Electricity: power supply or regulation systems – In shunt with source or load – Using choke and switch across source
Patent
1997-09-29
1999-03-16
Berhane, Adolf Deneke
Electricity: power supply or regulation systems
In shunt with source or load
Using choke and switch across source
363126, G05F 1613, H02M 706
Patent
active
058835024
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a mains rectifier circuit for power supply units, in particular for switched-mode power supplies.
BACKGROUND INFORMATION
Power supply units, in particular switched-mode power supplies for connection to an AC mains, in the simplest case have a rectifier downstream of which an electrolytic capacitor is connected. The charging current profile of the capacitor leads to severe harmonics on the mains and loads said mains with a high apparent power. The mass use of power supply units within the last twenty years has for these reasons already led to serious problems in the power supply grids.
A brief presentation of these problems and various solution proposals, which are intended to lead to a balanced mains load, can be found in the article "Comparison of Standards and Power Supply Design Options for Limiting Harmonic Distortion in Power Systems", by Key and Lai, in "IEEE Transactions on Industry Applications" Vol. 20, No. 4, July/August 1993, pages 688 to 695. One of the circuits which are illustrated there and are also used in practice has a so-called "boost converter". A virtually sinusoidal input current profile can even be achieved using said boost converter, by means of a complex controller. As is noted in the article, however, the relatively high costs and relatively poor reliability, which is governed by additional components, preclude widespread introduction to the market.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a simple and cost-effective solution which leads to a marked reduction in the harmonic content and to an improvement in the power factor.
This object is achieved by a circuit of the type having a full-wave rectifier which is connected to the mains voltage and having a smoothing capacitor which is connected downstream of said full-wave rectifier, the smoothing capacitor being charged at a clock frequency which is considerably higher than the mains frequency, via a series circuit formed by a boost inductance and a diode. The junction point between the boost inductance and the diode is connected to earth via a controlled switch in which, according to the invention, the smoothing capacitor and the load are connected to the full-wave rectifier, an auxiliary rectifier is provided, from which the series circuit formed by the boost inductance and the diode leads to the smoothing capacitor, and the switch is controlled via a drive circuit such that additional charging current is supplied to the smoothing capacitor, via the boost inductance, in time periods around the zero crossings of the rectified half-cycles.
While current peaks occur only in the region of the peak values of the rectified half-cycles in the case of a pure rectifier circuit with a smoothing capacitor--in the normal load case--part of the charging current is shifted, as a result of the invention, using simple means, specifically into those regions around the zero crossings in which no current otherwise flows. In this case, the cost for additional components is absolutely kept within limits. A reduction in the harmonic content of the input current is achieved, as well as an improvement in the efficiency and the power factor.
It is advantageous if an auxiliary capacitor is connected directly downstream of the auxiliary rectifier. The clock frequency of the controlled switch is expediently in the kHz range.
The auxiliary rectifier is advantageously formed by two diodes which are connected as a half-bridge with respect to the full-wave rectifier.
The object is also achieved by a mains rectifier circuit for power supply units, in particular for switched-mode power supplies, having a full-wave rectifier which is connected to the mains voltage and having a smoothing capacitor, the smoothing capacitor being charged at a clock frequency, which is considerably higher than the mains frequency, via the series circuit formed by a boost inductance and a diode, in the case of which series circuit the junction point between the boost inductance and the diode
REFERENCES:
patent: 4215392 (1980-07-01), Rhoads
patent: 4437146 (1984-03-01), Carpenter
patent: 4533986 (1985-08-01), Jones
patent: 5619404 (1997-04-01), Zak
patent: 5734562 (1998-03-01), Redl
Berhane Adolf Deneke
Siemens Aktiengesellschaft
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