Circuit for driving linear compressor

Details Circuit for driving linear compressor Circuit for driving linear compressor

2001-10-26

2003-05-20

Freay, Charles G. (Department: 3746)

Pumps

Condition responsive control of pump drive motor

By control of electric or magnetic drive motor

C417S044110, C417S417000

Reexamination Certificate

active

06565327

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a circuit for driving a linear compressor enabling to reduce a cost in detecting voltage and current applied to a linear compressor by decreasing the number of precision resistors.
2. Background of the Related Art
Generally, a linear compressor having no crankshaft transforming a rotary motion into a straight-line motion enables to reduce its frictional loss, thereby being superior to other compressors in efficiency. And, the linear compressor variously transforms a voltage corresponding to a stroke applied to the linear compressor to vary a compression ratio. Therefore, the linear compressor is used for a variable cooling capacity control for a refrigerator, an air conditioner and the like.
FIG. 1
illustrates a circuit for driving a linear compressor according to related art.
Referring to
FIG. 1
, a circuit for driving a linear compressor according to related art includes a linear compressor
10
A controlling a cooling capacity (endothermic heat from surroundings during evaporation for a cooling operation as a material of 1 Kg passes through an evaporator) by varying a stroke(a distance from one end to the other end of a piston) through an up-and-down rectilinear motion of a piston, an electric circuit unit
10
controlling a current applied to the linear compressor
10
A by connecting a ground terminal between a current detect resistance R
1
and a triac Tr
1
and by shorting or disconnecting an alternating current in accordance with a switching signal of the triac Tr
1
, a current detection unit
20
detecting a current applied to the linear compressor
10
A and outputting the detected current, a voltage detection unit
30
receiving a voltage between two ends of the linear compressor
10
A to amplify differentially using a differential amplifier
30
A and including a level shifter
30
B carrying out a level shifting, a stroke calculation unit
40
receiving the detected current and voltage from the current and voltage detection units
20
and
30
and calculating a stroke of the linear compressor
10
A, and a microcomputer
50
comparing the stroke calculated by the stroke calculation unit
50
to an initial stroke reference and then supplying the electric circuit unit
10
with a switching signal for controlling a voltage applied to the linear compressor
10
A in accordance with a difference between the calculated stroke and initial stroke reference.
The voltage detection unit
30
includes a couple of OP amplifiers, in which a negative voltage terminal of the linear compressor
10
A is connected to an inversion terminal (−) of the differential amplifier
30
A through a precision resistor Ra
1
, a positive voltage terminal of the linear compressor
10
A is connected to a non-inversion terminal(+) of the differential amplifier
30
A through a precision resistor Ra
2
and a precision resistor Ra
3
of which one end is grounded, a precision resistor Ra
4
is connected between an output terminal of the differential amplifier
30
A and the inversion terminal(−) of the differential amplifier
30
A, the output terminal of the differential amplifier
30
A is connected to an inversion terminal(−) of the level shifter
30
B through a precision resistor Ra
5
, a power voltage supply of 5 V is inputted to the level shifter
30
B through a precision resistor Ra
6
and a precision resistor Ra
7
of which one end is grounded, and another precision resistor is connected between an output terminal and the inversion terminal(−) of the level shifter
30
B.
Operation and effect of the circuit for driving the linear compressor according to the related art are explained by referring to the attached drawing as follows.
A normal AC alternating current power supply voltage of 220 V is applied to the linear compressor
10
A through a current detect resistor R
1
, the triac Tr
1
, and a capacitor C. Thus, a current flows through the linear compressor
10
A and a piston of the linear compressor
10
A carries out a straight-line reciprocation motion by the current. The straight-line reciprocation determines a stroke as a straight-line reciprocation distance of the piston. Thus, the cooling capacity is controlled by varying the stroke.
In this case, the current detection unit
20
detects a current applied to the linear compressor
10
A through the current resistor R
1
and then inputs the detected current to the stroke calculation unit
40
. The voltage detection unit
30
, when the linear compressor
10
A is driven, detects a voltage between both ends of the linear compressor
10
A to input the voltage to the stroke calculation unit
40
. In this case, the voltage between both ends of the linear compressor
10
A is amplified by the differential amplifier
30
A through two precision resistors R
1
and R
2
. The value amplified by the differential amplifier
30
A is then compared to the power supply voltage of 5 V by the level shifter
30
B to be detected. Successively, the stroke calculation unit
40
receives the current and voltage detected from the linear compressor
10
A to calculate the stroke, and then inputs the calculated stroke value to the microcomputer
50
. The microcomputer
50
adjusts the voltage to be applied to the linear compressor
10
A using a speed peak control algorithm stored previously in a memory of the microcomputer
50
. Namely, the microcomputer
50
compares the stroke calculated by the stroke calculation unit
40
to the initial stroke reference. If the calculated stroke value is higher than the initial stroke reference, the microcomputer
50
outputs the switching signal turning off the triac Tr
1
as an AC switching device of the electric circuit unit
10
to reduce the voltage applied to the linear compressor
10
A.
On the other hand, if the calculated stroke, i.e. the present stroke, is lower than the initial stroke reference, the microcomputer
50
outputs the other switching signal turning on the triac Tr
1
as an AC switching device of the electric circuit unit
10
to increase the voltage applied to the linear compressor
10
A.
After all, through the two processes, the microcomputer
50
inputs the switching signal enabling to adjust the voltage applied to the linear compressor
10
A to the triac Tr
1
to make the present stroke follow the initial stroke reference.
Unfortunately, the circuit for driving the linear compressor according to the related art has to detect the voltage and current of the linear compressor using a plurality of the precision resistors to calculate a precise senseless stroke. Therefore, the circuit of the related art has to use the expensive precision resistors, thereby being unable to avoid increasing a product cost.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a circuit for driving a linear compressor that substantially obviates one or more problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a circuit for driving a linear compressor enabling to reduce its product cost by reducing the number of precision resistors and using a ground terminal in common for detecting voltage and current of a linear compressor.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, a circuit for driving a linear compressor according to the present invention includes a liner compressor controlling a cooling capacity by varying a stroke through an up-and-down straight-line motion of a piston, a

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