Abstract:
An apparatus for providing auxiliary power to an off-line switcher. The apparatus includes a high voltage semiconductor switch and a driver for the high voltage semiconductor switch. The driver includes a first switch, the first switch coupled to the a third terminal of the high voltage semiconductor switch and to ground, a second switch coupled to a first terminal of the high voltage semiconductor switch, a third switch coupled to the first terminal of the high voltage semiconductor switch and to ground. The driver further includes a diode, the anode of the diode coupled to the third terminal of the high voltage semiconductor switch and the cathode of the diode coupled to the second switch.

Description:
BACKGROUND 
     1. Field of Art 
     The disclosure generally relates to the field of off-line power supplies, and specifically to providing power for an off-line switcher of an off-line power supply. 
     2. Description of the Related Art 
     Off-line power supplies typically use an auxiliary power supply for the control circuitry and the power switchers. Isolated power supplies obtain the auxiliary power from auxiliary transformer windings. However, non-isolated power supplies, where transformers are not used, having a transformer for supplying the auxiliary power is not cost effective. 
     Typically, non-isolated power supplies use additional circuitry to provide power to the control circuitry and the power switchers. For instance, some off-line power supplies may use a high voltage linear regulator to provide the auxiliary power. Alternatively, other off-line power supplies may use an output voltage bootstrap diode. In many cases, these additional circuitry may use high voltage processes (e.g., 600 V or higher) and/or may be inefficient. 
     Thus, it would be advantageous to be able to efficiently provide auxiliary power for the control circuitry and the power switchers of an off-line power supply without using a high voltage process. 
     SUMMARY 
     An apparatus provides auxiliary power to an off-line switcher. The apparatus includes a high voltage semiconductor switch and a driver for the high voltage semiconductor switch. The driver includes a first switch, the first switch coupled to the a third terminal of the high voltage semiconductor switch and to ground, a second switch coupled to a first terminal of the high voltage semiconductor switch, a third switch coupled to the first terminal of the high voltage semiconductor switch and to ground. The driver further includes a diode, the anode of the diode coupled to the third terminal of the high voltage semiconductor switch and the cathode of the diode coupled to the second switch. 
     The features and advantages described in the specification are not all inclusive and, in particular, many additional features and advantages will be apparent to one of ordinary skill in the art in view of the drawings and specification. Moreover, it should be noted that the language used in the specification has been principally selected for readability and instructional purposes, and may not have been selected to delineate or circumscribe the inventive subject matter. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The disclosed embodiments have other advantages and features which will be more readily apparent from the detailed description, the appended claims, and the accompanying figures (or drawings). A brief introduction of the figures is below. 
         FIG. 1A  illustrates a functional block diagram of an off-line switcher with line compensated overload power. 
         FIG. 1B  illustrates a circuit diagram of an application of the off-line switcher of  FIG. 1A . 
         FIG. 2A  illustrates a functional block diagram of a low quiescent current off-line switcher. 
         FIG. 2B  illustrates a circuit diagram of an application of the off-line switcher of  FIG. 2A . 
         FIG. 3A  illustrates a circuit diagram of a high voltage semiconductor switch with a self-powered driver, according to one embodiment. 
         FIG. 3B  illustrates a timing diagram of various signals of the self-powered driver of  FIG. 3A , according to one embodiment. 
         FIG. 3C  illustrates an exemplary application of the self-powered driver of  FIG. 3A , according to one embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The figures (FIGS.) and the following description relate to preferred embodiments by way of illustration only. It should be noted that from the following discussion, alternative embodiments of the structures and methods disclosed herein will be readily recognized as viable alternatives that may be employed without departing from the principles of what is claimed. 
     Reference will now be made in detail to several embodiments, examples of which are illustrated in the accompanying figures. It is noted that wherever practicable similar or like reference numbers may be used in the figures and may indicate similar or like functionality. The figures depict embodiments of the disclosed system (or method) for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles described herein. 
     Switch Mode Power Supplies 
     Switch mode power supplies are power supplies that include a switching regulator to convert electrical power. In a switch mode power supply, a pass transistor switches between low-dissipation, full-on, and full-off states, while spending a small amount of time in the high dissipation state. Switch mode power supplies include an input rectifier and/or filter, a switcher, and an output rectifier and/or filter. 
     Off-Line Switchers 
       FIG. 1A  illustrates a functional block diagram of an off-line switcher  110  with line compensated overload power.  FIG. 1B  illustrates a circuit diagram of an application of the off-line switcher  110 . 
     The off-line switcher  110  combines a high-voltage power metal-oxide semiconductor field-effect transistor (MOSFET)  125  with a power supply controller in one device. The controller includes a 5.85 V regulator  120  that charges bypass capacitor C bp  connected to the BYPASS/MULTI-FUNCTION pin (BP/M). The regulator  120  charges the capacitor C bp  by drawing a current form the voltage on the DRAIN pin (D) when the MOSFET  130  is off. The BP/M pin is the internal voltage supply node of off-line switcher  110 . When the MOSFET  125  is on, the device operates from the energy stored in the bypass capacitor C bp . 
       FIG. 1B  illustrates an off-line power supply  130  using the off-line switcher  110 . Off-line power supply  130  receives a wide-range high-voltage DC input voltage (Vin) and generates a DC output voltage (Vout). Bypass capacitor C bp  is coupled to the BP/M pin of off-line switcher  110  and optocoupler  150  is coupled to the ENABLE/UNDERVOLTAGE (EN/UV) pin of off-line switcher  110 . The EN/UV pin controls the switching power of MOSFET  125 . The switching of MOSFET  125  is terminated when a current greater than a threshold current (e.g., 115 μA) is drawn from the EN/UV pin. Switching of MOSFET  125  resumes when the current drawn from the EN/UV pin drops below a threshold current (e.g., 75 μA). 
     One disadvantage of the off-line switcher  110  is that regulator  120  is inefficient and uses a high voltage process (e.g., 600 V or higher). 
       FIG. 2A  illustrates a functional block diagram of a low quiescent current off-line switcher  210 .  FIG. 2B  illustrates a circuit diagram of an application of the off-line switcher  210 . 
     The off-line switcher  210  includes a high voltage power MOSFET  225  and a controller in one monolithic device. The device also includes a high-voltage current source, enabling start up and operation directly from the rectified main voltage. The off-line switcher  210  generates an internal low-voltage supply (e.g., 5V) from the integrated high-voltage current source. 
     The off-line power supply  220  receives an input voltage Vin and generates an output voltage Vout. The off-line power supply  220  includes the off-line switcher  210 , a bootstrap circuitry  230 , and a load  240 . The bootstrap circuitry  230  includes a diode D b , capacitor C b , and resistors R 1  and R 2 . The components of the bootstrap circuitry  230  may use high voltage components. Additionally, the off-line switcher may use a supply voltage different than the output voltage Vout of the off-line power supply  220 . During start up, the output voltage Vout may not be high enough to power off-line switcher  210 . Additionally, during normal operation of the off-line power supply  220 , the output voltage Vout may be higher than the maximum supply voltage of off-line switcher  210 . 
       FIG. 3A  illustrates a circuit diagram of a high voltage semiconductor switch Q 1  with a self-powered driver  330 , according to one embodiment. In the circuit diagram of  FIG. 3A , the high voltage semiconductor switch Q 1  is a bipolar junction transistor (BJT), but other types of high voltage semiconductor switches, such as metal-oxide-semiconductor field effect transistors (MOSFET) may be used instead. 
     The emitter of the BJT Q 1  is coupled to a switch Q 2 . In some embodiments, switch Q 2  is a field-effect transistor (FET). When closed, switch Q 2  couples the emitter of BJT Q 1  to ground. The base of BJT Q 1  is coupled to a resistor R base  and switch S 1 , and switch S 1  is coupled to capacitor C. When closed, switch S 1  couples resistor R base  and the base of BJT Q 1  to capacitor C. In some embodiments, the base of the BJT is coupled to a current source instead of resistor R base . The current source supplies current to the base of the BJT to turn the BJT on. The base of BJT Q 1  is further coupled to switch S 2 . When closed, switch S 2  couples the base of BJT Q 1  to ground. 
     A diode D 1  is coupled between the emitter of BJT Q 1  and capacitor C. When forward biased, diode D 1  charges capacitor C. In some embodiments, a diode connected transistor is coupled between the emitter of the BJT Q 1  and capacitor C instead of a diode. For instance, a diode connected BJT, where the base and the collector of the diode connected BJT are connected to each other is used. Alternatively, a diode connected MOSFET, where the gate and the drain of the diode connected MOSFET are connected to each other is used. 
     In some embodiments a load is coupled between the collector of BJT Q 1  and a supply voltage V bus . In the circuit diagram of  FIG. 3C , the load is represented as a load resistor R load  but any other types of loads may be coupled between the collector of the BJT Q 1  and power supply V bus . In some embodiments, a load is coupled between the ground of the driver  330  and a negative terminal of a power supply (not shown). 
     In some embodiments, a field effect transistor FET is used instead of BJT Q 1 . In this embodiment, the source of FET Q 1  is coupled to switch Q 2 , and the gate of FET Q 1  is coupled to resistor R base  and switch S 1 . Additionally, a load, such as R load , may be coupled to the drain of FET Q 1 . 
     In some embodiments, every element of  FIG. 3A  is fabricated in a monolithic integrated circuit. In other embodiments, some components, such as, the load, BJT Q 1  and/or capacitor C are provided as an external component to the integrated circuit. That is, switches Q 2 , S 1 , and S 2 , diode D 1 , and resistors R base  are fabricated in a single integrated circuit and load resistor R load , BJT Q 1  and capacitor C are external to the integrated circuit. In yet other embodiments, every component is a discrete circuit element and the components are integrated using a printed circuit board (PCB). 
     In some embodiments, additional circuitry is included to generate the control signals to close and open switches Q 2 , S 1 , and S 2 . In other embodiments, the control signals are generated by an external component. In one embodiment, feedback is used to generate the control signals. For instance, the amount of charge stored in capacitor C of self-powered driver  330  may be sensed and the control signals to close and open switches Q 2 , S 1 , and S 2  may be generated based on the sensed amount of charge stored in capacitor C. 
       FIG. 3B  illustrates a timing diagram of various signals of the self-powered driver  330 , according to one embodiment. At time t 1  switches Q 2  and S 1  are closed. Switch Q 2  couples the emitter of BJT Q 1  to ground and switch S 1  couples the base of BJT Q 1  to capacitor C. When switches Q 2  and S 1  are closed, BJT Q 1  turns on and a load current I load  starts flowing through resistor R load  and BJT Q 1 . Current I load  generates a voltage difference across resistor R load  reducing the collector voltage V. 
     At time t 2 , switches Q 2  and S 1  are opened. Since switch Q 2  is closed, current I load  is not able to flow to ground through switch Q 2  and thus, forward biases diode D 1 . Diode D 1  conducts current I diode  into capacitor C, thus, charging capacitor C. 
     At time t 3 , switch S 2  is closed. Switch S 2  couples the base of BJT Q 1  to ground, turning off BJT Q 1 . In some embodiments, switch S 2  discharges a base capacitor of BJT Q 1 . As a result, the base current I base  is negative until the base capacitor is discharged. 
     At time t 4 , switch S 2  is opened. Since all switches Q 2 , S 1 , and S 2  are opened, BJT Q 1  remains off until switches Q 2  and S 1  are closed in a subsequent operating cycle. 
       FIG. 3C  illustrates an exemplary application of the self-powered driver  330 . The exemplary application of  FIG. 3C  uses a buck configuration, but other configurations, such as, a boost configuration, a buck-boost configuration, a flyback configuration, or any other power supply configuration may be used instead. 
       FIG. 3C  is a circuit diagram of a switch-mode power supply  320 . Switch-mode power supply  320  receives an input voltage Vin and generates an output voltage Vout. Switch-mode power supply  320  includes an off-line switcher  210 , a load  240 , load resistor R load , BJT Q 1 , and a self-powered driver  330 . The self-powered driver  330  provides power for driving the off-line switcher  210 . 
     In some embodiments, additional circuitry, such as feedback circuitry may be included. The feedback circuitry may be connected to the FB terminal of the off-line switcher  210 . 
     The self-powered driver  330  receives a supply voltage from the input of the switch-mode power supply  320  and charges capacitor C to power the off-line switcher  210 . 
     Additional Configuration Considerations 
     Throughout this specification, plural instances may implement components, operations, or structures described as a single instance. Although individual operations of one or more methods are illustrated and described as separate operations, one or more of the individual operations may be performed concurrently, and nothing requires that the operations be performed in the order illustrated. Structures and functionality presented as separate components in example configurations may be implemented as a combined structure or component. Similarly, structures and functionality presented as a single component may be implemented as separate components. These and other variations, modifications, additions, and improvements fall within the scope of the subject matter herein. 
     Certain embodiments are described herein as including logic or a number of components, modules, or mechanisms. Modules may constitute either software modules (e.g., code embodied on a machine-readable medium or in a transmission signal) or hardware modules. A hardware module is tangible unit capable of performing certain operations and may be configured or arranged in a certain manner. In example embodiments, one or more computer systems (e.g., a standalone, client or server computer system) or one or more hardware modules of a computer system (e.g., a processor or a group of processors) may be configured by software (e.g., an application or application portion) as a hardware module that operates to perform certain operations as described herein. 
     In various embodiments, a hardware module may be implemented mechanically or electronically. For example, a hardware module may comprise dedicated circuitry or logic that is permanently configured (e.g., as a special-purpose processor, such as a field programmable gate array (FPGA) or an application-specific integrated circuit (ASIC)) to perform certain operations. A hardware module may also comprise programmable logic or circuitry (e.g., as encompassed within a general-purpose processor or other programmable processor) that is temporarily configured by software to perform certain operations. It will be appreciated that the decision to implement a hardware module mechanically, in dedicated and permanently configured circuitry, or in temporarily configured circuitry (e.g., configured by software) may be driven by cost and time considerations. 
     The various operations of example methods described herein may be performed, at least partially, by one or more processors that are temporarily configured (e.g., by software) or permanently configured to perform the relevant operations. Whether temporarily or permanently configured, such processors may constitute processor-implemented modules that operate to perform one or more operations or functions. The modules referred to herein may, in some example embodiments, comprise processor-implemented modules. 
     The one or more processors may also operate to support performance of the relevant operations in a “cloud computing” environment or as a “software as a service” (SaaS). For example, at least some of the operations may be performed by a group of computers (as examples of machines including processors), these operations being accessible via a network (e.g., the Internet) and via one or more appropriate interfaces (e.g., application program interfaces (APIs).) 
     The performance of certain of the operations may be distributed among the one or more processors, not only residing within a single machine, but deployed across a number of machines. In some example embodiments, the one or more processors or processor-implemented modules may be located in a single geographic location (e.g., within a home environment, an office environment, or a server farm). In other example embodiments, the one or more processors or processor-implemented modules may be distributed across a number of geographic locations. 
     Some portions of this specification are presented in terms of algorithms or symbolic representations of operations on data stored as bits or binary digital signals within a machine memory (e.g., a computer memory). These algorithms or symbolic representations are examples of techniques used by those of ordinary skill in the data processing arts to convey the substance of their work to others skilled in the art. As used herein, an “algorithm” is a self-consistent sequence of operations or similar processing leading to a desired result. In this context, algorithms and operations involve physical manipulation of physical quantities. Typically, but not necessarily, such quantities may take the form of electrical, magnetic, or optical signals capable of being stored, accessed, transferred, combined, compared, or otherwise manipulated by a machine. It is convenient at times, principally for reasons of common usage, to refer to such signals using words such as “data,” “content,” “bits,” “values,” “elements,” “symbols,” “characters,” “terms,” “numbers,” “numerals,” or the like. These words, however, are merely convenient labels and are to be associated with appropriate physical quantities. 
     Unless specifically stated otherwise, discussions herein using words such as “processing,” “computing,” “calculating,” “determining,” “presenting,” “displaying,” or the like may refer to actions or processes of a machine (e.g., a computer) that manipulates or transforms data represented as physical (e.g., electronic, magnetic, or optical) quantities within one or more memories (e.g., volatile memory, non-volatile memory, or a combination thereof), registers, or other machine components that receive, store, transmit, or display information. 
     As used herein any reference to “one embodiment” or “an embodiment” means that a particular element, feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment. 
     Some embodiments may be described using the expression “coupled” and “connected” along with their derivatives. For example, some embodiments may be described using the term “coupled” to indicate that two or more elements are in direct physical or electrical contact. The term “coupled,” however, may also mean that two or more elements are not in direct contact with each other, but yet still co-operate or interact with each other. The embodiments are not limited in this context. 
     As used herein, the terms “comprises,” “comprising,” “includes,” “including,” “has,” “having” or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Further, unless expressly stated to the contrary, “or” refers to an inclusive or and not to an exclusive or. For example, a condition A or B is satisfied by any one of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present). 
     In addition, use of the “a” or “an” are employed to describe elements and components of the embodiments herein. This is done merely for convenience and to give a general sense of the invention. This description should be read to include one or at least one and the singular also includes the plural unless it is obvious that it is meant otherwise. 
     Upon reading this disclosure, those of skill in the art will appreciate still additional alternative structural and functional designs for a system and a process for providing an auxiliary power supply to off-line switchers in an off-line power supply through the disclosed principles herein. Thus, while particular embodiments and applications have been illustrated and described, it is to be understood that the disclosed embodiments are not limited to the precise construction and components disclosed herein. Various modifications, changes and variations, which will be apparent to those skilled in the art, may be made in the arrangement, operation, and details of the method and apparatus disclosed herein without departing from the spirit and scope defined in the appended claims.