Electricity: power supply or regulation systems – Output level responsive – Using a three or more terminal semiconductive device as the...
Reexamination Certificate
1999-08-27
2001-02-06
Wong, Peter S. (Department: 2838)
Electricity: power supply or regulation systems
Output level responsive
Using a three or more terminal semiconductive device as the...
C323S281000, C323S349000, C323S901000, C323S908000
Reexamination Certificate
active
06184663
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention generally relates to an apparatus for driving an electric load or a current consumer. This invention particularly relates to an apparatus for driving an electric load such as a coil, an inductor, or a lamp whose internal resistance varies as it is energized.
2. Description of the Related Art
As an electric load such as a coil or a lamp is energized, it is heated and hence its internal resistance increases. Generally, a switching element is used to turn on and off the electric load. It is known to use a switching element or a current adjusting device to control the magnitude of a current flowing through the electric load. At the start of the energization of the electric load, the internal resistance of the electric load is low and thus a great current tends to flow therethrough. Such a great current is referred to as a turn-on inrush surge current. In some cases, the turn-on inrush surge current damages the switching element or the current adjusting device.
U.S. Pat. No. 4,987,348 corresponding to Japanese published unexamined patent application 3-256407 discloses a bilevel current limiting control circuit which enables a semiconductor controlled power switch with a limited power handling capability to operate near the inside border of the safe operating area (SOA) characteristic of the power switch. The control circuit is especially useful in limiting the turn-on inrush surge current to an incandescent lamp load supplied via the semiconductor power switch. The control circuit includes a series circuit made up of the power switch, a current sensing resistor and a lamp load connected to the terminals of a source of supply voltage. First and second comparison circuits, arranged to provide first and second different current limits for the control circuit, are connected to the sensing resistor. A third comparison circuit compares the load voltage with a reference voltage to control a selector device that selects the output of the first or second comparison circuit as a function of the level of the load voltage. The output of the selected comparison circuit is applied via a feedback circuit to a control electrode of the power switch so as to control the load current to the first and second current limit values as selected in response to the load voltage.
In the control circuit of U.S. Pat. No. 4,987,348, the load current is controlled to the first and second current limit values. When the lamp load is turned on, the load current abruptly increases to the upper limit current value. Such an abrupt increase in the load current tends to cause spike noise, that is, high-frequency noise. When the lamp load is turned off, the load current abruptly drops to a null level. Such an abrupt drop in the load current tends to cause spike noise (high-frequency noise). The spike noise may cause wrong operation of another control apparatus if it is propagated thereto.
SUMMARY OF THE INVENTION
It is an object of this invention to provide an apparatus for driving an electric load such as a coil or a lamp which can suppress or prevent spike noise when the electric load is turned on and off.
A first aspect of this invention provides an apparatus for driving an electric load. The apparatus comprises a switch means interposed in a current feed path from a direct-current power source to the electric load; a sensing resistor connected in series with the switch means for detecting a load current as a voltage value, the load current flowing into the electric load via the switch means; a signal generation means for generating a trapezoidal wave signal in response to externally applied commands to turn on and turn off the electric load, the trapezoidal wave signal gradually varying from a first predetermined voltage to a second predetermined voltage when the electric load starts to be turned on, the trapezoidal wave signal gradually varying from the second predetermined voltage to the first predetermined voltage when the electric load starts to be turned off; and a control means for comparing the trapezoidal wave signal generated by the signal generation means and the voltage value provided by the sensing resistor, and for controlling the switch means in response to a result of the comparing so that the load current will vary in accordance with the trapezoidal wave signal.
A second aspect of this invention is based on the first aspect thereof, and provides an apparatus wherein the sensing resistor is interposed in a current feed path from the direct-current power source to the switch means.
A third aspect of this invention is based on the first aspect thereof, and provides an apparatus wherein the switch means comprises a transistor having a control terminal, the transistor controlling the load current in response to an input voltage to the control terminal, and wherein the control means comprises an operational amplifier for generating a voltage signal depending on a voltage difference between the trapezoidal wave signal generated by the signal generation means and the voltage value provided by the sensing resistor, and means for controlling the input voltage to the control terminal of the transistor in response to an output voltage of the operational amplifier.
A fourth aspect of this invention is based on the third aspect thereof, and provides an apparatus wherein the operational amplifier comprises means for generating an offset voltage which enables the switch means to be surely changed to its OFF state when the electric load is required to be turned off.
A fifth aspect of this invention is based on the fourth aspect thereof, and provides an apparatus wherein the operational amplifier comprises a differential amplifier circuit forming an input stage, the differential amplifier circuit having input terminals and load transistors corresponding to the input terminals respectively, the load transistors being different in size from each other to suitably determine the offset voltage.
A sixth aspect of this invention is based on the first aspect thereof, and provides an apparatus wherein the signal generation means comprises means for generating the trapezoidal wave signal in response to a pulse signal having a duty cycle which is controlled to implement PWM control of the load current.
A seventh aspect of this invention provides an apparatus for driving an electric load. The apparatus comprises means for gradually increasing a load current, which flows through the electric load, from a null level to a predetermined level in accordance with a former portion of a trapezoidal waveform when the electric load is required to be turned on; and means for gradually decreasing the load current from the predetermined level to the null level in accordance with a latter portion of the trapezoidal waveform when the electric load is required to be turned off.
An eighth aspect of this invention provides an apparatus for driving an electric load. The apparatus comprises means for generating a first signal when the electric load is required to be turned on, the first signal having a waveform corresponding to a former portion of a trapezoidal waveform; means for generating a second signal representing a load current flowing through the electric load; means responsive to the first signal and the second signal for, when the electric load is required to be turned on, gradually increasing the load current from a null level to a predetermined level in accordance with the waveform of the first signal on a feedback control basis; means for generating a third signal when the electric load is required to be turned off, the third signal having a waveform corresponding to a latter portion of the trapezoidal waveform; and means responsive to the second signal and the third signal for, when the electric load is required to be turned off, gradually decreasing the load current from the predetermined level to the null level in accordance with the waveform of the third signal on a feedback control basis.
REFERENCES:
patent: 4987348 (1991-01-01), Wong
patent: 5355390 (1994-10-0
Imai Hiroshi
Koyama Yoshiki
Mase Shunji
Denso Corporation
Laxton Gary L.
Pillsbury Madison & Sutro LLP
Wong Peter S.
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