JP7207840B2 - LED lighting device and LED lighting device - Google Patents

Description

The present invention relates to an LED lighting device and an LED lighting device using the same.

The LED lighting devices disclosed in Patent Literature 1 and Patent Literature 2 include a power factor correction circuit (PFC circuit) in the front stage and a step-down chopper circuit in the rear stage. In such an LED lighting device, the PFC circuit in the front stage boosts and stabilizes the input voltage to generate a secondary voltage, and the step-down chopper circuit in the back stage steps down the secondary voltage to generate an output voltage. A voltage is applied to the LED array. Since such a circuit configuration can obtain a high power factor even when the load is light, it is often used, for example, in an LED lighting device that is intended for particularly deep dimming.

JP 2017-142909 A JP 2018-88789 A

However, if the potential difference between the output voltage of the DC power supply circuit such as the PFC circuit in the preceding stage and the output voltage of the step-down chopper circuit in the subsequent stage is larger than necessary, as will be described later in detail, In both of the step-down chopper circuits, useless loss occurs and the circuit efficiency decreases. Therefore, in order to suppress this decrease in efficiency, it is desirable that the output voltage of the DC power supply circuit is appropriately controlled according to the LED voltage, which is the output voltage of the step-down chopper circuit.

Therefore, the present invention provides an LED lighting device capable of suppressing losses in both the front-stage DC power supply circuit and the rear-stage step-down chopper circuit for different LED loads and improving circuit efficiency, and an LED illumination using the same. An object is to provide an apparatus.

The LED lighting device of the present invention includes: a DC power supply circuit that converts an input primary voltage into a secondary voltage and outputs the secondary voltage; A step-down chopper circuit that applies a voltage to the LED array, a voltage detection circuit that directly or indirectly detects the step-down output voltage, and a secondary voltage that decreases in accordance with a decrease in the step-down output voltage detected by the voltage detection circuit. and a control circuit for controlling the driving state of the DC power supply circuit.

According to the above configuration, the secondary voltage, which is the output voltage of the DC power supply circuit, decreases/increases according to the decrease/increase of the step-down output voltage, which is the output voltage of the step-down chopper circuit. is suppressed. This makes it possible to suppress losses in both the DC power supply circuit at the front stage and the step-down chopper circuit at the rear stage and improve the circuit efficiency for different LED loads.

In the LED lighting device according to the first aspect of the present invention, the voltage detection circuit is a differential voltage detection circuit that detects a differential voltage, which is a difference between the secondary voltage and the stepped-down output voltage, and the control circuit detects a predetermined differential voltage. The drive state of the DC power supply circuit is controlled so that the set value of is constant. As a result, the above effect can be obtained with a very simple configuration. In addition, since the output of the DC power supply circuit is reduced as a result of the control described above in response to an increase in the differential voltage due to the occurrence of the output short-circuit state of the step-down chopper circuit, an output short-circuit protection function is also realized.

In the LED lighting device according to the second aspect of the present invention, the voltage detection circuit includes a differential voltage detection circuit that detects a differential voltage that is a difference between the secondary voltage and the stepped-down output voltage, and a secondary voltage detection circuit that detects the secondary voltage. The control circuit controls the drive state of the DC power supply circuit so that the ratio between the secondary voltage and the differential voltage is constant at a predetermined set value. As a result, the above effect can be obtained with a relatively simple configuration. In addition, since the output of the DC power supply circuit is reduced as a result of the control in response to the increase or decrease of the ratio due to the occurrence of the output short-circuit state of the step-down chopper circuit, the output short-circuit protection function is also realized.

In the LED lighting device according to the third aspect of the present invention, the voltage detection circuit includes a secondary voltage detection circuit that detects the secondary voltage and a step-down voltage detection circuit that detects the step-down output voltage, and the control circuit detects the secondary voltage and the stepped-down output voltage or the ratio between the secondary voltage and the stepped-down output voltage is kept constant at a predetermined set value. As a result, the above effect can be obtained with a relatively simple configuration.

In addition, the LED lighting device of the first or second embodiment further includes a protection circuit that reduces the secondary voltage in the DC power supply circuit when the differential voltage becomes equal to or less than a predetermined threshold regardless of the control of the drive state. good too. As a result, the outputs of the DC power supply circuit and the step-down chopper circuit are suppressed or stopped in the no-load state of the step-down chopper circuit, and the standby power consumption of the DC power supply circuit and the step-down chopper circuit can be reduced.

In addition, the LED lighting device of the first or second embodiment further includes a protection circuit that reduces the step-down output voltage of the step-down chopper circuit when the differential voltage becomes equal to or less than a predetermined threshold value regardless of control of the drive state. good too. As a result, the output of the step-down chopper circuit is suppressed or stopped in the no-load state of the step-down chopper circuit, and the standby power consumption of the step-down chopper circuit can be reduced with a simple circuit configuration.

In the LED lighting device of the first or second aspect, the step-down chopper circuit includes a choke coil, a switching element, and a regenerative diode, and when the LED array is connected, the DC power supply circuit is turned on when the switching element is on. A series circuit of the LED array, the choke coil and the switching element is formed from the high potential side to the low potential side of the output terminal of the LED array, the choke coil and the regenerative diode form a closed circuit when the switching element is in the OFF state, A differential voltage detection circuit is arranged to detect the voltage applied to the series circuit of the choke coil and the switching element. With such an arrangement, a differential voltage detection circuit is added with a simple configuration to a buck converter having a general configuration as a step-down chopper circuit, and an LED lighting device with the above effects is realized with a simple configuration.

An LED lighting device of the present invention includes any one of the LED lighting devices described above and an LED array. This realizes an LED lighting device capable of obtaining the above effects.

1 is a circuit diagram showing an LED lighting device and a lighting device according to a first embodiment; FIG. FIG. 4 is a circuit diagram showing an LED lighting device and a lighting device according to a modification of the first embodiment; FIG. 5 is a circuit diagram showing an LED lighting device and a lighting device according to a second embodiment; FIG. 11 is a circuit diagram showing an LED lighting device and a lighting device according to a third embodiment; It is a circuit diagram which shows the LED lighting device and illuminating device by a modification.

<First Embodiment>
FIG. 1 shows a circuit diagram of an LED lighting device 100 and an LED lighting device 300 including the LED lighting device 100 according to the first embodiment. LED lighting device 300 includes LED lighting device 100 and LED array 200 . The LED lighting device 100 converts a DC power supply DC from a battery or the like into an appropriate output voltage and supplies the DC output to the LED array 200 . The LED array 200 includes a plurality of LED elements connected in series or series-parallel. In the following description, the forward drop voltage Vf of the LED array 200 is also referred to as LED voltage VL.

The LED lighting device 100 includes an input circuit 110 , a flyback converter 120 (DC power supply circuit), a step-down chopper circuit 130 , a differential voltage detection circuit 140 , a control circuit 150 and a no-load protection circuit 160 . The input circuit 110 includes current fuses, noise filters, input capacitors, and the like. Note that when an AC power supply AC such as a commercial power supply is connected instead of the DC power supply DC, the input circuit 110 includes a full-wave rectifier circuit such as a diode bridge. In either case, a DC voltage is applied to the output of input circuit 110 , that is, the input of flyback converter 120 . Let the output voltage of the input circuit 110, that is, the input voltage of the flyback converter 120, be the primary voltage V1.

Flyback converter 120 includes transformer 1 , switching element 2 (hereinafter referred to as “FET 2 ”), diode 3 , smoothing capacitor 4 and driver circuit 5 . A primary voltage V1 is applied to the series circuit of the primary winding 1p of the transformer 1 and the FET2. The FET 2 is switched (PWM driven) by the driver circuit 5 . When the FET 2 is turned on, a current flows through the primary winding 1p of the transformer 1, and energy is stored in the transformer 1. When the FET 2 is turned off, the energy stored in the transformer 1 is output from the secondary winding 1s of the transformer 1 via the diode 3, and the smoothing capacitor 4 is charged. The voltage of the smoothing capacitor 4, that is, the output voltage of the flyback converter 120 is referred to as a secondary voltage V2. The driver circuit 5 is composed of, for example, a control IC for a general flyback converter and its peripheral circuits. Flyback converter 120 can be a boost converter, a buck converter, or a buck-boost converter, depending on the relationship between primary voltage V1 and secondary voltage V2. The reference potential on the primary side and the reference potential on the secondary side of the flyback converter 120 are referred to as a primary ground G1 and a secondary ground G2, respectively.

The step-down chopper circuit 130 includes a choke coil 6, a switching element 7 (hereinafter referred to as "FET7"), a regenerative diode 8, a filter capacitor 9, a driver circuit 10 and a current detection resistor 11, and constitutes a buck converter. The FET 7 is switched (PWM driven) by the driver circuit 10 . During the ON period of FET 7 , LED current flows through a closed circuit formed by smoothing capacitor 4 →LED array 200 →choke coil 6 →FET 7 →current detection resistor 11 →smoothing capacitor 4 . During the OFF period of the FET 7 , an LED current flows through a closed circuit formed by choke coil 6 →regenerative diode 8 →LED array 200 →choke coil 6 using the energy of choke coil 6 as a power source. A filter capacitor 9 filters the LED current and is connected as required. The driver circuit 10 is composed of, for example, a control IC for a general step-down chopper circuit and its peripheral circuits. The current detection resistor 11 consists of a low resistance element. The driver circuit 10 can PWM-drive the FET 7 so that the voltage generated in the current detection resistor 11 (that is, the LED current when the FET 7 is on) is constant. The output voltage of the step-down chopper circuit 130 is equal to the LED voltage VL. In the present disclosure, for convenience of explanation, the output voltage of the step-down chopper circuit 130 may be referred to as the LED voltage VL even when the LED array 200 is not connected to the LED lighting device 100 .

The differential voltage detection circuit 140 is connected between the connection point between the choke coil 6 and the filter capacitor 9 (that is, the cathode end of the LED array 200) and the secondary ground G2. In other words, since the voltage generated across the current detection resistor 11 is relatively sufficiently small, the differential voltage detection circuit 140 substantially detects the voltage applied to the series circuit of the choke coil 6 and FET7. The differential voltage detection circuit 140 includes a series circuit of resistors 12 and 13 and constitutes a resistor voltage dividing circuit. A differential voltage VD (VD=V2−VL), which is the difference between the secondary voltage V2 and the LED voltage VL, is applied to the differential voltage detection circuit 140 . A divided voltage value of the differential voltage VD (that is, the voltage generated across the resistor 13) is input to the control circuit 150 and the no-load protection circuit 160 as the differential voltage detection value _VD .

The control circuit 150 and the no-load protection circuit 160 are supplied with a control voltage from an auxiliary power supply circuit (not shown). The auxiliary power supply circuit includes, for example, a circuit that steps down the voltage generated in the smoothing capacitor 4 and converts it into a constant voltage to generate a control voltage, and a circuit that rectifies and constant voltages the voltage generated in an auxiliary winding (not shown) provided in the transformer 1 . Any circuit or a combination thereof may be used as long as it converts to generate a control voltage.

Control circuit 150 includes operational amplifier 14 , reference voltage source 15 , feedback element 16 , photocoupler 17 , voltage source 18 , resistor 19 , resistor 20 and diode 21 . A differential voltage detection value V _D detected by the differential voltage detection circuit 140 is input to the inverting input terminal of the operational amplifier 14 . A reference voltage source 15 is connected to the non-inverting input terminal of the operational amplifier 14 . The voltage of the reference voltage source 15 may be, for example, a voltage generated by dividing the control voltage. may be Feedback element 16 is a circuit consisting of a resistor, a capacitor, or a combination thereof connected between the inverting input terminal and the output terminal of operational amplifier 14 . The output terminal of the operational amplifier 14 is connected through the diode 21 to the cathode of the photodiode 17d of the photocoupler 17. FIG. The anode of photodiode 17 d is connected to voltage source 18 via resistor 19 . A voltage source 18 corresponds, for example, to the control voltage mentioned above. A resistor 20 is connected between the anode and cathode of the photodiode 17d. The collector of the phototransistor 17t of the photocoupler 17 is connected to the driver circuit 5 and its emitter is connected to the primary ground G1.

The operational amplifier 14 amplifies the error between the differential voltage detection value _VD and the voltage of the reference voltage source 15 and outputs it. The voltage of the reference voltage source 15 corresponds to the set value VDs of the differential voltage VD. The amplification error output by the operational amplifier 14 is transmitted to the driver circuit 5 by the photocoupler 17 . The driver circuit 5 determines the pulse width in the PWM driving of the FET2 in the direction of canceling this amplification error. Specifically, the lower the voltage of the output terminal of the operational amplifier 14, the larger the current flowing through the photodiode 17d and the phototransistor 17t. For example, the driver circuit 5 decreases/increases the pulse width (on time or on-duty) in the PWM drive of the FET2 according to the increase/decrease of the current flowing through the phototransistor 17t, thereby decreasing/increasing the secondary voltage V2. shall consist of

That is, the control circuit 150 feedback-controls the PWM drive (pulse width) in the flyback converter 120 so that the differential voltage VD is constant at the set value VDs. Note that the circuit shown with respect to the photocoupler 17 in this embodiment is an example, and as long as the feedback operation is realized in the relationship between the control circuit 150 and the driver circuit 5, other aspects (other logic configuration, connection configuration, etc.) can also be adopted.

Here, consider a conventional LED lighting device in which the control circuit 150 is not provided. In such an LED lighting device, a sufficiently high secondary voltage V2 is set and fixed to accommodate a wide range of LED voltages VL. For example, when the LED voltage VL is assumed to be 50V to 150V, the maximum LED voltage VL (150V) and the secondary voltage V2, for example 200V, are set according to the variation range thereof. A voltage corresponding to the primary voltage V1+secondary voltage V2×turns ratio of the transformer 1 (hereinafter referred to as “VFET”) is applied to the FET2 of the flyback converter 120. FIG.

For example, in the transformer 1, when the winding ratio (the number of turns of the primary winding 1p:the number of turns of the secondary winding 1s) is 2:1, VFET=V1+V2×2=600V. Here, when the LED voltage VL of the LED array connected in such an LED lighting device is 50V, in the step-down chopper circuit 130, the difference between the secondary voltage V2 and the LED voltage VL is 150V (=200V-50V). becomes. When the difference between the secondary voltage V2 and the LED voltage VL becomes as large as 150V with respect to the LED voltage VL of 50V, this causes unnecessary circuit loss. In addition, due to the secondary voltage V2 being higher than necessary, a voltage higher than necessary (600 V in this example) is applied to the FET2 of the flyback converter 120, resulting in unnecessary switching loss. . That is, if the secondary voltage V2 that is higher than necessary is fixed, both the flyback converter 120 and the step-down chopper circuit 130 will suffer unnecessary loss, resulting in a decrease in circuit efficiency.

On the other hand, in the LED lighting device 100 of the present embodiment, the differential voltage VD, which is the difference between the secondary voltage V2 and the LED voltage VL, is controlled to be constant at the set value VDs. Here, as described above, it is assumed that the primary voltage is V1=200V and the winding ratio (the number of turns of the primary winding 1p:the number of turns of the secondary winding 1s) is 2:1. It is assumed that the set value VDs of the differential voltage VD is 30 V, for example.

When the LED voltage VL of the connected LED array 200 is 150V, the secondary voltage V2 (=VL+VD) is 180V as a result of the above control. Then, VFET=V1+V2×2=560 V is applied to FET2 of the flyback converter 120 . Thus, it is not necessary to give a large margin to the secondary voltage V2 in consideration of variations in the LED voltage VL (the forward voltage Vf of the LED array 200). Therefore, even if the LED voltage VL is the same 150 V, V2=200 V and VFET=600 V in the conventional LED lighting device, whereas V2=180 V and VFET=560 V in this embodiment. , the secondary voltage V2 can be reduced. This reduces loss in both the flyback converter 120 and the step-down chopper circuit 130, improving circuit efficiency.

Further, when the LED voltage VL of the connected LED array 200 is 50V, the secondary voltage V2 (=VL+VD) becomes 80V as a result of the above control. VFET=V1+V2×2=360 V is applied to FET2 of the flyback converter 120. FIG. Thus, even if the LED voltage VL is the same 50 V, the secondary voltage V2=200 V and VFET=600 V in the conventional LED lighting device, whereas V2=80 V in this embodiment. , VFET=360V, and the secondary voltage V2 can be greatly reduced. As a result, losses are significantly reduced in both flyback converter 120 and step-down chopper circuit 130, and circuit efficiency is greatly improved.

Further, in an output short-circuit state of the step-down chopper circuit 130 (for example, a short-circuit failure of the LED array 200, etc.), the differential voltage VD becomes equal to the secondary voltage V2. In this case, the feedback operation of the control circuit 150 acts to reduce the differential voltage VD, the pulse width in the PWM driving of the FET2 by the driver circuit 5 is minimized, or the driving of the FET2 by the driver circuit 5 is stopped. In other words, the control circuit 150 not only reduces the loss of the flyback converter 120 and the step-down chopper circuit 130, that is, improves the efficiency, but also achieves the protection function against the output short circuit of the step-down chopper circuit 130. FIG.

No-load protection circuit 160 includes comparator 22 , threshold voltage source 23 and diode 24 . The no-load protection circuit 160 detects a no-load state of the step-down chopper circuit 130 and triggers protection operation, and is connected as required. This no-load state corresponds to the case where the LED array 200 is not connected or the LED array 200 is disconnected. A differential voltage detection value V _D detected by the differential voltage detection circuit 140 is input to the inverting input terminal of the comparator 22 . The non-inverting input terminal of comparator 22 is connected to threshold voltage source 23 . The threshold voltage source 23 may be, for example, a threshold generated by dividing the control power supply, or may be a voltage input from the microcomputer (not shown) when the LED lighting device 100 includes a microcomputer. may This threshold corresponds to the voltage threshold for detecting when the differential voltage VD has become substantially zero.

The output terminal of the comparator 22 is connected through the diode 24 to the anode of the photodiode 17d of the photocoupler 17. FIG. Diode 21 and diode 24 form a diode OR circuit. That is, this diode OR circuit is turned on with respect to the lower one of the output voltage of the operational amplifier 14 and the output voltage of the comparator 22 . If the no-load protection circuit 160 is not connected, the diode 21 of the control circuit 150 becomes unnecessary. Also, the comparator 22 may be configured by an operational amplifier (eg, another operational amplifier included in the operational amplifier IC in which the operational amplifier 14 is packaged).

The comparator 22 outputs a low level when the differential voltage detection value _VD exceeds the threshold (when the LED array 200 is normally connected), and outputs a low level when the differential voltage detection value _VD is equal to or less than the threshold (no load state), it outputs a high level. That is, when the differential voltage VD exceeds the voltage threshold, the diode 24 is turned off, and the current flowing through the photodiode 17d and the phototransistor 17t is determined only by the operation of the operational amplifier 14. FIG. On the other hand, when the differential voltage VD is equal to or less than the voltage threshold, the diode 24 is turned on and the current flowing through the photodiode 17d and the phototransistor 17t is maximized. As a result, the pulse width in the PWM driving of the FET2 by the driver circuit 5 is minimized, or the driving of the FET2 by the driver circuit 5 is stopped. Thereby, the secondary voltage V2 becomes a sufficiently low voltage or zero when there is no load.

Here, FIG. 2 shows an LED lighting device 100 and an LED lighting device 300 according to modifications of the present embodiment. In this modified example, the configuration of the no-load protection circuit is different from that of FIG. In this modified example, the same reference numerals are given to the same configurations as in the above-described embodiment, and duplicate descriptions thereof will be omitted.

As shown in FIG. 2 , the LED lighting device 100 includes a no-load protection circuit 165 that includes a comparator 22 and a threshold voltage source 23 . The differential voltage detection value _VD is input to the inverting input terminal of the comparator 22, and the non-inverting input terminal of the comparator 22 is connected to the threshold voltage source 23, as in the above embodiment (FIG. 1). On the other hand, in this modified example, the output terminal of the comparator 22 is connected to the driver circuit 10 . The driver circuit 10 is configured to stop driving the FET 7 when the input from the comparator 22 becomes high level. For example, if the driver circuit 10 includes a control IC, the output terminal of the comparator 22 can be connected to an enable pin or the like of the control IC via an appropriate pull-up circuit or the like.

When the differential voltage detection value _VD is equal to or less than the threshold (in the no-load state), the output of the comparator 22 becomes high level, so that the driving of the FET 7 by the driver circuit 10 is stopped. In this modification, the driver circuit 10 is configured to stop driving the FET 7 in response to a high level output from the no-load protection circuit 165. may be configured to reduce the pulse width of the PWM drive of FET7. In either case, the output voltage of step-down chopper circuit 130 is reduced (ie, zero or a sufficiently low voltage) when there is no load. Further, depending on the specifications of the driver circuit 10, the driving of the FET 7 may be stopped when the output of the comparator 22 is at low level. In this case, the differential voltage detection value V _D is input to the non-inverting input terminal of the comparator 22 , and the inverting input terminal of the comparator 22 is connected to the threshold voltage source 23 .

As described above, the LED lighting device 100 of the present embodiment includes the flyback converter 120 (DC power supply circuit) that converts the input primary voltage V1 into the secondary voltage V2 and outputs the secondary voltage V2, and the secondary A step-down chopper circuit 130 that steps down the voltage V2 to generate an LED voltage VL (step-down output voltage) and applies the LED voltage VL to the LED array 200, and a differential voltage VD that is the difference between the secondary voltage V2 and the LED voltage VL. and a control circuit 150 for controlling the drive state of the flyback converter 120 so that the differential voltage VD is constant at the set value VDs.

Thus, the driving state of the flyback converter 120 is controlled so that the differential voltage VD, which is the difference between the secondary voltage V2 and the LED voltage VL, is kept constant at the set value VDs. That is, since the secondary voltage V2 of the flyback converter 120 decreases/increases according to the decrease/increase of the LED voltage VL, the difference between the secondary voltage V2 and the LED voltage VL is suppressed. This makes it possible to suppress losses in both the DC power supply circuit at the front stage and the step-down chopper circuit at the rear stage and improve the circuit efficiency for different LED loads. Furthermore, the fact that it is not necessary to fix the secondary voltage V2 with a margin in consideration of variations in the forward voltage Vf of the LED array 200 also contributes to the above loss reduction and efficiency improvement. In addition, as a secondary effect, the differential voltage VD increases (maximum VD=V2) due to the occurrence of the output short-circuit state of the step-down chopper circuit 130, and the output of the flyback converter 120 is minimized by the feedback control. or suspended. This also realizes the function of output short circuit protection.

Further, the LED lighting device 100 may include a no-load protection circuit 160 that reduces the secondary voltage V2 of the flyback converter 120 when the differential voltage VD becomes equal to or less than a predetermined threshold value regardless of control of the drive state. As a result, the outputs of the flyback converter 120 and the step-down chopper circuit 130 are suppressed or stopped in the no-load state of the step-down chopper circuit 130, and the standby power consumption of the flyback converter 120 and the step-down chopper circuit 130 can be reduced.

Further, the LED lighting device 100 may include a no-load protection circuit 165 that reduces the output voltage of the step-down chopper circuit 130 when the differential voltage VD becomes equal to or less than a predetermined threshold value regardless of control of the drive state. As a result, the output of the step-down chopper circuit 130 is suppressed or stopped in the no-load state of the step-down chopper circuit 130, and the standby power consumption of the step-down chopper circuit 130 can be reduced with a simple circuit configuration.

Also, in the LED lighting device 100, the step-down chopper circuit 130 includes the choke coil 6, the FET 7, and the regenerative diode 8, and when the LED array 200 is connected, the output end of the flyback converter 120 is reduced when the FET 7 is on. A series circuit of the LED array 200, the choke coil 6 and the FET 7 is formed from the high potential side to the low potential side. A differential voltage detection circuit 140 is arranged to detect the voltage applied to the series circuit of the choke coil 6 and the FET 7 . As a result, the difference voltage detection circuit 140 is added with a simple configuration to a buck converter having a general configuration as a step-down chopper circuit, and the LED lighting device 100 that exhibits the above effects is realized with a simple configuration.

<Second embodiment>
In the first embodiment, the differential voltage VD is configured to be constant at the set value, but in the present embodiment, the ratio of the differential voltage VD to the secondary voltage V2 is configured to be constant at the set value. Here is an example of what is

FIG. 3 shows an LED lighting device 100 and an LED lighting device 300 according to this embodiment. In this embodiment, the same reference numerals are given to the same configurations as in the first embodiment, and redundant descriptions thereof are omitted or simplified. In this embodiment, a differential voltage detection circuit 140 and a secondary voltage detection circuit 170 are provided as voltage detection circuits, and the secondary voltage detection circuit 170 and the divider 27 are added to the first embodiment.

The secondary voltage detection circuit 170 is connected in parallel with the smoothing capacitor 4 and the secondary voltage V2 is applied to the secondary voltage detection circuit 170 . The secondary voltage detection circuit 170 includes a series circuit of resistors 25 and 26 to form a resistive voltage dividing circuit. A divided voltage value of the secondary voltage V2 (that is, the voltage generated across the resistor 26) is input to the divider 27. FIG. A divided voltage value of the secondary voltage V2 is referred to as a _secondary voltage detection value V2. A differential voltage detection value VD of the differential voltage _VD by the differential voltage detection circuit 140 is also input to the divider 27 .

In control circuit 150 , divider 27 is connected to the front stage of the inverting input terminal of operational amplifier 14 . The divider 27 is realized, for example, in a microcomputer (not shown), and calculates a value (=Vd/V ₂ ) obtained by dividing the differential voltage detection value _VD by the secondary voltage detection value V ₂ . For convenience of explanation, it is assumed that the resistance voltage division ratio in the differential voltage detection circuit 140 and the resistance voltage division ratio in the secondary voltage detection circuit 170 are the same, and V _D /V ₂ =VD/V2. However, both voltage division ratios may be different. The divider 27 inputs the division result=VD/V2 (hereinafter referred to as “ratio R”) to the inverting input terminal of the operational amplifier 14 .

The operational amplifier 14 amplifies the error between the output voltage (ratio R) of the divider 27 and the voltage of the reference voltage source 15 and outputs it. The voltage of the reference voltage source 15 corresponds to the set value Rs of the ratio R. The amplification error output by the operational amplifier 14 is transmitted to the driver circuit 5 by the photocoupler 17, and the driver circuit 5 determines the pulse width in the PWM drive of the FET2 in the direction of canceling this amplification error. That is, control circuit 150 feedback-controls flyback converter 120 so that ratio R is constant at set value Rs.

Here, as in the first embodiment, it is assumed that the primary voltage is V1=200 V and the turn ratio (the number of turns of the primary winding 1p:the number of turns of the secondary winding 1s) is 2:1. It is assumed that the set value Rs of R (=VD/V2) is, for example, 1/6.

When the LED voltage VL of the connected LED array 200 is 150V, the secondary voltage V2 (=VL×1.2) is 180V as a result of the above control. Then, V1+V2×2=560V is applied to FET2 of the flyback converter 120 . Thus, it is not necessary to give a large margin to the secondary voltage V2 in consideration of variations in the LED voltage VL (forward voltage Vf). Therefore, even if the LED voltage VL is the same 150 V, V2=200 V and VFET=600 V in the conventional LED lighting device, whereas V2=180 V and VFET=560 V in this embodiment. , the secondary voltage V2 can be reduced. This reduces loss in both the flyback converter 120 and the step-down chopper circuit 130, improving circuit efficiency.

Also, when the LED voltage VL of the connected LED array 200 is 50V, the secondary voltage V2 (=VL×1.2) is 60V as a result of the above control. Then, VFET=V1+V2×2=320 V is applied to FET2 of the flyback converter 120 . Thus, even if the LED voltage VL is the same 50 V, V2=200 V and VFET=600 V in the conventional LED lighting device, whereas V2=60 V and VFET=600 V in this embodiment. 320 V, and the secondary voltage V2 can be significantly reduced. As a result, losses are significantly reduced in both flyback converter 120 and step-down chopper circuit 130, and circuit efficiency is greatly improved.

Further, in an output short-circuit state of the step-down chopper circuit 130 (for example, a short-circuit failure of the LED array 200, etc.), the differential voltage VD becomes equal to the secondary voltage V2 and the ratio R becomes equal to one. In this case, the feedback operation of the control circuit 150 acts to reduce the ratio R, the pulse width in the PWM driving of the FET2 by the driver circuit 5 is minimized, or the driving of the FET2 by the driver circuit 5 is stopped. In other words, the control circuit 150 not only reduces the loss of the flyback converter 120 and the step-down chopper circuit 130, that is, improves the efficiency, but also achieves the protection function against the output short circuit of the step-down chopper circuit 130. FIG.

In the present embodiment, the ratio R is defined as the ratio of the differential voltage VD to the secondary voltage V2 (=VD/V2), but the ratio R is the ratio of the secondary voltage V2 to the differential voltage VD (=V2/VD). , and appropriately configuring the logic of the control circuit 150, it is possible to perform the same control as described above. FIG. 3 shows a configuration in which the no-load protection circuit 160 is connected to the control circuit 150 as in the first embodiment (FIG. 1), but it is different from the modification of the first embodiment (FIG. 2). Similarly, a configuration in which no-load protection circuit 165 is connected to driver circuit 10 may be employed.

As described above, the LED lighting device 100 according to the present embodiment includes the flyback converter 120 (DC power supply circuit) that converts the input primary voltage V1 into the secondary voltage V2 and outputs the secondary voltage V2, and the secondary A step-down chopper circuit 130 that steps down the voltage V2 to generate an LED voltage VL (step-down output voltage) and applies the LED voltage VL to the LED array 200, and a differential voltage VD that is the difference between the secondary voltage V2 and the LED voltage VL. a secondary voltage detection circuit 170 for detecting the secondary voltage V2; and a control circuit 150 that controls the driving state of the converter 120 .

In this manner, the drive state of flyback converter 120 is controlled such that ratio R between secondary voltage V2 and differential voltage VD is constant at a set value. That is, since the secondary voltage V2 of the flyback converter 120 decreases/increases according to the decrease/increase of the LED voltage VL, the difference between the secondary voltage V2 and the LED voltage VL is suppressed. This makes it possible to suppress losses in both the flyback converter 120 at the front stage and the step-down chopper circuit 130 at the rear stage and improve the circuit efficiency for different LED loads. Furthermore, the fact that it is not necessary to fix the secondary voltage V2 with a margin in consideration of variations in the forward voltage Vf of the LED array 200 also contributes to the above loss reduction and efficiency improvement. Also, as a secondary effect, the ratio R increases or decreases (maximum or minimum R=1) due to the occurrence of the output short circuit state of the step-down chopper circuit 130, and the feedback function minimizes the output of the flyback converter 120. or be stopped. This also realizes the function of output short circuit protection. Also in the present embodiment, the effects obtained by the no-load protection circuit 160 or 165 and the effects regarding the placement of the differential voltage detection circuit 140 in the step-down chopper circuit 130 are the same as in the first embodiment.

<Third Embodiment>
In the above first and second embodiments, the step-down chopper circuit 130 constituting the buck converter has the configuration in which the LED array 200 is arranged on the higher potential side than the choke coil 6 and the FET 7 . On the other hand, this embodiment shows a configuration in which the LED array 200 is arranged on the lower potential side than the choke coil 6 and the FET 7 in the step-down chopper circuit 130' that constitutes the buck converter.

FIG. 4 shows an LED lighting device 100 and an LED lighting device 300 according to this embodiment. In this embodiment, the same reference numerals are assigned to substantially the same configurations as in the first or second embodiment, and redundant descriptions thereof will be omitted or simplified. In this embodiment, a step-down chopper circuit 130' is used instead of the step-down chopper circuit 130, and a secondary voltage detection circuit 170 and a step-down voltage detection circuit 180 are provided as voltage detection circuits.

As shown in FIG. 4, the step-down chopper circuit 130' of this embodiment is a buck converter, but its connection configuration is different from that of the step-down chopper circuits 130 of the first and second embodiments. In the step-down chopper circuit 130', an LED current flows through a closed circuit formed by the smoothing capacitor 4→FET7→choke coil 6→LED array 200→current detection resistor 11→smoothing capacitor 4 during the ON time of FET7. During the OFF period of the FET 7 , an LED current flows through a closed circuit formed by the choke coil 6 →the LED array 200 →the regenerative diode 8 →the choke coil 6 using the energy of the choke coil 6 as a power source. The driver circuit 10' is composed of, for example, a control IC for a step-down chopper circuit and its peripheral circuits. The driver circuit 10' can PWM-drive the FET 7 so that the voltage (that is, the LED current) generated in the current detection resistor 11 is constant.

In this embodiment, the step-down voltage detection circuit 180 is connected in parallel to the LED array 200, and the LED voltage VL is applied to the step-down voltage detection circuit 180. FIG. The step-down voltage detection circuit 180 includes a series circuit of resistors 28 and 29 and constitutes a resistor voltage dividing circuit. A divided voltage value of the LED voltage VL (that is, the voltage generated across the resistor 29) is input to the control circuit 150 as the LED voltage detection value _VL .

In control circuit 150 , subtractor/divider 30 is connected to the front stage of the inverting input terminal of operational amplifier 14 . The secondary voltage detection value V2 detected by the _secondary voltage detection circuit 170 and the LED voltage detection value _VL detected by the step-down voltage detection circuit 180 are input to the subtractor/divider 30 . The subtractor/divider 30 is implemented, for example, in a microcomputer (not shown), and is the difference between the secondary voltage detection value V ₂ and the LED voltage detection value V _L (=V ₂ −V _L ) or the secondary voltage detection value V ₂ A ratio R' ( _{= VL} /V2) of the LED voltage detection value _VL to is calculated. For convenience of explanation, it is assumed that the resistance voltage division ratio in the secondary voltage detection circuit 170 and the resistance voltage division ratio in the step-down voltage detection circuit 180 are the same, and the explanation is given as V _L /V ₂ =VL/V2. However, both voltage division ratios may be different. The subtractor/divider 30 inputs the operation result to the inverting input terminal of the operational amplifier 14 .

The operational amplifier 14 amplifies the error between the output voltage of the subtractor/divider 30 and the voltage of the reference voltage source 15 and outputs it. The voltage of the reference voltage source 15 corresponds to the set value VDs of the differential voltage VD (=V2-VL) or the set value Rs' of the ratio R' of the LED voltage VL to the secondary voltage V2. The amplification error output from the operational amplifier 14 is transmitted to the driver circuit 5 by the photocoupler 17, and the driver circuit 5 determines the pulse width in the PWM driving of the FET2 in the direction of canceling this amplification error. That is, the control circuit 150 feedback-controls the flyback converter 120 so that the differential voltage D or the ratio R' is constant at the set value VDs or Rs'.

Note that the set value VDs for the differential voltage VD may be the same as the set value VDs in the first embodiment. This makes it possible to obtain the same actions and effects as those of the first embodiment. Also, the set value Rs' of the ratio R' may be the same as the set value for (1-R) with respect to the ratio R in the second embodiment. For example, since Rs=1/6 in the second embodiment, the ratio Rs'=5/6 may be used in the present embodiment. This makes it possible to obtain the same actions and effects as those of the second embodiment.

In this embodiment, the ratio R' is defined as the ratio of the LED voltage VL to the secondary voltage V2 (=VL/V2), but the ratio R' is the ratio of the secondary voltage V2 to the LED voltage VL (=V2/ VL) and appropriately configuring the logic of the control circuit 150, it is also possible to perform the same control as described above. FIG. 4 shows a configuration in which the no-load protection circuit 160 is connected to the control circuit 150 as in the first embodiment (FIG. 1), but it is different from the modification of the first embodiment (FIG. 2). Similarly, a configuration in which the no-load protection circuit 165 is connected to the driver circuit 10' may be adopted.

As described above, the LED lighting device 100 according to the present embodiment includes the flyback converter 120 (DC power supply circuit) that converts the input primary voltage V1 into the secondary voltage V2 and outputs the secondary voltage V2, and the secondary a step-down chopper circuit 130' that steps down the voltage V2 to generate an LED voltage VL (step-down output voltage) and applies the LED voltage VL to the LED array 200; a secondary voltage detection circuit 170 that detects the secondary voltage V2; A step-down voltage detection circuit 180 for detecting the LED voltage VL, and the difference (VD) between the secondary voltage V2 and the LED voltage VL or the ratio R' between the secondary voltage V2 and the LED voltage VL is a predetermined set value VDs or Rs'. and a control circuit 150 for controlling the drive state of the flyback converter 120 to be constant.

As a result, the drive state of the flyback converter 120 is adjusted so that the differential voltage VD between the secondary voltage V2 and the LED voltage VL or the ratio R' between the secondary voltage V2 and the LED voltage VL is constant at the set value VDs or Rs'. controlled. That is, since the secondary voltage V2 of the flyback converter 120 decreases/increases according to the decrease/increase of the LED voltage VL, the difference between the two voltages is suppressed. This makes it possible to suppress losses in both the flyback converter 120 at the front stage and the step-down chopper circuit 130' at the rear stage for different LED loads, thereby improving the circuit efficiency. Furthermore, the fact that it is not necessary to fix the secondary voltage V2 with a margin in consideration of variations in the forward voltage Vf of the LED array 200 also contributes to the above loss reduction and efficiency improvement. Also in this embodiment, the effect obtained by the no-load protection circuit 160 or 165 is the same as that of the first embodiment.

<Summary>
As described above, the LED lighting device 100 of the present invention includes the flyback converter 120 (DC power supply circuit) that converts the input primary voltage V1 into the secondary voltage V2 and outputs the secondary voltage V2, and the secondary voltage A voltage detection circuit ( 140, 170 or 180) and controls the driving state of the flyback converter 120 to decrease/increase the secondary voltage V2 in accordance with the decrease/increase of the LED voltage VL detected by the voltage detection circuit. and a control circuit 150 . According to this configuration, the secondary voltage V2, which is the output voltage of the flyback converter 120, decreases/increases according to the decrease/increase of the LED voltage VL, which is the output voltage of the step-down chopper circuit 130 or 130'. The difference between V2 and LED voltage VL is suppressed. This realizes an LED lighting device and an LED lighting device using the LED lighting device that can improve circuit efficiency by suppressing losses in both the DC power supply circuit in the front stage and the step-down chopper circuit in the rear stage for different LED loads. be done.

<Modification>
Although preferred embodiments of the present invention have been described above, the present invention can be modified in various ways, for example, as shown below.

(1) Modifications regarding the LED array 200 In each of the above embodiments, the LED array 200 was shown as the light source, but it is intended that the term “LED” in the present disclosure may include not only so-called light-emitting diodes but also organic light-emitting diodes (OLEDs). ing.

(2) Modifications Regarding Flyback Converter 120 In each of the above-described embodiments, the flyback converter 120 is shown as the DC power supply circuit. On the other hand, if the DC power supply circuit is a booster circuit and insulation between the primary side and the secondary side is not required, a boost chopper circuit 125 is employed instead of the flyback converter 120 as shown in FIG. may In this modified example, the same reference numerals are assigned to substantially the same configurations as those of the first to third embodiments, and redundant description thereof will be omitted or simplified. The boost chopper circuit 125 includes a coil 31 , a switching element 32 (hereinafter referred to as “FET 32 ”), a diode 33 , a smoothing capacitor 4 and a driver IC 35 . The FET 32 is switched (PWM driven) by the driver circuit 35 . As in each embodiment, the boost chopper circuit 125 receives the primary voltage V1, and the voltage generated in the smoothing capacitor 4 becomes the secondary voltage V2 as the output of the boost chopper circuit 125. FIG. The driver circuit 35 is composed of, for example, a boost chopper circuit control IC and its peripheral circuits, and receives an output from the control circuit 150 .

The control circuit 150 feedback-controls the pulse width in the PWM drive of the FET 32 of the boost chopper circuit 125 so that the differential voltage VD is kept constant at the set value VDs. In this modification, since the boost chopper circuit 125 and the step-down chopper circuit 130 have the same reference potential, there is no need to provide a photocoupler between the output terminal of the operational amplifier 14 and the driver circuit 35 . Therefore, the output terminal of operational amplifier 14 is connected to driver circuit 35 . It is assumed that the driver circuit 35 has a function of decreasing/increasing the pulse width in the PWM driving of the FET 32 in accordance with the decrease/increase of the voltage input from the control circuit 150 .

This modified example shows a configuration in which feedback control is performed so that the differential voltage VD is kept constant at the set value VDs in relation to the first embodiment. On the other hand, in this modified example, the second embodiment (configuration using the differential voltage detection circuit 140 and the secondary voltage detection circuit 170) or the third embodiment (configuration using the secondary voltage detection circuit 170 and the step-down voltage detection circuit 180) configuration) may perform the same feedback control as in each embodiment.

Further, in this modification, it is preferable that a no-load protection circuit 165 is connected to the driver circuit 10 as shown in FIG. This is because the primary voltage V1 is applied to the step-down chopper circuit 130 even if the operation of the step-up chopper circuit 125 is stopped, and the output of the step-down chopper circuit 130 may not be reduced or stopped. In other words, in order to reduce the output of the step-down chopper circuit 130 to a desired level or stop it completely, the no-load protection circuit 165 needs to reduce or stop driving the FET 7 . Alternatively, the no-load protection circuits 160 and 165 may be used together to stop driving both the boost chopper circuit 125 (FET32) and the step-down chopper circuit 130 (FET7).

6 choke coil 7 switching element 8 regenerative diode 100 LED lighting device 120 flyback converter (DC power supply circuit)
125 boost chopper circuit (DC power supply circuit)
130 step-down chopper circuit 140 differential voltage detection circuit 150 control circuits 160, 165 no-load protection circuit (protection circuit)
170 secondary voltage detection circuit 180 step-down voltage detection circuit 200 LED array 300 LED lighting device

Claims (7)

An LED lighting device,
a DC power supply circuit that converts an input primary voltage into a secondary voltage and outputs the secondary voltage;
a step-down chopper circuit for stepping down the secondary voltage to generate a stepped-down output voltage and applying the stepped-down output voltage to an LED array;
a voltage detection circuit that directly or indirectly detects the step-down output voltage;
a control circuit for controlling the drive state of the DC power supply circuit so as to reduce the secondary voltage in accordance with the reduction in the step-down output voltage detected by the voltage detection circuit;
with
wherein the voltage detection circuit is a differential voltage detection circuit that detects a differential voltage that is a difference between the secondary voltage and the stepped-down output voltage;
The LED lighting device , wherein the control circuit controls the drive state of the DC power supply circuit so that the differential voltage is constant at a predetermined set value. An LED lighting device,
a DC power supply circuit that converts an input primary voltage into a secondary voltage and outputs the secondary voltage;
a step-down chopper circuit for stepping down the secondary voltage to generate a stepped-down output voltage and applying the stepped-down output voltage to an LED array;
a voltage detection circuit that directly or indirectly detects the step-down output voltage;
a control circuit for controlling the drive state of the DC power supply circuit so as to reduce the secondary voltage in accordance with the reduction in the step-down output voltage detected by the voltage detection circuit;
with
The voltage detection circuit includes a differential voltage detection circuit that detects a differential voltage that is a difference between the secondary voltage and the stepped-down output voltage, and a secondary voltage detection circuit that detects the secondary voltage,
The LED lighting device , wherein the control circuit controls the drive state of the DC power supply circuit so that the ratio between the secondary voltage and the differential voltage is constant at a predetermined set value. 3. The LED lighting device according to claim 1 , further comprising a protection circuit for reducing the secondary voltage in the DC power supply circuit when the differential voltage becomes equal to or less than a predetermined threshold regardless of control of the driving state. 3. The LED lighting device according to claim 1 , further comprising a protection circuit that reduces the step-down output voltage of the step-down chopper circuit when the differential voltage becomes equal to or less than a predetermined threshold regardless of control of the drive state. The step-down chopper circuit includes a choke coil, a switching element and a regenerative diode,
When the LED array is connected, a series circuit of the LED array, the choke coil, and the switching element is formed from the high potential side to the low potential side of the output end of the DC power supply circuit when the switching element is in an ON state. A closed circuit is formed by the LED array, the choke coil and the regenerative diode when the switching element is in an off state,
The LED lighting device according to any one of claims 1 to 4, wherein the differential voltage detection circuit is arranged to detect a voltage applied to a series circuit of the choke coil and the switching element. An LED lighting device,
a DC power supply circuit that converts an input primary voltage into a secondary voltage and outputs the secondary voltage;
a step-down chopper circuit for stepping down the secondary voltage to generate a stepped-down output voltage and applying the stepped-down output voltage to an LED array;
a voltage detection circuit that directly or indirectly detects the step-down output voltage;
a control circuit for controlling the drive state of the DC power supply circuit so as to reduce the secondary voltage in accordance with the reduction in the step-down output voltage detected by the voltage detection circuit;
with
the voltage detection circuit includes a secondary voltage detection circuit that detects the secondary voltage and a step-down voltage detection circuit that detects the step-down output voltage;
The control circuit controls the driving state of the DC power supply circuit so that the difference between the secondary voltage and the stepped-down output voltage or the ratio between the secondary voltage and the stepped-down output voltage is constant at a predetermined set value. LED lighting device. An LED lighting device comprising the LED lighting device according to claim 1 and the LED array.

Images