Electricity: power supply or regulation systems – Output level responsive – Using a three or more terminal semiconductive device as the...
Reexamination Certificate
2002-05-24
2003-12-30
Vu, Bao Q. (Department: 2838)
Electricity: power supply or regulation systems
Output level responsive
Using a three or more terminal semiconductive device as the...
C327S108000, C327S110000, C307S402000, C307S402000
Reexamination Certificate
active
06670796
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to driver circuits. More particularly, the present invention relates to driver circuits with an inductive load.
BACKGROUND
Current driver circuits and other driver circuits are generally known and used for many applications. A basic current driver circuit
100
of the prior art is shown in FIG.
1
. The driver circuit
100
has a signal input
105
. The signal input
105
is connected to the positive terminal of amplifier
115
and to one end of resistor R
1
110
. The other end of resistor
110
is connected to ground. The output of amplifier
115
is connected to one end of driver resistor
120
. The other end of resistor
120
is connected to the base of transistor
125
. The negative terminal of amplifier
115
is connected to the emitter of amplifier
125
and to one end of current sensor resistor
140
. The other end of resistor
140
is connected to ground. A voltage source
130
is connected to one end of an inductance load
135
. The other end of the inductance load
135
is connected to the collector of transistor
125
.
In operation, transistor
125
of the current driver sinks a current through the inductive load
135
. Signal input
105
applies input signal v
i
to the positive terminal of amplifier
115
and to resistor
110
. The voltage at the negative terminal of amplifier
115
is approximately equal to the voltage applied to the positive terminal of the amplifier. The voltage at the emitter of the transistor is applied to the negative terminal of the amplifier, which in turn sets the voltage at the base of the transistor. In one embodiment, the voltage at the base of the transistor is approximately 0.7 volts more than the emitter. Assuming operation in the active state for transistor
125
, when the input signal v
i
is low, a voltage difference is applied across resistor
120
inducing a base current i
B
. When the base current i
B
is induced at the base, a current i
C
is induced at the collector whereby i
B
=((1−&agr;)/&agr;)* i
C
, where &agr; is a constant for the particular transistor. The collector current i
C
drives the inductive load
135
. When the input signal v
i
goes high, the voltage difference across resistor
120
increases and induces a larger current i
B
. This induces a larger i
C
current to flow through the inductive load
135
.
The current response to driver circuit
100
is shown in FIG.
2
and displays several disadvantages of drive circuit
100
. As shown in
FIG. 2
, the driver circuit
100
displays a slow rise time and a slow recovery time. A faster rise time can be achieved by increasing the amplifier supply voltage
130
. However, increasing the supply voltage results in decreasing the efficiency of the driver circuit. The current response of
FIG. 2
also displays a large negative spike voltage characteristic. Such a negative spike voltage of the driver circuit
100
may damage the drive transistor unless a capacitor or diode is used to eliminate it.
Another type of driver of the prior art is a current push/pull driver. A basic current push/pull driver circuit
300
is shown in FIG.
3
. An input signal is connected to resistor
310
and the positive terminal of driving amplifier
315
. The output of amplifier
315
is applied to one terminal of resistor
320
and inductive load
330
. The negative terminal of the amplifier
315
is connected to the other terminal of resistor
320
, inductive load
330
, and to one terminal of current sensing resistor
325
. The other terminal of current sensing resistor
325
is connected to ground.
In operation, the signal input
305
applies signal v
i
to resistor
310
and to the positive terminal of driving amplifier
315
. The output of the amplifier
315
is applied to one end of resistor
320
and one end of the inductive load
330
. The voltage at the negative terminal of driving amplifier
315
is approximately the same as the voltage at the positive terminal of driving amplifier
315
. The voltage at the negative terminal of the drive amplifier applies a voltage to one terminal of current sensing resistor
325
. The voltage difference across current sensing resistor
325
induces a current through resistor
325
towards the grounded terminal of the resistor and through resistor
320
towards resistor
325
. Resistor values for resistor
320
and
325
are chosen such that the current driven through resistor
325
will be more or less than the current through resistor
320
depending on whether the input signal goes high or low. When input signal v
i
is low, the voltage difference across resistor
320
induces a current across resistor
320
towards node
340
. This provides a current across resistor
320
smaller than the current drawn by current sensor resistor
325
. As a result, current is pushed through inductor
330
towards node
340
. When input signal v
i
is high, the voltage difference placed across resistor
320
is now higher then when v
i
was low and higher than the current drawn by current resistor
325
away from node
340
. As a result, current is pulled through inductor
330
away from node
340
.
The current response of the push/pull driver circuit
300
is shown in FIG.
4
. The current response of circuit
300
is improved over the current response of circuit
200
. The negative spike voltage characteristic has been eliminated due to the push/pull characteristic of circuit
300
. The push/pull operation to the inductive load operates to remove some of the energy stored in the inductive load. Current driver
300
still possess a slow rise time characteristic is shown in FIG.
4
. Though the rise time of circuit
300
could be improved by increasing the supply voltage, this would decrease efficiency and require additional elements such as heat sink components.
What is needed is an improved circuit for driving an inductive load. The circuit should generate a high enough voltage to drive an inductive load at high speeds and display a favorable rise time. Further, a driving circuit is needed that can provide a low level of noise, high frequency capability, and be otherwise configurable to meet different system requirements as needed.
SUMMARY
A driving circuit for driving an inductive load in accordance with the present invention includes a high frequency driver and low frequency driver. A low frequency component and high frequency component is taken from an input signal. The separate low and high signal components are input to a low frequency driver and high frequency driver, respectively. The outputs of the high frequency and low frequency drivers are combined by combination circuitry. In one embodiment of the present invention, the high frequency component is also amplified by the combination circuitry. The combined signals generate a high voltage signal that drives an inductive load at fast speeds. The driver circuit of the present invention may be configured to provide low noise at low frequencies, pass band frequency response at the load terminal, different AC and DC open loop gains, and other characteristics depending upon system requirements.
REFERENCES:
patent: 3947776 (1976-03-01), Stevens et al.
patent: 4661766 (1987-04-01), Hoffman et al.
patent: 5126647 (1992-06-01), Blackburn et al.
patent: 5338977 (1994-08-01), Carobolante
patent: 6351162 (2002-02-01), Schwartz
patent: 6507177 (2003-01-01), Flock et al.
Anritsu Company
Fliesler Dubb Meyer & Lovejoy LLP
Vu Bao Q.
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