Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Current driver
Reexamination Certificate
2003-06-17
2004-10-05
Ton, My-Trang Nu (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Current driver
C327S538000
Reexamination Certificate
active
06801063
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a new circuit and method for controlling the driving of a load, and more specifically, a driving circuit, controlled by a pulse width modulated signal, that is capable of driving a load at a maximum power level.
BACKGROUND OF THE INVENTION
A variety of today's electrical systems rely on pulse width modulation (PWM) of a signal to control analog circuits and devices in a digital manner. According to basic PWM techniques, a voltage or current source is supplied to an analog load, such as a motor, by means of a repeating series of on or off pulses. The power supply is fully on and applied to a load only during the on-times defined by the repeating series of on and off pulses. The subsequent ratio of on-time to period of the signal is known as the duty cycle of a PWM signal and is expressed in percentages. Thus, a PWM signal with a 50% duty cycle represents a signal comprised of on pulses for half of the time, while a 100% duty cycle represents the power supply being continuously applied to a load.
PWM signal control is often utilized with bootstrap-type driving circuits, which rely on the use of a first power supply to activate or turn “on” a circuit that subsequently drives a load using a second power supply.
FIG. 1
illustrates the general layout of a known bootstrap-type driving circuit
100
that utilizes a pulse width modulated control signal. In general, the purpose of circuit
100
is to drive load
130
using a primary power supply Vp. This is carried out by means of switch
120
. When switch
120
is placed in an “on” state, electrical current to flows from the primary power supply Vp, through the switch
120
, to the load
130
, and when switch
120
is “off”, no current flows from primary power supply Vp to the load.
Controlling the “on” and “off” state of primary switch
120
is a secondary switch
140
that “flips” between a first and second state, thereby connecting either a first path (A) or second path (B) to capacitance
150
, depending on a PWM control signal Vin. Specifically, when the control signal Vin is off/low, switch
140
is placed in a first state whereby capacitance
150
is connected to an auxiliary power supply Va, such as, for example, a 12 Volt source, through first circuit path (A). Accordingly, when control signal Vin is off/low, switch
120
remains in its default “off” state. At the same time, capacitance
150
is charged by electrical current that is permitted to flow from the auxiliary power supply Va, to the capacitance
150
, and then through the load
130
.
When control signal Vin is on/high, secondary switch
140
is placed in a second state whereby capacitance
150
is connected to primary switch
120
by means of the second path (B). This results in primary switch
120
turning “on” due to application of the built-up charge stored in capacitance
150
. Consequently, with switch
120
“on”, the primary power supply Vp is able to drive load
130
.
Accordingly, when the PWM control signal Vin, applied to secondary switch
140
, is off/low, primary switch
120
remains off while capacitance
150
is charged. Conversely, when control signal Vin is high, the built-up charge on capacitance
150
is applied to primary switch
120
, thereby placing switch
120
in an “on” state and allowing the primary power supply Vp to drive load
130
until the PWM control signal Vin goes off/low again.
The bootstrap-type driving circuit described above works sufficiently for driving a load
130
at less than maximum power levels, such as, for example, upon application of a control signal Vin having less than a 100% duty cycle. However, complications arise when one attempts to fully drive load
130
at a maximum power level. This is because bootstrap-type driving circuits utilizing PWM control, as generally described above, are unable to function properly upon the application of a PWM control signal Vin having a sufficiently high duty cycle. The reason for this is because at sufficiently high duty cycle levels, such as, for example, a 100% duty cycle, PWM signals are effectively converted from a series of on and off pulses to a constant voltage or current signal. Application of an essentially constant control signal Vin to circuit
100
above results in secondary switch
140
being placed in its secondary state. Furthermore, secondary switch
140
will remain in its secondary state for as long as the essentially constant control signal Vin is applied. During this time period, capacitance
150
is connected to primary switch
120
, with the charge on capacitance
150
placing switch
120
in an “on” state. However, capacitance
150
, like all capacitances, is subject to a condition known as “voltage droop”, whereby, in the absence of periodic recharging, which normally occurs at lower duty cycles, the stored charge on capacitance
150
quickly diminishes due to current leakage. Consider, for example, the situation where a control signal having a 100% duty cycle is applied to the circuit. Unless capacitance
150
is periodically recharged, the stored charge on capacitance
150
may only last a few milliseconds before being reduced to an insufficient voltage amount. Yet, because of the high duty cycle of the control signal, capacitance
150
will not be provided with a chance to recharge. As a result, after those few milliseconds, the charge stored on capacitance
150
is no longer sufficient to maintain the primary switch
120
in an “on” state.
Accordingly, the application of a PWM input signal Vin having a sufficiently high enough duty cycle results in a lack of periodic recharging of capacitance
150
. Consequently, without periodic recharging of capacitance
150
, voltage droop becomes a significant factor, leading to capacitance
150
having an insufficient charge to maintain primary switch
120
in an “on” state. As a result, the inventor of the present invention has realized the need for a bootstrap-type driving circuit that utilizes a pulse width modulated (PWM) control signal to control the variable driving of a load, including driving the load at or near a maximum power level upon the application of a sufficiently high enough PWM control signal.
SUMMARY OF THE INVENTION
The present invention relates to a circuit and method for electrically driving a load. The circuit includes the use of a driving circuit for variably driving the load in response to a pulse width modulated control signal. Also included is a compensation circuit that permits the driving circuit to drive the load at a maximum power level when the pulse width modulation control signal has a sufficiently high enough duty cycle.
REFERENCES:
patent: 4049979 (1977-09-01), Shieu et al.
patent: 4284905 (1981-08-01), Rosenzweig
patent: 4376252 (1983-03-01), Masenas, Jr.
patent: 4772812 (1988-09-01), Desmarais
patent: 4992749 (1991-02-01), Tokumo et al.
patent: 5498995 (1996-03-01), Szepesi et al.
patent: 5708343 (1998-01-01), Hara et al.
patent: 6002269 (1999-12-01), Dartnell et al.
patent: 6107860 (2000-08-01), Vinciarelli
patent: 6201717 (2001-03-01), Grant
patent: 6246296 (2001-06-01), Smith
patent: 6489758 (2002-12-01), Moriconi et al.
Nu Ton My-Trang
Radar Fishman & Grauer PLLC
Yazaki North America, Inc.
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