Electric power conversion systems – Current conversion – Using semiconductor-type converter
Patent
1991-11-01
1992-12-22
Beha, Jr., William H.
Electric power conversion systems
Current conversion
Using semiconductor-type converter
328 26, 342 51, 363147, H02M 7217
Patent
active
051738490
DESCRIPTION:
BRIEF SUMMARY
FIELD OF INVENTION
The present invention relates to power rectifying apparatus. Specifically, the present invention relates to an integratable rectifier structure utilising various MOS, including NMOS or CMOS implemented transistors. The invention may be of particular value where apparatus is to receive power via electromagnetic or capacitive coupling. Exemplary applications include remote identification devices and "smart" credit cards.
PRIOR ART
A simple rectifier circuit is shown in FIG. 1. It will be noticed that the circuit has been changed from the conventional representation (which would see the rectifying diode placed in the upper branch of the circuit). FIG. 1 is in accordance with a copending Australian Patent Application No. PI 5479 (inventor G. Murdoch), which describes this particular arrangement for certain applications.
The operation of the circuit is generally known, and is illustrated diagrammatically in FIG. 2. If the upper circuit branch is regarded as GROUND, FIG. 2 shows how the applied AC power causes the voltage at Point X to oscillate sinusoidally about Ground. Whenever Point X is more negative than Point Y, the diode conducts (shown by the shaded bands in the lower part of FIG. 2), and the capacitor C receives charge. At other times, the diode does not conduct, and the DC load (not shown) is supplied from the charge remaining on C, causing the voltage at Point Y to rise towards zero volts. At the next AC cycle, C is recharged as described above, and Point Y resumes its more negative voltage.
Because only one half (here, the negative half) of the AC wave is actually utilised, this circuit is termed a "half-wave" rectifier.
Prior art rectifying diodes are commonly fabricated as P-N semiconductor junctions, and as such, have been included in bipolar integrated circuit products, permitting such chips to operate directly from an AC power source, rather than requiring conversion to DC power. Examples of such bipolar products include light dimmers and Residual Current Circuit Breakers (RCCB's).
However, such rectifying devices are inherently difficult to fabricate on Very Large-Scale Integration (VLSI) production lines (which are optimised to produce Field-Effect, rather than Bipolar, devices). If the MOS (field-effect) transistors produced by such lines, are connected as diodes (by connecting the Gate and Drain terminals together), the resulting device is very inefficient, and exhibits a large forward voltage-drop, which limits the circuit efficiency. Likewise, the inherent rectification property existing between the "channel" and "substrate" (for explanation of these terms, see any standard text on VLSI design, such as Mead & Conway, "Introduction to VLSI Systems", Addison-Wesley, 1980) of a MOS transistor has been previously exploited as a power rectifier. This suffers from the twin drawbacks of frequently exhibiting poor forward conductivity, and being poorly controlled on a typical MOS fabrication line (it being not a usual mode of operating a MOS transistor). Such techniques have been used in prior art inventions, such as by "Ellsworth & Moll" in WO 88/01448.
Certain prior art inventions also disclose "full-wave" rectifying devices (e.g. "Ellsworth & Moll"). For many low-power applications, this is considered a needless complexity; a half-wave rectifier is usually adequate.
Furthermore, if the diode D were replaced by a switch, and that switch is caused to open and close at the same time as the Diode, the circuit would operate in a similar manner to that aforesaid. This arrangement is known as a "Synchronous Rectifier", since its operation depends on synchronising the operation of such a Switch with the incoming AC wave.
The inherently lower cost and lower power requirements of circuit functions (especially digital logic functions) when implemented in MOS, rather than bipolar, technology provides definite commercial advantages.
OBJECTS OF THE INVENTION
An object of the present invention is to provide a rectifier capable of being totally integrated using VLSI techniques.
A fur
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Beha Jr. William H.
Magellan Corporation (Australia) Pty. Ltd.
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