Patent Publication Number: US-9888534-B2

Title: Trigger circuit, light apparatus comprising the same and trigger method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit under 35 USC 119(a) of Korean Patent Application No. 10-2015-0102567 filed on Jul. 20, 2015 in the Korean Intellectual Property Office, the entire disclosure of which is incorporated herein by reference for all purposes. 
     BACKGROUND 
     1. Field 
     The following description relates to a driving technique of a trigger circuit. The following description also relates to such a trigger circuit and a light apparatus having such a trigger circuit that are capable of controlling a turn-off time of a driving switching element to provide a boundary conduction mode. 
     2. Description of Related Art 
     A power factor correction converter generally operates in a continuous conduction mode and in a boundary conduction mode. The continuous conduction mode may use a fixed frequency of an integrated circuit (IC) to control an inductor current or a driving current. The boundary conduction mode may use a variable frequency to turn on a driving switch when the inductor current reaches a zero value. 
     A Light Emitting Diode (LED) light apparatus may be driven through a switching converter method. Also, a switching converter may be classified according to a Buck-type, a Boost-type and a Buck-Boost-type. A Buck-type converter is a DC-to-DC power converter which steps down voltage while stepping up current from its input to its output. A Boost-type converter is a DC-to-DC power converter which steps up voltage while stepping down current from its input to its output. A Buck-Boost-type converter is a converter that is able to operate as either a Buck-type converter or a Boost-type converter. Previously, the switching converter of the Boost-type was most commonly used, but more recently the Buck-type is used more commonly for a cost reduction of the integrated circuit (IC). In general, a type of the switching converter may be classified according to a ratio of an input voltage and an output voltage, as discussed, and may include a MOSFET in order to provide an average inductor current mode method. 
     An existing technology may use a drain voltage of the MOSFET for detecting a time point at which the inductor current reaches the zero value. The drain voltage of the MOSFET may rapidly decrease at the time point when the inductor current reaches the zero value, so the integrated circuit (IC) may use an external high breakdown voltage element for detecting the time point when the inductor current reaches the zero value. However, the existing technology uses the high breakdown voltage element, which causes a price competitiveness problem. 
     SUMMARY 
     This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. 
     In one general aspect, a trigger circuit includes an off-time controller configured to receive a sensing voltage by sensing a driving current and to compare the sensing voltage to first and second certain voltages that are close to a zero voltage value and symmetric to the zero voltage value to control a turn-off time of a driving switch in order for the sensing voltage to correspond to the zero voltage value at a turn-on time point of the driving switch, and a switching controller configured to provide a switching control signal for turning on the driving switch at the turn-on time point of the driving switch. 
     The off-time controller may include a first capacitor that is charged or discharged based on the sensing voltage and the first and second certain voltages to control the turn-off time of the driving switch. 
     The off-time controller may provide a charge switching signal associated with a charge of the first capacitor in response to the sensing voltage being larger than the first certain voltage. 
     The off-time controller may provide a discharge switching signal associated with a discharge of the first capacitor in response to the sensing voltage being smaller than the second certain voltage. 
     The off-time controller may provide a leading switching signal associated with a charge of the first capacitor during a certain time from a time point at which the driving switch is turned on. 
     The off-time controller may discharge the first capacitor using a first constant current during a section in which the sensing voltage is smaller than the second certain voltage. 
     The off-time controller may charge the first capacitor using a first constant current during a certain time from the time point that the driving switch is turned on in response the sensing voltage being larger than the first certain voltage. 
     The off-time controller may include a buffer amplifier in order to control an operating section of the sensing voltage. 
     The off-time controller may compare an output of the buffer amplifier and first and second reference voltages to detect a time point at which the sensing voltage reaches the first and second certain voltages. 
     The buffer amplifier may be provided using an inverting amplifier or a non-inverting amplifier. 
     The trigger circuit may further include a sawtooth wave voltage generator configured to charge a second capacitor with a second constant current during a turn-off section of the operation of the driving switch to generate a sawtooth wave voltage applied to both terminals of the second capacitor. 
     The sawtooth wave voltage generator may initialize the sawtooth wave voltage at the turn-on time point of the driving switch. 
     The trigger circuit may further include a pulse width controller configured to provide a pulse width control signal at the turn-off time point of the driving switch in order to control a pulse width of a switching control signal for turning on the driving switch. 
     The switching controller may output the switching control signal in response to the sawtooth wave voltage reaching an off-time control voltage applied to both terminals of the first capacitor. 
     The first certain voltage may correspond to a positive voltage that is close to the zero voltage value and the second certain voltage may correspond to a negative voltage that is close to the zero voltage value. 
     The switching controller may include a switching trigger configured to output a switching trigger signal, a storage configured to turn on or turn off the driving switch based on an output variance time point of the switching trigger signal, and a gate driver configured to output the switching control signal for turning on the driving switch. 
     The storage may be provided using an SR latch. 
     The gate driver may output the switching control signal through a gate pin. 
     In another general aspect, a light emitting diode light apparatus includes a light emitting diode (LED) device, an inductor connected in series to the LED device, a driving switch connected in series to the inductor, and a trigger circuit configured to sense a driving current for driving the LED device in order to control a turn-off time of the driving switch, wherein the trigger circuit includes an off-time controller configured to receive a sensing voltage by sensing the driving current and comparing the sensing voltage to first and second certain voltages that are close to a zero voltage value and symmetrical to the zero voltage value to control a turn-off time of the driving switch in order for the sensing voltage to correspond to the zero voltage value at a turn-on time point of the driving switch, and a switching controller configured to provide a switching control signal in order to turn on the driving switch at the turn-on time point of the driving switch. 
     In another general aspect, a trigger method includes receiving a sensing voltage by sensing a driving current and comparing the sensing voltage to first and second certain voltages that are close to a zero voltage value and symmetrical to the zero voltage value to charge or discharge a first capacitor, comparing an off-time control voltage applied to both terminals of the first capacitor to a sawtooth wave voltage applied to both terminals of a second capacitor, and turning on the driving switching element in response to the sawtooth wave voltage reaching the off-time control voltage. 
     Other features and aspects will be apparent from the following detailed description, the drawings, and the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a circuit diagram illustrating a trigger circuit and a light apparatus having the same, according to an embodiment. 
         FIG. 2  is a block diagram illustrating a trigger circuit in the embodiment of  FIG. 1 . 
         FIG. 3  is a circuit diagram illustrating a trigger circuit in the embodiment of  FIG. 1 . 
         FIG. 4  is a circuit diagram illustrating a trigger circuit provided as a non-inverting amplifier in a buffer amplifier of the trigger circuit in the embodiment of  FIG. 1 . 
         FIG. 5  is a waveform diagram illustrating an operation of a trigger circuit and a light apparatus having the trigger circuit in the embodiment of  FIG. 1 . 
         FIG. 6  is a flow chart illustrating a driving method of a trigger circuit and a light apparatus having the circuit in the embodiment of  FIG. 1 . 
     
    
    
     Throughout the drawings and the detailed description, the same reference numerals refer to the same elements. The drawings may not be to scale, and the relative size, proportions, and depiction of elements in the drawings may be exaggerated for clarity, illustration, and convenience. 
     DETAILED DESCRIPTION 
     The following detailed description is provided to assist the reader in gaining a comprehensive understanding of the methods, apparatuses, and/or systems described herein. However, various changes, modifications, and equivalents of the methods, apparatuses, and/or systems described herein will be apparent to one of ordinary skill in the art. The sequences of operations described herein are merely examples, and are not limited to those set forth herein, but may be changed as will be apparent to one of ordinary skill in the art, with the exception of operations necessarily occurring in a certain order. Also, descriptions of functions and constructions that are well known to one of ordinary skill in the art may be omitted for increased clarity and conciseness. 
     The features described herein may be embodied in different forms, and are not to be construed as being limited to the examples described herein. Rather, the examples described herein have been provided so that this disclosure will be thorough and complete, and will convey the full scope of the disclosure to one of ordinary skill in the art. 
     While terms such as “first,” “second,” and the like, may be used to describe various components, such components are not to be understood as being limited to the terms. The terms are merely used to help the reader to distinguish one component from another. 
     It is to be understood that when an element is referred to as being “connected to” or “connected with” another element, the element is possibly directly connected to the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly connected to” another element, no intervening elements are present, except where the context makes it clear that other intervening elements may be present. In addition, unless explicitly described to the contrary, the word “comprise” and variations such as “comprises” or “comprising,” or synonyms such as “including” or “having,” are to be understood to imply the inclusion of stated elements but not the exclusion of any other elements. Meanwhile, other expressions describing relationships between components such as “between”, “immediately between” or “adjacent to” and “directly adjacent to” may be construed similarly. 
     Singular forms “a”, “an” and “the” in the present disclosure are intended to include the plural forms as well, unless the context clearly indicates otherwise. 
     Devices that are in communication with each other need not be in continuous communication with each other, unless expressly specified otherwise. In addition, devices that are in communication with each other may communicate directly or indirectly through one or more intermediaries. 
     Although process steps, method steps, algorithms, or the like, may be described in a sequential order, such processes, methods and algorithms may be configured to work in alternate orders. In other words, any sequence or order of steps that may be described does not necessarily indicate a requirement that the steps be performed in that order. The steps of the processes, methods or algorithms described herein may be performed in any order practical. Further, some steps may be performed simultaneously. 
     When a single device or article is described herein, it is to be readily apparent that more than one device or article may be used in place of a single device or article. Similarly, where more than one device or article is described herein, it is to be readily apparent that a single device or article may be used in place of the more than one device or article. The functionality or the features of a device may be alternatively embodied by one or more other devices that are not explicitly described as having such functionality or features. 
     According to one embodiment, a trigger circuit, a light apparatus having the trigger circuit, and a trigger method may not use an external high breakdown voltage element to control a turn-off time of a driving switching element. 
     According to one embodiment, a trigger circuit, a light apparatus having the trigger circuit, and a trigger method may control a turn-off time of a driving switch in order for a driving current to correspond a zero current at a turn-on time point of a driving switch. 
     According to one embodiment, a trigger circuit, a light apparatus having the trigger circuit, and a trigger method may not use an external high breakdown voltage device to provide a boundary conduction mode for improving price competitiveness. 
       FIG. 1  is a circuit diagram illustrating a trigger circuit and a light apparatus having the same according to an embodiment. 
     Referring to the embodiment of  FIG. 1 , a light emitting diode light apparatus includes a LED module or LED device  10 , an inductor  20 , a diode  30 , a driving switch  40 , a sensing resistance  50  and a trigger circuit  100 . 
     The light emitting diode light apparatus may be provided with an input voltage V IN  from an input power supply. In this example, the input power supply corresponds to a source of the input voltage V IN . For example, the input voltage V IN  may correspond to a DC voltage V DC  or an AC voltage V AC . In one embodiment, when the input voltage V IN  corresponds to the DC voltage V DC , the input power supply may provide a stable DC power supply V DC . Alternatively, when the input voltage V IN  corresponds to the AC voltage V AC , a frequency of an AC input voltage V AC  may correspond to, but is not necessarily limited to corresponding to, 50 Hz or 60 Hz according to an electric power provider. 
     In one embodiment, the light emitting diode light apparatus may be driven through using a switching converter method. The light emitting diode light apparatus may optimize an output power through using the switching converter method. For example, the light emitting diode light apparatus may variably control the output power V OUT  in order to save the energy and decrease a caloric value of energy consumption. In some embodiment, the light emitting diode light apparatus is provided as a Buck-type converter. However, the light emitting diode light apparatus is not necessarily limited to a Buck-type converter, and it may be provided as a Boost-type converter or a Buck-Boost-type converter. 
     The LED device  10  may be formed into n, where n is a natural number, groups as a form including a series, parallel and series-parallel connection of each of LED to be disposed. For example, the LED device  10  may be driven by receiving the input voltage V IN . Accordingly, the light emitting diode light apparatus may control an output voltage V OUT  and a driving current I L  to regulate a brightness of the LED device  10 . In this example, the output voltage V OUT  corresponds to the voltage applied to both terminals of the LED device  10 . For example, the driving current I L  may drive the LED device  10  through the output voltage V OUT . Also, the driving current I L  may flow through the driving switch  40  when the driving switch  40  is turned on. 
     In one embodiment, the driving current I L  may include first and second driving current sections. In such an example, the driving current I L  may generate a ringing in the first driving current section. However the ringing may be removed when the boundary conduction mode is embodied in the second driving current section. Also, the trigger circuit  100  may not use an external high breakdown voltage device to remove the ringing. 
     In such an embodiment, the inductor  20  may be connected in parallel with the LED device  10 . Also, the driving switch  40  may electrically connected to the inductor  20  and the diode  30 . For example, the driving switch  40  may be disposed between the inductor  20  and the trigger circuit  100 . The driving switch  40  may receive a switching control signal from the trigger circuit  100 , so as to be turned on or turned off. When the driving switch  40  is turned on, the driving current I L  may flow into the sensing resistance  50 . By contrast, when the driving switch  40  is turned off, a flow of the driving current I L  may be cut off. Therefore, the light emitting diode light apparatus may control the output voltage V OUT  and the driving current I L  through using the switching control signal. 
     In one embodiment, when the driving switch  40  is turned on, the driving current I L  may flow through the driving switch  40  and the inductor  20  may be charged by the driving current I L . However, when the driving switch  40  is turned off, a current charged in the inductor  20  may be discharged so as to flow into the LED device  10  through the diode  30 . Accordingly, while the driving switch  40  is turned off, the inductor  20  may operate as a current source of the driving current I L . 
     In one embodiment, the driving switch  40  may be provided through using a Power MOSFET. When the driving switch  40  is provided through using the Power MOSFET, the switching control signal may be transmitted to a gate terminal of the Power MOSFET through a GATE pin and the switching control signal may control the flow of the driving current I L . For example, the switching control signal may turn on the driving switch  40  in case of receiving a positive value, such as a high level or 1, and may turn off the driving switch  40  in case of a negative value, such as a low level or 0. 
     In the embodiment of  FIG. 1 , the sensing resistance  50  may be electrically connected to the driving switch  40  and electrically connected to the trigger circuit  100 . In this embodiment, a voltage applied to both terminals of the sensing resistance  50  corresponds to the sensing voltage V CS  and the sensing voltage V CS  may also be applied to the trigger circuit  100  through a CS pin. That is, the sensing resistance  50  may be connected to a first terminal of the driving switch  40  in order to sense the driving current I L  passing through the driving switch  40 . 
       FIG. 2  is a block diagram illustrating a trigger circuit in the embodiment of  FIG. 1 . 
     Referring to the example of  FIG. 2 , the trigger circuit  100  includes an off-time control unit or off-time controller  110 , a sawtooth wave voltage generation unit or sawtooth wave voltage generator  120 , a pulse width control unit or pulse width controller  130  and a switching control unit or switching controller  140 . 
     The off-time controller  110  may receive the sensing voltage V CS  by sensing the driving current I L  and may compare the sensing voltage V CS  with first and second certain voltages. In this example, first and second certain voltages may be close to a zero voltage value and may be symmetrical to the zero voltage value. In one embodiment, the first certain voltage may correspond to the positive voltage being close to the zero voltage and the second certain voltage may correspond to the negative voltage being close to the zero voltage. Accordingly, the off-time controller  110  may control the turn-off time of the driving switch  40  in order for the sensing voltage to correspond to the zero voltage value at the turn-on time point of the driving switch  40 . 
     Also, the off-time controller  110  may include a buffer amplifier  112  and an off-time control device  114 . Furthermore, the buffer amplifier  112  may receive the sensing voltage V CS  through the CS pin. For example, the buffer amplifier  112  may detect the sensing voltage V CS  at an operation section of an integrated circuit (IC). In one embodiment, the buffer amplifier  112  may be provided using an inverting amplifier or a non-inverting amplifier. 
     For example, the off-time control device  114  may compare an output of the buffer amplifier  112  with first and second reference voltages to detect a time point that the sensing voltage reaches the first and second certain voltages. More specifically, the off-time control device  114  may compare the output of the buffer amplifier  112  with first and second reference voltages to generate an off-time control voltage V TOFF . The off-time control device  114  may control the off-time control voltage V TOFF  in order to control the turn-off time of the driving switch  40 . 
     In the embodiment of  FIG. 2 , the sawtooth wave voltage generator  120  may generate a sawtooth wave voltage V SAW  based on a pulse width modulation (PWM) signal. For example, the sawtooth wave voltage generator  120  may provide the sawtooth wave voltage V SAW  to the switching controller  140 . 
     The pulse width controller  130  may provide a pulse width control signal at the turn-off time point of the driving switch  40  for controlling the pulse width of the switching control signal. More specifically, when the driving switch  40  is turned on, the pulse width controller  130  may receive the sensing voltage V CS  generated by the driving current I L  passing through the driving switch  40  through the CS pin. For example, the pulse width controller  130  may provide the pulse width control signal at the turn-off time point of the driving switch  40  based on the sensing voltage V CS . 
     For example, the switching controller  140  may include a switching trigger  142 , a storage  144  and a gate driver  146 . The switching controller  140  may provide the switching control signal to the driving switch  40  through a gate pin at a turn-on time point or a turn-off time point of the driving switch  40 . For example, the switching trigger  142  may receive the off-time control voltage V TOFF  from the off-time controller  110  and may receive the sawtooth wave voltage V SAW  from the sawtooth wave voltage generator  120 . Furthermore, the switching trigger module  142  may compare the off-time control voltage V TOFF  and the sawtooth wave voltage V SAW . When the sawtooth wave voltage V SAW  reaches the off-time control voltage V TOFF , the switching trigger  142  may output the switching trigger signal for turning on the driving switch  40  and the switching trigger signal may correspond to the edge clock. Also, the switching controller  140  may provide the switching control signal for turning on the driving switch  40  based on the switching trigger signal. Furthermore, the switching controller  140  may provide the switching control signal for turning off the driving switch  40  based on the pulse width control signal. 
     The storage  144  may be electrically connected to the switching trigger  142  and the pulse width controller  130 . Also, the storage  144  may provide the output value for turning on or turning off of the driving switch  40  based on an output variance time point of the switching trigger  142  or the pulse width controller  130 . 
     For example, the gate driver  146  may receive the output value of the storage  144  to output the switching control signal. The switching control signal may be provided to the driving switch  40  through the gate pin. In one embodiment, the gate driver  146  may amplify the output of the storage  144  up to a voltage that is required for the turning-on or turning-off of the driving switch  40  and may output the switching control signal at a low impedance. Accordingly, the gate driver  146  may rapidly provide the switching control signal to the driving switch  40  based on the output value variance of the storage  144 . 
     In one embodiment, the storage  144  may be provided using a SR latch. For example, when the storage  144  receives the positive value, such as high level or 1, from the switching trigger  142  to transmit into the S terminal, the storage  144  may output the positive value, such as high level or 1, for turning on the driving switch  40 . However, when the storage  144  receives the positive value, such as high level or 1, from the pulse width controller  130  to transmit into the R terminal, the storage  144  may output the negative value, such as low level or 1, for turning off the driving switch  40 . That is, the gate driver  146  may output the switching control signal based on the output value of the storage  144 . 
       FIG. 3  is a circuit diagram illustrating a trigger circuit in the embodiment of  FIG. 1 . 
     Referring to the embodiment of  FIG. 3 , the buffer amplifier  112  may be provided as the inverting amplifier. When the buffer amplifier  112  is provided as the inverting amplifier, the buffer amplifier  112  may include a first comparator  112 - 1  and first and second resistances  112 - 2  and  112 - 3 . Also, the buffer amplifier  112  may receive the sensing voltage V CS  through the CS pin to invert the sensing voltage V CS . In one embodiment, the buffer amplifier  112  may output an inverting voltage V I   _   CS  for detecting the time point at which the sensing voltage V CS  reaches first and second certain voltages. Aspects of such first and second certain voltages have been discussed further, above. That is, the off-time controller  110  may compare the output of the buffer amplifier  112  and predetermined first and second reference voltages V REF   _   HIGH , V REF   _   LOW  to detect the time point when the sensing voltage V CS  reaches the first and second certain voltages. 
     For example, the off-time control device  114  may include a leading edge device  114 - 1 , a leading switch  114 - 2 , a charging switch  114 - 3 , a discharging switch  114 - 4 , a high comparator  114 - 5 , a low comparator  114 - 6  and a first capacitive capacitor  114 - 7 . The first capacitor  114 - 7  may be charged or discharged based on the sensing voltage and the first and second certain voltages to control the turn-off time of the driving switch  40 . More specifically, the off-time control device  114  may detect the time point when the inverting voltage V —CS  reaches first and second reference voltages V REF   _   HIGH , V REF   _   LOW  to detect the time point when the sensing voltage V CS  reaches the first and second certain voltages. When the inverting voltage V —CS  reaches the first or second reference voltages V REF   _   HIGH , V REF   _   LOW , the off-time control device  114  may charge or discharge the first capacitor  114 - 7  with a first constant current I TOFF . Accordingly, the first constant I TOFF  may have a constant current level. 
     In one embodiment, the off-time control voltage V TOFF  may be applied to both terminals of the first capacitor  114 - 7 . That is, when the first capacitor  114 - 7  is charged by the first constant current I TOFF , the off-time control voltage V TOFF  may linearly increase. When the first capacitor  114 - 7  is discharged by providing the first constant current I TOFF , the off-time control voltage V TOFF  may linearly decrease. 
     Accordingly, the off-time control device  114  may generate and control the off-time control voltage V TOFF  based on the inverting voltage V I   _   CS  and first and second reference voltages V REF   _   HIGH , V REF   _   LOW . More specifically, the off-time control device  114  may receive the inverting voltage V I   _   CS  to detect the time point at which the inverting voltage V I   _   CS  reaches first and second reference voltages V REF   _   HIGH , V REF   _   LOW . Accordingly, the leading edge device  114 - 1  may output a leading edge signal associated with charging the first capacitor  114 - 7  during the leading edge time from the time point when the driving switch  40  is turned on. The leading edge device  114 - 1  may provide the leading edge signal to the leading switch  114 - 2  and as a result, the leading switch  114 - 2  may be turned on by the leading edge signal. 
     The low comparator  114 - 6  may provide the charging switching signal to the charging switch  114 - 3  when the inverting voltage V I   _   CS  reaches the second reference voltage V REF   _   LOW . When the sensing voltage V CS  reaches the first certain voltage, such that the positive voltage is close to the zero voltage value, the inverting voltage V I   _   CS  may reach the second reference voltage V REF   _   LOW . That is, when the sensing voltage V CS  reaches the first certain voltage, the low comparator  114 - 6  may provide the charging switching signal to the charging switch  114 - 3 . 
     The off-time control device  114  may charge the first capacitor  114 - 7  with the first constant current I TOFF  when the inverting voltage V I   _   CS  reaches the second reference voltage V REF   _   LOW  in the leading edge time from the time point when the driving switch  40  is turned on. That is, the first capacitor  114 - 7  may be charged by the first constant current I TOFF  when the leading switch  114 - 2  and the charging switch  114 - 3  are turned on. In this example, the leading edge time may be predetermined for preventing the first capacitor  114 - 7  from continuously charging during the turn-on section of the driving switch  40 . Also, the leading edge time may be predetermined for providing the light emitting diode light apparatus in the boundary conduction mode. 
     The high comparator  114 - 5  may provide the discharging switching signal to the discharger  114 - 4  when the inverting voltage V I   _   CS  reaches the first reference voltage V REF   _   HIGH . When the sensing voltage V CS  reaches the second certain voltage, which is a negative voltage being close to the zero voltage, the inverting voltage V I   _   CS  may reach the first reference voltage V REF   _   HIGH . That is, the high comparator  114 - 5  may provide the discharging switching signal to the discharging switch  114 - 4  when the sensing voltage V CS  reaches the second certain voltage. 
     For example, the off-time control device  114  may discharge the first capacitor  114 - 7  using the first constant current I TOFF  when the inverting voltage V I   _   CS  reaches the first reference voltage V REF   _   HIGH . That is, the first capacitor  114 - 7  may be discharged using the first constant current I TOFF  when the discharge switch  114 - 4  is turned on. 
     Therefore, the off-time controller  110  may charge the first capacitor  114 - 7  when the sensing voltage V CS  is larger than the first certain voltage and may discharge the first capacitor  114 - 7  when the sensing voltage V CS  is smaller than the second certain voltage in the certain time from the time point at which the driving switch  40  is turned on in order to control the off-time control voltage V TOFF . 
     Also, the sawtooth wave voltage generator  120  may include an initialization switch  122  and a second capacitor  124 . In one embodiment, the sawtooth wave voltage generator  120  may charge the second capacitor  124  using a second constant current I SAW  during the section when the driving switch  40  is turned off. More specifically, when the driving switch  40  is turned off, the initialization switch  122  may be turned off. In such an example, the initialization switch  122  may determine the turn-on time point based on the pulse width modulation signal (PWM). The second capacitor  124  may be charged by the second constant current I SAW  when the initialization switch  122  is turned off and may be connected to both terminals of the second capacitor  124 . The second current I SAW  may have a constant level and the sawtooth wave voltage V SAW  may increase linearly. For example, the sawtooth wave voltage V SAW  may be provided to the switching trigger  142 . 
     In one embodiment, the sawtooth wave voltage generator  120  may initialize the sawtooth wave voltage V SAW  when the driving switch  40  is turned on. More specifically, the second capacitor  124  may be instantaneously discharged when the initialization switch  122  is turned on. When the initialization switch  122  is turned on, the second constant current I SAW  may not be charged in the second capacitor  124  to flow into a ground and the sawtooth wave voltage V SAW  applied to both terminals of the second capacitor  124  may be initialized. 
       FIG. 4  is a circuit diagram illustrating a trigger circuit provided as a non-inverting amplifier in a buffer amplifier of the trigger circuit in  FIG. 1 . 
     Referring to  FIG. 4 , the buffer amplifier  112  may be provided as the non-inverting amplifier. When the buffer amplifier  112  is provided as the non-inverting amplifier, the buffer amplifier  112  may include a second comparator  112 - 4 , and third to sixth resistances  112 - 5 ˜ 112 - 8 . The buffer amplifier  112  may receive the sensing voltage V CS  through the CS pin to output the non-inverting voltage V NI   _   CS  that has an identical phase with the sensing voltage V CS . 
     In one embodiment, when the sensing voltage V CS  reaches the negative voltage, the buffer amplifier  112  may provide a sensing reference voltage V CS   _   REF2  to a negative voltage, that is, Negative V CS , to output the non-inverting voltage V NI   _   CS  and a range of the non-inverting voltage V NI   _   CS  may be included in the operation section of the second comparator  112 - 4 . 
     The off-time control device  114  may generate and control the off-time control voltage V TOFF  based on the non-inverting voltage V NI   _   CS  and the first and second reference voltages V REF   _   HIGH , V REF   _   LOW . More specifically, the off-time control device  114  may receive the non-inverting voltage V NI   _   CS  in order to detect the time point at which the non-inverting voltage V NI   _   CS  reaches the first and second reference voltages V REF   _   HIGH , V REF   _   LOW . 
     In one embodiment, the high comparator  114 - 5  may provide the charging switching signal to the charging switch  114 - 3  when the non-inverting voltage V NI   _   CS  reaches the first reference voltage V REF   _   HIGH . When the sensing voltage V CS  reaches the first certain voltage, that is, a positive voltage being close to the zero voltage value, the non-inverting voltage V NI   _   CS  may reach the first reference voltage V REF   _   HIGH . That is, the high comparator  114 - 5  may provide the charging switching signal to the charging switch  114 - 3  when the sensing voltage V CS  reaches the first certain voltage. 
     The off-time control device  114  may provide charge to the first capacitor  114 - 7  by providing the first constant current I TOFF  in the leading edge time from the time point when the driving switch  40  is turned on until a time at which the non-inverting voltage V NI   _   CS  reaches the first reference voltage V REF   _   HIGH . That is, the first capacitor  114 - 7  may be charged by the first constant current I TOFF  when the leading switch  114 - 2  and the charging switch  114 - 3  are turned on. 
     In one embodiment, the low comparator  114 - 6  may provide the discharging switching signal to the discharging switch  114 - 4  when the non-inverting voltage V NI   _   CS  reaches the second reference voltage V REF   _   LOW . When the sensing voltage V CS  reaches the second certain voltage, that is, a negative voltage being close to the zero voltage, the non-inverting voltage V NI   _   CS  may reach the second reference voltage V REF   _   LOW . That is, the low comparator  114 - 6  may provide the discharging switching signal to the discharging switch  114 - 4  when the sensing voltage V CS  reaches the second certain voltage. 
     The off-time control device  114  may discharge the first capacitor  114 - 7  through the first constant current I TOFF  when the non-inverting voltage V NI   _   CS  reaches the second reference voltage V REF   _   LOW . That is, the first capacitor  114 - 7  may be discharged through providing the first constant current I TOFF  when the discharging switch  114 - 4  is turned on. 
     Therefore, the off-time controller  110  may charge the first capacitor  114 - 7  when the sensing voltage V CS  is larger than the first certain voltage and may discharge the first capacitor  114 - 7  when the sensing voltage V CS  is smaller than the second certain voltage in the certain time from the time point when the driving switch  40  is turned on in order to control the off-time control voltage V TOFF . 
       FIG. 5  is a waveform diagram illustrating an operation of a trigger circuit and a light apparatus having the trigger circuit in  FIG. 1 . 
     In one embodiment, the driving current I L  may include first and second driving current sections  510 ,  520 . The driving current I L  may generate the ringing in the first driving current section  510 . However the ringing may be removed when the boundary conduction mode is provided by the second driving current section  520 . Accordingly, the trigger circuit  100  may remove the ringing without using the external high breakdown voltage device. 
     For example, the driving current I L  may flow through the driving switch  40  when the driving switch  40  is turned on and may increase with a constant slope. In one embodiment, an increasing slope of the driving current I L  may be proportional to a voltage applied to a terminal between the inductor  20  and the LED device  10  and may be inversely proportional to an inductance L of the inductor  20 . At the time point at which the driving switch  40  is turned on, a voltage having a value of V IN −V OUT  may be applied to the terminal between the inductor  20  and the LED device  10 . That is, the slope of increase of the driving current I L  may correspond to (V IN −V OUT )/L, where L is an inductance. 
     Whereas, the driving current I L  may flow into the LED device  10  through the diode  30  when the driving switch  40  is turned off. That is, the driving current I L  may flow into the LED device  10  through the diode  30  at a voltage V DIODE  applied to both terminals of the diode  30 . When a driving switch  40  is turned off, a current charged in the inductor  20  is discharged. As a result, the driving current I L  may decrease with a constant slope. 
     In one embodiment, a slope of decrease of the driving current I L  may be proportional to the voltage applied to both terminals of the LED device  10  and may also be inversely proportional to the inductance of the inductor  20 . In the example of  FIG. 1 , a voltage of V OUT  may be applied to both terminals of the LED device  10 . That is, the decrease slope of the driving current I L  may correspond to −V OUT /L, where L is the inductance. More specifically, when the driving current I L  reaches the zero value, the voltage applied to both terminals of the inductor  20  may be the zero voltage value. Therefore, the driving current I L  may continuously decrease after reaching the zero current and may reach a minimum peak level at the turn-on time point of the driving switch  40 . 
     In one embodiment, the drain voltage V D  may maintain a constant voltage value of V IN +V DIODE  when the driving switch  40  is turned off and the drain current V D  may rapidly decrease when the driving current I L  falls below the certain current or the zero current. When the drain voltage V D  rapidly decreases to be identical to the voltage V IN −V OUT  applied to the terminal between the inductor  20  and the LED device  10 , such that V D =V IN −V OUT , the driving current I L  flows in the opposite direction and the sensing voltage V CS  lowers a negative voltage and the trigger circuit  100  detects that voltage charge to cause triggering in order for the driving switch to be turned-on. When the driving switch  40  is turned on, the driving current I L  may increase with the constant slope. 
     In one embodiment, because the driving current I L  increases when the driving switch  40  is turned on, the sensing voltage V CS  may increase with the constant slope. Because the driving current I L  does not flow into the sensing resistance  50  when the driving switch  40  is turned off, the sensing voltage V CS  maintains the zero voltage value. When the driving current I L  is lower the zero current so as to flow in the opposite direction, the sensing voltage V CS  may lower the negative voltage. Accordingly, the trigger circuit  100  may detect and turn-on, triggering the driving switch  40 . 
     In one embodiment, when the buffer amplifier  112  is provided as the inverting amplifier, the buffer amplifier  112  may invert the sensing voltage V CS  in order to output the inverting voltage V I   _   CS . For example, the phase of the inverting voltage V I   _   CS  may be opposite to the phase of the sensing voltage V CS . 
     In one embodiment, when the sensing voltage V CS  reaches the negative voltage, the inverting voltage V I   _   CS  may correspond to the positive voltage, such that V I   _   CS =2*V CS   _   REF −V CS . However, the sensing voltage V CS  may correspond to the positive voltage and the inverting voltage V I   _   CS  may correspond to the zero voltage value when the level of the sensing voltage V CS  is larger than the 2*sensing reference voltage, such that V CS &gt;2*V CS   _   REF . 
     In one embodiment, the off-time control voltage V TOFF  may be applied to both terminals of the first capacitor  114 - 7 . When the leading switch  114 - 2  and the charging switch  114 - 3  are turned on, the first capacitor  114 - 7  is charged by using the first constant current I TOFF  and the off-time control voltage V TOFF  may linearly increase. However, when the discharging switch  114 - 4  is turned on, the first capacitor  114 - 7  is discharged by using the first constant current I TOFF  and the off-time control voltage V TOFF  may linearly increase. 
     In one embodiment, the sawtooth wave voltage V SAW  may be applied to both terminals of the second capacitor  124 . When the driving switch  40  is turned off, the initialization switch  122  may be turned off as well and the second capacitor  124  may be charged by using the second constant current I SAW  and the sawtooth wave voltage V SAW  may linearly increase. However, when the driving switch  40  is turned on, the initialization switch  122  may be turned on and the second capacitor  124  may be instantaneously discharged and sawtooth wave voltage V SAW  may be initialized accordingly. 
     The leading edge device  114 - 1  may output the leading edge signal associated with the charging of the first capacitor  114 - 7  during the leading edge time from the time point when the driving switch  40  is turned on. Herein, the leading edge time may be predetermined to have an appropriate value for preventing the first capacitor  114 - 7  from continuously charging during turn-on section of the driving switch  40 . 
       FIG. 6  is a flow chart illustrating a driving method of a trigger circuit and a light apparatus having the trigger circuit in  FIG. 1 . For example, various steps included in the driving method may be performed by the off-time controller  110  and the switching controller  140 . 
     In step S 610 , the method may receive the sensing voltage V CS  sensing the driving current I L  including first and second driving current sections  510 ,  520 . For example, the off-time controller  110  may perform step S 610 . The sensing voltage V CS  may be provided to the off-time controller  110  through the CS pin. 
     In step S 620 , the method may charge the first capacitor  114 - 7  when the sensing voltage V CS  is larger than the first certain voltage. For example, the off-time controller  110  may perform step S 620 . The first capacitor  114 - 7  may be charged by using the first constant current I TOFF  and the off-time control voltage V TOFF  may linearly increase accordingly. 
     In step S 630 , the method may discharge the first capacitor  114 - 7  when the sensing voltage V CS  is smaller than the second certain voltage. For example, the off-time controller  110  may perform step S 630 . The first capacitor  114 - 7  may be discharged by using the first constant current I TOFF  and the off-time control voltage V TOFF  may linearly decrease accordingly. 
     In step S 640 , the method may compare the off-time control voltage V TOFF  applied to both terminals of the first capacitor  114 - 7  with the sawtooth wave voltage V SAW  applied to both terminals of the second capacitor  124 . For example, the switching controller  140  may perform step S 640 . 
     In step S 650 , the method may turn on the driving switch  40  when the sawtooth wave voltage V SAW  reaches the off-time control voltage V TOFF . For example, the switching controller  140  may perform step S 650 . 
     Accordingly, the trigger circuit and the light apparatus having the trigger circuit may not use the external high breakdown voltage device to control the turning-off time of the driving switch for the driving current so that it corresponds to the zero current value. Also, the trigger circuit  100  and the light apparatus having the trigger circuit  100  may not use the external high breakdown voltage device to provide the boundary conduction mode, and accordingly it is possible to improve the cost competitiveness of such examples. 
     While this disclosure includes specific examples, it will be apparent to one of ordinary skill in the art that various changes in form and details may be made in these examples without departing from the spirit and scope of the claims and their equivalents. The examples described herein are to be considered in a descriptive sense only, and not for purposes of limitation. Descriptions of features or aspects in each example are to be considered as being applicable to similar features or aspects in other examples. Suitable results may be achieved if the described techniques are performed in a different order, and/or if components in a described system, architecture, device, or circuit are combined in a different manner, and/or replaced or supplemented by other components or their equivalents. Therefore, the scope of the disclosure is defined not by the detailed description, but by the claims and their equivalents, and all variations within the scope of the claims and their equivalents are to be construed as being included in the disclosure.