JP2014226006A - Current controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a current controller that allows variably controlling the amount of constant current in a configuration in which a control circuit switching-controls the amount of constant current applied to a load.SOLUTION: In a driving device 1, a control IC 10 causes N-channel MOSFETs 3 and 8 to switching-operate so that a voltage Vfb of an input terminal 11, which is determined on the basis of a terminal voltage Vs of a current detection resistor 6 for detecting a load current I, becomes a predetermined voltage. A microcomputer 12 changes the duty ratio of a PWM signal outputted to an integration circuit 15 according to a control condition provided from the outside to control the load current I.

Description

  The present invention relates to a current control device that controls a current supplied to a load by switching a switching element by PWM control.

  For example, in Patent Document 1, in a power supply device using a step-up DC-DC converter that supplies power to a backlight of an LCD, a constant current is supplied to an LED that is a light source of the backlight. A configuration in which an ON / OFF control circuit controls a MOSFET by PWM or VFM as compared with a reference power supply by a comparator is disclosed (see FIG. 11).

JP 2005-117873 A

In the above configuration, since the drive current of the LED is determined by the resistance value of the current limiting resistor, there is a problem that the drive current, that is, the emission luminance of the LED cannot be changed.
The present invention has been made in view of the above circumstances, and an object thereof is to provide a current control device capable of variably controlling the constant current amount in a configuration in which a control circuit performs switching control of the constant current amount to be supplied to a load. It is in.

  According to the current control device of claim 1, the first control circuit is configured so that the voltage at the input terminal determined based on the terminal voltage of the current detection resistor element for detecting the load current becomes a predetermined voltage. The switching operation is performed. The internal control PWM signal output from the second control circuit is input to the integration circuit, and the output terminal of the integration circuit is connected to the input terminal of the first control circuit. The second control circuit controls the load current by changing the duty ratio of the internal control PWM signal in accordance with a control condition given from the outside.

  With this configuration, the potential of the output terminal of the integration circuit changes according to the duty ratio of the internal control PWM signal output from the second control circuit. The potential also changes. Therefore, the state of the switching control performed by the first control circuit also changes with the potential change of the input terminal. As a result, the constant current amount supplied to the load can be changed by the duty ratio of the internal control PWM signal output from the second control circuit, and the drive state of the load can be controlled.

  According to the current control device of the second aspect, the second control circuit is configured to also perform the enable control of the first control circuit, and when the power is turned on and started, the second control circuit disables the first control circuit. While maintaining the enabled state, an initial voltage signal for charging the capacitor constituting the integrating circuit is output. When the output of the initial voltage signal is stopped and the output of the internal control PWM signal is started, the first control circuit is switched to the enable state.

  If comprised in this way, before the 1st control circuit starts control of a switching element, the capacitor | condenser which comprises an integrating circuit will be charged by an initial voltage signal. Therefore, when the first control circuit starts controlling the switching element, the potential of the output terminal of the integrating circuit is raised to some extent, so that it is possible to prevent the initial energization current amount for the load from becoming excessive.

The figure which is 1st Embodiment and shows the electrical constitution of a LED drive device Flow chart showing control contents of microcomputer Timing chart showing the operation of the drive unit FIG. 3 equivalent diagram when the microcomputer does not perform the processing of steps S1 and S2. The figure explaining the principle by which the light emission luminance of LED is decided by the duty ratio of the PWM signal which a microcomputer outputs The figure which shows the relationship between duty ratio and drive current I FIG. 1 equivalent view showing the second embodiment 2 equivalent diagram 3 equivalent figure

(First embodiment)
As shown in FIG. 1, a DC power source (not shown) such as an in-vehicle battery is connected between the input terminals 2 a and 2 b of the driving device 1 (current control device). Further, a series circuit of an N-channel MOSFET (switching element) 3, a coil 4, a plurality of LEDs 5 (load) connected in series and a current detection resistor 6 (current detection resistor element) is connected between the input terminals 2a and 2b. Has been. A diode 7 in the reverse direction is connected between the source of the N-channel MOSFET 3 and the input terminal 2b, and an N-channel MOSFET 8 (switching element) is connected between the uppermost anode of the LED 5 and the input terminal 2b. Is connected.

  A common connection point between the lowermost cathode of the LED 5 and the current detection resistor 6 is connected to an input terminal 11 of a control IC 10 (first control circuit) via a resistor 9. The control IC 10 performs switching control on the N-channel MOSFETs 3 and 8 so that the potential of the input terminal 11 is constant, thereby controlling the drive current supplied to the LED 5 to be constant. That is, the N-channel MOSFETs 3 and 8, the coil 4, and the control IC 10 constitute a step-up / step-down DCDC converter. The LED 5 is, for example, a vehicle headlight, and the light emission luminance is determined according to the drive current value.

  The control IC 10 is enable-controlled by an enable signal EN output from a microcomputer 12. The output terminal of the microcomputer 12 (second control circuit) is connected to the input terminal of the integrating circuit 15 including the resistor 13 and the capacitor 14, and the output terminal of the integrating circuit 15 is connected to the control IC 10 via the resistor 16. It is connected to the input terminal 11.

  The microcomputer 12 acquires various information (control conditions) such as temperature, power supply voltage, ambient illuminance, navigation information (vehicle position), headlight position, etc. from various sensors (not shown). / D conversion and read). The power supply voltage may be divided and read as necessary. The microcomputer 12 controls the potential of the input terminal 11 by outputting a PWM signal (internal control PWM signal) to the integration circuit 15 as will be described later.

  Next, the operation of this embodiment will be described. When the power is turned on and the power-on reset of the microcomputer 12 is released (see FIGS. 3A and 3B), the microcomputer 12 first controls the enable signal EN to a low level as shown in FIG. The IC 10 is disabled (OFF) (S1, see FIG. 3C). At the same time, a 100% duty PWM signal (initial voltage signal) is output to the integrating circuit 15 (S2), and charging of the capacitor 14 is started (see FIGS. 3D and 3E; initial voltage control). Steps S1 and S2 in FIG. 2 are initial processing (Init processing).

  Then, the microcomputer 12 waits for a certain period of time so that the terminal voltage of the capacitor 14 is sufficiently increased (S3). When the certain period of time has elapsed (YES), the enable signal EN is set to high level to enable the control IC 10 ( ON) (S4, see FIG. 3C). Thereafter, the microcomputer 12 obtains various information (control conditions) such as temperature, power supply voltage, ambient illuminance, navigation information (vehicle position), headlight position, and the like from various sensors (S5). Then, the microcomputer 12 calculates the duty ratio of the PWM signal that determines the brightness of the headlight based on the information (S6), sets the calculated duty ratio, and outputs the PWM signal to the integration circuit 15 (S7). , See FIG. 3 (d)). Note that the processing in steps S3 to S7 is an infinite loop.

Here, the principle that the light emission luminance of the LED 5 is determined by the duty ratio of the PWM signal output from the microcomputer 12 will be described. As shown in FIG. 5, when the current flowing through the current detection resistor 6 (resistance value Rs) is I, the terminal voltage Vs of the current detection resistor 6 is
Vs = Rs × I (1)
It becomes. When the potential of the input terminal 11 is Vfb and the terminal voltage of the resistor 9 (resistance value R3) is V3, the terminal voltage V3 is
V3 = Vfb−Vs (2)
It becomes.

Assuming that the potential of the output terminal of the microcomputer 12 is Vpwm and the resistance values of the resistors 13 and 15 are R1 and R2, respectively, from the relationship between the equations (1) and (2) and the voltage dividing ratio by the resistor 9,
Vpwm = (Vfb−Vs) / {R3 / (R1 + R2 + R3)} (3)
I = Vfb / Rs−R3 / Rs / (R1 + R2 + R3) × Vpwm (4)
It becomes.

On the other hand, the output terminal potential Vpwm of the microcomputer 12 can be regarded as a constant voltage source through the relationship between the reference voltage Vref (high level) and the duty ratio Duty and the integration circuit 15.
Vpwm = Vref × Duty (5)
Therefore, by changing the duty ratio Duty from the equations (4) and (5), the load current I can be changed as shown in FIG.

  The reason why the microcomputer 12 performs the processes of steps S1 and S2 is as follows. As shown in FIG. 4, when the microcomputer 12 does not perform the above processing, the control IC 10 starts operation almost simultaneously with the microcomputer 12 (see (b) and (c)). Since the microcomputer 12 starts outputting a PWM signal having a predetermined duty ratio (see (d)), the terminal voltage of the capacitor 14 gradually increases (see (e)).

  Then, since the potential of the input terminal 11 at the time when the control IC 10 starts operating is low, the control IC 10 initially turns on the N-channel MOSFET 3 in response to the low potential, and a large load current I flows and overloads. A chute occurs (see (f)). Therefore, the microcomputer 12 keeps the control IC 10 in a disabled state at the time of start-up, and avoids the occurrence of overshoot by raising the terminal voltage of the capacitor 14 to some extent during that time.

  As described above, according to the present embodiment, in the driving device 1, the control IC 10 determines that the voltage Vfb of the input terminal 11 determined based on the terminal voltage Vs of the current detection resistor 6 for detecting the load current I is the predetermined voltage. Thus, the N-channel MOSFETs 3 and 8 are switched. Then, the microcomputer 12 controls the load current I by changing the duty ratio of the PWM signal output to the integrating circuit 15 in accordance with a control condition given from the outside.

  Thereby, the potential of the output terminal of the integrating circuit 15 is changed according to the duty ratio, and the potential Vfb of the input terminal 11 is changed. Therefore, the state of the switching control performed by the control IC 10 changes with the change of the potential Vfb, and the constant current amount I supplied to the LED 5 can be changed by the duty ratio to control the light emission luminance of the headlight.

  Further, when the microcomputer 12 performs enable control of the control IC 10 and is turned on and started, the microcomputer 12 charges the capacitor 14 constituting the integrating circuit 15 while the control IC 10 is held in a disabled state. A PWM signal with a duty of 100% is output. When the output of the signal is stopped and the output of a PWM signal having a predetermined duty ratio (<100%) is started, the control IC 10 is switched to an enable state.

  As a result, the capacitor 14 is charged before the control IC 10 starts to control the N-channel MOSFETs 3 and 8, and therefore, at the stage where the control IC 10 starts to control the N-channel MOSFETs 3 and 8, the potential of the output terminal of the integrating circuit 15 Has risen to some extent. Therefore, it is possible to suppress the occurrence of an overshoot due to an excessive amount of initial energization current to the LED 5.

(Second Embodiment)
Hereinafter, the same parts as those in the first embodiment are denoted by the same reference numerals, description thereof will be omitted, and different parts will be described below. As shown in FIG. 7, a microcomputer 22 (second control circuit) in place of the microcomputer 12 is arranged in the drive device 21 of the second embodiment. The microcomputer 22 reads the potential at the output terminal of the integrating circuit 15 by A / D conversion. Then, the initial voltage control of the capacitor 14 is performed while monitoring the potential.

  Next, the operation of the second embodiment will be described. As shown in FIG. 8, after executing step S2, the microcomputer 22 turns off (resets) the charge flag (S11). When the terminal voltage (charge information) of the capacitor 14 is obtained by A / D conversion (S12), it is determined whether or not the charge flag is OFF (S13). If the charge flag is not OFF (NO), the process proceeds to step S4 and the same process as in the first embodiment is performed.

  On the other hand, if the charge flag is OFF (YES), it is determined whether the terminal voltage of the capacitor is equal to or higher than a predetermined threshold (S14), and if it is less than the threshold (NO), the process proceeds to step S12 (infinite loop). If the terminal voltage of the capacitor is equal to or higher than the threshold (YES), the charging flag is turned on (set) (S15), and the process proceeds to step S4. That is, the initial voltage control is continued until “YES” is determined in step S14. Here, the threshold value may be set equal to the control target voltage by outputting a PWM signal having a predetermined duty ratio after the initial voltage control is completed.

  That is, by setting in this way, as shown in FIG. 9, the period during which the microcomputer 22 performs the initial voltage control becomes shorter (see (d) and (e)), and the control IC 10 starts the switching control faster. Will come to do. Further, when the control IC 10 starts the switching control, the output voltage of the integrating circuit 15 has reached the target voltage, so that the load current I reaches the control target value sooner.

  As described above, according to the second embodiment, the microcomputer 22 monitors the output voltage of the integration circuit 15 and determines the timing for starting the output of the PWM signal, so that the control IC 10 starts the switching control faster. Can do. Further, the microcomputer 22 starts outputting the PWM signal when the output voltage of the integrating circuit 15 becomes equal to the target voltage controlled by the output of the PWM signal. Therefore, the load current I reaches the control target value earlier, and the control response is further improved.

The present invention is not limited to the embodiments described above or shown in the drawings, and the following modifications or expansions are possible.
A P-channel MOSFET may be used in place of the N-channel MOSFET 3.
The second control circuit is not limited to the microcomputer 12 and may be configured by a DSP (Digital Signal Processor), an FPGA (Field Programmable Gate Array), or the like.
The present invention is not limited to a buck-boost converter, and may be applied to a boost converter and a buck converter.
The switching element is not limited to a MOSFET but may be a bipolar transistor or IGBT.
The load is not limited to the LED, and any load suitable for constant current driving can be applied.

  In the drawings, 1 is a drive device (current control device), 3 is an N channel MOSFET (switching element), 5 is an LED (load), 6 is a current detection resistor (current detection resistor element), and 8 is an N channel MOSFET (switching element). ) 10 is a control IC (first control circuit), 11 is an input terminal, 12 is a microcomputer (second control circuit), 14 is a capacitor, and 15 is an integration circuit.

Claims (4)

In a current control device that controls a current (hereinafter referred to as a load current) energized to the load (5) by switching the switching elements (3, 8) by PWM (Pulse Width Modulation) control.
A current detection resistor element (6) for detecting the load current;
A first control circuit (10) for switching the switching element so that the voltage of the input terminal determined based on the terminal voltage of the current detection resistor element becomes a predetermined voltage;
A second control circuit (12, 22) for outputting an internal control PWM signal;
An integration circuit (15) to which the internal control PWM signal is input,
An output terminal of the integrating circuit is connected to an input terminal of the first control circuit;
The current control device, wherein the second control circuit controls the load current by changing a duty ratio of the internal control PWM signal according to a control condition given from the outside. The second control circuit is configured to perform enable control of the first control circuit,
When the power is turned on and activated, an initial voltage signal for charging the capacitor (14) constituting the integrating circuit is output while the first control circuit is held in a disabled state.
2. The current control device according to claim 1, wherein when the output of the initial voltage signal is stopped and the output of the internal control PWM signal is started, the first control circuit is switched to an enable state.   3. The current control device according to claim 2, wherein the second control circuit (22) monitors the output voltage of the integration circuit and determines the timing for starting the output of the internal control PWM signal. 4.   The second control circuit starts output of the internal control PWM signal when the output voltage of the integration circuit becomes equal to a target voltage controlled by the output of the internal control PWM signal. 3. The current control device according to 3.

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