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  Clamp diode reset in a power converterUSPTO Application #: 20080043495Title: Clamp diode reset in a power converter Abstract: Generally, a DC/DC converter and its associated devices and processes are presented herein. The DC/DC converter may be a switched mode converter that includes a plurality of switching devices that couple between the first and second power supply rails. A transformer is coupled to the switching devices such that the switching devices exchange electrical energy through the transformer. A rectifier is coupled to the transformer to rectify the waveform from the transformer into a substantially DC output. The DC/DC converter also includes clamp diodes to relieve voltage stress on rectifier diodes. Resistors may be coupled in series with the clamp diodes to reduce a reset time of the DC/DC converter and thereby prevent catastrophic failure of the power supply during load transients. Additionally, the DC/DC converter may be configured with a power outage detection device that monitors gate drive signals of the converter. (end of abstract) Agent: Marsh, Fischmann & Breyfogle LLP - Aurora, CO, US Inventor: Aaron Jungreis USPTO Applicaton #: 20080043495 - Class: 363 17 (USPTO) The Patent Description & Claims data below is from USPTO Patent Application 20080043495. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATIONS [0001]This patent application is related to and claims priority from U.S. Provisional Patent Application Nos. 60/837,963 (filed Aug. 16, 2006 and entitled "Fast Reset of a Phase-Shifted Full-Bridge DC/DC Converter Clamp") and 60/837,978 (filed Aug. 16, 2006 and entitled "Fast AC Outage Detection"), the entire contents of each of which are incorporated within by reference. BACKGROUND [0002]A phase-shifted full-bridge DC/DC converter, in its basic form may include a primary side containing a set of switches used to control the application of an input voltage to the primary coil of a transformer, and a secondary side containing a set of output diode rectifiers that serve to produce a voltage with constant polarity. The converter may be in an active state, during which a differential voltage is applied across the primary coil of the transformer, or in a passive state, during which the same voltage is applied to both terminals of the transformer's primary coil. Thus, electrical energy flows in the converter during the active state. [0003]Switching losses occur when the semiconductor switches transition from on to off or vice versa. In order to achieve high efficiency in a phase-shifted full-bridge DC/DC converter, low switching losses are maintained over a wide range of operating conditions. This is typically achieved by adding a "resonant inductor" to the primary side of the converter and adding "dead time" delay between the two switches in each half-bridge to allow time for the output voltage of the half-bridge to commutate prior to activating the opposing switch. However, the inductive source impedance causes voltage overshoot and ringing during the decaying portion of the reverse current that occurs in the output rectifier diodes following a state transition in the converter. This voltage overshoot and ringing can generate excessive dynamic losses, unacceptable EMI, and increased voltage stress on the diodes at the secondary-side of the converter. Failure of the rectifier diodes can occur due to the increased voltage stress. A typical solution to this problem involves clamping the junction between the transformer and the resonant inductor to the supply rails with two diodes, known as clamp diodes. SUMMARY [0004]It is generally known that the clamp diode solution may not correctly protect the full-bridge converter during load transients to very small loads, a problem which is poorly understood and typically solved by adding large pre-loads to the converter. The invention described hereinbelow shows actual mechanisms involved in the poor performance of the clamp diode solution at small loads, and presents a relatively low-cost and efficient solution which will work over virtually all operating conditions of the converter. [0005]During an active-to-passive state transition (initiated by turning off the right-side half-bridge), load current flows through the capacitance of the right-side half-bridge and commutates the right-side half-bridge voltage prior to turning on the opposing right-side half-bridge switch. During a passive-to-active state transition (initiated by turning off the left-side half-bridge), the direction of load current is wrong for commutating the left-side half-bridge through the half-bridge capacitance. A resonant inductor is therefore added in line with the left-side half-bridge for commutating the voltage to obtain zero-voltage-switching. After the left-side half-bridge switch is turned off, the load current in the primary of the transformer is diverted to a clamp diode while the resonant inductor and half-bridge capacitance allows the left-side half-bridge voltage to commutate to the opposing rail prior to turning on the opposing left-side half-bridge switch. After the opposing left-side half-bridge switch is turned on, the voltage across the resonant inductor is equal to the difference between the half-bridge switch drain-source voltage and the clamp diode forward voltage. This is typically a very small voltage difference on the order of 1V. The small inductor voltage drives the resonant inductor current to zero, after which the clamp diode turns off and the left-side half-bridge carries the full load current. [0006]When a phase-shifted full-bridge DC/DC converter is operating under steady-state conditions, the duration of each active state is designed to be longer than the time needed to reset the resonant inductor current. Under these conditions, the current pulse flowing through the clamp diodes at the beginning of each active phase has sufficient time to reset to zero before the next passive phase. However, during a load transient, the duration of each active state may decrease significantly, leaving insufficient time to fully reset the resonant energy in the resonant inductor before the next passive phase. As a result, the clamp diode current increases on each subsequent cycle. As the resonant inductor current increases, the difference between the left-side half-bridge drain-source voltage and the clamp diode forward voltage decreases which further increases the required reset time for the resonant inductor current. The process of increasing inductor current and subsequent increasingly required reset time leads to heating of the clamp diode, thus lowering its forward voltage and making the problem worse. The eventual result is typically the destruction of the clamp diodes and thus the DC/DC converter. Operating the converter in no-load burst mode can produce a similar result. [0007]Some designs include a substantial preload at the output to prevent the converter from going into burst mode. However, addition of a preload often adds cost, consumes additional space, reduces efficiency, and adds to the thermal burden of the DC/DC converter. Regardless, the preload still does not prevent the DC/DC converter from operating in burst mode. Nor does the preload prevent the electric current through the clamp diodes from becoming relatively high during a load transient. [0008]Other designs may employ relatively large clamp diodes to handle overcurrents that occur due to the high currents during transients and/or relatively fast clamp diodes to increase the voltage drop in the clamp diodes and thereby reduce the reset time. Larger and/or faster clamp diodes, however, generally increase the cost of the DC/DC converter. Alternative designs have DC/DC converters operating at lower frequencies to provide enough time for the electric current to reset, which also generally increases the size and cost of the DC/DC converter. [0009]In one embodiment, a DC/DC converter (e.g., a phase-shifted full-bridge converter) includes first and second power supply rails, a plurality of switching devices that couple between the first and second power supply rails, and a transformer coupled to the switching devices. The switching devices (e.g., MOSFETs) exchange energy through the transformer. The converter also includes a rectifier coupled to the transformer that rectifies electrical energy through the transformer. The converter also includes a resonant inductor to prevent switching losses in the converter. To reduce ringing associate with the resonant inductor, the converter may includes one or more clamp diodes that are coupled between the first and second power supply rails, to the resonant inductor, and to the transformer. At least one load element is coupled between the one or more clamp diodes and the power supply rails for reducing a reset time of the DC/DC converter. [0010]The DC/DC converter may include a controller to provide four-state pulse width modulation. The switching devices may be metal oxide semiconductor field effect transistors. The at least one load may include a resistor (e.g., between about 100 milliOhms and 100 Ohms. A first load element and a first clamp diode may be coupled in series between the first power supply rail and the transformer. A second load element and a second clamp diode may be coupled in series between the transformer and the second power supply rail. The first and second load elements may have the same or different values and may include a diode or a diode-resistor combination. [0011]In another embodiment, a method of operating a DC/DC converter includes receiving electrical energy, first conducting the electrical energy through a transformer in a first polarity for a first duration, and second conducting the electrical energy through the transformer in a second polarity for a second duration. With at least two clamp diodes, the method further includes clamping voltage of the electrical energy through the transformer during said first and second conducting. With at least a first load element, the method also includes resetting current in a first of the at least two clamp diodes after said first conducting and before said second conducting. The method also includes rectifying the electrical energy to a substantially DC output responsive to said first and second conducting. [0012]A second load element may be used for resetting current in a second of the at least two clamp diodes after said second conducting. The load elements may be a resistor having a value between about 100 milli-Ohms and 100 Ohms. The current may be reset to substantially 0 Amps in response to a load transient or while the converter is in burst mode. This resetting of the current may provide voltage stress relief to the at least two clamp diodes. [0013]In another embodiment, an outage detection system is provided. For example, the power outage detection system may be configured for quickly determining an AC outage of a switched mode power supply, such as the DC/DC converter described herein. However, the power outage detection system is not intended to be limited to simply the DC/DC converter. Rather, the detection system may be configured with other types of switched mode power supplies or other circuits. The detection system includes an input/output module configured for receiving one or more pulsed control signals from a device and generating a control signal responsive thereto. The detection system also includes a filter communicatively coupled to the input/output module to filter the generated control signal of the input/output module and a processor communicatively coupled to the filter to receive the filtered control signal and determine an operational parameter (e.g., an AC outage) of the device therefrom. [0014]In order to implement the design in practice, it may be necessary to distinguish between AC outages and load transients that cause the input DC bus voltage to decrease. For example, when a load transient occurs, the comparator level for the outage detection is temporarily decreased so as not to cause false trips in the detector. To adjust the comparator level, it may be necessary to obtain a signal proportional to load current. Such a signal is often present in power supplies due to the need for current limiting. The signal then needs to go through a high-pass filter and added to the fast-AC detector comparator level. The speed of the high-pass filter will depend on the compensation loop of the converter, and should imitate the compensation loop speed. Typically, a first-order high-pass filter (formed by a single resistor and capacitor) should be adequate. In the case of the converter used in experiments, the microcontroller already had a signal proportional to load current, so it was capable of determining the effect of load transients with no additional circuitry. The microcontroller was capable of implementing the comparator and the high-pass filter digitally. Additionally, the microcontroller may adjust and intermediate bus voltage reference. [0015]In one embodiment, the detection system includes a signal processor that produces the inverse of the combined gate-drive logic in a converter; a filter for that combined inverse gate-drive signal; a reference adjusted for the expected intermediate bus voltage of the converter such that the reference is appropriately shifted to ignore load transients; and a comparator to compare the combined inverts the gate-drive signal to the adjusted intermediate bus voltage reference. [0016]As mentioned, the device may be a DC/DC converter or other type of switch mode power supply. In this regard, the one or more pulsed control signals are drive signals to switches in the DC/DC converter. [0017]The filter may be configured for smoothing transients in the one or more pulsed control signals. For example, the filter may be a high pass filter and the pulsed control signals may be pulsed width modulated gate drive signals of a switched mode power supply. The processor may determine the operational parameter of the device by comparing the filtered control signal to a threshold value (e.g., a reference voltage, such as an intermediate bus voltage or a representative thereof). [0018]The input/output module may include one or more diodes configured for respectively receiving the one or more pulsed control signals. The input/output module may include a least one control diode having an anode coupled to the one or more diodes and to a control signal source for generating the control signal responsive to the one or more pulsed control signals. Alternatively, the input/output module 611 may include a signal processor configured for generating an inverse of gate drive signals from a DC/DC converter. [0019]The processor may be further configured for determining an intermediate bus voltage of the DC/DC converter. The processor may include a comparator configured for comparing the filtered control signal to the intermediate bus voltage. Additionally, the processor may adjust the intermediate bus voltage based on load transients. [0020]In one embodiment, a method of detecting a power outage in a switched mode power supply, such as a DC/DC converter, includes monitoring a first one or more control signals that are used to control switching of the switched mode power supply and generating a second one or more control signals in response to monitoring the first one or more control signals. The method also includes filtering the second one or more control signals of transients associated with the first one or more control signals and processing the filtered second one or more control signals to determine operability of the switched mode power supply. [0021]Monitoring the first one or more control signals may include receiving the first one or more control signals with a corresponding number of diodes. For example, receiving the first one or more control signals with the corresponding number of diodes may include holding the diodes in a reverse bias state during on times of the first one or more control signals. Continue reading... Full patent description for Clamp diode reset in a power converter Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Clamp diode reset in a power converter patent application. Patent Applications in related categories: 20080192509 - Dc-dc converter with isolation - A power converter comprises a direct current (DC)-DC converter configured to receive an input voltage in a primary domain, a transformer coupled to and driven by the DC-DC converter and supplying an output voltage in a secondary domain, and a transmission path configured to pass a digital feedback signal through ... 20080192510 - Device for feeding electrical energy from an anergy source - A device (1) for feeding electrical energy from an energy source with variable source voltage into an electric power supply network (15), said device (1) including a transformer (112) for galvanic isolation, a resonant inverter (11) with semi-conductor switches (a-d; A, B), one or several resonant capacitors (17; 18, 19; ... 20080192511 - Power supply system and apparatus - The present invention relates to a switched mode power supply with programmable digital control and to a power supply system comprising a plurality of switched mode power supplies. The input terminals and the output terminals of the switched mode power supply system are separated by an insulation barrier, and the ... ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. Start now! - Receive info on patent apps like Clamp diode reset in a power converter or other areas of interest. ### Previous Patent Application: Resonant converter and burst mode starting method thereof Next Patent Application: Linear-predict sampling for measuring demagnetized voltage of transformer Industry Class: Electric power conversion systems ### FreshPatents.com Support Thank you for viewing the Clamp diode reset in a power converter patent info. IP-related news and info Results in 5.55843 seconds Other interesting Feshpatents.com categories: Novartis , Pfizer , Philips , Polaroid , Procter & Gamble , |
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