Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2002-02-21
2003-06-10
Berhane, Adolf Denske (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C363S097000, C363S012000
Reexamination Certificate
active
06577509
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a semiconductor circuit having a drive circuit, having a load that is disposed between a supply voltage, and having a controllable semiconductor switching element for switching the load. The invention furthermore relates to a switch-mode power supply having such a semiconductor circuit.
The expression controllable semiconductor switching element should be regarded as meaning a controllable (load-break) switch that, in addition to its actual functionality—namely the switching of currents and voltages, has additional functionalities, such as temperature protection and freewheeling protection. A controllable semiconductor switching element may contain, for example, a power transistor—for example a MOSFET—or an IGBT.
Controllable semiconductor switching elements have a load circuit and a control connection for driving the semiconductor switching element. To control these semiconductor switching elements, an additional supply voltage is generally required in addition to a supply voltage for the load circuit, with the control signal being derived from the additional supply voltage. Such a requirement applies, in particular, to those circuit applications in which a load voltage that is very much higher than the control voltage used. Circuit applications such as these, for example, switch-mode power supplies, power supplies, switch-mode regulators, and the like, are frequently operated directly from the mains voltage.
A switch-mode power supply is a regulated power supply unit that does not require any mains transformer at all. In a switch-mode power supply, the mains voltage is rectified directly, and is smoothed in an energy storage capacitor, so that a high DC voltage is available. A controllable switch “chops” the DC voltage so that a periodic square-wave pulse sequence is produced, which is transformed in a transformer in accordance with the desired transformation ratio of the transformer windings, and is then rectified and filtered once again. The configuration and method of operation of such a switch-mode power supply are described, for example, in CoolSET, TDA 16822, “Off-Line current mode controller with CoolMOS on board”, Datasheet, Version 1.0, April 2000, from Infineon Technologies AG, in particular, on page 4 of that document.
In switch-mode power supplies, the supply voltage for the drive circuit that drives the load-break switch can be produced, for example, by an additional primary transformer winding. The supply potential that is obtained from the additional primary transformer winding is then fed directly to the drive circuit. However, when not switched on, no supply potential can be tapped off on the additional primary transformer winding. Thus, when switching on a switch-mode power supply, it is necessary to ensure that the drive circuit is supplied with power immediately, in order to make it possible to drive the load-break switch appropriately. A starting circuit is used for such a purpose, which produces a starting charging current that is derived from the load voltage and initially builds up the supply voltage on a buffer capacitor. The energy for the first switching processes of the load-break switch is then drawn from the buffer capacitor until the supply voltage for the drive circuit of the switching-mode power supply is produced across the additional primary transformer winding.
Either a so-called start-up resistor or a current source in the form of a depletion MOSFET is typically used for the starting circuit. However, such a discrete configuration of a starting circuit is not a particularly cost-effective solution, particularly due to the additional space required for the starting circuit and the additional components.
Furthermore, the starting circuit produces undesirable power losses during operation of the switch-mode power supply in the situation where the starting current cannot be switched off after starting.
In addition to the discrete version of a starting circuit just described, an integrated solution also exists, using comparatively complex high-voltage technologies. In such an integrated version, the starting circuit, the drive circuit, and the load-break switch are formed monolithically on a single chip. One such circuit configuration is described, for example, in European Patent Application 0 585 788 B1, corresponding to U.S. Pat. No. 5,285,369 to Balakrishnan. The company Power Integrations markets the corresponding semiconductor circuits under the designations TOPSwitch and TinySwitch. However, because the drive circuit and the load-break switch are integrated monolithically, they cannot be optimized independently of one another, and such inability to optimize frequently leads to overdesign of the individual circuit elements and, hence, typically, to the load-break switch requiring a large area related to its switched-on resistance.
Furthermore, in many switch-mode power supplies and clocked power supplies, it is necessary to know the load current flowing through the load-break switch and its waveform precisely. For example, in quasi-resonant switch-mode power supplies, which are in the form of flyback converters, the time at which the load current is switched on, and, hence, the time at which the current through the primary winding of the transformer is switched on, is derived from the zero crossing of the load current in the secondary winding of the transformer. The derivation is done in a conventional manner by detecting the zero crossing of the drain-source voltage, from which the supply voltage for the drive circuit is obtained. In addition to the complexity for the additional transformer winding required for such a purpose, the drive circuit requires a corresponding additional detector input for an external additional circuit, which carries out the evaluation of the zero crossing. A quasi-resonant switch-mode power supply according to the prior art is marketed, for example, with the product designation TDA 4605 by the company Infineon Technologies AG, located in Munich, Germany.
A further requirement occurs, in particular, in safety-relevant applications of such semiconductor switching elements. In applications such as these, the voltage applied across the load-break switch must be evaluated. When the load-break switch is switched off, the load circuit voltage and any overvoltage across the load-break switch, or else any discrepancy in the load circuit voltage that is caused, for example, by oscillation or load chopping, can be derived therefrom. When the load-break switch is switched on, it can be checked for correct operation by evaluation of the voltage that is present across the load-break switch. Until now, an external or else integrated circuit that was produced specifically for such a check and that supplies the corresponding status information relating to the load circuit voltage, has been provided to determine the voltage that is present across the load-break switch. Until now, the load-break switch has not itself been configured to supply status information relating to the load current or to the voltage that is dropped across the load path of such a switch.
The provision of a starting circuit, which is intended specifically for starting a generic type of such a semiconductor circuit, of an additional circuit that is intended specifically for detecting the zero crossing of the load current, and of an evaluation circuit that is intended specifically for evaluating the load circuit voltage that is dropped across the load-break switch, is, furthermore complex and, hence, makes the overall circuit configuration very expensive.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a semiconductor circuit and a switch-mode power supply having such a semiconductor circuit that overcomes the hereinafore mentioned disadvantages of the heretofore-known devices of this general type and that at least partially satisfies the above requirements and that furthermore can be produced very much more easily in terms of its circuitry.
With the
Deboy Gerald
Mündel Gerald
Zöllinger Harald
Berhane Adolf Denske
Greenberg Laurence A.
Infineon - Technologies AG
Locher Ralph E.
Stemer Werner H.
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