WO2007045275A1

WO2007045275A1 - Switched-mode power supply arrangement

Info

Publication number: WO2007045275A1
Application number: PCT/EP2005/055332
Authority: WO
Inventors: Reinhard Kögel; Jean-Paul Louvel; Michael Meitzner
Original assignee: Tte Germany Gmbh
Priority date: 2005-10-18
Filing date: 2005-10-18
Publication date: 2007-04-26

Abstract

A switched-mode power supply arrangement for generating regulated output voltage (U1) comprises a master transformer (TR1) with a switching transistor (Tl) , which is connected in series to a primary winding (W1) of the master transformer (TR1) and at least one slave transformer (TR2, TR3) . The transformers (TR1, TR2, TR3) generate a cascade connection, in a way that a primary winding (W5, W9) of each of the slave transformers (TR2, TR3) is connected in series to a secondary winding (W2, W8) of the corresponding upstream transformer (TRl, TR2) , which is arranged in a forward mode. Additionally, by generating the output voltage Ul, one of the secondary windings (W10) of each of the transformers (TR1, TR2, TR3) , which are arranged in a flyback mode, are connected to a regulatory output level of the output voltage U1 .

Description

SWITCHED-MODE POWER SUPPLY ARRANGEMENT

BACKGROUND OF THE INVENTION

FIELD OF THE INVENTION

The present invention is related to a switched-mode power supply arrangement according to the preamble of claim 1. Power supply arrangements of this kind are used for home electronics, such as television sets, satellite receivers or video-recorders .

DESCRIPTION OF THE PRIOR ART A switched-mode power supply arrangement for generating a regulated output voltage, known by the public at large, comprises a transformer with a primary winding and at least one secondary winding and a switching transistor, which is connected in series to a primary winding of the transformer. The secondary winding is arranged in a flyback mode and delivers the output voltage. By regulating the output voltage, a regulation circuit senses the output voltage and controls the switching transistor. Further secondary windings are provided in order to deliver further output voltages, which depend on the regulated voltage.

The power, which is needed by an user of the output voltages, has to be stored as flyback energy in the transformer. As a result, the needed power determines the physical size of the storage media of the transformer, which typically is a ferrite core. Additionally, the number of the further output voltages is limited by physical construction, such as a maximum number of pins . The regulated voltage determines a fixed voltage per turn of the windings. This limits the design of the possible further output voltages.

A switched-mode power supply arrangement for generating a regulated output voltage is described in the DE 101 19 881 Al . By generating a multitude of output voltages a further transformer is provided. Its primary winding is connected in parallel to a secondary winding of the first transformer, which is arranged in a flyback mode. The whole power, which is needed by the users, must also be stored as magnetic energy in the main transformer and determines the size of main transformer.

SUMMARY OF THE INVENTION

It is therefore desirable to develop a switched-mode power supply arrangement to generate a regulated output voltage according to the preamble of claim 1, which provides an output voltage with high power without the need of a large transformer. The arrangement should also be able to provide a multitude of output voltages .

According to the invention this can be achieved by the features of claim 1. As further transformers one or more slave transformers are provided in a cascade connection with the main transformer, in a way that a primary winding of each of the slave transformers is connected in series to a secondary winding of a corresponding upstream transformer, which is arranged in a forward mode. Additionally, by generating the output voltage, one of the secondary windings of each of the transformers, which is arranged in a flyback mode, is connected to a regulatory output level of the output voltage . As a result, the regulated output voltage is generated by at least two of the flyback secondary windings, one of the master transformer and one of each of the slave transformers. The needed flyback energy is stored in the master transformer and at least in one of the slave transformers. This switched- mode power supply arrangement can deliver a regulated output voltage with a high current, which is suitable for a user which needs a high power. The pins of the slave transformers increase the number of possible output voltages. The voltage per turn of the master transformer and of the slave transformers can be different. This increases the flexibility to optimize the output winding, and by that the flexibility to choose the design of the output voltage. Only one single regulation circuit is needed to control all transformers. A further advantage of the arrangement is that only one galvanic separation is necessary. The slave transformers do not need such galvanic separations . The whole bobbin space of the slave transformer can be used for arranging the windings.

Possible advantageous developments of the invention are specified in the dependent claims.

By further generating the output voltage, at least one of the primary windings of the slave transformers, which is arranged in series to the secondary forward winding of its upstream transformer, is connected to the regulatory output level. By- using this forward energy the necessary flyback energy is reduced. This causes a lower ripple on the output voltage and, more important, on the output current. As a result the capacity of a capacitor, which smoothes the output voltage, can be reduced. The energy-storage elements of the transformers, namely the volume of the ferrite material, can be reduced.

By generating at least one further output voltage, at least one further secondary winding of the transformers, which is arranged in a flyback mode, is provided. The arrangement provides many different output voltages. Neither the number of further output voltages nor the design, e.g. the voltage range, of the output voltages is limited.

The master transformer is suited to operate in a discontinuous mode and the slave transformers are suited to operate in a continuous mode. When the user needs a specific load, the slave transformers begins to operate in a continuous mode, while the master transformer continues to operate in a discontinuous mode. As a result, the switching time or switching frequency ??? of the switching transistor remains almost constant. The inductance of the master transformer can be limited.Applying a regulation circuit with a fixed frequency, the duty time, when the switching transistor is switched on, will not further increase, as soon as the slave transformers begin to operate in a continuous mode. The duty time of the switching transistor keeps about constant in every cycle and is therefore limited. As a result, the maximum energy, which will be stored in the master transformer, can be defined very well with the size of the primary inductance of the master transformer.

A switched-mode power supply arrangement of the invention is able to provide a multitude of output voltages by means of a master transformer and a number of slave transformers without limitation of the number nor of the design of the output voltages and with only one voltage regulation circuit. The arrangement only needs a minimum of physical size; namely an minimum of magnetic storage material. The reduced amount of material causes lower initial and re-cycling costs . The arrangement has a high energy efficiency and is a simple and economical power supply arrangement.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in more detail using two embodiments, which are illustrated in the figures. It shows : figure 1, a simplified circuit diagram of a power switched- mode supply arrangement of a first embodiment and figure 2, a simplified circuit diagram of a power switched- mode supply arrangement of a second embodiment.

DETAILED DESCRIPTION OF A FIRST EMBODIMENT OF THE INVENTION

A switched-mode power supply arrangement for generating at least one output voltage Ul, shown in figure 1, comprises a master transformer TRl with a primary winding Wl and several secondary windings W2, W3, W4. The primary winding Wl is coupled to a mains DC voltage supply at its one end, while an energy-storage capacitor Cl is arranged between the mains DC voltage supply and the primary winding Wl . A switching transistor Tl is connected in series to the primary winding Wl at its other end. The switching transistor Tl causes the energy transfer from the primary winding Wl, to the secondary windings W2, W3, W4.

The transistor Tl is controlled by a two-part regulation circuit for the output voltage Ul . It has a first regulation circuit RCl, which is positioned on the primary side, and a second regulation circuit RC2, which is positioned on the secondary side of the master transformer TRl . The regulation of the output voltage Ul is done in the regulation circuit RCl, where the duty time of the switching transistor Tl is modulated according to the sensed output voltage Ul . The second regulation circuit RC2 provides the sensed output voltage Ul for transferring it to the first regulation circuit RCl. This two-part regulation circuit is called secondary regulation system. The second regulation circuit RC2, which senses the output voltage Ul, is connected to the first regulation circuit RCl via a galvanic separation, shown by a left arrow. A dashed line S shows a galvanic separation line between the primary and the secondary side of the master transformer TRl, as well as of the whole switched-mode power supply arrangement. The galvanic separation between the two parts RCl, RC2 of the regulation circuit can be generated by a galvanic separation element, such as an opto-coupler .

One of the secondary windings of the master transformer TRl, namely the winding W2, and a rectifying element D2, such as a diode, are connected in a way that a current is flowing when the switching transistor Tl is switched on; e.g. the secondary winding W2 is arranged in a forward mode.

The switched-mode power supply arrangement further comprises one slave transformer TR2. The master transformer TRl generates a cascade connection with the slave transformer TR2, in a way that a primary winding W5, of the slave transformer TR2, is connected in series to the secondary winding W2, of the master transformer TRl, which is arranged in a forward mode. In this embodiment with one master transformer TRl and only one slave transformer TR2, the master transformer TRl is an upstream transformer for the slave transformer TR2, and the slave transformer TR2 is the last transformer of the cascade connection.

By generating the output voltage Ul, one of the secondary- windings of this last slave transformer TR2, namely the winding W6, and a rectifying element D3, such as a diode, are connected in a way that they operate in a flyback mode. In short, the secondary winding W6 is arranged in a flyback mode. The rectifying element D3 is connected to a capacitor C3, which delivers the output voltage Ul, shown by an right arrow, at a regulatory output level. By sensing the output voltage Ul, the second regulation circuit RC2 is connected with the output voltage Ul, at this regulatory output level.

The second secondary winding W3 of the master transformer TRl and its corresponding rectifying element Dl, such as a diode, are connected in a way that they operate in a flyback mode. By further generating the output voltage Ul the secondary- winding W3 is connected to the regulatory output level via the rectifying element Dl.

The primary winding W5, of the slave transformer TR2, is arranged between the secondary winding W2 and the rectifying element D2 of the master transformer TRl. Also, by further generating the output voltage Ul, the primary winding W5 is connected to the regulatory output level via the rectifying element D2.

By generating a further output voltage, not shown, the third secondary winding W4 of the master transformer TRl and a rectifying element, not shown, are connected in a way that they operate in a flyback mode.

By generating another further output voltage, not shown, the second secondary winding W7 of the slave transformer TR2 and a rectifying element, not shown, are also connected in a way that they operate in a flyback mode.

The master transformer TRl is suited to operate in a discontinuous mode and the slave transformer TR2 is suited to operate in a continuous mode.

During operation in a flyback phase, in which the switching transistor Tl is off, a current, which is flowing through the rectifying element D3 into the capacitor C3, delivers a flyback energy, which is stored in the secondary winding W6 of the slave transformer TR2. The output voltage Ul is generated and regulated by the two-part regulation circuit RCl, RC2 as a secondary regulation system.

Additionally, in the flyback phase a current, which is flowing through the rectifying element Dl into the capacitor C3, delivers a flyback energy, which is stored in the secondary winding W3 of the master transformer TRl. As a result, the output voltage Ul is further generated.

Additionally, in a forward phase, in which the switching transistor is on, a forward energy is delivered by a current through the secondary winding W2 of the master transformer TRl, the primary winding W5 of the slave transformer TR2 and the rectifying element D2 into the capacitor C3. As a result, the output voltage Ul is further generated. This forward energy is neither stored in the master transformer TRl nor in the slave transformer TR2.

By depending on the regulated output voltage Ul, which is generated by the first secondary windings W3, W6 of the master transformer TRl and the first secondary winding W6 of the slave transformer TR2, all further output voltages, which are generated by further secondary flyback windings of the master transformer TRl and of the slave transformer TR2, such as the windings W4, W7, are regulated by only one regulation circuit . controlled by being coupled to the secondary windings W3, W6. Only one regulation circuit for the output voltage Ul is provided.

Alternatively, the rectifying element D2 can be connected between the secondary winding W2 and the primary winding W5. As an additionalAs a further alternative, the primary- winding W5the rectifying element D2, namely a cathode of the diode, can be connected grounded to GND or connected to another output voltage level .

Alternatively, the master transformer TRl can be provided with further secondary flyback windings, which generate further output voltages . Alternatively and additionally, the slave transformer TR2 can be provided with further secondary flyback windings, which generate further output voltages.

As an alternative, the regulation of the output voltage Ul can be done by a primary regulation system. Such a system can comprise a further primary winding of the master transformer TRl, which is well coupled to the flyback winding W3 and which supplies a regulation circuit on the primary side with the voltage, which should to be regulated.

DETAILED DESCRIPTION OF A SECOND EMBODIMENT OF THE INVENTION

A switched-mode power supply arrangement of a second embodiment, shown in figure 2, corresponds to a switched-mode power supply arrangement of the first embodiment in all ways, except for the following features :

The slave transformer TR2 is provided with a further secondary winding W8. This secondary winding W8 and a rectifying element D4, such as a diode, are connected in a way that they operate in a forward mode.

The switched-mode power supply arrangement further comprises a second slave transformer TR3. The master transformer TRl and the two slave transformers generate the cascade connection in a way, that a primary winding W5, W9 of each of the slave transformers TR2, TR3 is connected in series to the secondary windings W2, W8 of the corresponding upstream transformers TRl, TR2, which is arranged in a forward mode.

In this embodiment with the master transformer TRl and two slave transformers TR2, TR3, the master transformer TRl is the upstream transformer for the slave transformer TR2, while the slave transformer TR2 is the upstream transformer for the slave transformer TR3 and the slave transformer TR3 is the last transformer of the cascade connection.

One of the secondary windings of this last slave transformer TR3, namely the winding WlO, and a rectifying element D5, such as a diode, are connected in a way that they operate in a flyback mode. By further generating the output voltage Ul, the secondary winding WlO is connected to the regulatory- output level., via the rectifying element D5.

The primary winding W9 of the slave transformer TR3 is arranged between the secondary winding W8 and the rectifying element D4 of the slave transformer TR2. By further generating the output voltage Ul, the primary winding W9 is connected to the regulatory output level via the rectifying element D4.

By generating another further output voltage, not shown, the second secondary winding WlI of the slave transformer TR3 and a rectifying element, not shown, are also connected in a way that they operate in a flyback mode.

The second slave transformer TR3 is also suited to operate in a continuous mode.

The second embodiment operates in a similar way to that of the first embodiment, with one additional step due to the second slave transistorformer TR3.

In a forward phase, the master transformer TRl provides a current, which supplies the primary windings W5, W9 of all slave transformers TR2, TR3. As a result, the current is passed through all slave transformers TR2, TR3 and generates the output voltage Ul .

In a flyback phase, the stored energy of the slave transformers TR2, TR3 is transferred via the flyback windings W6, WlO to the output voltage Ul at the regulatory output level. As a result the output voltage Ul, which is further generated by the flyback windings W6, WlO, is regulated. As a further result, the further output voltages, which are generated by the flyback W7, WlI and which depends on the regulated output voltage Ul by being coupled to the windings W6, WlO, are controlled.

Alternatively, one or more further slave transformersistors can be provided.

Claims

1. A switched-mode power supply arrangement for generating a regulated output voltage (Ul) with a master transformer

(TRl) with a switching transistor (Tl) , which is connected in series to a primary winding (Wl) of the master transformer (TRl) , and with at least one further transformer, of which a primary winding (W5) is connected to a secondary winding (W2) of the master transformer (TRl) , characterised in that one or more slave transformers (TR2, TR3) are provided as further transformers in a cascade connection, in a way that a primary winding (W5, W9) of each of the slave transformers (TR2, TR3) is connected in series to a secondary winding (W2, W8) of a corresponding upstream transformer (TRl, TR2), which is arranged in a forward mode, and in that by generating the output voltage Ul, one of the secondary windings (WlO) of each of the transformers (TRl, TR2, TR3) , which are arranged in a flyback mode, are connected to a regulatory output level of the output voltage Ul .

2. The power supply arrangement according to claim 1, characterised in that by further generating the output voltage Ul, at least one of the primary windings (W5, W9) of the slave transformers (TR2, TR3) , which is arranged in series to the secondary forward winding (W2, W8) of the upstream transformers (TRl, TR2), is connected to the regulatory- output level .

3. The power supply arrangement according to claim 1 or 2, characterised in that by generating at least one further output voltage, at least one further secondary winding (W4, W7, WlI) of the transformers (TRl, TR2, TR3) , which is arranged in a flyback mode, is provided.

4. The power supply arrangement according to one of the claims 1 to 3, characterised in that the master transformer (TRl) is suited to operate in a discontinuous mode and the slave transformers (TR2, TR3) are suited to operate in a continuous mode.