Electric power conversion systems – Current conversion – Using semiconductor-type converter
Reexamination Certificate
2000-02-28
2001-02-13
Berhane, Adolf Deneke (Department: 2838)
Electric power conversion systems
Current conversion
Using semiconductor-type converter
Reexamination Certificate
active
06188593
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a voltage converter with a variable input and output and including transformer means from the secondary winding of which a dc voltage is derived.
A converter of that type is already known in the art. Therein, the secondary winding of the transformer means is generally coupled to the output via a diode, whilst a capacitor is connected across this output. In this known converter, the voltage drop across the diode leads to significant reduction of the converter efficiency. This is particularly true for low output voltage application and is not acceptable for applications where the efficiency is a critical parameter as for instance a Solid State Power Amplifier (SSPA) which is an essential element of any telecommunication satellite payload that amplifies the RF signal and sends it to the antenna.
To overcome the poor efficiency of the known diode-rectifying converter, synchronous rectifying converters are used.
Therefore, the present invention more particularly relates to a synchronous rectifying converter with a variable input and output, said converter including transformer means having a main secondary winding and a control secondary winding, said main secondary winding having a first main terminal coupled to a first output terminal of said converter, and a second main terminal coupled via a controlled electronic switch to a second output terminal of said converter, and said control secondary winding having a first control terminal coupled to said main secondary winding, and a second control terminal coupled to a control input terminal of said switch, a capacitor being coupled between the first and the second output terminal of said converter.
Such a synchronous rectifying converter using a controlled electronic switch instead of a diode is also already known in the art. The advantage with respect to the diode-rectifying converter is that it presents a smaller voltage drop at the cost of an additional control secondary winding used to control the electronic switch. However, the field of applications of the synchronous rectifying converter is more restricted than that of the diode-rectifying converter. Indeed, the output voltage range of the synchronous rectifying converter is linked to the maximum acceptable ‘on’ and ‘off’ voltages provided by the secondary control winding. The ‘on’ control voltage provided to the switch is proportional to the output voltage of the converter, i.e. to the voltage provided at the main secondary winding, whilst on the other hand, the ‘off’ control voltage provided to the switch is negative and proportional to the input voltage of the converter, i.e. to the voltage at the primary winding of the transformer. Hence, the input and output voltages of the converter have direct impacts on the control voltage range provided by the control secondary winding which becomes generally incompatible for operating the electronic switch.
SUMMARY OF THE INVENTION
An object of the present invention is to improve, preferably at low cost, the synchronous rectifying converter of the above known type by increasing its input and output voltage operating ranges.
According to the invention, this object is achieved due to the fact that said converter further includes, between said first main terminal and said second main terminal of said main secondary winding, the series connection of a diode and a second capacitor, and that said first control terminal of said control secondary winding is connected to the junction point of said diode with said second capacitor.
In this way, a reference voltage is generated across the second capacitor, and the control secondary winding is referred on this reference voltage, at the junction point between the diode and the second capacitor. In function of the ratio of the number of turns between the main and the control secondary windings, the ‘off’ control voltage may be adjusted to a predetermined value, e.g. zero, and be independent from the input voltage and the output voltage of the converter. The ‘on’ control voltage is given by the summation of the reference voltage and the voltage across the control secondary winding. The influence of the output voltage of the converter on the control voltage of the switch is thereby limited. This is particularly advantageous for low voltages. As a result, the variations of the control voltage with respect to the input and output voltages of the converter are relatively much lower than the one obtained with the known standard synchronous rectifying converter. The present converter is thus able to work at relatively larger input/output voltage ranges.
Since only a diode and a second capacitor have been added to the known standard synchronous rectifying converter, the complexity and the number of components of the converter of the invention have not dramatically increased and remain acceptable for almost all the possible applications.
Additionally, it is to be noted that the performances of the present synchronous rectifying converter may be optimized by a suitable adjustment of the number of turns of the control winding.
In more detail, the present invention is characterized in that said diode is forward biased between said first main terminal of said main secondary winding and said first control terminal of said control secondary winding.
In this way, the voltage across the control secondary winding is referred on a reference voltage that is generated by a forward auxiliary rectifying on the main secondary winding.
The present invention is further also characterized in that said first main terminal of said main secondary winding and said first control terminal of said control secondary winding have the same bias polarity.
The signals then have simultaneously a same polarity at these two terminals.
In a preferred embodiment, said main secondary winding and said control secondary winding have a same number of turns.
It can be proved that generally the best performances are so obtained.
Further characteristic features of the present synchronous rectifying converter are mentioned in the appended claims.
REFERENCES:
patent: 3735235 (1973-05-01), Hamilton et al.
patent: 4399499 (1983-08-01), Butcher et al.
patent: 5870299 (1999-02-01), Rozman
patent: 6069799 (2000-05-01), Bowman et al.
patent: 6072701 (2000-06-01), Sato et al.
patent: 37 27 170 A1 (1989-02-01), None
patent: WO 95/02917 (1995-01-01), None
Alcatel
Berhane Adolf Deneke
Sughrue Mion Zinn Macpeak & Seas, PLLC
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