Electricity: power supply or regulation systems – Output level responsive – Using a three or more terminal semiconductive device as the...
Reexamination Certificate
2002-11-19
2004-01-13
Vu, Bao Q. (Department: 2838)
Electricity: power supply or regulation systems
Output level responsive
Using a three or more terminal semiconductive device as the...
C322S025000, C322S028000
Reexamination Certificate
active
06677739
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally concerns improvements to voltage regulators, specifically including voltage regulators that are used to regulate alternators on vehicles.
The present invention particularly concerns improvements to vehicular electronic voltage regulators used in heavy duty, high current, high performance applications.
Because the main design intent of the present invention is concerned with the high-reliability voltage regulation of vehicular alternators deployed in heavy duty applications, the improvements of the present invention will be seen to be particularly useful for (i) revenue-generating vehicles such as trucks and buses, and (ii) emergency vehicles such as ambulances and fire trucks, supporting large electrical loads.
2. Description of Prior Art
Two basic design technologies have dominated the electronic voltage regulator art: (i) Frequency-On-Demand and (ii) Pulse-Width-Modulation.
2.1 Frequency-On-Demand
Frequency-On-Demand regulation of alternator voltage is by far the oldest, simplest, cheapest and most widely used design. Frequency-On-Demand voltage regulation provides adequate performance in most automotive and light duty applications.
Frequency-On-Demand voltage regulation works on the principle that an error signal is generated by comparing the vehicle's electrical system voltage to an internal reference in an error amplifier stage to produce an error signal. This error signal is then further amplified and used to drive an output stage of the voltage regulator. The regulator's output stage in turn controls the current through the alternator's field winding. An interaction between the output stage and the error amplifier stage (normally through an RC network), produces a sharply defined rectangular pulse-train whose duty cycle determines the excitation level in the alternator's field winding and hence, the current generating capacity of the alternator.
Due to increasing use of electrical power in vehicles, alternators have become larger, resulting in increased response time due to the very large field inductances and currents involved. When the response time of a large alternator is added to the response time of a commensurately robust voltage regulator itself, then a noticeable and objectionable voltage/current low-frequency fluctuation is observed to occur at the alternator's output. This phenomena is most noticeable both at no-load and near full-load conditions of the alternator.
In an attempt to deal with this problem, the modern Frequency-on-Demand voltage regulator is designed with a fast response time. The problem with this avenue of improvement has been that when the ON-OFF-ON transitions of the control pulse-train of the alternator are made to occur faster then the level of electrical noise introduced into the vehicle's electrical system is increased.
With the present (circa 2002) massive use of computers in vehicles, the demand for electrically clean, stable voltage in the vehicle's electrical system has become a driving factor forcing improvements over the traditional Frequency-on-Demand approach to voltage regulation.
2.2 Pulse-Width-Modulation
In Pulse-Width-Modulation regulation of alternator voltage, a constant frequency pulse-train is internally generated by the voltage regulator and the duty cycle (or pulse width) is then modulated to vary the excitation level in the alternator's field winding. Since the field-driving pulse-train has a constant frequency that does not depend on external variables such as the field inductance and current flowing into the field, this technology eliminates the low-frequency fluctuations of the Frequency-on-Demand systems. Also, rise and fall times of the ON-OFF-ON transitions can be made sufficiently slow to insert a minimum of electrical noise into the vehicle's electrical system.
Alas, these improvements result in both higher cost and higher complexity. Thus, although Pulse-Width-Modulation is a flexible and powerful approach to voltage regulation, up until present, circa 2002, cost and complexity issues have kept this technology available only in those applications that have demanded the highest levels of performance.
SUMMARY OF THE INVENTION
The present invention—which has been fully and thoroughly tested by its inventors—contemplates modifications to proven and highly-reliable Frequency-on-Demand voltage regulators towards the goal of modifying their performance so as to alter their operating mode from Frequency-on-Demand to constant-frequency Pulse-Width-Modulation.
The modifications required to accomplish this objective are as follows:
An “OUTPUT” stage of the voltage regulator is reconfigured as a bi-stable multivibrator (also known in electronics engineering as a “flip-flop”). This flip-flop circuit also provides an efficient and economical short-circuit protection function for the output power transistor.
An “OSCILLATOR”, implemented with any of a number of technologies both discrete and integrated, provides a “RESET” pulse to the flip-flop with a pre-defined pulse width and pulse period. This “RESET” pulse initiates the “ON” period of the “OUTPUT” stage.
An “ERROR AMPLIFIER” stage of conventional construction rapidly switches the “OUTPUT” stage “OFF” when system voltage synchronously reaches a preset value, thus terminating the “ON” period.
Incidental to this construction, the total capacitance across the gate-source terminals of the output stage transistor—normally an MOS power transistor—is selected and is intentionally used to slow down the negative- and positive-going transitions of the transistor to introduce a minimum of electrical noise into the vehicle's electrical system.
The collective modifications to a Frequency-on-Demand voltage regulator required to so improve its performance by making it into a Pulse-Width-Modulation voltage regulator do not significantly affect the existing (i) reliability or (ii) complexity of this voltage regulator. Indeed, Pulse-Width-Modulation voltage regulators in accordance with the present invention have a substantially similar (i) parts count, and (ii) reliability, to those current (circa 2002) state-of-the-art Frequency-on-Demand regulators which they serve to replace.
Furthermore, the cost of a Pulse-Width-Modulation voltage regulator in accordance with the present invention is only but slightly altered from the Frequency-on-Demand type that it supplants. This is the case even though the performance of a Pulse-Width-Modulation voltage regulator in accordance with the present invention realizes all the valuable features of a true Pulse-Width-Modulation electronic voltage regulator of considerably more complex design.
1. An Electronic Voltage Regulator
Accordingly, in one of its aspects the present invention can be considered to be embodied in an electronic voltage regulator for regulating an alternator to maintain constant a system voltage where a flip-flop, sensitive to a “RESET” pulse to initiate an “ON” condition, serves as an “OUTPUT” stage of the voltage regulator.
An oscillator produces a “RESET” pulse having a pre-defined pulse width and pulse period, and provides this “RESET” pulse to the “OUTPUT” stage flip-flop.
Meanwhile, an “ERROR AMPLIFIER” stage synchronously switches the “OUTPUT” stage flip-flop “OFF” when the system voltage reaches a preset value, thus terminating the “ON” period of the “OUTPUT” stage flip-flop.
By these components, and these connections, the oscillator, the error amplifier and the output stage flip-flop produce in combination a pulse-width-modulated signal.
The OUTPUT stage flip-flop may in particular include a Field Effect Transistor (FET) having gate and source terminals. The parasitic capacitance of the gate-source terminals of this FET—either acting alone or in combination with an external discrete capacitor—serves to slow both negative- and positive-going transitions of the OUTPUT stage flip-flop, therein introducing a minimum of electrical noise into an electrical system in which the electronic voltage
Bartol Luis E.
Bartol Muriel
Fuess & Davidenas
Vu Bao Q.
LandOfFree
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