Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Distributive type parameters
Reexamination Certificate
2001-10-16
2003-11-11
Patidar, Jay (Department: 2858)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Distributive type parameters
C324S654000, C361S094000, C323S272000
Reexamination Certificate
active
06646450
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention generally relates to electronic circuits, and more particularly to methods and apparatuses for near losslessly measuring inductor current.
In switching regulators and particularly multi-phase and other advanced power converters, current through inductors must be accurately measured in order for the control circuitry to timely provide control signals for controlling the operation of the devices. A typical conventional way to measure inductor current is illustrated in FIG.
1
.
As shown in
FIG. 1
, a sampling resistor
10
is connected in series with an inductor
12
and its internal resistance
14
. The voltage Vo across sampling resistor
10
is measured by an op-amp
16
. From this voltage Vo and the resistance value Rs of sampling resistor
10
, the inductor current i
L
can be derived to be Vo/Rs. This method, however, suffers from significant losses due to the additional power consumed by sampling resistor
10
, which in turn causes inefficiency in the circuit performance.
Another conventional way to measure inductor current is illustrated in FIG.
2
. As shown in
FIG. 2
, a RC network
20
composed of a resistor
22
and a capacitor
24
is used to measure the inductor current i
L
. In this method, the voltage across capacitor
24
, Vc, is measured. This voltage Vc is taken as the voltage across the inductor
12
, from which the inductor current i
L
is derived from the expression Vc/Rs. This approach, however, generates significant errors because the load resistance is not taken into account. Practically, this is never the case.
Therefore, there is a need for an improved way of measuring inductor current with minimum losses and errors.
SUMMARY OF THE INVENTION
The present invention provides an improved measuring circuit for measuring a current of an inductor with minimum losses and errors. According to one embodiment of the invention, the measuring circuit comprises an op-amp having first and second input terminals and an output terminal, with the second terminal for connecting a first end of the inductor; a RC network connected between the first input terminal and the output terminal of the op-amp; and a scaling resistor having a first end connected to the first input terminal of the op-amp and a second end for connecting to a second end of the inductor. In a specific embodiment, the RC network comprises a resistor and a capacitor connected to each other in parallel. According to the invention, by setting the RC constant of the RC network to be equal to the ratio of the inductor value over its internal resistance value, the inductor current can be derived independent of the frequencies of AC signals.
Other objects and attainments together with a fuller understanding of the invention will become apparent and appreciated by referring to the following description and claims taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 5181155 (1993-01-01), Beg et al.
patent: 5481178 (1996-01-01), Wilcox et al.
patent: 6469481 (2002-10-01), Tateishi
patent: 0 473 428 (1992-03-01), None
patent: WO 99 57578 (1999-11-01), None
Koninklijke Philips Electronics , N.V.
Nguyen Vincent Q.
Patidar Jay
Schmitt Michael
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