JP4873847B2 - LED lighting drive circuit - Google Patents

Description

  The present invention relates to an illumination LED lighting drive circuit, and more particularly to an LED lighting drive circuit that prevents an increase in current due to an abnormality in an LED line.

An example of a conventional LED lighting drive circuit shown in FIG. The conventional LED lighting drive circuit is provided with a plurality of LED lines 11, 12, 13, and 14 formed by connecting LEDs in series, and these LEDs are connected in parallel to turn on an illumination LED that constitutes the LED module 10. The drive circuit is current controlled with a constant current. In this control method, a change in potential at both ends of the current detection resistor R1 is detected, amplified by the current detection error amplifier EA1, and fed back to the control circuit to perform constant current control (see Patent Document 1 as another example). ).
JP-A-63-226079

  However, even when one LED line 11, 12, 13, 14 is opened due to an abnormality, the constant current value is determined by the reference voltage Vref of the current detection error amplifier EA1, so the current value flowing through the entire LED does not change. . Therefore, the current flowing in the abnormal line is dispersed and flows to other lines, the current increases, the illuminance and color temperature change, the LED current exceeds the rated current, and the life of the LED increases. The problem of shortening occurred.

  The present invention has been made in view of the above problems, and provides an LED lighting drive circuit that prevents an increase in current due to an abnormality in an LED line.

  In order to solve the above-described problems, an LED lighting drive circuit according to the present invention includes a plurality of LED lines formed by connecting LEDs in series, and these LEDs are connected in parallel to form an LED module. In the lighting driving circuit, a constant current control error amplifier that performs constant current control of the LED module and a normal line that detects the abnormal line when the LED module is opened from a constant current loop due to an abnormality such as a failure An operating current detection circuit is provided, and when an abnormality is detected by the normal operation current detection circuit, the constant voltage level of the LED lighting drive circuit as a whole is lowered by changing the reference voltage level of the constant current control error amplifier. And the current is made constant.

  The normal operating current detection circuit is connected between the output of each LED line and the constant current control error amplifier, and a series circuit of a diode and a resistor in a reverse direction to the normal current detection comparator is connected to the constant current control error. A normal operation current detection resistor is connected to a detection terminal of a normal current detection comparator and connected to a reference terminal of the amplifier.

  According to the present invention, even when an abnormality occurs in the LED line, when the abnormality of the LED line is detected, the constant voltage level of the entire LED lighting drive circuit is changed by changing the reference voltage level of the constant current control error amplifier. By making the current constant by lowering the current, it is possible to prevent an increase in the current of a normal LED line, suppress changes in illuminance and color temperature, and prevent the LED module from exceeding the rated current .

  A circuit diagram of the best mode for carrying out the invention is shown in FIG. The LED lighting drive circuit shown in FIG. 1 includes a step-down chopper type switching circuit 1, and an LED module 10 is configured at the output of the circuit 1. The LED module 10 according to this embodiment includes a plurality of LEDs connected in series, four LED lines 11, 12, 13, and 14 formed by connecting the LEDs in series, and connected in parallel to four systems. Parallel lines are configured.

  A constant current control error amplifier EA1 for performing constant current control of the LED module 10 and a normal operating current for detecting the abnormal line when the LED lines 11 to 14 are opened from the constant current loop due to an abnormality such as a failure. A detection circuit 20 is provided. An embodiment of the normal operating current detection circuit 20 will be described later.

  When the output of the normal operation current detection circuit 20 and the output of the LED module 10 are connected to the respective inputs of the constant current control error amplifier EA1, and the abnormality is detected by the normal operation current detection circuit 20, the reference of the constant current control error amplifier EA1 By changing the voltage level so as to decrease, the constant current level of the entire LED lighting drive circuit is decreased to make the current constant.

  The output terminal of the constant current control error amplifier EA1 is connected to the driver Dr. This driver Dr is connected to the base of the switch Tr provided in the switching circuit 1, and the switch Tr is set by the output of the constant current detection error amplifier EA1. The LED module 10 is configured to be switched so that a constant current flows.

  Next, the normal operating current detection circuit 20 will be described. The normal operating current detection circuit 20 according to this embodiment includes normal current detection comparators EA2 and EA3 between the outputs of the LED lines 11 to 14 and the positive input terminal on the reference voltage Vref setting side of the constant current control error amplifier EA1. , EA4, EA5, diodes D10, D11, D12, D13 in the reverse direction and resistors R7, R8, R9, R10 are connected in series.

  Specifically, the outputs of the LED lines 11 to 14 are connected to the detection terminals of the normal current detection comparators EA2 to EA5. A reference voltage circuit for a reference setting voltage V2 is connected to the reference terminals of the normal current detection comparators EA2 to EA5, and the reference setting voltage V2 and the output voltages of the LED lines 11 to 14 are compared. is there.

  The output terminals of the normal current detection comparators EA2 to EA5 are connected to the cathodes of the diodes D10, D11, D12, and D13, and the anodes of the diodes D10 to D13 are connected to the resistors R7, R8, R9, and R10. These resistors R7 to R10 are connected and integrated, and a reference voltage circuit is configured with a series circuit of the resistor R6 and the reference voltage power supply V1 so that the reference setting voltage V1 for detection is further applied, and further adjusted in parallel with this series circuit A resistor VR1 is connected to provide a reference voltage Vref of the constant current control error amplifier EA1, and is connected to a positive input terminal on the reference voltage Vref setting side of the constant current detection error amplifier EA1.

  Normal operation current detection resistors R2, R3, R4, and R5 are connected between the outputs of the LED lines 11 to 14 and the negative input terminal of the constant current control error amplifier EA1, and normal operation current detection resistors R2 to R5. Is connected to the LED current detection resistor R1.

  The LED lighting drive circuit configured as described above operates as follows. First, in the normal state, current flows through the LED lines 11 to 14, and therefore current flows through the current detection resistors R2 to R5 of the LED lines 11 to 14, so that the normal operation current detection circuit 20 is configured. This is because a voltage higher than the reference set voltage V2 is input to the positive inputs of the normal current detection comparators EA2 to EA5, and a high is output to the output, so that the resistor R7 constituting the series circuit of the normal operating current detection circuit 20 ~ R10 is blocked from conduction by diodes D10 to D13 constituting the series circuit. Therefore, the input reference voltage of the positive terminal of the constant current detection error amplifier EA1 is equal to the reference voltage V1, and the reference voltage Vref is Vref = (VR1 / (R6 + VR1)) * V1 + VF (D10). The driver Dr is constant-current controlled to match the voltage.

  Subsequently, when the LEDs constituting the LED line 11 are in an open state due to an element abnormality or the like, no current flows through the normal operating current detection resistor R2, and therefore the output of the normal current detection comparator EA2 connected to the LED line 11 is Become low. As a result, the resistors R8, R9, and R10 connected to the normal LED lines 12, 13, and 14 do not conduct, whereas the resistor R7 connected to the LED line 11 conducts, so that the reference voltage Vref is Vref = ( R7 // VR1 (R6 + R7 // VR1)) * V1 + VF (D10). Accordingly, the constant current set value is lowered, and the currents of other normal LED lines are controlled to be constant.

  As a specific example, when each LED line 11 to 14 is designed to pass a current at 300 mA, in this embodiment, the LED module 10 is configured with four parallel lines, so that when normal, 1200 mA. The reference voltage Vref is set so that, in the case of this embodiment, the LEDs constituting the LED line 11 are in an open state due to element abnormality or the like, and therefore the reference voltage Vref is varied to be 900 mA. Become.

  In the present embodiment, by operating as described above, even if an abnormality occurs in any of the LED lines 11 to 14, the reference of the constant current control error amplifier EA1 is detected when the abnormality of each LED line 11 to 14 is detected. By changing the voltage level to lower and reducing the constant current level of the entire LED lighting drive circuit to make the current constant, the increase in the current of the normal LED line is prevented, and the illuminance and color temperature Of the LED module 10 can be suppressed, and the overcurrent rating of the LED module 10 can be prevented.

  The same operation is performed when the LEDs of the other LED lines 12, 13, and 14 are in an open state due to element abnormality or the like. Moreover, in this embodiment, although the LED module 10 is comprised by the 4-system parallel line, it is not limited to a 4-system parallel line.

  According to the present invention, even when an abnormality occurs in the LED line, when the abnormality of the LED line is detected, the constant voltage level of the entire LED lighting drive circuit is changed by changing the reference voltage level of the constant current control error amplifier. By making the current constant by lowering the current, it is possible to prevent an increase in the current of the normal LED line, suppress changes in illuminance and color temperature, and prevent the rated current of the LED module from being exceeded.

It is a circuit diagram of the best form for implementing invention in the LED lighting drive circuit which concerns on this invention. It is a circuit diagram of the conventional LED lighting drive circuit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Switching circuit 10 LED module 11, 12, 13, 14 LED line 20 Normal operating current detection circuit
Tr switch
L inductor
R resistance
VR1 adjustment resistor
C capacitor
D diode
V1, V2 reference set voltage
EA1 Constant current control error amplifier
EA2, EA3, EA4, EA5 Normal current detection comparator
Dr driver
Vref reference voltage

Claims (1)

Constant current control for performing constant current control of the LED module in a lighting drive circuit of the LED for illumination, which is provided with a plurality of LED lines formed by connecting LEDs in series and connected in parallel. An error amplifier and a normal operating current detection circuit that detects the abnormal line when the LED module is opened from a constant current loop due to an abnormality such as a failure are detected, and the normal operation current detection circuit detects the abnormality. when the said varied to decrease the reference voltage level of the constant current control error amplifier, Ri configured tear to the current constant by decreasing the constant current level of the entire LED lighting driving circuit,
The normal operating current detection circuit is provided between a cathode of a downstream LED constituting each LED line and an input terminal of the constant current control error amplifier, and a cathode of the downstream LED constituting each LED line and the A normal operation current detection resistor is connected to the detection terminal of the constant current control error amplifier, and an LED current detection resistor is connected to the normal operation current detection resistor, and the cathode of the downstream LED constituting each LED line A circuit composed of a normal current detection comparator, a diode, and a resistor is connected between the reference terminal of the constant current control error amplifier, and the circuit connects the detection terminal of the normal current detection comparator to a downstream LED constituting the LED line. And connect the output terminal of the normal current detection comparator to the cathode of the diode. The anode of the LED is connected to a resistor, this resistor is connected to the reference terminal of the constant current control error amplifier, and the output terminal of the constant current control error amplifier is connected to the driver of the lighting drive circuit of the lighting LED LED lighting drive circuit according to claim Citea Rukoto.

Images