Over heat protection circuit for a brushless dc motor

• US 7,064,940 B2
• Filed: 05/21/2003
• Issued: 06/20/2006
• Est. Priority Date: 02/24/2003
• Status: Expired due to Fees

• Current Assignee: Sunonwealth Electric Machine Industry Company Limited
• Original Assignee: Sunonwealth Electric Machine Industry Company Limited
• Inventors: Horng, Alex, Ko, Ta-Lun
• Primary Examiner(s): Jackson, Stephen W.
• Assistant Examiner(s): Demakis, James A.
• Application Number:
  US10/442,157
• Publication Number:
  US 20040165325A1
• Time in Patent Office: 1,126 Days
• Field of Search: 361/25
• US Class Current: 361/25
• CPC Class Codes: H02H 5/042 using temperature dependent resistors
• CPC Class Codes: H02H 7/0852 directly responsive to abnormal temperature by using a temperature sensor in a control circuit H02H7/0833

Abstract

A over heat protection circuit for a brushless dc motor includes a thermal sensitive resistor, a resistor and a transistor. The thermal sensitive resistor and the resistor are commonly connected to a base of the transistor while an emitter of the transistor connecting to a motor coil. The thermal sensitive resistor has a resistance value which can be changed in response to an operational temperature. The thermal sensitive resistor is preset to operate at a safety temperature within a predetermined thermal preference. When the operational temperature of the motor coil exceeds the safety temperature, the over heat protection circuit may to cut off a motor current so that the motor coil is protected.

Claims

1. An over heat protection circuit for protecting a brushless dc motor, comprising:

a thermal sensitive resistor having a resistance value adapted to change within a predetermined thermal preference in response to changing of an operational temperature of the motor;

a resistor serially connected to the thermal sensitive resistor at a connection point at which to commonly provide an adjustable voltage value which is supplied from a voltage source;

a transistor including a base, a collector and an emitter, wherein the base is connected to the connection point located between the thermal sensitive resistor and the resistor so that the adjustable voltage value is input to the base;

the collector is connected to the voltage source; and

the emitter is connected to the motor for controlling operation of the motor;

wherein when the operational temperature of the motor is greater than a safety temperature or the motor is overheated, the resistance value of the thermal sensitive resistor is correspondingly adjusted with respect to a predetermined reference such that the adjustable voltage value of the thermal sensitive resistor and the resistor is inadequate to turn on the base of the transistor so as to cut off a motor current and thereby stop the motor to reduce the operational temperature of the motor; and

wherein when the operational temperature of the motor is lower than the safety temperature or the motor has cooled, the resistance value of the thermal sensitive resistor is correspondingly adjusted with respect to the predetermined reference such that the adjustable voltage value of the thermal sensitive resistor and the resistor is adequate to turn on the base of the transistor so as to resupply a motor current and thereby restart the motor.

2. The over heat protection circuit for the brushless dc motor as defined in claim 1, wherein the thermal sensitive resistor is a negative temperature coefficient type resistor;

a first end of the resistor is connected to the voltage source and a second end of the resistor is connected to a first end of the thermal sensitive resistor; and

a second end of the thermal sensitive resistor is connected to ground.

3. The over heat protection circuit for the brushless dc motor as defined in claim 1, wherein the thermal sensitive resistor is a positive temperature coefficient type resistor;

a first end of the thermal sensitive resistor is connected to the voltage source and a second end of the thermal sensitive resistor is connected to a first end of the resistor; and

a second end of the resistor is connected to ground.

4. The over heat protection circuit for the brushless dc motor as defined in claim 1, wherein the motor includes a motor coil through which the motor current is passed;

the motor coil having a first end connected to the voltage source, and a second end connected to the over heat protection circuit.

5. The over heat protection circuit for the brushless dc motor as defined in claim 1, wherein the motor includes a drive IC connected to the transistor of the over heat protection circuit.