Current control circuit

• US 4,547,715 A
• Filed: 07/09/1984
• Issued: 10/15/1985
• Est. Priority Date: 07/09/1984
• Status: Expired due to Term

• Current Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Li, Edward
• Primary Examiner(s): Weldon, Ulysses
• Application Number:
  US06/629,148
• Time in Patent Office: 463 Days
• Field of Search: 318/317, 318/341, 318/434, 318/345 B, 318/345 F, 318/331, 361/30, 361/31, 361/79, 361/87, 361/91, 361/93, 361/101
• US Class Current: 388/822
• CPC Class Codes: H02H 3/087 for dc applications
• CPC Class Codes: Y10S 388/903 Protective, e.g. voltage or current limit
• CPC Class Codes: Y10S 388/91 Operational/differential amplifier

Abstract

An overcurrent protection circuit for inductive loads such as motors is provided. A source voltage is input to a divider circuit including semiconductor switching devices. The inductive load is also connected to the voltage source through the divider circuit. A voltage output from the divider circuit which is proportional to the current through the inductive load is input to a comparator circuit. Another input to the comparator circuit comprises a reference voltage selected to correspond to the maximum desired current through the inductive load. If the comparator circuit senses that the current through the inductive load is greater than the predetermined maximum current, it provides an output to a pulse generator device. The output from the pulse generator device is input to a switching circuit which can cut off the voltage source supply to the inductive load.

Claims

1. A control circuit comprising:

(a) a voltage source;

(b) a divider circuit having at least one input connected to said voltage source, said divider circuit further including a first transistor and a second transistor;

(c) a voltage monitor connected to an output of said first transistor;

(d) an inductive load connected to an output of said second transistor for connecting said inductive load to said voltage source;

(e) a voltage comparator including a source of reference potential and an input from said voltage monitor;

(f) a pulse source connected to an output from said voltage comparator; and

(g) a switching circuit including an input from said pulse source, said switching circuit capable of controlling said divider circuit to selectively disconnect said inductive load from said voltage source.

2. The control circuit of claim 1 wherein the voltage output from said voltage monitor is proportional to the current through said inductive load.

3. The control circuit of claim 1 wherein said inductive load comprises a motor.

4. The control circuit of claim 2 wherein said source of reference potential comprises a voltage source and resistive elements selected to establish said reference potential so that said voltage comparator can compare the output from said voltage monitor with said reference potential to provide an appropriate output to said pulse source to enable said pulse source to provide an output to said switching circuit to disconnect said inductive load from said divider circuit voltage source when the output from said voltage monitor exceeds said reference potential.