Motor driving circuit

• US 5,703,451 A
• Filed: 01/21/1997
• Issued: 12/30/1997
• Est. Priority Date: 01/24/1996
• Status: Expired due to Term

• Current Assignee: ROHM Co., Ltd.
• Original Assignee: ROHM Co., Ltd.
• Inventors: Yamamichi, Yoshifumi
• Primary Examiner(s): Ro, Bentsu
• Application Number:
  US08/785,270
• Time in Patent Office: 343 Days
• Field of Search: 318/368, 318/379, 318/430, 318/434, 318/459, 318/492, 318/500, 318/501, 318/519, 388/903, 388/907.2, 388/928.1, 361/33
• US Class Current: 318/492
• CPC Class Codes: H02H 9/047 Free-wheeling circuits
• CPC Class Codes: H03K 17/08146 in bipolar transistor switches
• CPC Class Codes: Y10S 388/903 Protective, e.g. voltage or current limit

Abstract

Between one end of a motor coil and the ground, a drive transistor is connected. When the drive transistor is turned off, and in particular at the moment when a current flowing through the motor coil drops to zero, a back electromotive force is induced at said one end of the motor coil. The back electromotive force is clamped by a pnp-type transistor with its base supplied with a constant voltage and its emitter connected to said one end of the motor coil.

Claims

1. A motor driving circuit,

wherein a back electromotive force that is induced at one end of a motor coil at a moment when a current flowing through the motor coil drops to zero as a result of turning off of a drive transistor connected between said end of the motor coil and a ground line is clamped by a pnp-type transistor with its base supplied with a fixed voltage and its emitter connected to said end of the motor coil, and wherein said drive transistor is turned on by a collector current of the pnp-type transistor.

2. A motor driving circuit comprising:

first and second transistors of an npn type that are connected between a power line and a ground line with their collector-emitter paths connected in series;

third and fourth transistors of a npn type that are connected between a power line and a ground line with their collector-emitter paths connected in series;

means for controlling said transistors to be alternately in a first state where the first and fourth transistors are on and the second and third transistors are off and in a second state where the first and fourth transistors are off and the second and third transistors are on;

a motor coil connected between a first node connecting an emitter of the first transistor to a collector of the second transistor and a second node connecting an emitter of the third transistor to a collector of the fourth transistor;

a fifth transistor of a pnp type with its base connected to said power line, its emitter connected to the first node, and its collector connected to a base of the second transistor; and

a sixth transistor of a pnp type with its base connected to said power line, its emitter connected to the second node, and its collector connected to a base of the fourth transistor.

3. A motor driving circuit comprising:

first and second transistors of an npn type that are connected between a first power line and a ground line with their collector-emitter paths connected in series;

third and fourth transistors of a npn type that are connected between the first power line and a ground line with their collector-emitter paths connected in series;

means for controlling said transistors to be alternately in a first state where the first and fourth transistors are on and the second and third transistors are off and in a second state where the first and fourth transistors are off and the second and third transistors are on;

a motor coil connected between a first node connecting an emitter of the first transistor to a collector of the second transistor and a second node connecting an emitter of the third transistor to a collector of the fourth transistor;

a second power line;

a fifth transistor of a pnp type with its base connected to said second power line, its emitter connected to the first node, and its collector connected to a base of the second transistor; and

a sixth transistor of a pnp type with its base connected to the second power line, its emitter connected to the second node, and its collector connected to a base of the fourth transistor.