Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2002-07-15
2003-11-04
Han, Jessica (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C363S019000, C363S131000, C323S225000
Reexamination Certificate
active
06643144
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a circuit configuration for applying a clocked application of a supply voltage to a load.
Such circuit configurations are used, by way of example, in switched-mode power supplies or power factor controllers, in which an inductor is respectively connected to a supply voltage in clocked fashion based upon actuation signals. In such a case, the actuation signals for the first switch, which is connected in series with the load, are produced by the control circuit, whose correct operation requires a supply voltage applied to its voltage supply terminals.
A prior art circuit configuration of such a type is disclosed in European Patent Application 0 585 788 A1, corresponding to U.S. Pat. No. 5,285,369 to Balakrishnan, particularly, in
FIG. 3
thereof. In such a case, the circuit configuration is part of a switched-mode power supply, where a series circuit including the primary coil of a transformer and a first switch, in the form of a MOSFET, is connected between output terminals of a bridge rectifier. To actuate the MOSFET, a control circuit is provided. To supply the control circuit with voltage, a depletion-mode MOSFET or a JFET (Junction FET) is connected between the primary coil and the MOSFET, with one supply terminal of the control circuit being connected to a node that is common to the JFET and to the MOSFET in order to output a supply voltage for the control circuit when the MOSFET is off. Furthermore, in addition to the secondary winding of the transformer, the secondary side is provided with an auxiliary winding having a downstream rectifier, the auxiliary winding likewise being used to supply voltage to the control circuit.
When the MOSFET acting as a switch in this apparatus is on, the JFET connected in series with it is also on. When the MOSFET turns off, the JFET also starts to turn off, which results in approximately all of the supply voltage appearing across the JFET. In a transition phase, a current then still flows through the JFET into the control circuit, but this is associated with a high power loss on the JFET.
A secondary-side auxiliary winding having a rectifier, use of which for supplying voltage to a control circuit even without the JFET from the cited print is already in the prior art, requires the use of discrete components whose cost has an adverse effect on the total price of the power supply unit or power factor controller. This is particularly true for switched-mode power supplies in power classes between 5 W and 20 W, which are used to safeguard the “standby mode” in electronic appliances and that are subject to an especial cost pressure.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a circuit configuration for applying a supply voltage to a load that overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices and methods of this general type and that dispenses with an auxiliary winding and with the use of discrete components for the voltage supply to the control circuit and in which there is no or only very little power loss when providing the supply voltage for the control circuit.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a circuit configuration for clocked application of a supply voltage to a load, the circuit configuration including a first switch having a first control connection, the first switch connected in series with the load, a control circuit connected to the first switch, the control circuit having a first output terminal connected to the first control connection for actuating the first switch and first and second voltage supply terminals, and a second switch having a second control connection to which an actuation signal is supplied, the second switch connected between the load and the first voltage supply terminal.
Accordingly, in addition to the first switch connected in series with the load, the circuit configuration has a second switch that is connected between the load and the first voltage supply terminal of the control circuit. In such a case, when the first switch has turned off, the second switch, which is on and is preferably likewise actuated by the control circuit, takes on the current flowing through the load and supplies it to the control circuit through the first voltage supply terminal thereof. The current flowing through the second switch is preferably buffered in a capacitor connected in parallel with the voltage supply terminals of the control circuit to provide a continuous, only slowly decreasing supply voltage for the control circuit after the second switch has turned off until it next turns on.
In the on state, the voltage drop across the second switch is only small in relation to the total voltage on account of the low conduction resistance, which means that the power loss on the second switch is low. A large part of the voltage drops across the load, with inductive loads involving storage of energy that is subsequently used in a switched-mode power supply or power factor controller.
The second switch can be implemented, almost without additional cost requirement, as an integrated component in the integrated circuit for the control circuit or in the integrated circuit for the first switch—with the control circuit and the first switch also being able to be accommodated in an integrated circuit.
In accordance with another feature of the invention, the control circuit has a second output terminal connected to the second control connection for actuating the second switch.
In accordance with a further feature of the invention, there is provided a capacitor is connected between the first and second voltage supply terminals and in parallel with the control circuit.
In accordance with an added feature of the invention, there is provided a series circuit including the second switch and the control circuit is connected in parallel with the first switch. So long as the first switch in such an embodiment is on, the voltage appearing across the series circuit including the second switch and the control circuit is not sufficient to cause a flow of current, when the second switch is on, into the control circuit and to the capacitor connected in parallel with the control circuit. When the first switch is turned off, the voltage appearing across its load path rises until a voltage has been reached that allows a current to flow to the capacitor through the second switch, which is on. The second switch is preferably likewise actuated using the control circuit, with a second output terminal of the control circuit being connected to a control connection of the second switch.
The second switch can be actuated in various ways. Thus, the second switch can already be on when the first switch is on. Alternatively, the second switch can be turned on only shortly before or at the same time as the first switch turns off in order to supply current to the control circuit for a period of time. The period for which the second switch remains on after the first switch has turned off is dependent, in the control circuit, on the voltage present across the voltage supply terminals or across the capacitor. Preferably, the second switch remains on until the capacitor has been “filled” again with the charge drawn since the last charging operation or until the voltage across the capacitor reaches a prescribable nominal value.
In accordance with an additional feature of the invention, there is provided a diode connected between the first voltage supply terminal and the second switch.
In accordance with yet another feature of the invention, the first switch and the second switch have a common node and a diode is connected between the common node and the first voltage supply terminal of the control circuit.
In accordance with yet a further feature of the invention, there is provided a diode connected between the first voltage supply terminal and the second control connection.
In accordance with yet an added feature of the invention, the second switch is connec
Greenberg Laurence A.
Han Jessica
Infineon - Technologies AG
Locher Ralph E.
Stemer Werner H.
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