JP6292503B2 - Power supply device and LED lighting device - Google Patents

Description

  The present invention relates to a power supply apparatus corresponding to a plurality of types of loads having different rated voltages, and an LED lighting apparatus in which the load is an LED (light emitting diode).

  As a conventional example, a power supply device and a lighting device described in Patent Document 1 are illustrated. The conventional example described in Patent Document 1 lights a straight tube type LED lamp that is detachably attached to a lamp socket, and reduces the DC voltage supplied from a DC power source to the rated voltage of the LED lamp. A step-down chopper circuit (power supply device) is provided.

  Here, in Japan Light Bulb Industry Association standard JEL801 “Straight-tube LED lamp system with L-shaped pin cap GX16t-5 (for general lighting)”, the rated voltage of straight-tube LED lamps is in a wide range of 45 to 95 volts. It is set (in the case of 40 type).

  In the conventional example described in Patent Document 1, the step-down chopper circuit operates in the critical mode when the rated voltage of the straight tube LED lamp serving as a load is high, and the step-down chopper circuit operates in the continuous mode when the rated voltage is low. It is configured.

JP2013-165598A

  By the way, straight tube LED lamps having a rated voltage lower than the standard value of the standard are on the market. In this way, when a straight tube LED lamp deviating from the standard is used as the load of the conventional example, and the step-down chopper circuit operates in the continuous mode, there is a possibility that an unexpected problem may occur. That is, in the conventional example described in Patent Document 1, the step-down chopper circuit is designed to operate normally even when a straight tube LED lamp having the lowest rated voltage (45 volts) conforming to the standard is used as a load. However, when a straight tube type LED lamp whose rated voltage is lower than the standard is used as a load as described above, the loss of the semiconductor switching element constituting the step-down chopper circuit exceeds the design value, and the life of the semiconductor switching element is shortened. There is a risk of problems such as shortening.

  This invention is made | formed in view of the said subject, and it aims at suppressing generation | occurrence | production of the malfunction in the case of a light load.

  The power supply device of the present invention includes a step-down chopper circuit that steps down a DC input voltage supplied from a DC power source and supplies the voltage to a load, and a control circuit that controls the operation of the step-down chopper circuit, A semiconductor switching element that interrupts the input voltage; and an inductor that releases energy stored when the input voltage is applied via the semiconductor switching element when the input voltage is not applied. The control circuit, after turning on the semiconductor switching element, turns off the semiconductor switching element when the inductor current flowing through the inductor reaches a predetermined peak value, and the process from the time when the semiconductor switching element is turned on. If the inductor current becomes zero before the time reaches a predetermined restart period, The semiconductor switching element is turned on when the restart period is reached, and if the inductor current becomes zero after the elapsed time reaches the restart period, the inductor current becomes zero. The semiconductor switching element is configured to be turned on.

In this power supply apparatus, the control circuit includes a driver unit that drives the semiconductor switching element, and a step-down control unit that controls the driver unit to operate the step-down chopper circuit in a discontinuous mode or a critical mode. The step-down control unit controls the driver unit to turn on the semiconductor switching element, and then turns off the semiconductor switching element when an inductor current flowing through the inductor reaches a predetermined peak value. If the inductor current becomes zero before the elapsed time from the time of turning on the predetermined restart period, the semiconductor switching element is turned on when the elapsed time reaches the restart period, Configured to operate the step-down chopper circuit in the discontinuous mode; The step-down control unit further controls the driver unit to turn on the semiconductor switching element, and then turns off the semiconductor switching element when an inductor current flowing through the inductor reaches a predetermined peak value. If the inductor current becomes zero after the elapsed time from when the element is turned on reaches the restart period, the step-down chopper is turned on by turning on the semiconductor switching element when the inductor current becomes zero. Preferably, the circuit is configured to operate in the critical mode.
The LED lighting device of the present invention includes the power supply device, and is configured such that an LED load is detachably connected between output terminals of the power supply device.

  In the power supply device and the LED lighting device of the present invention, when the load is not light, the control circuit operates the step-down chopper circuit in the discontinuous mode, and when the load is light load, the control circuit sets the step-down chopper circuit to the critical mode. Therefore, the step-down chopper circuit does not operate in the continuous mode even when the load is light. Therefore, compared to the conventional example in which the step-down chopper circuit operates in a continuous mode in the case of a light load, there is an effect that it is possible to suppress the occurrence of defects such as a shortened life of the semiconductor switching element.

It is a time chart for showing embodiment of a power supply device and a LED lighting device concerning the present invention, and explaining operation of a critical mode. It is a circuit diagram same as the above. It is a circuit diagram of the step-down control unit in the above. It is a time chart for demonstrating operation | movement of discontinuous mode same as the above.

  Hereinafter, embodiments of a power supply device and an LED lighting device according to the present invention will be described in detail with reference to FIGS.

  The LED lighting device of the present embodiment includes a step-down chopper circuit 1, a control block 2, and a DC power supply unit 3 as shown in FIG.

  The DC power supply unit 3 is configured to convert an AC voltage / AC current supplied from a commercial AC power supply 4 into a desired DC voltage / DC current. The DC power supply unit 3 includes a filter unit 30, a rectifier circuit 31, a PFC (Power Factor Correction) unit 32, and a smoothing capacitor C1. The filter unit 30 removes harmonic noise superimposed on the AC voltage / AC current input from the AC power supply 4 and harmonic noise generated in the PFC unit 32. The rectifier circuit 31 is formed of a diode bridge, and full-wave rectifies the AC voltage / AC current supplied from the AC power supply 4. The PFC unit 32 is a conventionally known step-up chopper circuit, and improves the power factor by converting the pulsating voltage that has been full-wave rectified by the rectifier circuit 31 into a desired DC voltage. The smoothing capacitor C1 smoothes the output voltage of the PFC unit 32. In the following description, a DC voltage input from the DC power supply unit 3 to the step-down chopper circuit 1 is referred to as a DC input voltage VDC. However, the DC power supply unit 3 is not limited to the above configuration, and may be, for example, a storage battery or a solar battery that outputs a DC voltage / DC current.

  The step-down chopper circuit 1 includes a semiconductor switching element (field effect transistor) Q1, an inductor T1, a diode D1, a capacitor C2, a detection resistor R1, resistors R2, R9, and the like. A series circuit of the semiconductor switching element Q 1, the inductor T 1, the capacitor C 2, and the detection resistor R 1 is connected between the output terminals of the DC power supply unit 3. The cathode of the diode D1 is connected to the connection point between the semiconductor switching element Q1 and the inductor T1, and the anode of the diode D1 is connected to the connection point between the detection resistor R1 and the resistor R9. The resistor R9 is connected in parallel with the diode D1, and one end of the resistor R2 is connected to the gate of the semiconductor switching element Q1. The LED load 5 is connected to both ends of the capacitor C2.

  The LED load 5 is, for example, a straight tube LED lamp described in the related art, and is detachably connected between the output ends (both ends of the capacitor C2) of the step-down chopper circuit 1 using a lamp socket or a connector (not shown). .

  The control block 2 includes a control IC 20 composed of a high voltage integrated circuit, an external circuit element, and a control power generation unit 27.

  The control power supply generation unit 27 includes a switching power supply circuit, and generates the control power supply Vcc from the DC input voltage VDC.

  The control IC 20 includes a step-down control unit 21, a high side driver unit 22, an operational amplifier 23, a switch 24, a sequence circuit unit 25, a PFC control unit 26, voltage dividing resistors R3 and R4, and the like. Further, the control IC 20 is provided with terminals such as CS terminal, ZCD terminal, OP + terminal, OP- terminal, OPout terminal, Ho terminal, HGND terminal, HVcc terminal, Vcc terminal, Do terminal, and GND terminal.

  The sequence circuit unit 25 is configured to measure the elapsed time from the time when the AC power supply 4 is turned on and the AC voltage starts to be input to the DC power supply unit 3 (hereinafter referred to as the power-on time). Further, the sequence circuit unit 25 outputs a boost operation start signal S1 to the PFC control unit 26 when the elapsed time reaches the boost operation start time (for example, 0.5 seconds), and the elapsed time is reduced operation start time (for example, 0.7 seconds), the step-down operation start signal S2 is output to the step-down control unit 21.

  When the step-up operation start signal S1 is output from the sequence circuit unit 25, the PFC control unit 26 outputs a drive signal from the Do terminal, and switches a semiconductor switching element (not shown) constituting the PFC unit 32. Further, the PFC control unit 26 is configured to feedback control the on-duty ratio of the semiconductor switching element of the PFC unit 32 so that the output voltage (DC input voltage VDC) of the DC power supply unit 3 is a predetermined constant voltage. The However, since such a PFC control unit 26 is well known in the art, a detailed configuration and operation illustration and description are omitted.

  The high-side driver unit 22 drives the semiconductor switching element Q1 of the step-down chopper circuit 1, and outputs a drive signal from the Ho terminal to the gate of the semiconductor switching element Q1 using the voltage supplied from the HVcc terminal. Configured as follows. Note that a bootstrap circuit for boosting the control voltage Vcc is externally attached to the HVcc terminal. The bootstrap circuit includes a capacitor C3 connected between the HGND terminal and the HVcc terminal, and a diode D2 having an anode connected to the Vcc terminal to which the control power supply Vcc is input and a cathode connected to the HVcc terminal. . In other words, the bootstrap circuit charges the capacitor C3 through the path from the control power supply generation unit 27 to the diode D2, the capacitor C3, and the resistor R9 of the step-down chopper circuit 1, and the voltage higher than the control power supply voltage Vcc by the charging voltage of the capacitor C3. Is input to the HVcc terminal.

  In the operational amplifier 23, the reference voltage Vs is input to the non-inverting input terminal (OP + terminal), the voltage across the detection resistor R1 is input to the inverting input terminal (OP- terminal), and the output terminal (OPout terminal) and the inverting input terminal A parallel circuit of a feedback resistor R2 and a capacitor C4 is connected between them. The reference voltage Vs is a voltage obtained by dividing the control power supply voltage Vcc by the voltage dividing resistors R5 and R6 (Vs = Vcc × R6 / (R5 + R6)). The voltage across the detection resistor R1 (hereinafter referred to as the detection voltage Vx) is a voltage proportional to the output current Io of the step-down chopper circuit 1.

  Thus, an inverting amplifier circuit is configured by the operational amplifier 23 and the parallel circuit of the feedback resistor R2 and the capacitor C4. This inverting amplifier circuit inverts and amplifies the difference between the detection voltage Vx and the reference voltage Vs and applies it to the series circuit of the voltage dividing resistors R3 and R4. One end of the series circuit of the voltage dividing resistors R3 and R4 is connected to the output terminal of the operational amplifier 23, and the other end is connected to the ground via the GND terminal. Then, the voltage divided by the voltage dividing resistors R3 and R4 is input to the step-down control unit 21 as the threshold voltage X1. The operational amplifier 23 is applied with the control power supply voltage Vcc through the switch 24, operates when the switch 24 is on, and stops when the switch 24 is off. .

  As shown in FIG. 3, the step-down control unit 21 includes a first comparator 210, an upper limit clamp circuit 211, a lower limit clamp circuit 212, a second comparator 213, a flip-flop (FF) circuit 214, a restart timer circuit 215, a one-shot The circuit 216 includes a plurality of logic circuits.

  The upper limit clamp circuit 211 is configured to clamp the terminal voltage of the ZCD terminal (voltage induced in the auxiliary winding T2 of the inductor T1 of the step-down chopper circuit 1) Vzc to a predetermined upper limit value. The lower limit clamp circuit 212 is configured to clamp the terminal voltage Vzc of the ZCD terminal to a predetermined lower limit value.

  In the first comparator 210, the terminal voltage Vzc of the ZCD terminal is input to the minus terminal, and two types of threshold values VH and VL are alternatively input to the plus terminal. That is, the first comparator 210 compares the terminal voltage Vzc of the ZCD terminal with the higher threshold value (hereinafter referred to as the high threshold value) VH when the semiconductor switching element Q1 is on. When the terminal voltage Vzc exceeds the high threshold VH, the output is inverted from the high level to the low level. When the terminal voltage Vzc exceeds the high threshold value VH, the threshold value input to the positive terminal of the first comparator 210 is lower than the high threshold value VH (hereinafter referred to as the lower threshold value). Called threshold.) Switch to VL. The first comparator 210 compares the terminal voltage Vzc of the ZCD terminal with the high threshold VH when the semiconductor switching element Q1 is off, and if the terminal voltage Vzc falls below the low threshold VL. The output is inverted from low level to high level. The output of the first comparator 210 is ANDed with a restart output VT of a restart timer circuit 215 described later in the first AND circuit AND1.

  The second comparator 213 compares the terminal voltage (detection voltage Vx) of the CS terminal with the threshold voltage X1, and when the detection voltage Vx is equal to or higher than the threshold voltage X1, the output CSout is set to high level to detect The output CSout is set to a low level when the voltage Vx is lower than the threshold voltage X1. The output CSout of the second comparator 213 is logically ORed with a signal obtained by inverting the step-down operation start signal S2 with the inverter INV in the first OR circuit OR1.

  In the FF circuit 214, the output LED_S of the first AND circuit AND1 is input to the set terminal, the output CSout of the first OR circuit OR1 is input to the reset terminal, and the output terminal is one input of the third AND circuit AND3. Connected to the terminal. In other words, the FF circuit 214 outputs a high level when the output LED_S of the first AND circuit AND1 becomes high level, and outputs when the output CSout of the first OR circuit OR1 becomes high level when the output is high level. Become low level.

  The third AND circuit AND3 calculates a logical product of the output of the FF circuit 214 and the step-down operation start signal S2. The output of the third AND circuit AND3 is given to the high side driver unit 22. That is, the high-side driver unit 22 outputs a drive signal during a period when the output of the third AND circuit AND3 is at a high level to turn on the semiconductor switching element Q1, and a period when the output of the third AND circuit AND3 is at a low level. The semiconductor switching element Q1 is configured to be turned off.

  The one-shot circuit 216 outputs a one-shot pulse signal PS to the second AND circuit AND2 in synchronization with the rise of the output of the third AND circuit AND3. The second AND circuit AND2 calculates a logical product of the one-shot pulse signal PS and the step-down operation start signal S2. The output terminal of the second AND circuit AND2 is connected to the gate of a field effect transistor 2150 that is externally attached to the restart timer circuit 215. That is, when the step-down operation start signal S2 is at a high level, the second AND circuit AND2 sets the output to a high level and turns on the field effect transistor 2150 only in a short time when the one-shot pulse signal PS is at a high level. Composed.

  The restart timer circuit 215 charges an internal capacitor (not shown) with a constant current when the external field effect transistor 2150 is off, and the voltage across the capacitor (restart input voltage Vin) is charged. When the threshold is reached, the restart output VT is raised to a high level. The restart timer circuit 215 is configured to discharge the capacitor when the output of the second AND circuit AND2 becomes high level and the field effect transistor 2150 is turned on. Here, the field effect transistor 2150 is turned on only for a short time when the one-shot pulse signal PS becomes high level, and turned off when the one-shot pulse signal PS becomes low level. Therefore, the restart timer circuit 215 is configured to repeat the operation of charging the capacitor with a constant current at a constant period (restart period) T after discharging the capacitor during the ON period of the field effect transistor 2150. Is done. However, the restart period T is determined by the capacitance of the restart timer circuit 215, the magnitude of the charging current, and the threshold value.

  Next, the operation of the step-down control unit 21 will be described in detail with reference to the time charts of FIGS.

  First, the case where the LED load 5 having a relatively high rated voltage is connected to the output terminal of the step-down chopper circuit 1 will be described with reference to FIG.

  When the AC power supply 4 is turned on, a DC input voltage VDC that is full-wave rectified by the rectifier circuit 31, passes through the PFC unit 32, and is smoothed by the smoothing capacitor C 1 is input to the control power generation unit 21. Then, the control power supply generation unit 21 generates a control power supply from the time when the DC input voltage VDC is input (time t = t0, hereinafter referred to as a power-on time) and supplies the control power to each unit.

  When the control power supply voltage Vcc rises, the sequence circuit unit 25 starts operating. The sequence circuit unit 25 causes the PFC control unit 26 to raise the boost operation start signal S1 to a high level when the boost operation start time has elapsed since the power was turned on. The PFC control unit 26 starts the operation of the PFC unit 32 when the boosting operation start signal S1 becomes a high level. When the PFC unit 32 operates, the control power source is generated by the control power source generation unit 21 and the control power source voltage Vcc is supplied to the step-down control unit 21.

  Furthermore, the step-down operation start signal S2 output from the sequence circuit unit 25 to the step-down control unit 21 is high when the step-down operation start time (> step-up operation start time) has elapsed since the power-on (time t = t0). It becomes. Since the step-down operation start signal S2 is at the low level during the period from the time when the power is turned on to the time t = t0, the output of the third AND circuit AND3 is at the low level. Is not output.

  The restart timer circuit 215 starts charging the capacitor from the time when the step-down operation start signal S2 becomes high level (time t = t0), and the voltage across the capacitor (restart input voltage Vin) reaches the threshold value. At that time (time t = t1), the restart output VT is raised to a high level. The time (t1-t0) from when the step-down operation start signal S2 becomes high level (time t = t0) to when the restart output VT rises to high level is equal to the restart period T.

  Since the step-down chopper circuit 1 is not operating at time t = t1, no voltage is induced in the auxiliary winding T2, the terminal voltage Vzc of the ZCD terminal is low, and the high voltage of the first comparator 210 is high. Since it is lower than the threshold value VH, the output of the first comparator 210 is maintained at a high level.

  On the other hand, when the restart output VT rises to high level at time t = t1, the output LED_S of the first AND circuit AND1 rises to high level, and the output of the FF circuit 214 rises to high level. When the output of the FF circuit 214 becomes high level, the inputs of the third AND circuit AND3 all become high level, so that the output of the third AND circuit AND3 rises to high level. As a result, a drive signal is output from the high-side driver unit 22, the semiconductor switching element Q1 is turned on, the step-down chopper circuit 1 starts operating, and the output current Io (inductor current IL) gradually increases.

  Further, the one-shot pulse signal PS is output from the one-shot circuit 216 when the output of the third AND circuit AND3 becomes high level. The second AND circuit AND2 sets the output to a high level in synchronization with the rising edge of the one-shot pulse signal PS and sets the output to a low level in synchronization with the falling edge of the one-shot pulse signal PS. The restart timer circuit 215 discharges the capacitor in a short time during which the field effect transistor 2150 is turned on, and starts charging the capacitor again (counting of the restart period T) from the time when the field effect transistor 2150 is turned off.

  As the output current Io increases, the detection voltage Vx also rises, and the output CSout of the second comparator 213 becomes high level when the detection voltage Vx reaches the threshold voltage X1 (time t = t2). The first OR circuit OR1 raises the output LED_R to high level when the output CSout of the second comparator 213 rises to high level. Then, since the reset terminal of the FF circuit 214 becomes high level, the output of the FF circuit 214 falls to low level. As a result, the output of the third AND circuit AND3 falls to a low level, and the drive signal is not output from the high side driver unit 22, whereby the semiconductor switching element Q1 is turned off.

  When the semiconductor switching element Q1 is turned off, the energy accumulated in the inductor T1 is released and a regenerative current (inductor current IL) flows. However, this regenerative current (inductor current IL) gradually decreases with time. Further, since the polarity of the voltage induced in the auxiliary winding T2 is reversed when the semiconductor switching element Q1 is turned off, the terminal voltage Vzc of the ZCD terminal rises to a high level and exceeds the high threshold value VH. As a result, the output of the first comparator 210 falls to a low level, and the threshold value of the first comparator 210 is switched from the high threshold value VH to the low threshold value VL.

  When the regenerative current (inductor current IL) becomes zero (time t = t3), the terminal voltage Vzc of the ZCD terminal falls to a low level and falls below the low threshold VL. As a result, the output of the first comparator 210 rises to a high level, and the threshold value of the first comparator 210 is switched from the low threshold value VL to the high threshold value VH.

  Here, as shown in FIG. 4, the elapsed time (= t3) from the time when the semiconductor switching element Q1 is turned off (time t = t2) to the time when the regenerative current (inductor current IL) becomes zero (time t = t3). -t2) is shorter than the restart period T of the restart timer circuit 215. Therefore, since the restart output VT remains at the low level at the time t = t3, the output LEDS_S of the first AND circuit AND1 also remains at the low level. Therefore, the output of the FF circuit 214 also remains at a low level, and the output of the third AND circuit AND3 is also at a low level, so that no drive signal is output from the high side driver unit 22.

  When all the energy accumulated in the inductor T1 is released and the regenerative current (inductor current IL) becomes zero, the voltage across the inductor T1 freely oscillates and the terminal voltage Vzc of the ZCD terminal also oscillates. However, since the threshold value of the first comparator 210 is switched from the low threshold value VL to the high threshold value VH, the peak value of the terminal voltage Vzc at the ZCD terminal does not exceed the high threshold value VH. The output of one comparator 210 is maintained at a high level. However, even if the peak value of the terminal voltage Vzc at the ZCD terminal exceeds the high threshold VH, the output of the first AND circuit AND1 rises to a high level because the restart output VT is at a low level. There is nothing.

  The restart timer circuit 215 outputs the restart output VT when the restart input voltage Vin reaches the threshold (time t = t4), that is, when the restart cycle T has elapsed from time t = t1. Launch to high level. The first AND circuit AND1 raises the output LED_S to high level when the restart output VT rises to high level. As a result, the output of the FF circuit 214 becomes high level, and further, the output of the third AND circuit AND3 also becomes high level, whereby the drive signal is output from the high side driver unit 22 and the semiconductor switching element Q1 is turned on. After this (from time t4), the operation from time t1 to t4 is repeated, and the rated voltage is applied from the step-down chopper circuit 1 so that the LED load 5 is lit. That is, the operation mode of the step-down control unit 21 shown in FIG. 4 is a discontinuous mode in which the inductor current IL flowing through the inductor T1 is discontinuous.

  Next, the case where the LED load 5 having a relatively low rated voltage is connected to the output terminal of the step-down chopper circuit 1 will be described with reference to FIG.

  However, the operation from the time of turning on the power until the time t = t2 elapses is the same as that in the discontinuous mode shown in FIG.

  The restart timer circuit 215 restarts when the restart input voltage Vin reaches a threshold value (time t = t3) after the semiconductor switching element Q1 is turned off at time t = t2, that is, from time t = t1. When the period T has elapsed, the restart output VT is raised to a high level. However, since the regenerative current (inductor current IL) does not decrease to zero at time t = t3, the terminal voltage Vzc of the ZCD terminal remains at the high level and does not fall below the low threshold VL. The output of the comparator 210 is maintained at a low level.

  Since the restart output VT is high and the output of the first comparator 210 is low, the output LED_S of the first AND circuit AND1 remains low and the output of the FF circuit 214 is also low. Will remain. As a result, since the output of the third AND circuit AND3 is also maintained at the low level, the drive signal is not output from the high side driver unit 22.

  When the regenerative current (inductor current IL) becomes zero (time t = t4), the terminal voltage Vzc of the ZCD terminal falls to a low level and falls below the low threshold VL. As a result, the output of the first comparator 210 rises to a high level, and the threshold value of the first comparator 210 is switched from the low threshold value VL to the high threshold value VH.

  Here, since the restart output VT is already at the high level, the output LEDS_S of the first AND circuit AND1 is at the high level when the regenerative current (inductor current IL) becomes zero (time t = t4). stand up. Therefore, since the output of the FF circuit 214 becomes high level and the output of the third AND circuit AND3 also becomes high level, the drive signal is outputted from the high side driver unit 22 and the semiconductor switching element Q1 is turned on. After this (from time t4), the operation from time t1 to t4 is repeated, and the rated voltage is applied from the step-down chopper circuit 1 so that the LED load 5 is lit. That is, when the inductor current IL flows for a longer period than the restart period T of the restart timer circuit 215, the step-down control unit 21 turns on the semiconductor switching element Q1 in synchronization with the zero crossing of the inductor current IL. Operate.

  As described above, the power supply device (LED lighting device) of the present embodiment steps down the DC input voltage supplied from the DC power supply (DC power supply unit 3) and supplies it to the load (LED load 5). And a control circuit (step-down control unit 21) for controlling the operation of the step-down chopper circuit 1.

  The step-down chopper circuit 1 includes a semiconductor switching element Q1 that interrupts the input voltage, and an inductor T1 that releases energy stored when the input voltage is applied via the semiconductor switching element Q1 when the input voltage is not applied. And have.

  After turning on the semiconductor switching element Q1, the control circuit (step-down control unit 21) turns off the semiconductor switching element Q1 when the inductor current IL flowing through the inductor T1 reaches a predetermined peak value. Further, the control circuit (step-down control unit 21) determines that the elapsed time is restarted if the inductor current IL becomes zero before the elapsed time from when the semiconductor switching element Q1 is turned on reaches the predetermined restart cycle T. When T is reached, the semiconductor switching element Q1 is turned on. Further, if the inductor current IL becomes zero after the elapsed time reaches the restart cycle T, the control circuit (step-down control unit 21) turns on the semiconductor switching element Q1 when the inductor current IL becomes zero. Configured.

  The power supply device (LED lighting device) of the present embodiment allows the step-down chopper circuit 1 to operate in the continuous mode even when the load is a light load (the LED load 5 having a relatively low rated voltage) due to the above configuration. There is no. Therefore, compared with the conventional example in which the step-down chopper circuit operates in a continuous mode in the case of a light load, it is possible to suppress the occurrence of problems such as a shortened life of the semiconductor switching element Q1.

  Note that the power supply device (LED lighting device) of the present embodiment is configured to connect the semiconductor switching element Q1 of the step-down chopper circuit 1 to a higher potential side than the inductor T1. This is because the input voltage of the step-down chopper circuit 1 is stipulated to be 300 volts or less in the Japan Light Bulb Industry Association standard JEL801 “Straight-tube LED lamp system with L-shaped pin cap GX16t-5 (for general lighting)”. is there. That is, when the semiconductor switching element Q1 of the step-down chopper circuit 1 is connected to a potential lower than that of the inductor T1, the input voltage of the step-down chopper circuit 1 exceeds 300 volts.

  In addition, the restart cycle T is 20 μsec (for example) in order to avoid 33 to 40 kHz of the frequency band used for the infrared remote control of home appliances in consideration of the variation (± 20%) of the cycle setting in the high voltage integrated circuit. It is preferably set to 50 kilohertz). With this setting, even when the LED load 5 having a considerably low rated voltage is mistakenly connected, the power mode is changed to the critical mode and the switching frequency of the semiconductor switching element Q1 only overlaps the frequency band of the infrared remote controller. (LED lighting device) will not break down.

1 Step-down chopper circuit 2 Control block 5 LED load (load)
21 Step-down controller (control circuit)
Q1 Semiconductor switching element
T1 inductor

Claims (3)

A step-down chopper circuit that steps down a DC input voltage supplied from a DC power source and supplies the voltage to a load; and a control circuit that controls the operation of the step-down chopper circuit,
The step-down chopper circuit discharges the energy stored when the input voltage is applied via the semiconductor switching element and the semiconductor switching element that interrupts the input voltage when the input voltage is not applied. An inductor,
The control circuit, after turning on the semiconductor switching element, turns off the semiconductor switching element when an inductor current flowing through the inductor reaches a predetermined peak value, and an elapsed time from when the semiconductor switching element is turned on If the inductor current becomes zero before reaching the predetermined restart period, the semiconductor switching element is turned on when the elapsed time reaches the restart period, and the elapsed time reaches the restart period. The power supply device is configured to turn on the semiconductor switching element when the inductor current becomes zero after the inductor current becomes zero. The control circuit includes a driver unit that drives the semiconductor switching element, and a step-down control unit that controls the driver unit to operate the step-down chopper circuit in a discontinuous mode or a critical mode.
The step-down control unit controls the driver unit to turn on the semiconductor switching element, and then turns off the semiconductor switching element when an inductor current flowing through the inductor reaches a predetermined peak value. If the inductor current becomes zero before the elapsed time from the time of turning on the predetermined restart period, the semiconductor switching element is turned on when the elapsed time reaches the restart period, Configured to operate the step-down chopper circuit in the discontinuous mode,
The step-down control unit further controls the driver unit to turn on the semiconductor switching element, and then turns off the semiconductor switching element when an inductor current flowing through the inductor reaches a predetermined peak value. If the inductor current becomes zero after the elapsed time from when the switching element is turned on reaches the restart cycle, the step-down voltage is obtained by turning on the semiconductor switching element when the inductor current becomes zero. The power supply apparatus according to claim 1, wherein the chopper circuit is configured to operate in the critical mode. An LED lighting device comprising: the power supply device according to claim 1 or 2, wherein an LED load is detachably connected between output terminals of the power supply device.

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