JP2009261158A - Power supply unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To drive a voltage control lamp and a current control lamp, while suppressing loss with one converter circuit. <P>SOLUTION: The converter circuit is controlled at a constant voltage with a control circuit 12. Furthermore, the control circuit 12 effects overcurrent control so as to prevent the overcurrent of a load based on a detected load current. When a halogen lamp 13 is used, a current value which should not be flowed into the halogen lamp 13 is set as a threshold for overcurrent control. On the other hand, when an LED 14 is connected to the load, a current value which should be flowed into the LED 14 normally is set as a threshold for overcurrent control. Thereby, the LED 14, when used, is current controlled all the time. Thus, one converter circuit can drive the voltage controlled halogen lamp 13 and current controlled LED. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a power supply device such as a lighting device that uses a voltage-controlled lamp and a current-controlled lamp.

  Conventionally, halogen lamps are sometimes used as lighting for indoor and outdoor commercial facilities. Halogen lamps have high color rendering properties and are used in various lighting devices because they maintain the initial luminous flux and color temperature until the end of their lifetime. In recent years, LEDs (light-emitting diodes) have also been adopted for illumination because of the advantage that the irradiation light contains almost no heat component and is adaptable to heat-sensitive objects.

As a power supply device for the halogen lamp, one that employs a switching power supply and performs constant voltage control is conceivable. On the other hand, as an LED power supply device, there is one described in Patent Document 1. The brightness of the LED is determined according to the value of the current flowing through the LED. The relationship between the current flowing through the LED and the forward voltage is affected by the ambient temperature, and the current flowing through the LED cannot be made constant even when driven at a constant voltage. For this reason, the LED needs to be driven at a constant current. Patent Document 1 discloses a power supply device that drives such an LED at a constant current.
JP 2007-157423 A

  In the above-mentioned Patent Document 1, it is considered that those skilled in the art can use both of these halogen lamps and LEDs. However, since the halogen lamp and the LED have different control methods, a common power supply circuit for these lamps has not been developed.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a power supply device capable of improving efficiency using a single converter circuit and lighting a first lamp driven by a constant voltage and a second lamp driven by a constant current. To do.

  A power supply apparatus according to claim 1 of the present invention detects a load current flowing in a load connected to the output terminal, a voltage output circuit that converts a DC voltage from a DC power source into a predetermined voltage and supplies the voltage to the output terminal. Current detection means for performing feedback control of the voltage output circuit based on the voltage at the output terminal of the voltage output circuit to generate the predetermined voltage in the voltage output circuit, and the load current is larger than a reference current Then, the control means for controlling the voltage output circuit so that the load current is equal to or less than the reference current, and when the first load for voltage control is connected to the output terminal as the load, the control means In the case where an overcurrent that should not flow to the first load as the reference current is set to prevent overcurrent, and a second load for current control is connected to the output terminal as the load, Set the normal current to be passed through the second load as the reference current to the control means is obtained by including a setting means for constant current control.

  According to the present invention, the efficiency can be improved by using one converter circuit, and the first lamp driven by constant voltage and the second lamp driven by constant current can be turned on.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a circuit diagram showing a power supply device according to a first embodiment of the present invention.

  As a power supply device that drives a first load that requires voltage control and a second load that requires current control, for example, there are two converter circuits: a converter circuit that performs voltage control and a converter circuit that performs current control. A circuit using can be considered. However, when two converter circuits are used, there is a disadvantage that loss increases. Therefore, in this embodiment, only one converter circuit is employed as a voltage output circuit that outputs a predetermined voltage, and the control of the converter circuit can be switched between voltage control and current control according to the load. Thus, it is possible to drive the first load by constant voltage driving and the second load by constant current driving while suppressing loss. In the present embodiment, an example in which a step-down chopper circuit is employed as a converter circuit that performs voltage / current control will be described.

  In FIG. 1, a DC power supply 11 supplies a DC voltage between a reference potential point and a positive output terminal. The positive output terminal of the DC power supply 11 is connected to the source of the transistor Q1, and the drain of the transistor Q1 is connected to one end of the coil L1. One end of the coil L1 is also connected to the reference potential point via the diode D1, and the other end is connected to the reference potential point via the smoothing capacitor C1. These transistor Q1, diode D1, coil L1, and capacitor C1 constitute a step-down chopper circuit.

  A drive signal is supplied from the control circuit 12 to the gate of the transistor Q1. The transistor Q1 is turned on / off according to the drive signal, and a voltage corresponding to the on-duty of the drive signal is generated at both ends of the capacitor C1. The voltage generated across the capacitor C1 is supplied to the output terminals O1 to O3.

  For example, a halogen lamp 13 can be connected between the output terminals O1 and O2 as a first load requiring voltage control via the switch SW1. Further, between the output terminals O1 and O3, for example, an LED (light emitting diode) 14 can be connected via a switch SW2 as a second load requiring current control. The switches SW1 and SW2 are turned on and off in conjunction with each other, and when one is on, the other is off.

  The output terminal O2 is connected to a reference potential point via a load current detection resistor R1, and the output terminal O3 is connected to a reference potential point via a load current detection resistor R2. The resistance values of the resistors R1 and R2 are Ra and Rb, respectively.

  The control circuit 12 has a GND terminal connected to the reference potential point, and outputs a drive signal from the output terminal V0 to the gate of the transistor Q1. In the control circuit 12, the terminal voltage of the capacitor C1 is fed back to the F / B terminal. The control circuit 12 generates a drive signal so that the terminal voltage of the capacitor C1 fed back to the F / B terminal becomes a predetermined value. Thereby, a predetermined constant voltage can be generated at both ends of the capacitor C1.

  The control circuit 12 further includes control terminals CLM1 and CLM2 for preventing overcurrent. When the load current becomes an overcurrent, the control circuit 12 controls the drive signal so as to limit the load current to a predetermined current value. That is, the control circuit 12 performs overcurrent control based on the inputs of the control terminals CLM1 and CLM2 with priority over feedback control based on the inputs of the F / B terminals. A voltage across the resistor R1 is applied to the control terminal CLM1. Further, the voltage across the resistor R2 is applied to the control terminal CLM2.

  Now, it is assumed that the first load current flowing through the resistor R1 is Ia. A voltage Ra · Ia corresponding to the first load current is applied to the control terminal CLM1. If the voltage Ra · Ia exceeds the predetermined threshold value Vref, the control circuit 12 causes the overcurrent so that the voltage Ra · Ia becomes the threshold value Vref, that is, the load current Ia becomes equal to or less than the reference current Iref1. Take control. This prevents overcurrent from flowing through the halogen lamp 13 as the first load.

  On the other hand, when the LED 14 which is the second load is connected, the second load current flowing through the resistor R2 is Ib. A voltage Rb · Ib corresponding to the second load current is applied to the control terminal CLM2. When the voltage Rb · Ib exceeds the predetermined threshold value Vref, the control circuit 12 performs current control so that the voltage Rb · Ib becomes the threshold value Vref. Using this overcurrent control, in the present embodiment, a reference current Iref2 for determining whether or not an overcurrent is set is set based on a current that should flow during normal use of the LED 14. If it is determined that the current is an overcurrent, an overcurrent control that suppresses the load current within the reference current Iref2 works, and the load can be controlled at a constant current.

  That is, by setting the resistance value Rb of the resistor R2 such that the product Rb · Ib of the current value Ib flowing through the LED 14 and the resistance value Rb during normal use of the LED 14 becomes Vref, the voltage Rb during normal use of the LED 14 is set. -Constant current control with Ib ≦ Vref is performed.

  Note that, by the constant voltage control of the control circuit 12 based on the input at the F / B end, an output voltage at which overcurrent control always works when the LED 14 is driven is set, and when the LED 14 is driven, the voltage Rb · Ib = Vref The constant current control is performed.

  Next, the operation of the embodiment configured as described above will be described with reference to FIGS. FIG. 2 is a waveform diagram showing the output voltage Vo and output current (load current) Io of the step-down chopper circuit. FIG. 3 is a flowchart for explaining the control of the control circuit 12.

  Now, it is assumed that the switch SW1 is on and the switch SW2 is off, and the halogen lamp 13 is turned on. The control circuit 12 supplies a drive signal to the transistor Q1 to turn on / off the transistor Q1. A DC voltage from the DC power supply 11 is supplied to the coil L1 and the capacitor C1 via the transistor Q1, and a DC voltage corresponding to the on-duty of the transistor Q1 is generated across the capacitor C1.

  This DC voltage is supplied between the output terminals O1 and O2 or between the output terminals O1 and O3. The terminal voltage of the capacitor C1 is fed back to the F / B terminal of the control circuit 12, and the control circuit 12 generates a drive signal so that the voltage fed back to the F / B terminal becomes a predetermined constant voltage. By this feedback control, the step-down chopper circuit is controlled at a constant voltage (step S1). As shown in the constant voltage control period of FIG. 2, when the switch SW1 is turned on and the halogen lamp 13 is turned on, the output of the step-down chopper circuit becomes a constant voltage and the halogen lamp 13 is lit stably.

  In steps S2 and S3, the control circuit 12 detects the first and second load currents Ia and Ib. The switch SW2 is off and the second load current Ib is zero. The load current Ia can be detected by the voltage across the resistor R1, and the voltage across the resistor R1 is supplied to the control terminal CLM1. When the voltage across the resistor R1 is larger than the predetermined threshold value Vref, that is, when the load current Ia is larger than the reference current Iref1, the control circuit 12 proceeds to step S6 and overloads Ia · Ra ≦ Vref. Perform current control. If Ia <Iref1, the control circuit 12 returns to step S1 and repeats constant voltage control.

  Next, the LED 14 is turned on. In this case, in order to prevent the inrush current from flowing into the LED 14 due to the charge of the capacitor C1, the operation of the step-down chopper circuit is stopped and the output is set to 0V.

  Next, the switch SW1 is turned off, the switch SW2 is turned on, and the LED 14 is driven. In step S3, the control circuit 12 detects the second load current Ib. The load current Ib can be detected by the voltage across the resistor R2, and the voltage across the resistor R2 is supplied to the control terminal CLM2. When the voltage across the resistor R2 is larger than the predetermined threshold value Vref, that is, when the load current Ib is larger than the reference current Iref2, the control circuit 12 proceeds to step S7 and overloads Ib · Rb ≦ Vref. Perform current control.

  By setting the load current during normal use of the LED 14 to Iref2, constant current control with the load current always set to Iref2 is performed when the LED 14 is used.

  Thus, in the present embodiment, constant voltage control is performed when the first load requiring voltage control is connected, and the reference value for overcurrent control is set to the current value when driving the second load. The constant current control is enabled when the second load requiring current control is connected. By making one converter circuit switchable between constant voltage control and constant current control in accordance with the connected load, the first load driven at constant voltage and the second driven at constant current while suppressing loss. Can be driven.

  FIG. 4 is a circuit diagram showing a second embodiment of the present invention. In FIG. 4, the same components as those of FIG. FIG. 5 is a waveform diagram for explaining the second embodiment.

  The present embodiment is different from the first embodiment in that the capacitor C1 is omitted and a voltage detection circuit including a coil L2, a capacitor C2, a diode D2, and resistors R3 and R4 that form a transformer T together with the coil L1 is added. .

  In general, the output voltage of the converter circuit during constant current control for the LED 14 is lower than the output constant voltage for lighting the halogen lamp 13. For this reason, if it switches to lighting of LED14 at the time of lighting of the halogen lamp 13, inrush current will flow into LED14 with the charge of the capacitor | condenser C1.

  The output voltage Vo1 and the output current Io1 in FIG. 5 indicate this state. When the switch SW1 is switched from the on state to the switch SW2, the constant voltage control is switched to the constant current control. At the time of this switching, the output voltage gradually decreases and changes to the output voltage VF during constant current control. On the other hand, the output current increases due to the inrush current at the time of switching, and then gradually decreases to become a constant current at the time of constant current control. The LED 14 may be destroyed by this inrush current.

  Therefore, in the present embodiment, the capacitor C1 that generates the inrush current is omitted. If the capacitor C1 is omitted, the output voltage of the converter circuit is superimposed with high frequency ripple. Even in this case, the halogen lamp 13 and the LED 14 can be turned on. However, a DC voltage for constant voltage control of the converter circuit cannot be obtained. Therefore, in the present embodiment, the current flowing through the primary side coil L1 by the transformer coupling is taken out by the secondary side coil L2.

  The negative end of the coil L2 is connected to the reference potential point, and a diode D2 and a capacitor C2 are connected in series between the positive end and the negative end of the coil L2. A series circuit of resistors R3 and R4 is connected in parallel to the capacitor C2. A voltage generated in the coil L2 is converted into a DC voltage by the diode D2 and the capacitor C2, and a DC voltage based on the output of the coil L1 is generated in the resistor R3. The DC voltage generated in the resistor R3 is supplied to the F / B terminal of the control circuit 12 as a feedback voltage. The control circuit 12 generates a drive signal so that the voltage fed back to the F / B terminal becomes a predetermined constant voltage.

  In the embodiment configured as described above, the voltage at the output terminal of the coil L1 is detected by the voltage detection circuit including the coil L2, the diode D2, the capacitor C2, and the resistors R3 and R4, and the F / B of the control circuit 12 is detected. Supplied to the end. Thereby, the control circuit 12 can perform constant voltage control of the converter circuit. As shown by the output voltage Vo2 in FIG. 5, when the switch SW1 is on and the halogen lamp 13 is lit, the halogen lamp 13 is driven at a constant voltage by feedback control based on the voltage across the resistor R3.

  When the switch SW1 is turned off and the switch SW2 is turned on, the current Ib tends to be larger than the reference current Iref2, and the control circuit 12 performs constant current control such that Ib · Rb = Vref. In this case, since no capacitor is provided at the output terminal of the converter circuit, inrush current does not flow into the LED 14 when the switches SW1 and SW2 are switched. As shown in FIG. Switching to constant current control is instantaneous.

  Thus, also in this embodiment, the same effect as that of the first embodiment can be obtained. In the present embodiment, even when the lamp to be used is instantaneously switched from the halogen lamp to the LED, no inrush current flows through the LED.

  In the above-described embodiment, the example in which the output of the converter circuit is extracted by transformer coupling and used as the feedback voltage has been described. However, various methods for acquiring the output of the converter circuit are conceivable. For example, the effective value of the pulse output from the converter circuit functioning as the pulse output circuit may be obtained by omitting the capacitor, and this effective value may be used for feedback control.

The circuit diagram which shows the power supply device which concerns on the 1st Embodiment of this invention. The wave form diagram which shows the output voltage Vo and output current (load current) Io of a step-down chopper circuit. 7 is a flowchart for explaining control of the control circuit 12; The circuit diagram which shows the 2nd Embodiment of this invention. The wave form diagram for demonstrating 2nd Embodiment.

Explanation of symbols

    DESCRIPTION OF SYMBOLS 10 ... Power supply device, 11 ... DC power supply, 12 ... Control circuit, 13 ... Halogen lamp, 14 ... LED, Q1 ... Transistor, D1 ... Diode, L1 ... Coil, C1 ... Capacitor, R1, R2 ... Resistance.

Claims (2)

A voltage output circuit that converts a DC voltage from a DC power source into a predetermined voltage and supplies the voltage to the output terminal;
Current detection means for detecting a load current flowing in a load connected to the output terminal;
The voltage output circuit is feedback-controlled based on the voltage at the output terminal of the voltage output circuit to generate the predetermined voltage in the voltage output circuit, and when the load current becomes larger than a reference current, the load current is Control means for controlling the voltage output circuit so as to be equal to or lower than a reference current;
When a first load of voltage control is connected to the output terminal as the load, an overcurrent that should not flow to the first load as the reference current is set in the control means to prevent overcurrent. When a second load of current control is connected to the output terminal as the load, the control means is configured to set a current that should normally flow through the second load as the reference current and perform constant current control. And a power supply apparatus. The voltage output circuit generates a pulse voltage as a predetermined voltage,
The power supply apparatus according to claim 1, wherein the control unit detects a DC voltage based on an output voltage of the voltage output circuit and feedback-controls the voltage output circuit.

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