JP2014108018A - Power supply device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that since an output capacity just after power supply is not sufficiently charged in a power supply device including a DC/DC conversion circuit, it is erroneously determined that the short circuit of an LED has occurred even when the LED to which the DC output voltage of the DC/DC conversion circuit is applied has no failure.SOLUTION: A power supply device (10) includes: a DC/DC conversion circuit (3) for converting a first DC voltage (Vdc1) into a second DC voltage (Vdc2); and a switching control part (6) for controlling the DC/DC conversion circuit. The conductive state of a first switch element (M1) and a second switch element (M2) for controlling the currents of a first coil (L1) is controlled by a switch element drive signal (drv). When an output voltage detection signal (vo) is not more than a short circuit determination voltage (vo_min1) during the conductive period of the first switch element and the second switch element after activation, the switching control part sets the first switch element and the second switch element in a non-conductive state.

Description

  The present invention relates to a power supply device, and more particularly to a power supply device for LED lighting.

  As a method of determining an output short circuit abnormality of the LED lighting power supply device, the voltage between the output terminals of the light emitting diode (hereinafter referred to as LED) as a load is monitored, and when the voltage is out of the specified voltage range, It is known to determine as a load short circuit or open abnormality. When the load is short-circuited, this is equivalent to the case where the load resistance is 0Ω. Therefore, when the output current of the LED lighting power supply device does not change, the voltage between the output terminals of the load decreases to 0V. Further, when the load is released, this is equivalent to the case where the load resistance is infinite. Therefore, when the output current does not change, the voltage between the output terminals of the load increases.

  The control circuit of the LED lighting power supply device periodically monitors the voltage between the output terminals of the load, and determines the occurrence of a load short circuit abnormality and a load opening abnormality. When the voltage between the output terminals of the load falls below the lower limit of the specified voltage range and rises above the upper limit of the specified voltage range, it is determined that a load short circuit has occurred and a load has been released, respectively. Based on the determination result, the control circuit performs an abnormal control such as stopping the voltage application between the output terminals of the load.

  Patent Document 1 discloses a power converter that applies an output voltage to two LED lamps connected in series, a first voltage detector that detects an output voltage of the power converter, and a voltage that is applied to one of the two LED lamps. An LED lighting device is disclosed that includes a second voltage detection unit that detects the voltage and a control unit that controls the output current of the power conversion unit to be a target value. The control unit, when at least one of the voltage of the second voltage detection unit or the voltage difference between the voltage of the first voltage detection unit and the voltage of the second voltage detection unit is out of a predetermined normal range, Reduce output voltage.

  Patent Document 2 discloses an LED driving device including a lighting circuit unit including a converter that supplies a DC voltage to the LED light source, and a protection circuit unit disposed on an output path from the lighting circuit unit to the LED light source. . When power supply to the LED driving device is started, the lighting circuit unit applies a predetermined steady voltage to the LED light source. Thereafter, when the LED light source is disconnected, the lighting circuit unit decreases the output voltage according to the set standby mode or stop mode.

  Patent Document 3 discloses a series circuit of a first transistor for applying an output voltage of a full-wave rectifier circuit and a reactor, a series circuit of a second transistor and a capacitor connected in parallel to the reactor, a first transistor, and a first transistor. An illumination LED drive circuit comprising a control circuit for controlling the conduction state of two transistors is disclosed.

JP 2012-142358 A JP 2006-210271 A JP 2011-65874 A

  A one-stage power supply device that controls a power factor correction circuit and a load drive circuit with a common switching control signal charges an output capacitor immediately after power-on. The voltage between the output terminals of the load connected to the power supply device does not rise sufficiently until the charging of the output capacitance is completed. As a result, there is a problem that even if there is no abnormality in the LED, it is erroneously determined that the LED is short-circuited.

  The present invention converts a first DC voltage applied between a pair of input nodes into a second DC voltage by converting the AC voltage into a first DC voltage and outputs the first DC voltage, and outputs it between the pair of output nodes. A power supply apparatus comprising: a DC / DC conversion unit that performs a switching control unit that controls the DC / DC conversion unit, wherein the DC / DC conversion unit controls a first coil and a current of the first coil. An output voltage detection circuit that generates an output voltage detection signal based on a voltage between the pair of output nodes, and the switching control unit includes the first switch element and the second switch element. Is generated for a predetermined time, and the output voltage detection signal does not exceed the first short-circuit determination voltage during the conduction period of the first switch element and the second switch element after startup. , The switching control unit sets the first switching element and second switching element non-conductive, a power supply device.

  In the power supply device of the present invention, the switching control unit controls the conduction time of the switch element drive signal in response to the dimming mode setting signal.

  The present invention converts an AC voltage into a first DC voltage and outputs it between a first node and a second node; converts a first DC voltage into a second DC voltage; A power supply device comprising: a DC / DC converter that outputs between five nodes; and a switching controller that controls the DC / DC converter, wherein the DC / DC converter is between the first node and the third node. A first switch element connected; a first diode having an anode and a cathode connected to the second node and the third node; a first coil connected between the third node and the fourth node; A second switch element and a first resistor connected in series between the four nodes and the second node; a second diode having an anode and a cathode connected to the fourth node and the fifth node, respectively; Yo An output voltage detection circuit connected between the fifth node and a switching control unit, the output voltage detection circuit generates an output voltage detection signal based on the voltage between the second node and the fifth node; The switching control unit generates a switch element drive signal for setting the first switch element and the second switch element to a conductive state for a predetermined time, and detects an output voltage in the conductive period of the first switch element and the second switch element after startup. When the signal does not exceed the first short circuit determination voltage, the switching control unit is a power supply device that sets the first switch element and the second switch element to a non-conductive state.

  According to the present invention, it is possible to improve the determination accuracy of occurrence of LED short circuit.

1 is a configuration diagram of a power supply device according to a first embodiment. It is a timing diagram explaining operation | movement of the power supply device which concerns on Embodiment 1 to which LED which has a normal characteristic was connected. It is a timing diagram explaining operation | movement of the power supply device which concerns on Embodiment 1 to which LED which has a short circuit abnormality was connected. 6 is a configuration diagram of a modification of the power supply device according to Embodiment 1. FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the description of the embodiments, when the number, amount, or the like is referred to, the scope of the present invention is not necessarily limited to the number, amount, or the like unless otherwise specified. In the drawings of the embodiments, the same reference numerals and reference numerals represent the same or corresponding parts. Further, in the description of the embodiments, the overlapping description may not be repeated for the portions with the same reference numerals and the like.

<Embodiment 1>
With reference to FIG. 1, the structure of the power supply device 10 which concerns on Embodiment 1 is demonstrated.

  The power supply device 10 includes a rectification unit 2, a DC / DC conversion unit 3, and a switching control unit 6.

  The rectifying unit 2 converts the AC voltage of the AC power supply 1 applied between the node N1 and the node N2 into the first DC voltage Vdc1, and outputs the first DC voltage Vdc1 to the node N4.

  The rectifying unit 2 rectifies the AC power supply 1 applied between the node N1 and the node N2 with the diodes D1 to D4, and outputs the rectified voltage to the node N4 as the first DC voltage Vdc1. The anode of diode D3 and the cathode of diode D2 are connected to node N1, and the anode of diode D1 and the cathode of diode D4 are connected to node N2. The anode of diode D2 and the anode of diode D4 are connected to node N3, and the cathode of diode D1 and the cathode of diode D3 are connected to node N4. Node N3 is set to ground voltage GND.

  The DC / DC converter 3 transforms the first DC voltage Vdc1 applied to the node N3 and the node N4 (hereinafter also referred to as a pair of input nodes) to generate a second DC voltage Vdc2. , Node N7 and node N8 (hereinafter also referred to as a pair of output nodes). The second DC voltage Vdc2 is applied in the forward direction to the LED 4 connected to the pair of output nodes.

The DC / DC conversion unit 3 includes a power factor improvement unit 3a and a load driving unit 3b.
The power factor improving unit 3a includes a capacitor C1 connected between the node N3 and the node N4, a resistor R1 and a resistor R2 connected in series between the node N3 and the node N4, a node N4 and a node N5, respectively, An n-type transistor M1 to which a source is connected, a diode D5 to which an anode and a cathode are connected, and a coil L1 and a coil L2 are provided between a node N3 and a node N5, respectively.

  One end and the other end of coil L1 are connected to nodes N5 and N6, respectively. One end of the coil L2 is connected to the node N3, and the other end is connected to the switching control unit 6. The coil L2 detects the timing when the current of the coil L1 becomes zero, and outputs a zero current detection signal zdc. An AC voltage detection signal acv having a value corresponding to the AC voltage output from the AC power supply 1 is output from the connection point between the resistors R1 and R2. A switch element drive signal drv output from the switching control unit 6 is applied to the gate of the n-type transistor M1.

  The load driving unit 3b includes an n-type transistor M2 having a drain connected to the node N6 and a source connected to one end of the resistor R3. The other end of the resistor R3 is connected to the node N3. A switch element overcurrent detection signal swoc having a value corresponding to the current flowing through the n-type transistor M2 is output from the connection point between the source of the n-type transistor M2 and the resistor R3. A switch element drive signal drv is applied to the gate of the n-type transistor M2.

  The load driving unit 3b further includes a diode D6 having an anode and a cathode connected to the node N6 and the node N8, a capacitor C2 connected between the node N8 and the node N3, and a series connection between the node N8 and the node N3, respectively. And an output voltage detection circuit having a resistor R4 and a resistor R5 connected to each other. The output voltage detection circuit outputs an output voltage detection signal vo having a value corresponding to the second DC voltage Vdc2 from the connection point between the resistors R4 and R5.

  The load driving unit 3b further includes a resistor R6 connected between the node N3 and the node N7, a resistor R7 having one end connected to the node N7 and the other end connected to one end of the capacitor C3. The ground voltage GND is applied to the other end of the capacitor C3. An output current detection signal io having a value corresponding to the output current of the DC / DC converter 3 is output from the connection point of the resistor R7 and the capacitor C3.

The function of the DC / DC converter 3 will be described.
The power factor improving unit 3a and the load driving unit 3b function as a step-down converter and a step-up converter, respectively. The first DC voltage Vdc1 is applied to one end (node N5) of the coil L1 of the power factor improving unit 3a via the n-type transistor M1. When the conduction state of the n-type transistor M1 is controlled in response to the switch element drive signal drv, a voltage obtained by stepping down the first DC voltage Vdc1 is generated at the node N6.

  The current of the coil L1 of the power factor improving unit 3a is further controlled by the n-type transistor M2 and the resistor R3 of the load driving unit 3b. When the conduction state of n-type transistor M2 is controlled in response to switch element drive signal drv, a voltage obtained by boosting the voltage at node N5 is generated at node N8.

  The conduction states of the n-type transistor M1 of the power factor improving unit 3a and the n-type transistor M2 of the load driving unit 3b are simultaneously controlled by the switch element drive signal drv. As a result, the DC / DC conversion unit 3 finally converts the first DC voltage Vdc1 into a second DC voltage Vdc2 having a desired value and outputs it. In FIG. 1, the coil L1 is assumed to belong to the power factor improvement unit 3a. However, the coil L1 is simultaneously controlled by the power factor improvement unit 3a that functions as a step-down converter and the load drive unit 3b that functions as a step-up converter. Therefore, it should be considered that the coil L1 and the coil L2 are shared by the power factor improving unit 3a and the load driving unit 3b.

  The power factor improvement unit 3 a further functions as a power factor improvement circuit of the DC / DC conversion unit 3. The current of the coil L1 is controlled by the n-type transistor M1 and the n-type transistor M2. The conduction start time and conduction time of both transistors are controlled by the rising timing and pulse width of the switch element drive signal drv, respectively. The switching controller 6 determines the rising timing and pulse width of the switch element drive signal drv based on the output voltage detection signal vo and the zero current detection signal zdc. As a result, the power factor of the AC power source 1 is improved.

The function of the switching control unit 6 will be described.
The switching control unit 6 generates a switch element drive signal drv that is a PWM (pulse width modulation) signal. The generation timing of the switch element drive signal drv is set in response to the detection of the zero current detection signal zdc. The pulse width of the switch element drive signal drv is set so as to maintain the value of the output current detection signal io, that is, the current supplied to the LED 4 at a constant value. The setting timing of the pulse width is performed in synchronization with the zero cross detection signal acz output from the AC zero cross detection unit 5 that detects the zero voltage of the AC power supply 1 or at an arbitrary cycle.

  The switching control unit 6 supports an overpower protection function. When the overcurrent of the DC / DC converter 3 is detected by the switch element overcurrent detection signal swoc or the output current detection signal io, the switch element drive signal drv is set from the high level to the low level. As a result, the n-type transistor M1 and the n-type transistor M2 are urgently stopped (set to a non-conductive state), and destruction of the DC / DC conversion unit 3 due to overpower is avoided. The setting range of the output current detection signal io for detecting the overcurrent is set based on the AC voltage detection signal acv.

  The switching control unit 6 supports a UVLO function (low voltage malfunction prevention function). When the AC voltage detection signal acv falls below the set value, the switch element drive signal drv is set from the high level to the low level. As a result, when the AC voltage of the AC power supply 1 becomes a specified value or less, the operation of the DC / DC conversion unit 3 is stopped.

  The switching control unit 6 supports an overvoltage protection function. When the output voltage detection signal vo exceeds the set value, the switch element drive signal drv is set from the high level to the low level. As a result, destruction of the DC / DC converter 3 due to an abnormal increase in the second DC voltage Vdc2 due to load release or the like is avoided.

  With reference to FIG. 2, the operation of power supply apparatus 10 according to the first embodiment to which LED 4 having normal characteristics is connected will be described.

  In addition to the functions described above, the power supply device 10 has a load short-circuit erroneous determination prevention function when the voltage of the AC power supply 1 is applied to the power supply device 10 (hereinafter sometimes referred to as “power-on or startup”). . FIG. 2 is a timing chart showing the operation of the power supply device 10 at the time of startup. In this case, it is assumed that a normal LED 4 having no abnormality such as a short circuit is connected to the power supply device 10. 2A to 2C, the horizontal axis indicates time. The vertical axis shows the change of each signal on an arbitrary scale.

  FIG. 2B shows the waveform of the switch element drive signal drv after the power source 10 is turned on. When the power supply device 10 is turned on at time ts, the switching control unit 6 starts initial setting of a built-in register or the like. At time td11 after completion of the initial setting, the switching control unit 6 raises the switch element drive signal drv from a low level (GND) to a high level that is appropriately set. From time td11, at time td12 after the passage of time corresponding to the pulse width Tdrv1, the switch element drive signal drv is set from high level to low level.

  FIG. 2C shows the waveform of the output voltage detection signal vo generated by the DC / DC converter 3. During the period from time td11 to time td12, the n-type transistor M1 and the n-type transistor M2 of the DC / DC conversion unit 3 cause a current to flow through the coil L1. As a result, charging of the capacitor C2 (see FIG. 1) is started, and the voltage between the pair of output nodes of the DC / DC conversion unit 3 reaches a predetermined value after time t0. Accordingly, the output voltage detection signal vo that was at the low level at time t0 becomes equal to or higher than the short-circuit determination voltage vo_min1 described later at time t1.

  FIG. 2A shows the waveform of the zero current detection signal zdc generated by the DC / DC converter 3. After the time td12, when the current of the coil L1 becomes zero, the zero current detection signal zdc rises from a low level to a suitably set high level at a time tz2.

  The switch element drive signal drv shown in FIG. 2B is set to the high level from time td21 to time td22 after the passage of time corresponding to the pulse width Tdrv2 in response to the rising edge of the zero current detection signal zdc. . By this switch element drive signal drv, the output voltage detection signal vo starts to rise again.

  With reference to FIG. 3, the operation of the power supply apparatus 10 according to the first embodiment to which the LED 4 having a short circuit abnormality is connected will be described.

  FIG. 3 is a timing chart showing the operation of the power supply device 10 at the time of startup. In this case, it is assumed that the LED 4 having a short circuit abnormality is connected to the power supply device 10. In FIG. 3A to FIG. 3C, the horizontal axis indicates time. The vertical axis shows the change of each signal on an arbitrary scale.

  FIG. 3B shows a waveform of the switch element drive signal drv after the power source 10 is turned on. When the power supply device 10 is turned on at time ts, the switching control unit 6 starts initial setting of a built-in register or the like. At time td11 after completion of the initial setting, the switching control unit 6 raises the switch element drive signal drv from a low level (GND) to a high level that is appropriately set. From time td11, at time td12 after the passage of time corresponding to the pulse width Tdrv1, the switch element drive signal drv is set from high level to low level.

  FIG. 3C shows the waveform of the output voltage detection signal vo generated by the DC / DC converter 3. During the period from time td11 to time td12, the n-type transistor M1 and the n-type transistor M2 of the DC / DC conversion unit 3 cause a current to flow through the coil L1. As a result, charging of the capacitor C2 (see FIG. 1) is started, and the voltage between the pair of output nodes of the DC / DC conversion unit 3 starts to increase after time t0. Accordingly, the output voltage detection signal vo that was at the low level at time t0 starts to rise.

  When the LED 4 connected between the pair of output nodes of the DC / DC converter 3 has a short circuit abnormality, the rising gradient of the output voltage detection signal vo is the output voltage detection signal shown in FIG. It becomes smaller than the rising gradient of vo. This is because the inter-terminal impedance of the LED 4 having a short circuit abnormality is smaller than that of the LED 4 having normal characteristics. Accordingly, in FIG. 3C, the value of the output voltage detection signal vo at time t1 is smaller than the short circuit determination voltage vo_min1.

  In the rising period T1 from time td11 to time t1, the switch element drive signal drv having the pulse width Tdrv1 is output to the DC / DC converter 3 after the power supply device 10 to which the LED 4 having normal characteristics is connected is started. This is the period until the output voltage detection signal vo reaches the short circuit determination voltage vo_min1 in the period. The value of the short circuit determination voltage vo_min1 is set in consideration of the setting value of the second DC voltage Vdc2 output from the DC / DC conversion unit 3, the characteristics of the LED 4 connected to the power supply device 10, and the like.

  As shown in FIG. 3C, in the determination period T2 from time t1 to time td12, when the output voltage detection signal vo does not rise to the short circuit determination voltage vo_min1, the switching control unit 6 detects the short circuit abnormality of the LED 4. To do. That is, if the output voltage detection signal vo does not exceed the short circuit determination voltage vo_min1 in the first period in which the switch element drive signal drv having the pulse width Tdrv1 is generated after the power supply device 10 is activated, the LED 4 has a short circuit abnormality. It is determined that

  This determination period T2 is output during the period in which the switch element drive signal drv having the pulse width Tdrv1 is output to the DC / DC converter 3 after the power supply device 10 to which the LED 4 having normal characteristics is connected is started. This is a period during which the voltage detection signal vo is equal to or higher than the short circuit determination voltage vo_min1.

  As shown in FIG. 3C, when the short circuit abnormality of the LED 4 is detected, the switching control unit 6 does not generate the switch element drive signal drv having the pulse width Tdrv2 from the time td21 to the time td22. That is, the n-type transistor M1 and the n-type transistor M2 included in the DC / DC conversion unit 3 are set in a non-conductive state.

  According to the power supply device 10 according to the first embodiment, the output voltage detection signal vo and the short-circuit determination voltage vo_min1 in the determination period T2 are compared, so that the occurrence of a short circuit in the LED 4 can be accurately detected when the power supply device 10 is activated. It is possible to detect well.

<Modification of Embodiment 1>
With reference to FIG. 4, a configuration of power supply device 11 which is a modification of power supply device 10 according to Embodiment 1 will be described.

  The power supply device 11 is different from the power supply device 10 in the following points. That is, the switching control unit 61 has a function of controlling the pulse width of the switch element drive signal drv in response to the dimming mode setting signal mode. In the power supply device 11, components having the same reference numerals have the same configuration and will not be described repeatedly.

  The dimming mode setting signal mode sets the dimming mode of the LED 4. Examples of the dimming mode include an all-light mode, a light-off mode, a gradation adjustment mode, and a nightlight mode. In the present specification, of the four dimming modes exemplified above, a mode other than the off mode is defined as a non-off mode.

  The power supply device 11 generates the second DC voltage Vdc2 corresponding to various dimming modes of the LED 4 set by the dimming mode setting signal mode. The switching control unit 61 included in the power supply device 11 holds the input dimming mode setting signal. The switching control unit 61 to which the dimming mode setting signal mode for setting the non-extinguishing mode is input outputs the switch element drive signal drv having a pulse width corresponding to each dimming mode to the DC / DC conversion unit 3. When the extinguishing mode is set, the switching control unit 61 does not output the switch element drive signal drv to the DC / DC conversion unit 3.

  The switching control unit 61 detects the short circuit abnormality of the LED 4 based on the comparison result between the output voltage detection signal vo and the short circuit determination voltage vo_min1 in the determination period T2 (see FIG. 3). When the short circuit abnormality of the LED 4 is detected, the switching control unit 61 does not generate the switch element drive signal drv in the next cycle. Thereby, even in the power supply device 11 in which the dimming mode can be set, it is possible to correctly detect the occurrence of the short circuit of the LED 4.

  The set value of the short circuit determination voltage vo_min2 may be changed for each dimming mode included in the non-extinguishing mode. In each dimming mode included in the non-lighting mode, the pulse width of the switch element drive signal drv is set to a value suitable for each dimming mode. By setting each short-circuit determination voltage vo_min2 suitable for the pulse width, the detection accuracy of occurrence of a short-circuit in each dimming mode is improved.

  In the power supply device 10 according to the first embodiment, the switch element drive signal drv output from one terminal of the switching control unit 6 is applied to each gate of the n-type transistors M1 / M2. The configuration for applying the switch element drive signal drv to the n-type transistors M1 / M2 is not limited thereto, and the switching control unit 6 is provided with two terminals for outputting the switch element drive signal drv, and the switch elements are provided from each output terminal to each transistor. The drive signal drv may be applied. The same applies to the power supply device 11 which is a modification of the power supply device 10 according to the first embodiment.

  As a specific example of the switching control unit 6 and the switching control unit 61, a microcomputer is applied. The DC / DC converter 3 is controlled by an arithmetic processing function and an interface function provided in the microcomputer.

Embodiments of the present invention can be summarized as follows.
(Claim 1)
A rectification unit (2) that converts the AC voltage (1) into a first DC voltage (Vdc1) and outputs the first DC voltage applied between a pair of input nodes (N3-N4) is converted into a second DC voltage. A power supply comprising: a DC / DC converter (3) that converts (Vdc2) to output between a pair of output nodes (N7-N8); and a switching controller (6) that controls the DC / DC converter In the device (10), the DC / DC converter includes a first coil (L1), a first switch element (M1) and a second switch element (M2) for controlling a current of the first coil, An output voltage detection circuit (R4 / R5) that generates an output voltage detection signal (vo) based on a voltage between the pair of output nodes, wherein the switching control unit includes the first switch element and the second switch element. Switch element is on for a specified time A switch element drive signal (drv) to be set is generated, and in the conduction period (Tdrv) of the first switch element and the second switch element after startup, the output voltage detection signal is set to the first short-circuit determination voltage (vo_min1). If not exceeding, the switching control unit sets the first switch element and the second switch element to a non-conductive state.

(Effects corresponding to claim 1)
It is possible to accurately detect the occurrence of a short circuit in the LED 4 when the power supply device is started.

(Claim 2)
The power supply apparatus according to claim 1, wherein the switching control unit controls a conduction time of the switch element drive signal in response to a dimming mode setting signal (mode).

(Effects corresponding to claim 2)
The power supply device capable of setting the dimming mode has the same effect as that of the first aspect.

(Claim 3)
The DC / DC converter further includes a second coil (L2) that detects a zero current of the first coil and outputs a zero current detection signal (zdc), and the switching control unit includes the zero current. The power supply device according to claim 1, wherein the switch element drive signal is generated in response to a detection signal.

(Effects corresponding to claim 3)
The power supply device having the power factor correction circuit also has the same effect as that of the first aspect.

(Claim 4)
The AC voltage (1) is converted into a first DC voltage (Vdc1) and output between the first node (N4) and the second node (N3), and the first DC voltage is converted into a second voltage. A DC / DC converter (3) that converts the DC voltage (Vdc2) and outputs it between the second node and the fifth node (N8), and a switching controller (6) that controls the DC / DC converter. The DC / DC converter comprises: a first switch element (M1) connected between the first node (N4) and a third node (N5); A first diode (D5) having an anode and a cathode connected to the second node and the third node, respectively, and a first coil (L1) connected between the third node and the fourth node (N6) The fourth node and the second node A second switching element (M2) and a first resistor (R3) connected in series between each other, and a second diode (D6) having an anode and a cathode connected to the fourth node and the fifth node, respectively. , An output voltage detection circuit (R4 / R5) connected between the second node and the fifth node, and a switching control unit (6), wherein the output voltage detection circuit includes the second node and Based on the voltage between the fifth nodes, an output voltage detection signal (vo) is generated, and the switching control unit sets a switch element drive signal for setting the first switch element and the second switch element to a conductive state for a predetermined time. (Drv) is generated, and in the conduction period (Tdrv) of the first switch element and the second switch element after startup, the output voltage detection signal is converted into a first short-circuit determination voltage. If not exceeding (vo_min1), the switching control unit sets the first switching element and the second switching element non-conductive, the power supply device.

(Effects corresponding to claim 4)
An effect similar to that of the first aspect is obtained.

(Claim 5)
The DC / DC conversion unit further includes a second coil (L2) having one end connected to the second node and the other end connected to the switching control unit, and the second coil includes the first coil The power supply according to claim 5, wherein the zero current of the coil is detected to generate a zero current detection signal (zdc), and the switching control unit generates the switch element drive signal in response to the zero current detection signal. apparatus.

(Effects corresponding to claim 5)
The power supply device having the power factor correction circuit also has the same effect as that of the fourth aspect.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  DESCRIPTION OF SYMBOLS 1 AC power supply, 2 Rectification part, 3 DC / DC conversion part, 3a Power factor improvement part, 3b Load drive part, 5 AC zero cross detection part, 6,61 Switching control part, 10,11 Power supply device, acv AC voltage detection signal , Acz zero cross detection signal, C1, C2, C3 capacitance, D1-D6 diode, drv switch element drive signal, GND ground voltage, io output current detection signal, L1, L2 coil, M1, M2 n-type transistor, mode dimming mode Setting signal, N1-N8 node, R1-R7 resistance, swoc switch element overcurrent detection signal, T1 rising period, T2 determination period, Tdrv1, Tdrv2, Tdrv3 pulse width, Vdc1 first DC voltage, Vdc2 second DC voltage, vo Output voltage detection signal, vo_min1, vo_min2 short circuit determination Pressure, ZDC zero current detection signal.

Claims (5)

A rectifying unit that converts an AC voltage into a first DC voltage and outputs the first DC voltage;
A DC / DC converter that converts the first DC voltage applied between a pair of input nodes into a second DC voltage and outputs the second DC voltage between the pair of output nodes;
A switching control unit for controlling the DC / DC conversion unit,
The DC / DC converter generates an output voltage detection signal based on a first coil, a first switch element and a second switch element that control a current of the first coil, and a voltage between the pair of output nodes. An output voltage detection circuit,
The switching control unit generates a switch element drive signal for setting the first switch element and the second switch element to a conductive state for a predetermined time;
When the output voltage detection signal does not exceed the first short circuit determination voltage in the conduction period of the first switch element and the second switch element after startup, the switching control unit is configured to switch the first switch element and the second switch element. A power supply device that sets a switch element to a non-conductive state.   The power supply device according to claim 1, wherein the switching control unit controls a conduction time of the switch element drive signal in response to a dimming mode setting signal. The DC / DC converter further includes a second coil that detects a zero current of the first coil and outputs a zero current detection signal,
The power supply apparatus according to claim 1, wherein the switching control unit generates the switch element drive signal in response to the zero current detection signal. A rectifying unit that converts an AC voltage into a first DC voltage and outputs the first DC voltage between the first node and the second node;
A DC / DC converter that converts the first DC voltage to a second DC voltage and outputs the second DC voltage between the second node and the fifth node;
A switching control unit for controlling the DC / DC conversion unit,
The DC / DC converter is
A first switch element connected between the first node and the third node;
A first diode having an anode and a cathode connected to the second node and the third node, respectively;
A first coil connected between the third node and the fourth node;
A second switch element and a first resistor connected in series between the fourth node and the second node;
A second diode having an anode and a cathode connected to the fourth node and the fifth node, respectively;
An output voltage detection circuit connected between the second node and the fifth node;
A switching control unit,
The output voltage detection circuit generates an output voltage detection signal based on a voltage between the second node and the fifth node;
The switching control unit generates a switch element drive signal for setting the first switch element and the second switch element to a conductive state for a predetermined time;
When the output voltage detection signal does not exceed the first short circuit determination voltage in the conduction period of the first switch element and the second switch element after startup, the switching control unit is configured to switch the first switch element and the second switch element. A power supply device that sets a switch element to a non-conductive state. The DC / DC converter further includes a second coil having one end connected to the second node and the other end connected to the switching controller.
The second coil detects a zero current of the first coil to generate a zero current detection signal;
The power supply device according to claim 4, wherein the switching control unit generates the switch element drive signal in response to the zero current detection signal.

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