JP2005259565A - Led driving circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an LED driving circuit which is shared among a variety of LED lighting units and reduced in power consumption. <P>SOLUTION: The LED driving circuit drives a variety of LED lighting units 14A, 14B, and 14C having different rating voltages. The circuit is configured of: a variable voltage power supply 1 with a DC power supply 2; a programmable constant current source 4 which supplies a constant current of driving power to the LED lighting units; and an output voltage controlling circuit 11 which controls output voltage applied to the constant current source 4 by the variable voltage power supply 1 to be approximately constant. This configuration keeps constant applied voltage from the constant current power supply 1 to the programmable constant current source 4, eliminates power loss due to an application of excessive voltage to the constant current source 4, and reduces power consumption even in the case where a common LED driving circuit is used for a variety of LED units having different rated voltages. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an LED drive circuit for driving an LED illumination unit using LEDs (light emitting diodes).

In the field of manufacturing electronic equipment such as an electronic component mounting apparatus, a light source device using LEDs is often used as a light source for illumination when performing imaging with a camera. This light source device includes an LED illumination unit in which a plurality of LEDs are combined according to an illumination target, and an LED drive circuit that drives the LED illumination unit to emit light. This LED drive circuit includes a constant current circuit that always keeps the current flowing through the LED constant in order to cause the LED to emit light with constant brightness (see, for example, Patent Document 1).
JP 60-198872 A

  By the way, in an illuminating device used for an electronic component mounting apparatus or the like, the LED lighting unit is often replaceable depending on the type of illumination target. In such a case, a wide variety of LEDs are used with a common LED driving circuit. It is desirable to be able to drive the lighting unit. However, the LED driving circuit as shown in the above prior art example has a configuration in which the LED lighting unit is driven by a constant voltage power source. Therefore, when a plurality of types of LED lighting units having different rated voltages are used, Such inconvenience occurs.

  That is, in the conventional LED driving circuit, the current flowing to the LED is always controlled by the function of the constant current circuit, but the voltage applied to the constant current element connected in series with the LED in the constant current circuit is: It varies depending on the rated voltage of each LED lighting unit. For example, when an LED lighting unit with a low rated voltage is used, a voltage higher than necessary is applied to the constant current element, and as a result, power is converted into heat, leading to a wasteful increase in heat generation and power consumption of the device. It was.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an LED drive circuit that can be used for various types of LED lighting units and can reduce power consumption.

  The LED drive circuit of the present invention is an LED drive circuit for driving an LED lighting unit, and supplies a constant current to the LED lighting unit and a variable voltage to the constant current supply unit. A variable voltage power supply; and an output voltage control circuit that controls the variable current source so that an output voltage applied to the constant current supply means by the variable voltage power supply is substantially constant.

  According to the present invention, by adopting a configuration in which the output voltage control circuit controls the constant current supply means for supplying a substantially constant current to the LED so that the output voltage applied by the variable voltage power supply becomes substantially constant, Even when a common LED drive circuit is used for multiple types of LED units with different rated voltages, it eliminates power loss caused by unnecessary high voltage applied to the constant current supply means, saving power consumption. can do.

  Next, embodiments of the present invention will be described with reference to the drawings. 1, 2 and 3 are circuit diagrams of an LED driving circuit according to an embodiment of the present invention.

  The configuration of the LED drive circuit will be described with reference to FIG. This LED drive circuit is used to drive an LED illumination unit used as an illumination light source when an electronic component or board is imaged by a camera in an electronic component mounting apparatus or the like. As shown in FIG. 1, the LED driving circuit has a variable voltage power source 1, an output voltage control circuit 11 and a programmable constant current source 4 as main components, and a DC voltage output from the programmable constant current source 4 is converted into a driving load. Apply to the LED lighting unit.

  The LED lighting units used here may be of the same type, but in the present embodiment, as shown in FIG. 1, a plurality of types of LED lighting units 14A, 14B, and 14C having different rated voltages are used in a mixed manner. Each LED lighting unit has a configuration in which resistors and LEDs having different ratings are combined. The LED lighting unit 14A includes resistors 15A and 16A, the LED lighting unit 14B includes resistors 15B and 16B, and LED lighting. The unit 14C is configured by combining a resistor 15C and an LED 16C in series.

  These LED lighting units 14A, 14B, and 14C are connected to a common programmable constant current source 4 through a switching circuit 13 (switching means) such as a switch in a form in which the cathode side of each LED is grounded. Then, the switching power is output from the programmable constant current source 4 to a specific LED lighting unit by switching control of the switching circuit 13 by the switching command unit 12. Therefore, the switching command unit 12 and the switching circuit 13 are switching circuits that switch the supply destination of the current supplied from the programmable constant current source 4 to any of a plurality of LED lighting units having different rated voltages.

  The variable voltage power source 1 includes a DC power source 2 and a switching regulator 3 including an IC and the like. The direct current power source 2 is an external direct current power source such as a battery, and supplies direct current of a constant voltage (for example, 24V). The switching regulator 3 steps down the direct current supplied from the direct current power source 2 and outputs it to the programmable constant current source 4. At this time, the switching regulator 3 outputs a direct current of a voltage corresponding to the control signal from the output voltage control circuit 11, and the output voltage control circuit 11 detects the voltage across the programmable constant current source 4. Thus, a signal is output to the switching regulator 3 so that this voltage becomes a constant voltage value.

  The programmable constant current source 4 has a function of supplying a constant current according to a current command from the outside to the load side, and includes a current detection resistor 5, a current detection circuit 6, a constant current element 7, and a constant current control circuit 8. , An error amplification circuit 9 and a current value command unit 10. A drive current value of each LED illumination unit is input to the current value command unit 10 from an external control device (not shown) such as a control unit of the electronic component mounting apparatus for brightness adjustment or the like.

  The current output from the variable voltage power source 1 passes through the current detection resistor 5 and the constant current element 7 connected in series, and is connected to the LED lighting unit 14A, LED lighting unit 14B, and LED via the switching circuit 13. It is output to one of the lighting units 14C. At this time, a current flowing through the programmable constant current source 4 is detected by detecting the potential difference between both ends of the current detection resistor 5 by the current detection circuit 6, and the detected current value is transmitted to the error amplification circuit 9.

The error amplification circuit 9 detects an error by taking this current value and the current value commanded from the current value command unit 10 and compares them, and transmits an error signal obtained by amplifying the detected error to the constant current control circuit 8. To do. The constant current control circuit 8 is an n-type MOS-FET or the like, and has a function of controlling the constant current element 7 using a p-type MOS-FET or the like according to an error signal from the error amplification circuit 9. Yes. Based on this error signal, the constant current control circuit 8 controls the constant current element 7, so that the current flowing through the constant current element 7 becomes the current value commanded by the current value command unit 10, that is, the drive target. The appropriate driving current of the LED lighting unit is maintained.

  Therefore, the programmable constant current source 4 is a constant current supply means for supplying a substantially constant current to the LED lighting unit. In this configuration, the output voltage control circuit 11 is controlled by the variable voltage power source 1. The variable voltage power supply 1 is controlled so that the output voltage applied to is substantially constant. The programmable constant current source 4 has a series circuit in which a current detection resistor 5 and a constant voltage element 7 are connected in series. In voltage control by the output voltage control circuit 11, the output voltage control circuit 11 is connected in series. The variable voltage power supply 1 is controlled so that the voltage applied to both ends of the circuit becomes substantially constant.

  As a result, when a plurality of types of LED lighting units having different rated voltages are driven by a common LED driving circuit, the current flowing through the LED lighting unit by the programmable constant current source 4 is maintained at an appropriate driving current for each LED lighting unit. The voltage applied to the current detection resistor 5 and the constant current element 7 of the programmable constant current source 4 can be constantly controlled regardless of the rated voltage of the LED lighting unit.

  For this reason, it is possible to reduce the power loss due to an unnecessarily high voltage applied to the series circuit portion of the programmable constant current source 4 and to reduce power consumption. It is not necessary to take measures against heat generation such as installation, and the LED drive circuit as a power supply device can be simplified and reduced in cost.

  In the example shown in FIG. 1, when the output voltage control circuit 11 controls the output voltage from the variable voltage power supply 1, the voltage applied to the current detection resistor 5 and the constant current element 7 connected in series is Although the voltage is controlled to be constant, the voltage at both ends of the constant current element 7 is input to the output voltage control circuit 11 as in the programmable constant current source 4A shown in FIG. The circuit may be configured so that is constant.

  That is, in this example, the programmable constant current source 4 has a series circuit in which a current detection resistor 5 and a constant voltage element 7 are connected in series, and the output voltage control circuit 11 has a voltage applied to both ends of the constant voltage element 7. Control to be substantially constant. In this case, since the current detection resistor 5 is excluded from the voltage control target range, the amount of power loss due to excessive heat generation of the current detection resistor 5 is excluded, but substantially the same effect as the example shown in FIG. Can be obtained.

  Furthermore, the configuration of the programmable constant current source 4 shown in FIG. 1 may be simplified to form a circuit like the programmable constant current source 4B shown in FIG. In this example, the constant current element 7 and the constant current control circuit 8 are excluded from the programmable constant current source 4 in the example shown in FIG. 1. The output voltage control circuit 11 controls the current value command unit 10. Based on the command and the detection result of the current detection circuit 6, control is performed so that the voltage across the current detection resistor 5 is constant.

  That is, in this example, the programmable constant current source 4 has a current detection resistor 5, and the output voltage control circuit 11 is configured to control so that the voltage applied to both ends of the current detection resistor 5 is substantially constant. . Since this configuration is a simple configuration that does not use a constant current element, it is possible to manufacture a power-saving LED drive circuit that can save power consumption at a low cost, and has an excellent effect of facilitating maintenance. Have. In FIG. 3, the error amplifying circuit 9 and the output voltage control circuit 11 are illustrated separately from each other, but both may be configured as a single circuit.

  The LED drive circuit of the present invention can reduce power consumption by keeping the applied voltage of the constant voltage power source constant even when a common LED drive circuit is used for a plurality of types of LED lighting units having different rated voltages. This is useful for a lighting device of a type that uses a plurality of LED lighting units interchangeably according to the object.

The circuit diagram of the LED drive circuit of one embodiment of the present invention The circuit diagram of the LED drive circuit of one embodiment of the present invention The circuit diagram of the LED drive circuit of one embodiment of the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Variable voltage power supply 2 DC power supply 3 Switching regulator 4, 4A, 4B Programmable constant current source 5 Current detection resistor 6 Current detection circuit 7 Constant current element 8 Constant current control circuit 9 Error amplification circuit 10 Current value command part 11 Output voltage control circuit 12 switching command section 13 switching circuit 14A, 14B, 14C LED lighting unit 15A, 15B, 15C resistance 16A, 16B, 16C LED

Claims (5)

  An LED driving circuit for driving an LED lighting unit, a constant current supply unit that supplies a substantially constant current to the LED lighting unit, a variable voltage power source that outputs a variable voltage to the constant current supply unit, and the variable voltage An LED driving circuit, comprising: an output voltage control circuit that controls the variable current source so that an output voltage applied to the constant current supply means by a power source is substantially constant.   The constant current supply means has a series circuit in which a current detection resistor and a constant voltage element are connected in series, and the output voltage control circuit controls the voltage applied to both ends of the series circuit to be substantially constant. The LED driving circuit according to claim 1.   The constant current supply means has a series circuit in which a current detection resistor and a constant voltage element are connected in series, and the output voltage control circuit controls the voltage applied to both ends of the constant voltage element to be substantially constant. The LED driving circuit according to claim 1, wherein:   2. The LED according to claim 1, wherein the constant current supply means has a current detection resistor, and the output voltage control circuit controls the voltage applied to both ends of the current detection resistor to be substantially constant. Driving circuit. 5. The switch according to claim 1, further comprising a switching unit that switches a supply destination of the current supplied from the constant current supply unit to any of a plurality of LED lighting units having different rated voltages. LED drive circuit.

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