US 4,581,565 AGranted

H-bridge power amplifier and method for controlling the same

AssigneeStorage Technology Corporation

InventorsRichard W. Van Pelt, Veda R. Huffman

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Abstract

An improved H-bridge power amplifier for controllably driving a dc motor is presented. The motor is connected in the center of the H-bridge in conventional manner. The H-bridge includes a current sense resistor placed between the power supply and a common tie point of the upper transistors of the bridge. Free wheeling diodes are connected from the motor directly to the power supply. This arrangement allows current to flow through the current sense resistor only when one of the upper transistors is on. The power amplifier is operated by selecting an appropriate pair of upper and lower transistors on opposite sides of the bridge so as to cause the current to flow through the motor in a desired direction. Both the upper and lower transistors of the selected pair are held ON until the current as sensed in the current sense resistor equals or exceeds a specified value, typically a desired current level. When this occurs, the upper transistor is turned OFF for a fixed off-time period, during which time the lower transistor is maintained ON. The motor current thereby decays through a path comprising the ON lower transistor, one of the free wheeling diodes, and the motor, which decay path significantly reduces the ripple associated with the motor current. At the end of the fixed off-time, the upper transistor is turned ON, and the process repeats itself. If braking is desired to slow the motor down, a plug inhibit mode is enabled wherein the lower transistor is turned off and the upper transistor is alternately turned ON and OFF.

Claims9

Dependent claims

An improved H-bridge power amplifier for controlling the current delivered to an inductive load, said H-bridge power amplifier comprising:

an upper pair of transistors, a first upper transistor of which couples a first terminal of said load to a positive potential of a dc power source, and a second upper transistor of which couples a second terminal of said load to said positive potential of said power source;
a lower pair of transistors, a first lower transistor of which couples said first terminal of said load to a negative potential of said dc power source, and a second lower transistor of which couples said second terminal of said load to said negative potential of said dc power source;
free wheeling diode means for providing a path for current from said inductive load to said dc power source when all four of said transistors are turned off;
current sensing means for sensing the current flowing from said dc power source to said upper transistors, whereby said current sensing means senses current only when one of said upper transistors is turned on, and further whereby the current sensed by said current sensing means will always be flowing in the same direction;
comparison means for comparing the current sensed by said current sensing means to a desired current signal, and for generating a drive satisfied signal whenever the sensed current reaches a predefined value of the desired current signal;
and
control means for generating switching control signals in response to said drive satisfied signal and external control signals, said control means comprising:
polarity means for enabling either a first transistor pair comprising said first upper transistor and said second lower transistor, or a second transistor pair comprising said second upper transistor and said first lower transistor, in response to a polarity signal, whereby the direction of current flow through said inductive load can be selected
constant off-time means for turning off the upper transistor of said selected first or second transistor pair for a fixed off-time period whenever said drive satisfied signal indicates the sensed current is at least equal to the desired current
drive means for turning on the upper transistor selected by said polarity means whenever said off-time means indicates said fixed off-time period has expired and said drive satisfied signal indicates the sensed current is less than the desired current and
plug inhibit means for disabling the lower transistors in response to a plug inhibit signal, said plug inhibit signal being generated whenever said drive satisfied signal indicates the sensed current has become greater than the desired current during a prescribed time period, said time period being substantially less than said fixed off-time period.

8 more elements

An improved method for controlling an inductive load, such as a dc motor, driven by an H-bridge power amplifier, said H-bridge power amplifier including an upper pair of transistors coupling respective sides of said motor to a positive potential of a dc power source, a lower pair of transistors coupling respective sides of said load to a negative potential of said dc power source, and a plurality of free wheeling diodes coupled in reverse bias direction between both sides of said load and said positive and negative potentials of said dc power source, said method comprising the steps of:

(a) selectively turning ON one upper transistor on one side of said load and the lower transistor on the other side of said load so as to cause a current to flow through said load in a desired direction;
(b) sensing with sensing means the magnitude of said load current by measuring the current flowing from said power source;
(c) comparing the value of said measured load current to a desired current;
(d) maintaining both of said selected upper and lower transistors ON until the measured load current assumes a fixed relationship with regard to said desired current as determined by the comparison of step (c);
(e) turning OFF the selected upper transistor having the sensed current flowing thereto or therefrom for a fixed off-time period as soon as the comparison of step (c) indicates the measured load current has reached the value specified in step (d), and maintaining the selected lower transistor ON during this fixed off-time period, whereby the load current may decay through a path comprising said ON lower transistor, one of said free wheeling diodes, and said load without being measured by the sensing means of step (b);
(f) turing ON the upper transistor that was turned OFF in step (e) at the conclusion of the fixed off-time period;
and
(g) repeating steps (c) through (f) as desired, thereby causing a load current of a desired average value to flow through the load in a desired direction.

5 more elements

Dependencies are inferred from the claim text.

Facts

Application: 06/653,750Filed 21 Sep 1984 · continuation in part
Priority: 1 Mar 1983
Granted: 8 Apr 1986
Term ends: Not estimatedThe source records don’t support an estimate.

Classification5 codes

H02P 7/04
For controlling the direction of rotation of DC motors: by means of a H-bridge circuit
Y10S 388/916
Specific control circuit element or device: threshold circuit
Y10S 388/921
Specific control circuit element or device: timer or time delay means
H02P
Control or regulation of electric motors, electric generators or dynamo-electric converters