JP2012079578A - Power supply device for led parallel driving - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power supply device capable of driving two or more parallelly connected LEDs in one output and continuously lighting remaining LEDs with the same brightness even if a trouble occurs in one LED.SOLUTION: A power supply device for LED parallel driving comprises: a regulator part 10 which stabilizes a DC input and outputs a DC and a feedback circuit 14 which creates a feedback signal for stabilization control based on a load current detection resistor provided in series in an LED which serves as a load and a drop voltage by the load current detection resistor and inputs the created signal to a feedback terminal of the regulator part. The power supply device for LED drives an LED with the DC output stabilized by the regulator part. A plurality of LEDs are provided in parallel for one DC output of the regulator part. A load current detection resistor R1 is connected between the cathode side of an LED 12a and a GND. A load current detection resistor R2 is connected between the cathode side of an LED 12b and the GND. The feedback circuit is provided with a diode OR circuit 16 connected to each load current detection resistor and creates a feedback signal based on a terminal voltage of a load current detection resistor having the largest voltage drop.

Description

  The present invention relates to a power supply device that drives a plurality of load LEDs provided in parallel with a single output. More specifically, even if one of the LEDs malfunctions and becomes open, the remaining normal The present invention relates to a power supply device for LED parallel driving that performs constant current control of a regulator unit using an OR function so that a current flowing through an LED does not fluctuate. This technique is useful for a power supply device for LED lighting or LED signboard.

  As a power supply device for driving an LED as a load, a load current detection resistor is connected to the cathode side of the LED, and the regulator IC is controlled so that the voltage drop at the load current detection resistor is kept constant. There is a circuit configuration that keeps the brightness constant by driving at a constant current (see Patent Document 1). In such a conventional power supply device, usually, one load LED is driven by one output.

  Here, when a conventional power supply device is used and a plurality of load LEDs are provided in parallel and driven by one power supply output, if any of the plurality of LEDs has a problem and becomes open, current flows through the LEDs. When the current disappears, the current is equally distributed to the remaining normal LEDs, and the amount of current flowing through the normal LEDs increases. As a result, the emission intensity of a normal LED may not only increase beyond the set value, but the lifetime may be shortened. This is because the conventional power supply apparatus performs constant current control by detecting the output current flowing through the load at one location.

  By the way, as a prior art, there is known a power supply apparatus of a type in which a protection circuit works to cut off an output when a problem occurs in one place of a parallel load. However, all the remaining normal LEDs are extinguished. That is, in the prior art, when a problem occurs in one of the load LEDs provided in parallel, the other LEDs are either brighter than the set value or all the LEDs are turned off. Therefore, in order to continue driving the remaining normal LEDs with the same brightness, it is necessary to individually install a power supply device for each LED so that one LED is driven with one output. there were. However, in such a configuration, it is necessary to provide as many regulator ICs as the number of LEDs, resulting in an increase in the number of parts and an increase in cost.

JP 2003-152224 A

  The problem to be solved by the present invention is that one output can drive two or more load LEDs connected in parallel, and even if a failure occurs in one LED, the remaining LEDs are lit at the same brightness. It is to continue.

  The present invention provides a regulator unit that stabilizes a DC input to provide a DC output, a load current detection resistor provided in series with a load LED, and a feedback for stabilization control based on a voltage drop caused by the load current detection resistor. In a power supply apparatus that includes a feedback circuit that creates a signal and inputs the signal to a feedback terminal of the regulator unit, and that drives a LED that is a load with a DC output stabilized by the regulator unit, the LED that is a load is the regulator unit A load current detection resistor is connected between the cathode side of each LED and GND, and the feedback circuit includes a diode OR circuit connected to each load current detection resistor. The feedback is based on the terminal voltage of the load current detection resistor having the largest voltage drop. Create a feedback signal in the road, and input the feedback signal to the feedback terminal of the regulator portion, a LED parallel drive power supply device, characterized in that the stabilization control the output.

  Here, for example, the feedback circuit includes a diode OR circuit and a current adjustment resistor. The diode OR circuit short-circuits the cathode ends of the same number of OR diodes as the load LEDs, and the anode ends are different from each other. The common cathode terminal of the diode OR circuit is connected to GND via the current adjustment resistor, and the voltage of the common cathode terminal of the diode OR circuit is a feedback signal. The input to the feedback terminal of the regulator unit, and each LED as a load is driven by constant current control.

  The LED parallel drive power supply device of the present invention detects a load current flowing through each LED as a drop voltage due to the load current detection resistor by connecting a load current detection resistor in series with each LED as a load, Since the diode OR circuit of the feedback circuit is configured to input to the feedback terminal of the regulator unit, a problem occurs in some of the LEDs connected in parallel to one output from the regulator unit. Even in the open state, since the load current flowing through other normal LEDs is detected by the OR function, the feedback signal input to the feedback terminal of the regulator unit hardly changes. Therefore, the current flowing through the remaining normal LEDs does not increase, and the same current continues to flow. Therefore, there is no problem that the brightness fluctuates, and there is no possibility that the lifetime of the LED will be shortened.

  Therefore, in the present invention, it is possible to replace a defective LED while the power supply device is operated. In addition, after the replacement, the replaced LED is also lit with the original brightness. Further, for example, even when one LED is removed, the value of the current flowing through the remaining LED does not increase, so the number of LEDs can be arbitrarily increased and decreased, and thinning drive for energy saving and the like is also possible. .

The circuit diagram which shows one Example of the power supply device for LED parallel drive which concerns on this invention.

  The LED parallel drive power supply device according to the present invention is a system in which a plurality of LEDs provided in parallel are collectively driven by one DC output from the regulator unit. This power supply device is based on a regulator unit that stabilizes a DC input for a regulator to produce a DC output, a load current detection resistor provided in series with an LED that is a load, and a stabilization control based on a voltage drop caused by the load current detection resistor A feedback circuit for generating a feedback signal for input to the feedback terminal of the regulator unit. The regulator DC input is obtained by rectifying and smoothing an AC input from a commercial power source.

  In the present invention, a plurality of the LEDs that are loads are provided in parallel to one DC output of the regulator unit, and a load current detection resistor is connected between the cathode side of each LED and GND, and the feedback circuit Includes a diode OR circuit connected to each load current detection resistor, and generates a feedback signal by the feedback circuit with reference to a terminal voltage of the load current detection resistor having the largest voltage drop, and the feedback signal is fed back to the regulator unit. The output is input to the terminal and the output is stabilized and controlled.

  As a result, even if a fault occurs in one of the LEDs provided in parallel and the current is not flowing due to an open state, the current that flows through the remaining normal LED is the load current that is connected to it. Since it is detected as a voltage drop due to the detection resistor and is fed back to the regulator unit by the OR function, a normal LED will continue to operate at the same brightness, with almost the same current flowing as before the malfunction occurred.

  FIG. 1 is a circuit diagram showing an embodiment of a power supply device for LED parallel driving according to the present invention. The load of the power supply device is composed of a plurality of (two in the example shown in FIG. 1) LEDs provided in parallel. The power supply device collectively drives the first LED 12a and the second LED 12b provided in parallel by one DC output stabilized by the regulator unit 10. Basically, the regulator unit 10 that stabilizes the DC input for the regulator to obtain a DC output, the load current detection resistors R1 and R2 provided in series with the LEDs that are the loads, and the load current detection resistors R1 and R2 A feedback circuit 14 is provided that generates a feedback signal for stabilizing control based on the voltage drop caused by the signal and inputs the feedback signal to the feedback terminal FB of the regulator unit 10. In this embodiment, a four-terminal series dropper regulator IC is used as the regulator unit 10. This IC has a function of detecting a current flowing through a load (LED) by converting it into a voltage using a load current detection resistor and controlling the output current to be constant. In addition, LED used as load here has arrange | positioned several LED element in series.

  As described above, the load current detection resistor is provided in series with each LED. The first load current detection resistor R1 is provided between the cathode side of the first LED 12a and GND, and the second load current detection resistor R2 is provided between the cathode side of the second LED 12b and GND. It is done. The feedback circuit 14 includes a diode OR circuit 16 and a current adjustment resistor R3. The diode OR circuit 16 short-circuits the cathode ends of the same number (and therefore two in this embodiment) of the OR diodes D1 and D2 as the load LEDs, and the anode ends correspond to the corresponding load current detection resistors R1. , R2 are connected. That is, the anode of the first OR diode D1 is connected to the connection point between the first LED 12a and the first load current detection resistor R1, and the anode of the second OR diode D2 is connected to the second LED 12b and the second load. Connected to the connection point with the current detection resistor R2. In addition, a commonly connected cathode end of the first OR diode D1 and the second OR diode D2 is connected to one end of the current adjustment resistor R3, and the other end of the current adjustment resistor R3 is connected to GND. Then, the cathode voltage commonly connected to both the OR diodes D1 and D2 becomes a feedback signal and is input to the feedback terminal FB of the regulator unit 10.

  Here, the LEDs having the same electrical characteristics are used as the LEDs and the load current detection resistors so that almost equal load currents flow. In addition, each of the OR diodes has the same electrical characteristics. The resistor R4 provided in series with each LED is a resistor that suppresses a current difference between the LEDs, and when provided, a resistor of about several hundreds Ω or less is used.

  During normal operation, a load current flows through each LED and each load current detection resistor corresponding to each LED, and both LEDs are lit at a predetermined brightness. Each load current is detected as a drop voltage in the first and second load current detection resistors R1 and R2. Therefore, the OR diode connected to the terminal having the highest terminal voltage of the load current detection resistor is turned on (conductive), the remaining OR diodes are turned off (non-passive), and the load having the largest load current flows. It becomes the standard of control. That is, a voltage obtained by subtracting the forward voltage drop of the OR diode from the higher terminal voltage Va of the first load current detection resistor R1 and the terminal voltage Vb of the second load current detection resistor R2 is used as the feedback signal. This is input to the feedback terminal FB of the regulator unit 10. The output of the regulator unit 10 is controlled by the feedback signal, and a constant current flows from each power source device to each LED as a load.

  Here, it is assumed that for some reason, one of the LEDs (for example, the first LED 12a) malfunctions and becomes open. Then, the load current flows only in the second LED 12b. Since no current flows through the first load current detection resistor R1, its terminal voltage is 0V, and the first OR diode D1 is off. On the other hand, since a current flows through the second load current detection resistor R2, the terminal voltage thereof is higher by the voltage drop, and the second OR diode D2 is on. Accordingly, the cathode voltage of the second OR diode D2 is input to the feedback terminal FB of the regulator unit 10 as a feedback signal. Since the output of the power supply device is controlled so that the feedback signal becomes constant, the current flowing through the second LED 12b hardly changes. In other words, even if a problem occurs in the first LED 12a, the brightness of the second LED 12b remains almost unchanged and remains on. Moreover, it will be restored if the defective LED is replaced.

  In the above embodiment, a four-terminal series dropper regulator IC is used. However, the present invention is not limited to this, and various isolated switching power supplies are used in addition to a step-down chopper circuit and a step-up chopper circuit. be able to.

  In the above embodiment, the load is composed of two LEDs, but it goes without saying that the present invention can be similarly applied when three or more LEDs are provided in parallel. A load current detection resistor may be provided for each LED, and an OR diode may be provided for each LED. Even if any one of the LEDs fails, the other LEDs continue to be lit at the same brightness. Of course, even if a defect occurs in a plurality of LEDs, if normal LEDs remain, those LEDs continue to be lit at the same brightness.

10 Regulator section 12a First LED
12b Second LED
14 feedback circuit 16 diode OR circuit R1 first load current detection resistor R2 second load current detection resistor

Claims (2)

Creates a feedback signal for stabilization control based on a regulator unit that stabilizes the DC input and outputs DC, a load current detection resistor provided in series with the LED that is the load, and a voltage drop caused by the load current detection resistor In a power supply apparatus that includes a feedback circuit that inputs to a feedback terminal of the regulator unit and drives an LED that is a load with a DC output stabilized by the regulator unit,
The LEDs that are loads are provided in parallel with one DC output of the regulator unit, load current detection resistors are connected between the cathode side of each LED and GND, and the feedback circuit includes each load current. Provided with a diode OR circuit connected to the detection resistor, a feedback signal is created by the feedback circuit based on the terminal voltage of the load current detection resistor having the largest voltage drop, and the feedback signal is input to the feedback terminal of the regulator unit. A power supply device for parallel LED driving, characterized by stabilizing the output.   The feedback circuit includes a diode OR circuit and a current adjustment resistor. The diode OR circuit short-circuits the cathode ends of the same number of OR diodes as the load LED, and the anode ends are different load current detection resistors. The common cathode end of the diode OR circuit is connected to GND via the current adjustment resistor, and the voltage at the common cathode end of the diode OR circuit serves as a feedback signal to the regulator. The LED parallel drive power supply device according to claim 1, wherein the LED is input to the feedback terminal of a unit and each LED serving as a load is driven by constant current control.

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