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Researchers Submit Patent Application, "Snubber Circuit for Dc-Dc Voltage Converter", for Approval

May 28, 2014

By a News Reporter-Staff News Editor at Electronics Newsweekly -- From Washington, D.C., VerticalNews journalists report that a patent application by the inventors Koch, Stefan (Kappelrodeck, DE); Tian, Jian (Buehl, DE), filed on April 3, 2012, was made available online on May 15, 2014.

The patent's assignee is Robert Bosch Gmbh.

News editors obtained the following quote from the background information supplied by the inventors: "The invention relates to a snubber circuit for a DC-DC voltage converter, in particular for a neutral point rectifier with synchronous rectification.

"Synchronous rectifier circuits are usually used for DC-DC voltage conversion, for example for the purpose of supplying a low-voltage electrical system of a vehicle. The power semiconductor switches, for example MOSFETs, used for this purpose currently have a lower voltage loss than diodes at relatively high direct currents, as a result of which the efficiency of the rectifier can be increased. The output capacitance of semiconductor switches which are turned off may result, in the case of electrically decoupled synchronous rectifiers, in the phenomenon of 'secondary ringing', that is to say the occurrence of unwanted oscillations of the current or voltage. In this case, resonance is effected between the leakage inductance of the secondary side of the transformer with the secondary-side inductance and the output capacitance of the semiconductor switches.

"Therefore, conventional synchronous rectifiers have attenuators, so-called 'snubber elements', which charge the oscillation energy of the oscillations to a capacitance if a critical voltage limit is exceeded. Passive snubber elements may consist of, for example, a series circuit comprising a capacitor and a resistor which can be connected in parallel with the semiconductor switch as an RC quenching combination. In contrast, active snubber elements have, in addition to the capacitor, a further semiconductor switch which can be used to discharge the excess charge, for example back into the secondary-side vehicle electrical system, if a critical amount of charge in the capacitor is exceeded.

"The document U.S. Pat. No. 6,771,521 B1 discloses an active snubber circuit for a synchronous rectifier with a damping capacitor which can be discharged in a switchable manner via a semiconductor switch.

"The document U.S. Pat. No. 5,898,581 discloses a neutral point rectifier circuit having an active snubber circuit, oscillation charge stored in a snubber capacitor being able to be fed back into the rectifier circuit via an inductive element.

"Conventional snubber circuits, for example those disclosed in the document U.S. Pat. No. 5,898,581, are designed for high voltages or high energies in order to keep power losses low (so-called 'lossless snubber'). In particular, the inductive components such as snubber inductors which are usually used in buck converters are associated with high unit costs since the components themselves are expensive and also give rise to high production costs during mounting."

As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventors' summary information for this patent application: "According to one embodiment, the present invention provides a DC-DC voltage converter having a transformer with a primary winding and a secondary winding with a center tap, an output inductance which is connected to the center tap and to a first output connection, a synchronous rectifier circuit with two synchronous rectifier switches which are each connected to the terminal taps of the secondary winding and are designed to produce a rectified output voltage at a second output connection, and a snubber circuit which is connected via the synchronous rectifier circuit. In this case, the snubber circuit has two diodes which are each coupled to the terminal taps of the secondary winding, a capacitor which is coupled to the two diodes and is designed to store resonant oscillation energy in the synchronous rectifier circuit, and a discharge circuit consisting of a series circuit comprising a discharge switch and a resistor, the discharge circuit being coupled between the first output connection and the capacitor and being designed to selectively feed stored charge in the capacitor back into the first output connection.

"One concept of the present invention is to provide a snubber circuit for a DC-DC voltage converter which can be produced in a simpler and more cost-effective manner in the case of applications in which power losses are negligible on account of the low energy during secondary ringing and reverse recovery. For this purpose, inductive components such as a snubber inductor of an active snubber circuit are replaced with a current-limiting resistor. The power losses in this resistor are negligible with respect to the efficiency.

"Another concept of the present invention is to dispense with a freewheeling diode in the feedback path of the capacitor since no inductive components are used.


"Further features and advantages of embodiments of the invention emerge from the following description with reference to the accompanying drawings.

"In the drawings:

"FIG. 1 shows a schematic illustration of a DC-DC voltage converter according to one embodiment of the invention, and

"FIG. 2 shows a schematic illustration of a DC-DC voltage converter according to another embodiment of the invention."

For additional information on this patent application, see: Koch, Stefan; Tian, Jian. Snubber Circuit for Dc-Dc Voltage Converter. Filed April 3, 2012 and posted May 15, 2014. Patent URL:

Keywords for this news article include: Electronics, Semiconductor, Robert Bosch Gmbh.

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Source: Electronics Newsweekly

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