Miscellaneous active electrical nonlinear devices – circuits – and – External effect – Temperature
Reexamination Certificate
2000-08-16
2001-10-09
Callahan, Timothy P. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
External effect
Temperature
C327S378000, C327S538000, C323S907000
Reexamination Certificate
active
06300818
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention is directed, in general, to power conversion and, more particularly, to a temperature compensation circuit for semiconductor switch and method of operation thereof.
BACKGROUND OF THE INVENTION
The use of DC-DC power converters is wide spread in many important industries including those associated with larger telecommunication and computer installations. The converters are often expected to operate reliably over a variety of load and temperature conditions. The converters usually transform an input DC voltage by converting it first to an AC signal, passing it through a transformer and then rectifying it to provide the desired value of output DC voltage. By employing various switching techniques, the power density of the converters may be increased.
Most DC-DC converters are also expected to operate properly over widely varying values of load current. Many DC-DC converters are designed to supply a rated value of load current while maintaining a highly regulated output voltage. As the load current increases beyond the rated value, the output voltage is driven to zero to protect the converter from heat induced failure. Protection circuits are designed to protect the power rectifiers and other components of the converter from overly large load currents that may cause permanent component failure. Wide temperature operating requirements exacerbate the problems of over-voltage and over-current protection techniques, since the active circuit components of the converter have electrical characteristics that vary with temperature.
For example, the ON resistance of a power MOSFET employable as the power switch in a power converter varies directly with temperature. In the operating range of −40 degrees Celsius to 125 degrees Celsius, which is an operating range usually required for outdoor environments, the ON resistance of a typical MOSFET device may change more than 100%. In conjunction therewith, the ON voltage of the device, for a given current, also varies with temperature. If the ON voltage of the device is being used to provide current sensing in the converter, then a significant shift in the current protection point change may result due, in pertinent part, to the temperature-dependent characteristics of the device. Also, the protection system is further complicated by the fact that the sensed voltage of the switch is usually very noisy. The above described attributes, therefore, usually dictate that while the sensed voltage characteristic may be employed in protection systems, it is not the characteristic of choice for current-mode control of the converter. Additionally, while other sensing techniques involving bulky transformers and resistor networks may be employed, it is at the expense of higher costs and lossy control systems.
Accordingly, what is needed in the art is a system and related method adapted to sense and compensate for temperature effects on components of a power converter that effectively enhances current protection accuracy and stabilizes converter control.
SUMMARY OF THE INVENTION
To address the above-described deficiencies of the prior art, the present invention provides, for use with a semiconductor switch that exhibits a temperature-dependent electrical characteristic and a current sense circuit that employs the characteristic of the switch to derive a switch current signal, a temperature compensation circuit, method of operation thereof and controller employing the same. In one embodiment, the circuit includes: (1) an electrical component, locatable in thermal communication with the switch and having a temperature-dependent electrical characteristic that bears an inverse relationship to the characteristic of the switch, that generates an intermediate signal based on an actual temperature of the switch and (2) a signal conditioning circuit, coupled to the electrical component, that scales the intermediate signal to yield a compensation signal that counteracts temperature-dependent variations in the switch current signal.
In one embodiment of the present invention, the electrical characteristic is resistance. In many semiconductor switches, the ON resistance of the device varies directly with temperature. In other semiconductor devices, the ON resistance varies indirectly. In either case the temperature variation may be accommodated for effective compensation.
In one embodiment of the present invention, the electrical component is a Schottky diode. Schottky diodes exhibit temperature effects that may be used to effectively compensate for the temperature effects in other devices.
In one embodiment of the present invention, the semiconductor switch is a field-effect transistor (FET). Of course, other semiconductor switches are well within the broad scope of the present invention.
In one embodiment of the present invention, the current sense circuit comprises a comparison circuit that combines the switch current signal and the compensation signal to yield a temperature-compensated switch current signal. This switch current signal may be then employed to compensate for temperature differences over a wide range of temperatures.
In one embodiment of the present invention, the signal conditioning circuit further skews the intermediate signal to yield the compensation signal. Skewing of the intermediate signal allows it to be applied in a broad range of compensation circuits.
In one embodiment of the present invention, the signal conditioning circuit is a resistor divider network. Conversely, the signal conditioning circuit may be other networks that allow proper presentation of the required signal conditioning circuit.
The foregoing has outlined, rather broadly, preferred and alternative features of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.
REFERENCES:
patent: 3763440 (1973-10-01), Garcia et al.
patent: 5796309 (1998-08-01), Nguyen
patent: 5939863 (1999-08-01), Miller
patent: 6023178 (2000-02-01), Shioya et al.
Callahan Timothy P.
Lucent Technologies - Inc.
Nguyen Minh
LandOfFree
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