Pulse-width modulated circuit for applying current to a load

• US 5,365,422 A
• Filed: 06/01/1993
• Issued: 11/15/1994
• Est. Priority Date: 06/01/1993
• Status: Expired due to Term

• Current Assignee: Hitachi Medical Corporation (Hitachi, Ltd.)
• Original Assignee: Performance Controls, Inc. (Fujifilm Holdings Corporation)
• Inventors: Close, Eric C., Yost, Donald A., Goff, Jerry K.
• Primary Examiner(s): Voeltz, Emanuel T.
• Assistant Examiner(s): NGUYEN, MATTHEW VAN
• Application Number:
  US08/069,789
• Time in Patent Office: 532 Days
• Field of Search: 363/17, 363/95, 363/97, 363/98, 363/131, 363/132, 318/811, 315/209 R, 315/DIG. 7
• US Class Current: 363/98
• CPC Class Codes: H02M 7/53871 with automatic control of output voltage or current
• CPC Class Codes: H02M 7/53878 by time shifting switching signals of one diagonal pair of the bridge with respect to the other diagonal pair

Abstract

A pulse-width modulated (PWM) circuit alternately applies voltage from a power supply across a load, and alternately establishes one or more non-powered, closed paths for freewheeling current. The circuit includes pairs of switches connected to the load and also connected to the power supply. PWM signals derived from a command signal drive the switches in such a manner as to create the freewheeling current paths in a desired pattern and sequence. The circuit effectively reduces ripple current in the load while also substantially reducing the amount of current flowing through the power supply filter capacitor. Thus, the size and rating of the power supply can be reduced. One can use the invention to drive a load in a multiple-phase environment, and also in the context of a three-phase trapezoidal drive.

Claims

1. A circuit for applying current to a load, the circuit comprising:

a) a power supply,

b) four switches, all of the switches having at least two terminals, one terminal of each switch being connected to the power supply and the other terminal being connected to the load, wherein the switches comprise means for defining paths for current from the power supply, to the load, and back to the power supply, and wherein the switches also comprise means for defining at least one closed path for current flow, wherein said closed path excludes the power supply, and

c) means for generating pulse-width modulated signals, wherein said signals control the switches, and wherein the signals are arranged such that they alternate between providing a path for current from the power supply through the load and back to the power supply, and establishing said closed path which excludes the power supply, wherein there are at least two independent pulse-width modulated signals for controlling the switches.

2. A circuit for applying current to a load, the circuit comprising:

a) a power supply,

b) a plurality of switches, all of the switches being connected to the power supply and to the load, wherein the switches comprise means for defining paths for current from the power supply, to the load, and back to the power supply, and wherein the switches also comprise means for defining at least two closed paths for current flow, wherein said closed paths exclude the power supply, and

c) means for opening and closing the switches, wherein the opening and closing means comprises means for establishing at least one current path from the power supply through the load and back to the power supply, and for establishing either of said closed paths which exclude the power supply.

3. The circuit of claim 2, wherein the opening and closing means comprises means for generating pulse-width modulated signals, wherein the pulse-width modulated signals are connected to the switches so as to control the switches.

4. The circuit of claim 3, wherein there are at least two independent pulse-width modulated signals for controlling the switches.

5. A circuit for applying current to a load, the circuit comprising:

a) a power supply,

b) a plurality of switches, all of the switches being connected to the power supply and to the load, wherein the switches comprise means for defining paths for current from the power supply, to the load, and back to the power supply, and wherein the switches also comprise means for defining at least one closed path for current flow, wherein said closed path excludes the power supply, and

c) at least two independent means for opening and closing the switches, wherein the opening and closing means comprise means for establishing at least one current path from the power supply through the load and back to the power supply, and for establishing said closed path which excludes the power supply.

6. A pulse-width modulated circuit for varying the flow of current to a load, the circuit comprising:

a) switching means for connecting the load to a source of power such that current flows through the load,

b) the switching means also including means for connecting the load to at least one closed circuit which does not include the power source, wherein current flowing through the load can continue to flow through said closed circuit, and

c) at least two independent pulse means for controlling the switching means such that, for at least a portion of an operating cycle, the load is connected to the power source, and for another portion of the operating cycle the load is connected to at least one of said closed circuits.

7. The circuit of claim 6, wherein said at least one closed circuit comprises closed circuits, and wherein the pulse means comprises means for connecting the load, in sequence, to the power source, to one of said closed circuits, to the power source again, to the other of said closed circuits, and so forth.

9. The method of claim 7, wherein each of the switches has an open state and a closed state, and wherein the configuring and reconfiguring steps comprise the steps of converting an error signal into a set of pulse trains and using said pulse trains to control the switches.

10. The method of claim 9, wherein there are at least two independent pulse trains.

8. A method of applying current to a load, the method comprising the steps of:

a) configuring a plurality of switches connected between the load and a power supply so that current flows from the power supply to the load and back to the power supply,

b) reconfiguring the switches such that current flows through the load in a closed loop which excludes the power supply, and

c) alternately repeating steps (a) and (b),

wherein step (b) is performed alternately with different closed loops.

11. A method of applying current to a load, the method comprising the steps of:

a) configuring a plurality of switches connected between the load and a power supply so that current flows from the power supply to the load and back to the power supply,

b) reconfiguring the switches such that current flows through the load in a closed loop which excludes the power supply, and

c) repeating steps (a) and (b) such that step (b) is performed at least once between successive repetitions of step (a), and such that current flows in different closed loops which exclude the power supply.