WO2008155600A1

WO2008155600A1 - Improved switched-mode power converter and method

Info

Publication number: WO2008155600A1
Application number: PCT/IB2007/001669
Authority: WO
Inventors: Timo Tapani Lindqvist
Original assignee: Nokia Corporation
Priority date: 2007-06-20
Filing date: 2007-06-20
Publication date: 2008-12-24

Abstract

It is presented a switched-mode power converter comprising: a first switch configured to be used for effecting a desired output voltage or a desired output current on an output of the switched-mode power converter; and an over-voltage controller configured to detect an input voltage and to control the first switch. The over-voltage controller is configured to, as a result of detecting an over-voltage of the input voltage, decrease a resistance of the first switch such that any over-voltage on the output is attenuated. A corresponding method is also presented, as well as the switched mode power converter comprised in a mobile communication terminal and a charger for electronic apparatuses.

Description

IMPROVED SWITCHED-MODE POWER CONVERTER AND METHOD

Field of the Invention

The present invention generally relates to power converters in general and more particularly to switched-mode power converters.

Background of the Invention

In electronic apparatuses, there are usually external electrical interfaces. For example in mobile communication terminals, there can be interfaces to a power supply and/or a charger as well as USB (Universal Serial Bus). Whenever external power is connected, there is a need for protection against over-voltages and voltage spikes, or transients. Such phenomena can cause damage to components within the electronic apparatus.

In the prior art, this problem has been addressed using several types of voltage suppressors and current limiters. e.g. transient voltage suppressors, or voltage dependent resistors. However, the inclusion of such components add to the complexity of the electronic apparatus. Moreover, it requires more space in the apparatus and generates more cost.

Consequently, there is a need to provide an improved way to attenuate over-voltage.

Summary

In view of the above, an objective of the invention is to solve or at least reduce the problems discussed above. Generally, the above objectives are achieved by the attached independent patent claims.

According to a first aspect of the present invention there has been provided a switched-mode power converter comprising: a first switch configured to be used for effecting a desired output voltage or a desired output current on an output of the switched-mode power converter; and an over-voltage controller configured to detect an input voltage and to control the first switch; wherein the over-voltage controller is configured to, as a result of detecting an over-voltage of the input voltage, decrease a resistance of the first switch such that any over-voltage on the output is attenuated. In other words, components already present for a switched-mode power converter can be used to attenuate an over-voltage. This allows for cost and space efficiency compared to the solutions in the prior art.

The switched-mode power converter may further comprise a second switch, wherein the over-voltage controller is configured to, as a result of detecting an over-power, decrease a resistance of the second switch. A switched mode power converter often has at least two switches. By controlling two switches, the over-voltage controller gains more control of the output voltage, offering better protection. The switched-mode power converter may further comprise a fuse, wherein the fuse is connected such that it blows when the resistance of the second switch is decreased, and an input power of the switched-mode power converter is sufficiently high, such that power conversion in the switched- mode power converter is disabled. When the amount of power absorbed in the converter risks damaging components, the over-voltage controller can thus make a fuse blow to effectively disconnect the over-voltage from the converter.

The switched-mode power converter may further comprise a power conversion controller, the power conversion controller being configured to control an output voltage or output current of the switched-mode power converter by controlling the first switch.

A first switch control signal combiner may be connected to the first switch and to both the over-voltage controller and the power conversion controller. The switch control signal combiner can thus appropriately combine the signals from the two controller according to pre-set rules.

A second switch control signal combiner may be connected to the second switch and to both the over-voltage controller and the power conversion controller.

The switched mode power converter may be configured to convert an input direct current to an output direct current.

The switched mode power converter may be a converter selected from the group consisting of a buck converter, a boost converter, a SEPIC converter, and a Cuk converter.

The over-voltage controller and the power conversion controller may be two separate controllers.

The over-voltage controller and the power conversion controller may be housed within one controller. A second aspect of the invention is a mobile communication terminal comprising a switched mode power converter according to the first aspect.

A third aspect of the invention is a charger for an electronic apparatus comprising a switched mode power converter according to the first aspect. A fourth aspect of the invention is a method comprising: detecting an over-voltage of an input voltage of a switched mode power converter; decreasing a resistance of a first switch also configured to be used for effecting a desired output voltage or a desired output current of the switched- mode power converter such that any over-voltage on the output is attenuated. Optionally, the decreasing a resistance the resistance only occurs when the first switch is not shorted due to control of a power conversion controller.

Other objectives, features and advantages of the present invention will appear from the following detailed disclosure, from the attached dependent claims as well as from the drawings.

Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an/the [element, device, component, means, step, etc]" are to be interpreted openly as referring to at least one instance of the element, device, component, means, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated.

Brief Description of the Drawings Embodiments of the present invention will now be described in more detail, reference being made to the enclosed drawings, in which:

Fig 1 is a schematic illustration of terminals of an electronic apparatus, as an example of an environment in which the present invention may be applied. Fig 2 is a circuit diagram illustrating an embodiment of the present invention applied to a buck converter.

Fig 3 is a circuit diagram illustrating an embodiment of the present invention applied to a boost converter.

Fig 4 is a flow chart illustrating a method which can be processed in the buck converter of Fig 2. Detailed Description of Embodiments Fig 1 is a schematic illustration of a terminals of an electronic apparatus, as an example of an environment in which the present invention may be applied. A mobile communication terminal 102 comprises a switched mode power converter 100 with input terminals 104 and 105 for direct current (DC) input and output terminals 106 and 107 for DC output. The input terminals 104 and 105 can be any DC connection to the mobile terminal, e.g. charger input, USB input, etc. Terminals 105 and 107 are ground terminals. It is to be noted that switched mode power converter 100 according to the invention can be embodied in any apparatus with power connectors, such as, 12V DC to mobile phone chargers, to attenuate over-voltage.

Fig 2 is a circuit diagram illustrating an embodiment of the present invention applied to a buck converter, also known as a step-down converter. The buck converter converts an input DC voltage to a lower output DC voltage. The general operation of a buck converter is described in the web page referenced by the URL http://en.wikipedia.org/wiki/Buck_converter at the time of filing this patent application. A control amplifier, or power conversion controller 119 receives two inputs, the output voltage at terminal 106 and a reference voltage 121. The power conversion controller is connected to a pulse width modulator 118 which generates pulses to control output voltage. The signal from the pulse width modulator 118 is passed through switch control signal combiners 112 and 114 to control switches 110a and 116a, respectively. The switch control signal combiners combine signals from several sources to control a switch connected to the switch control signal combiner. The switch control signal combiner can for example be implemented using a buffer. Inductance 111 is used as to store energy between the phases of switches being open and shorted. Capacitance 115 evens out the load over time as seen from input terminal 104 and 105 and capacitance 117 evens out the output voltage as seen between output points 106 and 107.

An over-voltage controller 113a measures input voltage at point 104. When an over-voltage is detected, e.g. by the input voltage being higher than a threshold voltage, in a first stage, the over-voltage controller 113a sends a signal to the parallel switch control signal combiner 114 to decrease the resistance of the parallel switch 116a. More current will then flow through the parallel switch 116a and, attenuating the power applied to the output. The power dissipation of the parallel switch 116a will be fed back to the over- voltage controller 113a, e.g. by measuring the temperature of or current through the parallel switch 116a, by measuring the time of over-voltage or integrating the over-voltage over time. If the over-voltage is a short transient, the actions of this first stage may be enough to shield the output. However, if the power dissipation of the parallel switch 116a is too high, the over-voltage controller, in a second stage, sends a signal to the serial switch control signal combiner 112 to decrease the resistance of or even short the serial switch 110a, whereby a fuse 120 is blown.

Another case is if reverse polarities are connected to the inputs 104,105. In this situation switches 110a and 116a can be shorted by the over- voltage controller. The fuse 120 can then blow, protecting components from the reverse polarity.

Fig 3 is a circuit diagram illustrating an embodiment of the present invention applied to a boost converter, also known as a step-up converter. The general operation of a boost converter is described in the web page referenced by the URL http://en.wikipedia.org/wiki/Boost_converter at the time of filing this patent application. The boost converter converts an input DC voltage to a higher output DC voltage. The power conversion controller 119, the pulse width modulator 118, the capacitors 115, 117, input and output terminals 104-107 and the switch control signal combiners 112 and 114 all have similar functions as described above and will not be described here again.

A over-voltage controller 113b measures the input voltage at point 104. When an over-voltage is detected, e.g. by the input voltage being higher than a threshold voltage, in a first stage, the over-voltage controller 113b sends a signal to the parallel switch control signal combiner 114 to decrease the resistance of the parallel switch 116b. More current will then flow through the parallel switch 116b and, attenuating the power applied to the output. If the power in the input 104 is excessive, the fuse 120 blows. Optionally, in a second stage, the over-voltage controller 113b also sends a signal to the serial switch control signal combiner 112 to open the serial switch 110b. This prevents any over-voltage from reaching the output 106.

It is to be noted that the over-voltage controllers 113a/b can take into account the current state of the switches, since the switches are also controlled by the power conversion controller 119. For example, for the buck converter of Fig 2, if the power conversion controller 119 controls the serial switch 110a to be shorted and the parallel switch 116a to be open, upon detection of an over-voltage, the over-voltage controller 113a reduces the resistance of the parallel switch 116a as described above. However, if the power conversion controller 119 controls the serial switch 110a to be open and the parallel switch 116a to be shorted, and an over-voltage is detected, this voltage is separated from the output 106 by the switch 110a.

Consequently, it is primarily when the serial switch 110a is shorted by the power conversion controller 119 that the over-voltage controller 113a needs to control the parallel switch 116a. The power conversion controller 113a would then need to have an input indicating the state of the parallel switch 116a. Optionally, the parallel switch control signal combiner 114 is responsible for combining the signals from the two controllers 113a and 118 in accordance with the reasoning above.

Regarding the over-voltage controller 113b in the boost converter of Fig 3, it is primarily when the serial switch 110b is shorted by the power conversion controller 119 that the over-voltage controller 113b needs to control the parallel switch 116b, using the same mechanisms as described above.

Fig 4 is a flow chart illustrating a method which can be processed in the buck converter of Fig 2. In a first detect over-voltage step 130, an over- voltage is detected of the input terminals of the buck converter, the process then continues to a decrease resistance of first switch step 132, whereby the over-voltage of the output terminals is reduced.

In a conditional over-power step 134, it is determined whether the first switch is risking to absorb too much power. If this is not the case, the process ends.

On the other hand, if over-power is determined, the process continues to a decrease resistance of second switch step 136. In this second stage, the second switch resistance is decreased, or even shorted, whereby a fuse can blow. Components within the switched mode power converter and connected to the output are thereby protected from the over-voltage and over-power applied on the input of the buck converter. Although this may require that the fuse of the switched mode power converter needs to be replaced, this is a better scenario than components getting damaged which would require more time and effort to repair. While the process of fig 4 is described as processed in the buck converter of Fig 2, it can equally well be processed in the boost converter of Fig 3. It is to be noted that while the present invention has been described as embodied in a boost converter and a buck converter, the invention is applicable to any switched mode power converter including also, but not limited to, a SEPIC converter and a Cuk converter. It is to be noted that the present invention can be embodied in any switched mode power converter, with internal and/or external interfaces. Over-voltage protection can be applicable in many different situations.

Whilst endeavoring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon. Moreover, it should be appreciated that those skilled in the art, upon consideration of the present disclosure, may make modifications and/or improvements on the apparatus hereof and yet remain within the scope and spirit hereof as set forth in the following claims.

Claims

1. A switched-mode power converter comprising: a first switch configured to be used for effecting a desired output voltage or a desired output current on an output of said switched-mode power converter; and an over-voltage controller configured to detect an input voltage and to control said first switch; wherein said over-voltage controller is configured to, as a result of detecting an over-voltage of said input voltage, decrease a resistance of said first switch such that any over-voltage on said output is attenuated.

2. The switched-mode power converter according to any one of the preceding claims, further comprising a second switch, wherein said over- voltage controller is configured to, as a result of detecting an over-power, decrease a resistance of said second switch.

3. The switched-mode power converter according to claim 2, further comprising a fuse, wherein said fuse is connected such that it blows when the resistance of said second switch is decreased, and an input power of said switched-mode power converter is sufficiently high, such that power conversion in said switched-mode power converter is disabled.

4. The switched-mode power converter according to any one of the preceding claims, further comprising a power conversion controller, said power conversion controller being configured to control an output voltage or output current of said switched-mode power converter by controlling said first switch.

5. The switched-mode power converter according to claim 4, wherein a first switch control signal combiner is connected to said first switch and to both said over-voltage controller and said power conversion controller.

6. The switched-mode power converter according to claim 4 when dependant on claim 2, wherein a second switch control signal combiner is connected to said second switch and to both said over-voltage controller and said power conversion controller.

7. The switched-mode power converter according to claim 6, wherein said switched mode power converter is configured to convert an input direct current to an output direct current.

8. The switched-mode power converter according to claim 7, wherein said switched mode power converter is a converter selected from the group consisting of a buck converter, a boost converter, a SEPIC converter, and a Cuk converter.

9. The switched-mode power converter according to any one of claims 4 to 8, wherein said over-voltage controller and said power conversion controller are two separate controllers.

10. The switched-mode power converter according to any one of claims 4 to 8, wherein said over-voltage controller and said power conversion controller are housed within one controller.

11. A mobile communication terminal comprising a switched mode power converter according to any one of claims 1 to 10.

12. A charger for an electronic apparatus comprising a switched mode power converter according to any one of claims 1 to 10.

13. A method comprising: detecting an over-voltage of an input voltage of a switched mode power converter; decreasing a resistance of a first switch also configured to be used for effecting a desired output voltage or a desired output current of said switched- mode power converter such that any over-voltage on said output is attenuated.

14. The method according to claim 13, wherein said decreasing a resistance said resistance only occurs when said first switch is not shorted due to control of a power conversion controller.