and the first reference voltage, and the signal holding circuit outputs the output of the voltage detection circuit (hereinafter referred to as a second voltage detection circuit). The feedback voltage) is being sampled,
The auxiliary feedback control state is:
The signal holding circuit holds and outputs the second feedback voltage (hereinafter referred to as a second reference voltage) sampled in the main feedback control state, and the negative feedback control circuit uses the second feedback voltage as the feedback voltage. And selecting the second reference voltage as the comparison voltage and driving the power conversion circuit so as to reduce the difference between the second feedback voltage and the second reference voltage. A load driving device. A first switching unit configured to energize or interrupt a current flowing through the load in the load channel;
A second switching unit configured to select one of the first feedback voltage and the second feedback voltage to be input and output the selected one to the one input terminal of the error amplifier;
A third switching unit configured to switch whether or not to input the second feedback voltage from the voltage detection circuit to the signal holding circuit;
A fourth switching unit configured to select one of the input first reference voltage or the second reference voltage and output the selected one to the other input terminal of the error amplifier;
The main feedback control state is
Controlling the first switching unit to energize the current flowing through the load;
Controlling the second switching unit to select and output the first feedback voltage to one input terminal of the error amplifier;
Controlling the third switching unit so that the second feedback voltage is input from the voltage detection circuit to the signal holding circuit;
And controlling the fourth switching unit to select and output the first reference voltage to the other input terminal of the error amplifier,
The auxiliary feedback control state is:
Controlling the first switching unit to interrupt the current flowing through the load;
Controlling the second switching unit to select and output the second feedback voltage to one input terminal of the error amplifier;
Controlling the third switching unit so that the second feedback voltage is not input from the voltage detection circuit to the signal holding circuit;
2. The load driving device according to claim 1, wherein the fourth switching unit is controlled to select the second reference voltage and output the second reference voltage to the other input terminal of the error amplifier. (For multiple load channels)
The load driving device according to claim 1, wherein the current driving circuit element is a constant current source and the load channels are plural.   The negative feedback control circuit enters the main feedback control state when current flows through at least one of the loads of each of the plurality of load channels, and current flows through all the loads of the plurality of load channels. The load driving device according to claim 3, wherein the load driving device is configured to be in the auxiliary feedback control state when not.   The negative feedback control circuit is configured to select a minimum voltage among the voltages applied to the constant current sources of the plurality of load channels as the first feedback voltage in the main feedback control state. Item 4. The load driving device according to Item 3. A load, a first switching unit configured to energize or cut off a current flowing through the load based on a current drive command, a detection terminal that detects an output voltage of the load, and the constant current source. For multiple load channels in this order,
A second switching unit configured to switch whether or not to input the second feedback voltage from the voltage detection circuit to the signal holding circuit;
The first reference voltage and the second reference voltage are input, and one of the first reference voltage and the second reference voltage is selected and output to one input terminal of the error amplifier. A third switching unit,
The first feedback voltage or the second feedback voltage is input, and one of the first feedback voltage or the second feedback voltage is selected and output to the other input terminal of the error amplifier. A fourth switching unit,
The current drive command for each of the plurality of load channels and the output voltage of the load detected at the detection end of each of the plurality of load channels are input, and a plurality of current drive commands are input based on the plurality of current drive commands. A minimum value detection circuit configured to detect a minimum voltage that is output when the current flows through the load from the output voltage of the load and output the detected voltage as the first feedback voltage; With
The negative feedback control circuit is:
In the main feedback control state, the second switching unit is controlled so that the first reference voltage is selected and output to one input terminal of the error amplifier, and the first feedback voltage is selected. The third switching unit is controlled to output to one input terminal of the error amplifier, and the fourth feedback voltage is input from the voltage detection circuit to the signal holding circuit. Control the switching part of
In the auxiliary feedback control state, the second switching unit is controlled so that the second feedback voltage is not input from the voltage detection circuit to the signal holding circuit, and the second reference voltage is selected and the second feedback voltage is selected. The third switching unit is controlled to output to the other input terminal of the error amplifier, and the second feedback voltage is selected and output to the one input terminal of the error amplifier. The load driving device according to claim 3 which controls a switching part. A load, a detection terminal for detecting an output voltage of the load, a first switching unit configured to energize or cut off a current flowing through the load based on a current drive command, and the constant current source. For multiple load channels in this order,
A second switching unit configured to switch whether or not to input the second feedback voltage from the voltage detection circuit to the signal holding circuit;
A third switching unit configured to select one of the input first reference voltage or the second reference voltage and output the selected one to the one input terminal of the error amplifier;
An output voltage of the load detected at the detection end of each of the plurality of load channels and the second feedback voltage output from the voltage detection circuit are input, and any of the loads of each of the plurality of load channels is input. When the current is flowing, the minimum voltage is detected and output as the first feedback voltage among the output voltages of the plurality of loads when the current flows through the load. A minimum value detection circuit configured to output the second feedback voltage when no current flows through all the loads of each of the plurality of load channels, and
The negative feedback control circuit is:
In the main feedback control state, the second switching unit is controlled to select and output the first feedback voltage to one input terminal of the error amplifier, and from the voltage detection circuit to the signal holding circuit Controlling the third switching unit so that the second feedback voltage is input to
In the auxiliary feedback control state, the second switching unit is controlled to select and output the second feedback voltage to one input terminal of the error amplifier, and from the voltage detection circuit to the signal holding circuit The load driving device according to claim 3, wherein the third switching unit is controlled so that the second feedback voltage is not input to the first switching unit. The load driving device according to claim 1, wherein the load is a light emitting element.

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